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Contents
Series Preface
vii
About this Book
viii
Section A: Living Organisms in the
Environment
1
2
3
4
5
2
The Variety of Living Organisms
Characteristics of life
The major groups of organisms
Classification of organisms on the basis of visible
characteristics
The binomial system
Chapter summary
Answers To ITQs
Examination-style questions
9
10
12
13
13
Ecology and the Impact of Abiotic Factors on
Living Organisms
Ecology
Environmental factors
Ecosystem, habitat, population, community
Distribution of species
Chapter summary
Answers To ITOs
Examination-style questions
15
15
16
17
21
22
24
Feeding Relationships between Organisms
Producers and consumers
Herbivores, carnivores and omnivores
Predators and prey
Food webs
Decomposers and detritivores
Special relationships
Chapter summary
Answers To ITQs
Examination-style questions
Ecosystem, Habitat, Population, Community
Trapping the Sun's energy
Pyramids of energy
Pyramids of numbers
Pyramids of biomass
Bioaccumulation
Chapter summary
Answers To ITQs
Examination-style questions
The Cycling of Nutrients
Biogeochemical cycles
The carbon cycle
The nitrogen cycle
Acid rain
Chapter summary
Answers To ITOs
Examination-style questions
3
3
15
6
7
24
Population Growth, Natural Resources and
their Limits
Growth of natural populations
Resources and their limits
Chapter summary
Answers To ITQs
Examination-style questions
The Effects of Human Activity on the Environment
Humans and the environment
Endangered and vulnerable organisms
Other effects of human activity
Impact of human activities on marine and wetland
environments
Impact of increase in greenhouse gases
Conservation and restoration of the environment
Chapter summary
Answers To ITQs
Examination-style questions
24
25
26
27 Section B: Life Processes and Disease
28
29 8 Cells
Why we need microscopes
30
Plant and animal cells
30
Unicellular microbes
31
33
33
37
37
38
39 9
40
40
40
42
42
43
46
49
50
50
51
52
52
55
60
60
62
63
63
64
66
70
72
72
74
74
75
Cell specialisation in multicellular organisms
Movement of substances into and out of cells
Chapter summary
Answers To ITQs
Examination-style questions
78
78
79
80
81
83
87
88
89
Photosynthesis
Plants are the food supply for animals
Photosynthesis
Products of photosynthesis
Limiting factors in photosynthesis
Etiolation
Chapter summary
Answers To ITQs
Examination-style questions
91
92
96
96
97
98
98
99
91
iii
10 Feeding and Digestion
11
100 16 Excretion, Osmoregulation and Homeostasis
181
Diet
A balanced diet
Malnutrition
Holozoic nutrition
Digestion and absorption along the alimentary canal
Assimilation
Functions of the liver
Chapter summary
Answers To ITQs
Examination-style questions
101
106
107
108
111
116
117
117
118
119
181
182
183
184
189
189
192
Respiration
Aerobic respiration
Anaerobic respiration
Chapter summary
Answers To /TQs
Examination-style questions
122
12 Gaseous Exchange
The importance of transport in plants
Transport systems of plants
Movement of water through a plant
Transpiration
Adaptations in plants to conserve water
Uptake and movement of mineral salts
Transport of manufactured food
Chapter summary
Answers To ITQs
Examination-style questions
15 Storage in Plants and Animals
Why do organisms store food?
Food storage in plants
Food storage in animals
Chapter summary
Answers To ITQs
Examination-style questions
iv
196
196
197
199
205
205
206
130 18 Irritability, Sensitivity and Coordination
208
122
125
127
128
128
Irritability
Stimulus
The sense organs of humans
The nervous system
The endocrine system
Drugs and the effects of drug abuse
Chapter summary
Answers To /TQs
Examination-style questions
142 19 The Eye, the Ear and the Skin
The need for a transport system
142
143
The circulatory system of humans
Blood
149
Hypertension
152
The role of blood in defending the body against disease153
Chapter summary
156
Answers To ITQs
157
Examination-style questions
159
14 Transport in Plants
17 Movement
1~3
194
The importance of movement in animals
Movement in plants
The skeleton of humans
Chapter summary
Answers To ITQs
Examination-style questions
Importance of gaseous exchange in humans
130
Mechanism of gaseous exchange in humans
131
Importance and mechanism of gaseous exchange
in plants
135
Characteristics common to gaseous exchange surfaces 135
The effects of smoking
137
Chapter summary
139
Answers To ITQs
140
Examination-style questions
140
13 Transport and Defence in Animals
Metabolism
Excretory products in animals
Excretory products in plants
The human excretory system
Osmoregulation
Homeostasis
Chapter summary
Answers To ITQs
Examination-style questions
160
The eye
How we see
Sight defects and their corrections
The ear
How we hear
Balance
The skin
Temperature regulation in humans
Temperature regulation in birds
Skin care
Chapter summary
Answers To ITQs
Examination-style questions
160
161
163
166
167 20 Reproduction in Animals
168
Reproduction
168
Reproduction in humans
170
The male reproductive system
170
The female reproductive system
172
Hormones of the gonads
Fertilisation
173
Development of the embryo, fetus and placenta
173
Birth
173
The role of contraception
178
HIV/AIDS and other STDs
179
Chapter summary
179
Answers To /TQs
180
Examination-style questions
209
209
210
211
217
219
222
223
224
225
226
227
230
232
233
234
235
237
239
239
240
240
242
244
244
246
246
247
248
250
250
252
253
254
256
256
258
21
Reproduction in Plants
Life cycle of a plant
Structure of a flower
Pollination
Fertilisation and development of seed
Dispersal
Chapter summary
Answers To ITQs
Examination-style questions
22 Disease and Humans
Health and disease
Pathogenic diseases and vectors
Social and economic implications of disease
Chapter summary
Answers To ITQs
Examination-style questions
259 24 Meiosis
259
The importance of meiosis
261
The process of meiosis
262
Significance of meiosis
263
Chapter summary
264
Answers To ITQs
267
Examination-style questions
267
25 Heredity and Genetics
269
23 Mitosis
Chromosome number
The cell cycle
Importance of maintaining species chromosome
number
The process of mitosis
Mitosis and asexual reproduction
Chapter summary
Answers To ITQs
Examination-style questions
Genes
Examples of genetic effects
Pedigree charts
Chapter summary
Answers To /TQs
Examination-style questions
296
297
302
304
306
306
309
Genetic variation
Importance of genetic variation
DNA testing and forensic science
Natural selection
Artificial selection
Mutation
Genetic engineering
Chapter summary
Answers To ITQs
Examination-style questions
310
310
312
313
313
317
319
321
323
324
325
Practical work in Biology
School-Based Assessment contents
328
328
332
271
271
273
275
275
276
26 Variation and Evolution
276
Section C: Continuity and Variation
278
278
279
290
290
291
293
294
295
295
281
282
282
287
287 Section D: School-Based Assessment
288
27 School-Based Assessment
Index
368
v
Series Preface, 3rd edition
Macmillan's textbooks for the Caribbean Secondary Education Certificate (CSEC)
Science subjects have been written by teachers with many years' experience of
preparing students for success in their examinations. These revised third editions
have been written to align with the new CXC syllabuses (to be first examined in
2015). Additional practical activities have been included to reflect the new emphasis
on practical work, and new [eatures (such as group work and discussion activities)
will help teachers to cater to a variety of different learning styles within the
classroom.
These books are specially designed to stimulate learning, whatever the reader's
needs. Students starting a topic from scratch may need to be led through the
explanation one step at a time, while those with prior knowledge of a topic may
need to clarify a detail, or reinforce their understanding. Others may simply need to
cl1eck that they understand the material.
Each CSEC science syllabus specifies the areas to be used for the School-Based
Assessment (SBA). Each book in the series has a section designed to help students
with their SBA, by offering advice on how to approach the task, presenting
examples of good SBA work or suggesting suitable material to use within it.
Teachers are free to photocopy these pages.
The CSEC Science series covers everything a student needs pass their CSEC
examination, as well as providing a firm foundation for more advanced study at
CAPE level.
Dr Mike Taylor
-<:~~
~'°~
Series Editor
vii
About this Book
This book isn't just words o n a page.
This book conra ins a range of different features to introduce, tea ch and highlight key information
throughout the course. These pages explain h ow to use them. The larger column contains the main text
and diagrams; you can read straight down it without interruption.
The smaller column contains other useful facts, so make sure you use it to check your understanding.
You sh ould remember to spend time stud yi ng the figures and diagrams as well as the text.
This icon shows how you can
make links be1ween lhis
concept and other topics in Biology.
11 is important to remember that
you arc not just learning facts in
isolation but 10 think about how
they relate to your world and your
experiences .
Where you see this icon, you
will find an In-Text Question (ITQ). These
are spread throughout each chapter and will help
you to check your progress. If you can't answer the
ITQ, you should refresh your knowledge by rereading the relevant paragraphs in the main text.
Answers to the ITQs are found at the end of each
chapter.
This symbol means that you can find
additional practice for this topic on the
Macmillan CSEC Science digital resources. These
stand-alone components will help you to learn
and revise key areas of the course. For more
information please visit: http://www.macmillancaribbean.com/pages.aspx/educationalbooks/
secondary/science. interactive_science_csec/.
. .Anaerobic respiration in humans
Human cells respire nonnally <1erobicall}'· However, during strcnuuu~ cxcrci.M!.
mm.de cells need much more energy for lhc extra work that the)' arc doing.
Thl' hrcathlng rate and hcJrt r.11c increase in an attempt lO i:et more oxygen
to 1hc~c cells. Sweatin)? occurs to helµ lose some of 1he extra enNgy a~ heat.
With im.l'cast<d rl-spir.ulon. ,, Im of heat ls produced which ls lost from the skin
jchaptl'r 19). After a period of SUSI.lined exercise, 1he oxygen sup1>ly becomes
inadequat('. even wi1h panting ror air and 1he increased hl'.in r.lte. The muscle
cell~ 1hcn respire anaerobia lly.
Encrg) h )lill produced when cell) respire anaerobicall y, although h Is a
much ~mailer amount for each molecule of glucose. Thi~ means that they c m
con1lnue 10 dn work (cuntr.1C1 and rdax).
Anaerobic respiration in bacte
L~
Sometimes bacteria can be found
In canned foods or tins, desp1te the
lact that the cans and tins are sealed
so that no air can enter. How Is this
possible?
Some baocria a lso respire anaerobically. LikC' ani
acid as a wastl' 1noduct. We make use of 1hb in 1
and cheese (Og urc 1 1.9 ),
lnoculatlon
ClCOtd 10 40°C n a 'statttt' CUii.i'ii of
• nat'mhic fC'\J,l ~1lon
e.g.~toboc:lb~
}:lurosc - -- -- - l actic acid+ energy
In musclt- cdl~
.~
\;'-'
Humans respire mosUy aerobically.
When do humans respire enaeroblcally?
f9f?Mnt11Uon
n::uoeraa in twge Yd1lt (.CO cc tar lltX)I
Lactic acid is a waste produa of th.ls reaction. It builds up In the muscles and
a u ses 1hem to ache (rig ure 11 .6). This is often called fallgue . A her cxcrdsc:,
rho bod1 ha> to gel rid of 1hc lact ic acid as quickly as pos<iblc. This is done
by usin~ o xygen lO changr II bad~ 10 a chemical like glucose c;o tha1 ii can be
IJro~cn down completely in .u:robic respiration. When anaerobic rcspir<Jllon
occ:ur11 in muscles his in addition 10 aerobic respiration and not in phlCL' of ii.
A perso n continucc; to 'bre011hc: hard ' or p.lnl for some time a her exerd~e .n
oxy gen Is needed 10 get rid of the lactic acid. The oxygen required to gel rtd o(
the lactic acid i< called 1hc o.><ygen debt (figure 11.7).
~ a>nYlrted IO lllct.c acid orodl.a1Q
cool, tldd frurtt. etc.
package and distribute
814..5°CthltllCtenltll'T'l8#\lllvebl.
lerm!rutJOn OCCU'I al liw lemp
~
stont •2°C
\;'-'
What is alcoholic fennentation and
what are two of its uses?
Rgute II 9
Ch a p ter s umma ry
All cells respire lo release energy to carry out the P'
• Resp1ration takes place In the mitochondria of cells.
Food Is oxidised dunno respiratioo. and carbon diox11
waste products:
C,H110, + 60, - energy+ 6H,O+ 6CO,
Energy Is stored In phosphate bonds In ATP (aclenosl
• There are many advantages to storing energy as sm
• There are two types of respiration: aerobic and anae
Aerobic respiration uses oxygen and releases a lot DI
• Anaerobic respiration releases a small amount of II'"
Humans usually respire aerobically but tflelr muscle
during prolonged exercise.
• Lactic acid Is produced during anaerobic respiration
oxygen debt which has to be repaid.
Anaerobic respira11on in ~t produces ethanol whu
and carbon tfiOxlde which is used In making bread.
• Anaerobic respiration In bacferta is used In the makl1
f1a.1;r.1914•..14e1mm1
-
· sugar--~
Anaerobic respiration in yeast
·-IO----·--.... -
Rarc:h 'Mldl • btoMr1 doM'I
• .,._ a.-1he
maru:.. ... ..,.. of
~ and fenreltEl101
oc:an
· ~N91SblCJbles OCC0i
gMCll.ght ..... _
· ~~ltw~lnd
~- lhlleetw1QI
During an.Jcrohic respiratio n in yc<i st. c1hanol and carbon
dioxide arc produced as wash~ produas. EthJ:nol is an alcohol
.ind the process b known as a lroholk fermenta1ion .
Yeast h vc:ry lmponant m the makint-: nr alcohol and bread
(figure 11 .8 ). The c1hanol can be prod u ced In man y ways to
make .1 \\id~ rnngc ol alcoholi c drinks. indudlnJ.: beer and wine.
which arc enjoyed by humans.
The produc1lon of carbon dioxidt' h used in bread·maklng
10 make dough rise . The carbon dioxide produced by lhc ycae>t
a~ ii rt.''§:p1res .u cumula1es inside the do ugh in '\mall pocl.l·t~.
The d ough is e>een IO get bigger ur ri~ a s 1hc gas l"xpands with
warm1h. E1hanol is also produced but in s mall quanlilics - i i
evaporates when 1he bread is OOking in the: oven.
The first time an important new word
appears in lhe text, it is highlighted at the
side. A definition or in-depth explanation
is given in the main text.
viii
As you can see on pl26. lhe smaller column
can contain key details. It is good practice to
spend time reading this column as well as lhe
main text so that you don't miss any important
information.
Each image has a
caption and a figure
number to help v. ith
cross-referencing.
Summaries of the key
facts from each chapter
will help you check
your understanding.
A list of objectives
at the beginning of
each chapter tells you
what topics you will
be covering. They will
help you to plan and
measure your learning.
I
understand the terms 'ecology', 'ecosystem' and •environment'
(/
distinguish between abiotlc and biotic fact ors
I/ distinguish between habitat and niche
'7l distinguish between community and population
tfj distinguish between population and species
./) relate the distribution of species to abiotic factors
Q'i describe the components of soll
(I
Tables and definitions
are printed in coloured
boxes for easy
recognition.
understand the advantages and disadvantages o f th e use of natural and
chemical fertilisers
ITQ1
Ablotlc factors
Biotic factors
The temperature ol water.
Feeding relatlooshlps, e.g. betWeen the lizard
and Insects tnat are l1s prey,
The amount of light available to the orvanlsms. Be!laviour of scad When attached by dolphin.
You ma}' haVl' noted 01hcr examples from 1he pictures.
ITQ2
A home.- aquariu m is a limit~i.1 ecosystem; ii <loan '1 contain tht·
divcr-.:ity of species that would be found in 1he na u1e. A l:k1cky.ird pond is more
likely IO be a compl ete eco;;ystcm wi1h ~1ll 1he divcrslly ncCt"~sary to sustain
itself.
JTQ3 (l) A habltiit Is 1hc place where an nrganism Jives. 1\ niche Is the role 0111
cells. 1hcv make lac1it
11a11ufoctu rc of yoghurt
0
•r
·1
This is the style of
question you may
come across in your
exaill. Your teacher
will suggest how you
can use them. but they
will measure what you
have learnt and help
to identify any gaps in
your knowledge so you
can revisit the relevant
sections of the book.
The School-Based
Assessment pages
contain activities which
enable you to explore
the theoretical concepts
in the chapter. They will
test your investigative
and problem-solving
skills and show realworld applications
of the facts you are
learning.
~es of life.
nd water are produced as
riphosphate),
1ackets of ATP.
C,
ergy.
'without the use of oxygen.
s can respire anaerobically
o
Examination-style questions
0) Explain, using examples. the meaning of the terms:
(a) abiotic factor.
(bl biotic factor.
01) Define:
(a) environment:
(b) habtla~
(c) population:
(d) community.
(iii) Describe. using examples, how ablotlc factors of the envirooment affect the
distribution of species.
(iv) (a) Amoebae live In fresh and sat! water habitats. Describe a major problem of
' in I
27 • School-Based Assessment
1.1 To observe visible characteristics of animals and plants
Chapter l The Variety of Living Organisms '
Syllabu s skills : O/R/R
Procedure: an imals
1. Visit a backyard garden, a nearby cocoa estate, a nature centre, foothills of forest (anywhere a range of
organisms can be seen).
2. Copy the table below into your lab book and observe five animals ~nclude three insects). Describe what
'
'
'
"
k.oUwJJll!!JJ..D'"""~-----"
.nlmals and creates an
; used in the alcohol Industry
1f yoghurt and cheese.
127
ix
Section A:
Living Organisms in
the Environment
9ihe Variety of Living
Organisms
0
understand why there exists a range of living organisms on Earth
0
list and define the characteristics of life
.,() describe the major groups of organisms
0
0
understand how a classification system is used to group all living organisms
observe and classify living organisms according to visible similarities and
differences
range of living organisms
characterisics
of life
growth
respiration
irritability
movement
nutrition
excretion
reproduction
Prokaryota
Protoctista
Fungi
Plantae
Animalia
classified according
to common features
Kingdom
Phylum
Class
Order
Family
Genus
Species
species - can
interbreed
with each other
breeds
varieties
races
The plan et Earth, the third planet from the Sun, has all the conditions
necessary to su pport life as we know it. Our pla net is position ed at such
a distance from the Sun that living organisms ca n survive in th e range of
temperatures on its surface (a lthough it is a fairly wide range). The presence of
water in all its forms (solid, liquid and gas) a nd the combination o f gases whi ch
make up the a tmosphe re (including n itrogen, oxygen and ca rbon dioxide) a re
all conditions that a re essential to life on Earth.
A h uge variety of living forms exist on the planet Earth . Th ey can inhabit
most of the Earth 's surface, land, air and water. They show an e normous range
in size a nd comp lexity - from the microscopic, which cann ot be seen by the
naked eye and are as simple as one cell, to giant whales which must live in
wa ter since th ey are too heavy to support themselves and move on la nd.
Characteristics of life
characteristics of life >
~
IT:.Q-1
V'-1
List three characteristics of the planet
Earth that enable it to sustain life.
Biology is the study of life and how living things stay alive. All Living
organisms, microscopic to gigantic, possess certain characteristics. These are the
characteristics of life that distinguish living things from non-living things.
There are seven of these characteristics.
Growth - Living organisms increase in mass, size and numbers.
2 Respiration -The energy released during respiration is needed to carry out
all life processes.
3 Irritability - Living organisms can respond to changes in their internal
environment and the world around them. These responses usually increase
their chances of survival.
4 Movement - Most living organisms can move. Plants show growth
movements such as growing towards the light. Most animals can move
from place to place to find food or a mate.
5 Nutrition - All living organisms need food which is used as a source of
energy. Plants make their food during photosynthesis. Animals get their
food by eating plants or other animals.
6 Excretion - All living things make waste products during metabolism.
These must be removed from the body.
7 Reproduction - This is the production of new organisms.
Living organisms are able to carry out all these processes on Earth. Most
organisms are adapted to live on land or in water, more or less close to sea
level. Some survive in 'extreme' places such as:
• in hot sulfur springs where chemical conditions are toxic to most living things;
• in extreme cold, such as at the North and South Pole;
• in deep parts of the ocean where no light can reach, such as the Marianas
Trench;
• in the upper atmosphere;
• in extremely hot deserts, such as the Gobi desert;
• inside other living organisms.
Wherever they live, as long as they are able to carry out the processes of life
living organisms survive and produce offspring. Most places on Earth can
support life.
~
IT:.Q2
V'-1
Animals and plants are able to carry
out certain processes which distinguish
them from non-living things. Describe
briefly how a plant (i) feeds (ii) moves.
The major groups of organisms
All organisms used to be classified or placed in two kingdoms or main groups
- animals and plants, depending on whether they get their food from other
organisms or make their own food. However, living things are more diverse than
this and a classification system of five kingdoms is now used. These kingdoms
are the Prokaryotes, Protoctists, Fungi, Plants and Animals (figure l. l ).
Living organisms
___________,__ ------------ -- ---------------- -
Prr l .. ~
(chromosomes
not enclosed
in a nucleus)
Eukaryotes
(chromosomes enclosed
in a nucleus)
Fungi
unicellular
- --
Viruses
Piart,
multicellular
Figure 1.1 Living organisms are placed in five major kingdoms (shown In red).
Anirm:1.. d
-
-
-
Living Orge111jsm_s·-iG.'1!.tle~£11vii:_~l)_rfla!J!1__- _
The kingdoms have scientific names that are
slightly different from their common names.
Prokaryota
Protoctista
Fungi
Plantae
Animalia
_ _ __ _
_ ~--
_o
~
Viruses do not fil into this dassi.fication. They are the smallest organisms,
though it is difficult to think of them as living because they can only 'live'
inside anoth er living cell. They also do not have a tru e cellular structure Like
other organisms (figure l.2).
Viruses that attack humans
HIV or
human immunodeficiency virus
Influenza virus
0
protein/
lipid coat
~
virus RNA
IT:Q3
1....l'-1
What are the five major groups of lifeforms or organisms?
Viruses that attack bacteria are called bacteriophages or simply phages
Phage 2
bacteriophage
phage DNA
~
IT:Q~
1....l'-1
Bacteria are described as being
microscopic and unicellular organisms.
What do these terms mean?
Phage DNA Is Injected into the bacterium
where it makes copies of itself (20-1000)
which are released to infect further bacteria.
surface of bacterium
Rgure 1.2 The structure of some viruses.
Billions of viruses 'exist' around us and it is only when they enter the cells
of an organisms that they sh ow some of the d1ara cteristics of life. There they
can reproduce and grow in numbers.
Viruses have a great impact on life on Earth because they can live inside
every type of Uving organism, from bacteria to plants and animals. It is believed
that they have changed the course of human history because of diseases like
smallpox, measles and now AIDS.
Rgure 1. 3 Eschenchia coliis a rodshaped bacterium which is part of the
normal gut 'flora' of humans and other
vertebrates.
Rgure 1.4 Anabaena is a bacterium where
the cells stick together in long chains.
4
Prokaryotes
The prokaryotes are orga nisms that are commonly called bacteria. They occupy
many en viromnents such as soil. dust, water. air. and in or on animals and
plants (figure 1.3). Some are found Lu hot springs where temperatures may be
higher than 78 °C . Some can survive freezing in ice. Some ha ve been found
in deep cracks in the ocean floor, at very high pressures and temperatures of
360 °C. They can be found in every part of the living world.
They are the most ancient group
cytoplasm
of organisms. They are also the
smallest organisms that have a cell ular
_......... cell wall
structure. Man y exist as single cells,
others are found in groups (figure 1.4).
Their cells have a m uch simpler
stru cture than those of the eukaryotes
strand of DNA
(figure 1.5).
Rgure 1.5 Structure of a typical bacterium,
Prokaryotes are vital to all other
e
g. Eschenchia co/1. The chromosomes are
organisms sin ce th ey cause decay
not enclosed in a nucleus and there is little
of dead plant and animal material
whi ch releases nutrients back into the
structure in the cytoplasm.
1 · The Variety of Living Organrsrns
CHAPTER 16, CHAPTER 22
environment. They are essential to the nitrogen cycle. They are also important
co humans because they cause disease (e.g. cholera and TB - chapter 22 ) and
are used in biotechnology (e.g. in insulin production - chapter 16).
Protoctists
Most protoctists are unicellular, that is made of one cell. This ce ll shows all the
characteristics of life. Algae and protozoa are two kinds of protoctist.
• Protozoa are unicellular and feed on other organisms (heterotrophlcally).
They are found in all environments, especia lly in water, and examples
include Amoeba and Paramecium (figure 1.6 and figure 1.7). They are
important to humans because diseases such as malaria and sleeping sickness
are ca used by protozoan parasites.
• Algae live in the sea and in fresh water, and some live on land where the
Figure 1.6 Amoeba proteus (x200).
surface is damp. They make their own food by photosynthesis (figure 1.8).
Some live as single cells, others are found in groups or colonies. A few, such
cytoplasm
as the seaweeds, can grow extremely large. These have structures that look
cell membrane
nucleus
like stems, roots and leaves, but they are much simpler than true planes.
Rapid growth (blooms) of algae can form scums on the surface of ponds,
food
lakes and rivers, turning them green.
p seudopodia
contractile
vacuole
Ma laria infects millions of people each year and it is estimated that 2.7 million
people worldwide ?ie from this disease each year.
Fungi
Figure 1.7 The structure of Amoeba.
~ flagella
Fungi range in size from unicellular yeasts to large toadstools. Some are
used by humans for medicinal and dietary purposes. They are heterotroph ic
organisms and obtain their food from the environment. However, they do not
tak e in large particles of food that need to be broken down. They digest their
food outside the body using enzymes which make it soluble. Then they absorb
the food. So, they are usually found living in or on their food, whlch can be a
dead or living organism (figure 1.9).
cytoplasm
spore body
light-sensitive
spot
chloroplast
r---+.--~ starch
storage
Figure 1.8 Ch/ore/la. a photosynthetic
alga Note the presence of the chloroplast,
where photosynthesis takes place.
mycelium
absorbed
into fungus
vesicles release
enzyme and
food is digested
soluble
food
Ill enzymes
insoluble
food
Figure 1.9 The hyphae of fungi extend into their food u.:JliSllOn occurs outside Lhe bod;.
5
~
IT:QS
l/'-1
Using one named example of each,
describe one similarity and one
difference between algae and
protozoans.
Figure 1.1O Penicillin spores are made in
sexual reproduction (x600).
Fungi reproduce by producing spores asexually or sexually (figure 1.10).
These are dispersed by the wind and water and some rely on animals to take
them to new environments. Common fungi are:
• moulds (figure 1.10);
• yeasts (figu re 1.11 );
• mushrooms and toadstools (figure 1.12).
Figure 1.11 Yeast cells bud to make new cells 1n asexual reproduction.
Importance of fungi to humans
• Important in the making of the antibiotic penicillin.
• Essential to many fermentation processes, such as those used in making
bread, wine, beer and other alcoholic beverages.
• Used to make a range of chemical products, such as anaesthetics, birth
control pills and meat tenderiser.
• Moulds and ru st are fungi that are important in damaging growing crops.
• Ca use of spoilage of food.
• Source of food and used to make food, such as sufu in Ease Asia.
Plants (Plantae)
Figure 1 12 Mushrooms are 11.; oor
bodies of some fungi.
~
IT:Q6
l/'-1
Name three kinds of fungi and a
possible use of each.
6
The plant kingdom includes
mosses, liverworcs, ferns,
coni fers and fl owering
plants. Almost all p lants are
photosynthetic.
Many plants are a source
of food for humans and
other animals (figure 1.13).
Some provide a rich ad
diverse habitat (figure 1.14) .
Some plants can be used as
medicines. Bidens is a weed
which has a small dajsy-
Rgure 1. 13 Bananas
a food source for many
animals.
Rgure 1.14 Mangroves a
rich habitat
1 · Tite Variety of Living Organisms
like flower (figure 1.1 5).
The leaves and fl owers are
steeped and u sed to 'cool
the blood' (prickly h eat) and
to relieve a sick stoma ch.
Sometimes it is given to
children to cure worms.
Flowering plants
angiosperms >
.~
Rgure 1.15 Bidens - Shepherds needle, Spanish needle,
The fl owering plants have
Beggar-ticks,
st1cktight.
true fl ow ers and so m ake
seeds. They are a lso called
angiosperms and are divided into two groups:
• the m onocotyledons;
• the dicotyledons.
Table L. l shows the distinguishing features of monocoi:yledons and dicotyledons.
l/'-1
(i)
Plants range in size from
unicellular to giant. Put these
plants in order of size starting
from the smallest: fern, mango
tree, croton, moss and lettuce.
(ii) List five reasons why plants are
important.
Feature
Monocotyledons
Dicotyledons
seed
has one cotyledon or seed leaf
has two cotyledons or seed leaves
leaf
has parallel veins
has net-like or branching veins
example
corn (Zea mays)
Hibiscus
Table 1. 1 D1stmgwshmg features of monocotyledons and dicotyledons.
Angiosperms a re th e la rgest group of plants. They include most crop plants,
orna men tal pla nts and plants used as he rbs or m edicin al plants. They vary
in size fro m the very sm all to gigan tic (over 90 m ta ll) and are ofte n very
bea utiful (figu re 1.1 6). They can live in a wide variety of habitats, from deserts
to ra inforests.
Figure 1.16 Flame tree.
Phyla is the plural of phylum.
Animals (Animalia)
The animal kingdom conta ins multicellular, heterotrop hi c orga nisms. Th ey a re
grouped in phy la as sh own in figure 1.17.
Animalla
Cnidaria
Platyhelminthes
• lh.
Annelida
invertebrates
Nematoda
vertebrates
Figure 1. 17 Animals are placed in phyla. (Tho:;e .>hown mred are described in more detail
overleaf.)
7
Living Organisms 1n the Environment
Table I .2 shows examples of each animal phylum.
Phylum
Examples
Cnidaria
jellyfish, sea anemone, coral
Platyhelminthes
flatworms, e.g. tapeworm
Mollusca
slug, snail, mussel, octopus
Annelida
roundworm , earthworm, leech
Arthropoda
insect, spider, lobster, millipede, centipede
Nematoda
roundworms
Chordata
fish, amphibian , reptile, bird, mammal
Table 1.2 Example:s of the animal phyla.
Arthro'pods (Arthropoda)
Figure 1.18 An invertebrate that lives on
land , a snail.
Arthropods dominate life on Earth. They include the crustaceans, millipedes,
centipedes, arachnids and insects. They all have an exoskeleton (outer skeleton
of chitin) and jointed limbs.
• The cru stacea n s a re aquatic or live in damp pla ces . They include woodlice,
crayfish, crabs, lobsters a nd barnacles.
• The arachnids include spide rs, scorpions, mi tes and ticks. They have four
pairs of wa lking legs and are mainly terrestrial and carnivorous.
• The insects have a distinct head, thorax and abdomen, and three pairs of
walking legs. They include locu sts, bees, ants, beetles, aphids and fleas.
Molluscs (Mollusca)
Rgure 1. 19 An invertebrate that lives in
water, a sea cucumber.
The molluscs have a soft body which is often covered by a shell. They include
con ch, sna ils, slugs, cockles, mussels, octopus, squid, clams and oysters.
Figures 1. 18 a nd 1.19 show examples o f mollusccs.
Some molluscs like conch and oysters are important to Caribbean people as
a source of food and an exotic trea t to loca ls and tourists. Farming of mo ll uscs
is pra ctised on some islands as demand exceeds supply from wild pop ula tions.
These a nimals are a renewable resource but popula tions can decline rap idly
because of over- harvesting from their natural habitat.
Chordates (Chordata)
Most ch ordates are also vertebrates because t hey have a vertebral column. The
vertebra tes include the fishes (ca rti laginous and bony), amphibians, reptiles,
birds and mammals (figure 1.20).
8
1 · The Variety of Living Organisms
frog (ampilibian)
lizard (reptile)
scarlet ibis (bircf)
monkey (mammal)
Figure 120 There are five groups of vertebrates: fish amphibians. reptiles. birds and mammals.
Birds (Aves) have the fo llowing ch aracte ristic [ea tures:
• front pair o[ limbs modified to form wings;
• skin covered with [eath ers;
• produce hard-shelled eggs (reproduction);
fish
• are warm-blooded.
Q9.:.,
l:tQ8
vv
Name the five groups of vertebrates,
giving two examples of each.
Mammals (Mammali a) have the followin g chara cteristics:
• four limbs;
• sk in covered with hair;
• most give birth to live you ng;
• feed their yo ung with milk made by the mother (suckle);
• are warm-blooded.
Classification of organisms on the basis of
visible characteristics
:X Practical activity
SBA 1.1 : To observe visible
characteristics of plants and animals.
page 333
artificial classification >
natural classification >
The simplest way co classify organisms is according to similariti es in their visible
ch aracteristics. For example, if we see a number of organisms, we could stan to
group them by putting those with w ings together. We can make another group
of those with eight legs. We cou ld also put the ha iry ones together. And so on .
However, where do we put those th at are both h airy and winged?
There are two types of classification, artificia l and natural. Artificial
classification is based on easily observed ch a racteristics, like colour, shape or
number of legs. This is a convenient and easy method of groupi ng organisms
and is designed for a practica l purpose. However, worms and snakes have the
sam e sh ape, but snakes have a backbone while worms do not.
Natural classification tries to use natural relation ships between organisms
using both internal and external characteristics. For example, organisms with
backbones are grouped together because th ey all have backbones and many
other similarities. Similarities in anatomy, physiology and behaviour may all be
considered when grouping organisms in a natural classification.
Organisms are grouped by similarities that sh ow descent from shared ancestors.
For example, a bird wing and a human arm show descent from a ve rtebrate
ancestor. A bird w ing an d an insect wing are derived from different stru ctures.
9
Similarities in DNA (deoxyribonudeic acid) sequ ences are increasingly
being relied on to determine ancestry. The more alike the DNA sequences a re
for two types of organisms, the recently they diverged from a shared ancestor.
Remember that each organism has its own DNA 'fingerprint'. Biologists
can now construct new evolution ary tree diagrams that sh ow how existing
orga nisms are related to one another using their DNA .
~
IT:Q9
l..)'...J
Classify these organisms according to similarities in their visible characteristics
into three groups.
Dichotomous keys
A dichotomous key is a tool that enables classification of organisms. It works
by asking a series of qu estions in a step-by-step fashion until you are led to
the name of the orga nism. Dichotomous mea ns 'divide d into two parts' and a
dichotomous key always offers two answers to each question.
Sii:nple example of part of a dichotomous key
Does it have wings?
2
3
yes - go to question 2
no - go to question 5
Does it have feathers?
yes - it is a bird
no - go to question 3
Are the wings brightly coloured? yes - it is a moth or butterfly
no - go to qu estion 4
And so on.
Dichotomous keys can be used to dassify organisms according to both
artificial or n atural criteria, including DNA information where it is available.
The binomial system
Carl Linnaeus was a scientist in the 18th cen tury who first grouped organ isms
together by a natural classification. Many people had tried grouping o rganisms
before, but they ha d all used artificial classification. Linnaeus' classification
10
binomial system >
Genera is the plural of genus.
made it easier to study organisms, since the enormous variety is organised into
closely related groups.
Carl Linnaeus also put forward a system for naming each species of
organism with a biological name, which is called the binomial system. He
did this because organisms may have many common names. For example the
plant called shadow benny, bandania and cilantro in Trinidad and Tobago, is
called sit weed or spirit weed in Jamaica, and in Martinique and Guadeloupe it
is known as bandanie. Each biological name has two parts which are the sa·me
in all these countries and all over the world - the biological name for the pla~ t
is Eryngium foetidum. Th e first word of this name is the genus name and always
starts with a capital letter. If you are writing it several times, the first word may
be shortened. Fo r exa mple Eryngiumfoetidum may be abbreviated to E.foetidum.
The second word is the species name.
Every known species has a place in this classification . It starts with
major groups of general features, which are broken down into smaller and
smaller groups that get more and more specific. Look at the example of the
classification of humans in figure 1.21.
Living organisms
Placed In five main groups (kingdoms)
Kingdom
Prokaryotes
Protoctista
Phylum
Fungi
Plantae
Animalia
Annelida
Arthropoda
Chordata
invertebrates
Sub-phylum
Class
Order
Vertebrata
(possess a vertebral column)
Reptilia
(reptiles)
Aves
(birds)
Mammalia
(hairy, warm-blooded, suckle young)
Primates
(monkeys)
Carnivora
I
Family
Hominidae
(human-like apes)
Genus
Homo
I
------- I
Species
erectus
I
..,.,..
(-II-developed brain)
Agure t .21 The classification of humans.
11
Human beings belong in the kingdom Animalia because we are multicellular
and heterotrophic. We belong in the phylum Chordata and the sub-phylum
Vertebrata because we have a backbone. We are in the class Mammalia
because we have hair, are warm-blooded and suckle our young. We are in the
order Primates with all the other monkeys and apes. We belong to the family
Hominidae which are the human-like apes. In the past, this family bas included
several genera including the genus Homo, grouped by the structure of the skull
and teeth . There have also been other species of Homo in th e past, for example
Homo erectus. However, that species is separated from the modern Homo sapiens .
because they had more body hair and a smaller brain . AJI people today belong
to the species H omo sapiens because they all have the same characteristics.
Table 1.3 sh ows how the ocelot starts in the sam e large groups as humans
but is pla ced in a dillerent group from the level of Order down. It is grouped
with all the other kinds of cat.
Classification group
Humans
Ocelot
Kingdom
Animalia
Animalia
Phylum
Chordata
Chordata
Sub-phylum
Vertebrata
Vertebrata
Class
Mammalia
Mammalia
Order
Primates
Carnivora
Family
Hominidae
Felidae
Genus
Homo
Leopardus
Species
sapiens
pardalis
Table 1.3 Classification of humans and ocelot.
1Chapter summary
-
------
• A huge variety of living forms exist on planet Earth .
• All living organisms show the seven characteristics of life: growth, respiration,
irritability, movement, nutrition, excretion and reproduction.
• Living organisms are grouped into five kingdoms: prokaryotes, protoctists, fungi,
plants and animals. ·
• The prokaryotes are bacteria.
• The protoctists include algae and protozoa.
• The fungi include yeasts and toadstools.
• The plants are mostly photosynthetic (make their own food).
• The animals need to get their food by eating plants or other animals.
• The phyla of animals are cnidarians, platyhelminths, molluscs, annelids, arthropods,
nematodes and chordates.
• The chordates include fish, amphibian, reptiles, birds and mammals.
• Each major group or phylum is broken down into smaller groups.
• Organisms can be classified according to similarities in their visible characteristics.
• A dichotomous key is a tool for classifying organisms by asking a series of yes/no
questions in a step-by-step fashion until you are led to the name of the organism.
• Each species has a common name and a scientific name.
• A species is a group of similar organisms that can interbreed.
12
~
·Jiii
The presence of water, suitable temperature range, the presence of
gases in the atmosphere, like oxygen and carbon dioxide.
ITQ2 (i) Most plants are able to make their own food in a process called
photosynthesis.
(ii) A plant moves by growing towards light from the environment.
ITQ3 Prokaryotes (bacteria) , protoctists (algae and protozoans), fungi
(moulds, yeasts and mushrooms} , plants (mosses, liverworts, ferns, conifers
and flowering plants), animals (invertebrates and vertebrates).
ITQ4 Microscopic means cannot be seen with the eye without the use of a
microscope because they are so small. Unicellular means made up of one cell.
A bacterium is a single cell which can carry out all the processes of life.
ITQS
Algae: Chlorella; protozoan: Amoeba. Both orgarusms have 'true' nuclei;
the chromosomes are enclosed in a membrane which is called a nucleus (so they
belong to the eukaryotes). (Bacteria differ from this and are prokaryotes.)
A difference between Ch/ore/la and Amoeba is that Chlorella has a chloroplast
and is able to photosynthesise or make its own food, while Amoeba cannot
photosynthesise and must feed on other organisms.
ITQ6 Yeast: to make bread. Mushrooms: for food. Moulds: to make the
antibiotic penicillin.
ITQ7 (i) Moss, lettuce, fern, croton and mango tree.
(ii) They produce oxygen which is need by anima ls for respiration.
They are a food source.
They can be used for medicinal purposes (herbs).
They hold topsoil in place.
They provide homes for animals.
ITQ8 Fish: shark, guppy. Amphibian: frog, toad . Reptile: snake, lizard. Bird:
parrot, duck. Mammal: lion, goat. (You may have thought of many other
examples.)
ITQ9 Two pairs of wings, three pairs of legs, body divided into three parts.
ITQ1
Examination-style questions
(i) (a) List the characteristics of life.
(b) Describe the importance of two of these characteristics.
(ii) Explain the difference between:
(a) the growth of a crystal and the growth of a plant.
(b) the movement of a cloud and the movement of an animal.
(iii) Robots have been built that move, detect and respond to various stimuli.
(a) In what ways is a robot similar to a human?
(b) What are some differences between a robot and a human?
2
(i) Living organisms can be classified into five kingdoms. List these five groups giving a
named example of each.
(ii) Describe two differences between vertebrates and invertebrates.
..
(iii) List the main characteristics of dicotyledons and monocotyledons in order to
distinguish between them.
(iv) Discuss the importance of microorganisms to humans.
13
(i)
3
Animals can be found almost anywhere on Earth. Describe how:
(a) a bird is adapted for flying.
(b) a fish is adapted for swimming.
(c) a bird is similar to a fish.
(d) a bird is different from a fish.
(ii) Humans are said to be closely related to chimpanzees.
(a) Explain why this is so by comparing visible differences and similarities between
humans and chimpanzees.
(b) Are there any similarities in their behaviour? Explain fully.
4
(i) List two features common to the organisms shown below.
(ii) Using each feature, classify the organisms. List the members of each group.
D
B
E
G
H
:;
.'
•'
14
5 cology and the
Impact of Abiotic
Factors on Living
Organisms
0
understand the terms 'ecology', 'ecosystem' and 'environment'
0
0
0
distinguish between abiotic and biotic factors
0
distinguish between population and species
0
0
0
relate the distribution of species to abiotic factors
distinguish between habitat and niche
d istinguish between community and population
describe the components of soil
understand the advantages and disadvantages of the use of natural and
chemical fertilisers
ecology
(
I
)
ecological
study
{
biotic factors
environmental
I
abiotic factors
ecosystem
I
r
distribution of
plants and animals
'
community
r
population
I
species
I
'
habitat
niche
Ecology
Ecology is the study of the relationsh ips of organisms with each other and
their environment. Togeth er, all the external con diti ons in which an organism
lives con stitute its en vironment.
Environmental factors
Environmental factors may be of two kinds:
• abiotic or ph ysical factors (non -living);
• biotic factors (living) .
15
Abiotic or physical factors
edaphic factors >
~
IT:Q1
V'--J
Examine figure 2.1 and its caption.
List: (i). two abiotic factors (ii) two
biotic factors you can deduce from
the images.
biotic factors >
(a)
• Cli matic factors such as light, temperature, rainfall, wind and availability of
water.
• Edaphic factors (associated with the soil) such as pH, texture,
temperature, organic and mineral content.
• Aquatic factors such as salinity, wave action and dissolved oxygen.
• Topographic factors (associated with physical features of the Ea rth's surface)
such as the angle of the slope.
Biotic factors
Biotic factors result from the activities of Jiving organisms in the
environment. Factors like predation, symbiosis, competition and disease ail
involve rhe living elements of the environment. All the relationships that exist
between the living organisms, including the feeding relationships (food chains
and food webs), camouOage, pollina tion and dispersal make up the biotic part
o( the environment.
(b)
~
IT:Q2
V'--J
Why is a home aquarium not selfsustaining while a backyard pond
might be?
1;mmmu
ecos stem >
(C)
Rgure 2. 1 (a) The white-lip anole lizard lives in tropical rainforest and feeds on insects. (b) The
bottle-nosed dolphin is a fast-swimming marine mammal that feeds on big-eye scad. The scad
swim in big shoals and dart back and forth when attacked to try to confuse the dolphin. (c) The
Caribbean flamingo feeds on tiny algae and shrimp which it filters from soda lake water with its
specialised bill. Other birds cannot feed in these lakes because soda is caustic.
Ecosystem, habitat, population, community
An ecosystem is a sell-sustaining system of organisms interacting w ith each
other and their environment. It is made up of all the plants and animals
~
sharing an environment. It is self-sustained wh en it can take care of itself - no
IT:Q3
V'--J
human imervenrion is needed to keep it going.
Distinguish between (i) habitat and
The area in which an organism lives is called its habitat, for example a small
niche (ii) population and community.
pond, a swamp or a rocky shore. A very small habitat is called a microhabitat,
for example the soil at the bottom of a pond, the roots of a mangrove tree,
leU3ftJ the crevice of a rock. A niche describes the role an organism plays within the
ecosystem. It how the organism lives in its habaitat.
population >
A population is a group of organisms of the same species which live
in a particular habitat. For example, in a pond ecosystem, there may be a
community > population of beetles and a population of snails. A community consists of
~
all the populations which live in the same place and interact with each other.
IT:Q4
V'--J
The community in the pond ecosystem is made up of populations of different
Using figure 2.2, describe: (i) a
species of organisms, feeding on each other, competing with each other,
population (ii) a habitat (iii) a niche (iv)
hiding and protecting each oth er and also communicating with each oth er
a community.
(figure 2.2).
16
Abiotic factors
Biotic factors
Water's edge Water column
Bottom
Water surface
Water column
B ottom
Water's edge
Waterlogged
soil
Variable light
Variable light
Birds - red seal coot
Variable 0 2
0 2 maybe low
Insects - water strider
Temperature
may vary
Dead/decaying
matter
Variable sediments
Plants - water lettuce
Microscopic organisms zooplankton, phytoplankton
Insects - water
boatman, diving beetle
Fish - guppy,
molly, tilapia, tarpon
Bacteria including
blue-greens
micro- and macro-algae
Shrimp
Snails
Dragonfly larvae
Flowering plants grasses, sedges
Crabs - land crab,
fiddler crab
Birds - egret,
sandpiper
Figure 2.2 The biotic and abiotic factors in a pond habitat, including the community and
populations of organisms living in the pond habitat.
Distribution of species
The distribution of species is related to the physical or abiotic fa ctors of the
environment as well as the availability of food or prey. A species is adapted t0
live in its environment. For example, camels are adapted to survive and live
in the desert, an extremely harsh environment. Other species simply cannot
live there. On ly animals that can tolera te dehydration and survive extremes of
temperature can be found there.
Effects of water on distribution
~
IT:QS
\./'-I
What are some factors or qualities
of water that determine the types of
organism that live in water?
Water is an abiotic factor that affects the distribution of species. Organism s like
fish and jellyfish that live in water must be able to use oxygen dissolved in
water or take their oxygen from the air above the water, like whales. If they
do not attach themselves to rocks or bury themselves in the seabed, they must
also be adapted to move in water.
There are two main kinds of water found on Earth :
• fresh water found in lakes, rivers and ponds;
• salt water found in the ocea ns and seas.
17
Living Organisms in tha Environment
Fresh water is low in salt and mineral content, but salt water can be very
concentrated. Where these two kinds of water meet, such as in estuaries, the
waters m ix to give brackish water.
Most anima l species are adapted to Live in either fresh water or salt water
(figure 2.3). Only a very few that live in estuaries or regularly migrate from
sea to river or back again (s uch as salmon and ee ls), can cope with the
different conditions.
Fish in a marine environment
Fish in a freshwater environment
gills actively excrete salt
to the water passing over them
gills actively ab sorb salt
from the water passing over them
drinks
sea water
t
does not
drink
fresh water
water constantly enters the
organism and collects in a vacuole
small amounts of
concentrated urine produced
too much salt is a problem
and is actively gotten rid of
l
large amounts of
dilute urine produced
too much water is a problem it is not actively taken in and
is actively gotten rid of
Agure 2.3 Adaptations of bony fishes to live in marine or freshwater environments.
Freshwater animals, like Amoeba, have mechan isms to get rid of the excess
water that enters their body by osmosis (figure 2.4).
~l
vacuole moves
to the cell --""-4
membrane
The water is actively expelled
from the contractile vacuole
of the Amoeba.
Figure 2.4 Amoebae can live 1n fresh
water because they are adapted to get
rid of the excess water m their bodies.
(a)
Some species do not Live in water, but it still determines their distribution .
Toads and frogs Li ve and feed on land but must return to water to reproduce.
They are always found near rivers, pon ds and lakes. Others return to water to
cool down and are found in or around areas with water.
The distribution of planes is also related to water. Plants n eed a constant
suppl y of water from the soil. Some actually live in wa ter, like water lilies.
Plants that live in areas where water is in shon supply are called xerophytes.
They have special fea tures which help reduce transpiration and therefore water
loss (figure 2.5). Some of these features are:
• redu ction of leaves to fine spikes (e.g. cacti);
• the stomata are sunken in grooves and reduced in number (e.g. oleander);
• the leaves roll into a cylindrical shape (e.g. marram grass).
(b)
Figure 2.5 (a) Cacti have leaves reduced to spines to reduce transpiration (b) Tile leaves of
oleander have stomata sunken in grooves to reduce water loss.
18
-
- __-c- ~ • Ecology arid tt1e Impact of Abiotio Factors on Livin~ -011ganisiiis
The change from water to land along the edge of wa ter can create very clear
zones of vegetation. Plant species that are more tolerant of having their roots
submerged in water for long periods of time, such as the red mangrove, are
fo und at the edge of the water. These species are replaced further inland by
th ose which can tolerate some su bmersion, such as the black mangrove, and
even further inland by those whkh are adapted to cope with on ly a li ttle
submersion, such as the white mangrove (fi gure 2.6).
Red mangrove
Black mangrove
White mangrove
pneumatophores that
are wider, knobby and
less dense
thick stilt roots or prop roots
support and spread the weight
of the tree in the soft soil
slender aerial roots
hang from the trees
nutritive roots
absorb nutrients
anchoring roots
Excrete salt through
their leaves
An indication of drier,
better soil. They have
normal root systems.
Excrete salt through
glands in the petioles
J
Excrete salt through
salt glands
Low tide
SEA (SALl) WATER
Mangrove zonation
Rgure 2.6 Zonation of vegetation along the edge of a mangrove swamp.
19
,; . ~Living Organisms in the Environmer't
_.
Effect of light on distribution
~
ll!Q6
\../V
Name some herbivores that come
out at night to feed, hoping to
escape their predators.
(ii} Predators that hunt at night may
use mechanisms other than light
to detect their prey. Describe,
using examples, two other means
apart from light that can be used
to detect prey.
(i}
Light also affects the distribution of plants and animals throughout the Earth.
Animals use light mainly to see their prey (figure 2.7). Some use the absence of
light to escape predators.
Light is vita l to planes because it is needed for photosynthesis. Without light
a plant w ill die. Plants are not found in those areas of the Earth without light,
like deep caves and deep ocean fl oors. Two aspects of light, its duration and
its intensity, are important for the distribution of species, particularly plants . .
However, heat is usually associated with high light intensity or bright light, and
temperature is also an abiotic factor that affects species distribution.
Effect of temperature on distribution
Temperature also affects the distribution of species. Poikilothermic animal s are
particularly affected because their body temperature reflects the temperature
of the surroundings. If it is too cold, they cannot generate
eno ugh energy to move around to find food or escape
predators; if it is too hot, the proteins in their bodies start
to break down and they die.
Homeotbermic animals, such as mamma ls and birds,
may be able to live in a greater range of temperatures
but they show adaptations to cope with extremes of
temperature. Camels are adapted for desert life. Desert
hares have long ears which give off heat to keep the
animal cooL but arctic hares have very short ears to
reduce heat loss. Other mammals that live in the polar
regions, like the polar bear, have thick layers of body fat
and fur to keep them warm. Mammals such as whales,
walruses and seals, are also able to live in cold polar
waters because they have a thick layer of fat, called
Rgure 2.7 Chameleon actively hunts its prey.
blubber, just beneath the skin. This insulates them Crom
the cold: whale blubber can be up to 50 cm thick.
Effect of heavy metals on distribution
micronutrients >
20
Our environment, and in particular the sea, contains in large or smaller
amounts almost every metal known to humans. Life began in the sea and so
most living things, through the process of evolution, have acq uired a tolerance
for sma ll concentra tions of these metals. Some of them, such as copper, are
essential in trace quantities and are called micronut rients.
Metals such as copper, mercury and lead (called the heavy metals) are not
tolerated in more than trace amounts. In larger conce ntrations they become
toxic to animal and plant life, and we think of them as pollutants. These large
concentrations often arise as a result of human activities. For example, some
slag heaps on the island of Anglesey in the United Kingdom are so rich in
copper that nothing, except a few clumps of horsetail grass, will grow on them.
Mercury and lead are particularly dangerous to humans. The poisonous
effects of mercury have been known since Roman times. By the J 9th century,
mercury was widely used for 'silvering' mirrors, and for treating sexually
transmitted diseases. Makers of fe lt hats, who used mercury, suffered from
various nervous and mental disorders - hence the phrase 'mad as a hatter' .
As the chemical industry developed, organic compounds of mercury were
discovered. These are even more toxic because they bind to proteins and fats
in body cells. The cells of the brain and the nervous system appear to be more
. affected by these compounds and nowadays many mercury compounds which
were once commonly used, for example as seed dressings, are prohibited.
Lead is hardly less dangerous. Lead compounds damage the brain,
particularly in young children, and lead poisoning can ca use to serious
mental disorders. Th e three main ways in which lead was released into the
environment were from local water pipes, from lead compounds in paint and
from additives in petrol. In many countries alJ three are now prohibited.
Tolerance to heavy metals like lead, copper, zinc and mercury, is inherited
and passed on to offspring. Random mutations can result in some organisms
having greater tolerance to heavy metals th an others. Plants may be able to:
• trap heavy metals in the cellulose cell walls;
• confine the metals to the vacuoles;
• excrete the metals back in to the environment.
These heavy-metal tolerant plants are rarely found in unpolluted areas as they
are less competitive than other plants. They flourish in polluted areas as the
heavy metals kill the competing plants. Tolerant plants pass on th~ir tolerance
to their offspring.
Effect of soil on distribution
~
Practical activity
SBA 2.2: Water-holding capacity of three
types of soil, page 338
Practical activity
SBA 2.3: Percentage of water in a soil
sample, page 339
Practical activity
SBA 2.4: Percentage of air in a soil
sample. page 340
Soil supports terrestrial life. For plants, it provides an anchor for roots and is a
medium for nutrients. It acts as a ·sponge for water, holding it for absorption by
the roots of plants. Plants are able to grow where the soil can provide all their
needs. This means that soil type is very important to the distribu tion of plants.
Animals depend on plants which depend on soil. Thus soil is also and so
important to the distribution of terrestrial animals. It provides shelter for
subterranean animals, but more importantly, thousands of microbes exist in
soil tl1at replenish the microbes that live in the digestive tracts of herbivores.
Humans have adapted to life on land. We build homes on land and depend
on agriculture for our food. All crops require special types of soil. The soil
sustains all forms of life across the planet. .
,.Chapter summary
I~
II
• Ecology is the study of the relationships of organisms with each other and their
environment.
• There are two kinds of environmental factors: abiotic and biotic.
• Abiotic factors make up the non-living part of the environment.
• Biotic factors result from the activities of the living organisms in the environment.
• An ecological study involves looking at the biotic and abiotic factors of an area.
• Sampling methods include quadrats, line transects and sweep nets.
• A habitat is a place or area where an organism lives.
• A niche is the role an organism plays within the ecosystem.
• A species is a group of organisms that can interbreed and are adapted to live in their
environment.
• A population is a group of organisms of the same species living in an area.
• A community consists of all the populations living in the same area.
• The abiotic factors of an environment affect the distribution of the species found
there.
• Water and light are examples of abiotic factors that affect the distribution of species.
21
Living Organisms Jrr:t11 e~_En_1.1i_r:onn1e_n~,
-
.
_·
__ ~
ITQ1
J
Abiotic factors
Biotic factors
The temperature of water.
Feeding relationships, e.g. between the lizard
and insects that are its prey.
The amount of light available to the organisms. Behaviour of scad when attached by dolphin.
You may have noted other examples from the pictures.
A home aquarium is a limited ecosystem; it doesn't contain the
diversity of species that would be found in the naute. A backyard pond is more
likely to be a complete ecosystem with all the diversity necessa ry to sustain
itself.
ITQ3 (i) A habita t is the place where an orga nism li ves. A niche is the role an
organism plays in an ecosystem. (ii) population is a group of organisms of one
species living together in one habitat. A community is all the populations of all
the organisms living together in an ecosystem.
ITQ4 (i) A population is a group of organisms, all of the same species living
together in one habitat. In this pond there are populations of many different
species of fish and plants. (ii) A habitat is the place where an organism lives.
The habitat is the pond. (iii) A niche is the role an organism plays in an
ecosystem. Each organism in the pond has its own niche. (iv) A commun ity
is all the populations Jiving together. This pond community includes the
populations of au the plants, fish and other animals found there.
ITQS Water may be salt water or fresh water. Salt water makes up the
oceans and seas. Fresh water includes the lakes, rivers and ponds. Water
can be stagnant or fast-fl owing and all the stages in between. Rocky shores
have strong curren ts and wave action . Mangrove swamps have brackish
water, which is a mix of salt and fresh. Orga nisms are adapted to live in these
different habitats.
ITQ6 (i) Examples are fruit-eating bats, and agouti which feed on fruits
and seeds; there are many others that you might have thought of. (ii)
Snakes have heat sensors found in pits on their face which can determine
the presence of other living organisms. Snakes also use their forked tongue
to pick up tiny particles left by an organism in the air. The tongue is then
pushed into the pits of the mouth, and the snake 'tastes' the organism.
Many other organisms use scent to find food. Insect-eating bats use sonar, or
sound, to determine exactly what is around them and help them catch prey.
ITQ2
Examination-style questions
(i)
Explain, using examples, the meaning of the terms:
(a) abiotic factor;
(b) biotic factor.
(ii) Define:
(a) environment;
(b) habitat;
(c) population;
(d) community.
(iii) Describe, using examples, how abiotic factors of the environment affect the
distribution of species.
(iv) (a) Amoebae live in fresh and salt water habitats. Describe a major problem of
amoebae living in fresh water.
22
(b) Explain how Amoeba is adapted to live in fresh water.
An ecological study was conducted in a cocoa estate and the data collected by a
student are seen below.
2
Animals caught in the
sweep net
Animals seen
Plants seen
spider
beetle
caterpillar
grasshopper
other (unidentified)
frog
kiskadee
lizard
worm
squirrel
dog
iguana
millipede
grass
mango tree
cocoa tree
unknown shrubs
coffee tree
pea plant
pomerac tree
Quadrat throw
Millipedes
Spider
1
40
4
2
30
0
3
10
0
4
5
0
5
23
6
28
2
7
51
3
8
19
4
9
37
0
10
40
{
(i) Construct a possible food web from the plants and animals recorded.
(ii) These organisms interact with each other in a number of ways. Suggest two possible
relationships that may exist between the organisms recorded. Using names examples,
describe fully each example.
(iii) Suggest some sources of error when using sweep nets.
(iv) Calculate the population density of the millipede and spider.
(v) The area studied was approximately 12 m wide and 20 m long. Calculate the
population size for the millipede and spider.
(vi) Describe fully how a quadrat can be used to estimate the number of organisms
present in an area.
(vii) Compare the use of the quadrat for these two organisms, millipede and spiders. Which
do you think are the more accurate results? Explain why.
23
Fieeding Relationships
betvveen Organisms
0
understand the meaning of the terms producers and consumers in a food chain
and relate the position in the food chain to the mode of feeding
0
0
0
0
understand the terms herbivore, carnivore and omnivore
0
0
identify a food chain
identify predator/prey relationships
construct a food web that includes different trophic levels
explain the role of decomposers
understand that special relationships ex ist and discuss the advantages and
disadvantages of such relationships
food chain
first
trophic level
second
trophic level
third
trophic level
fourth
trophic level
producer
primary
consumer
secondary
consumer
tertiary
consumer
plants
herbivore
carnivore
carnivore
l
)
symbiosis - relationships
between organisms of
different species
decomposers
food web - interlinking
of food chains
I
parasitism
commensalism
mutualism
predator/prey
CHAPTER 9
Phytoplankton are microscopic organisms,
like algae and blue-green bacteria that live in
the oceans. They are seen in rivers, lakes and
puddles of water. They are important since they
start food chains in the world 's oceans or seas.
Around deep-ocean hot water vents, there are bacteria wh ich get their
n utrients and energy from the wa ter. These bacteria are the food for animals,
an d these food ch ains are the only ones we know on Earth which do not
depend on the Sun for th eir energy.
Life depends on photosynthesis which is carried out by planes (chapter 9).
Most animals get their n utrients (their source of energy) either directly or
indirectly from p lants. Plants photosynthesise or make food from water and
carbon dioxide, using light energy from the Sun to carry out the process. So
the Su n is the ultimate source of energy for almost all life on Earth.
Producers and consumers
Plants are called producers because they produce or make their own food.
They include mosses and green plants on land, and algae, aquatic planes and
phytoplankton in water. Organisms that consume the plants or producers,
ma in ly the animals, are ca lled consumers (figure 3. 1). Decomposers feed on
dead o rganic matter (figure 3.2).
nutrients (humus) made
available by decomposers
!
producer
consumer
consumer
plant - - - - - - caterpillar - - - - - + small bird
~
1 /
they all die and their bodies are eaten
~i/
decomposers
~turn nutrients to the soil
/
Figure 3.2
dead fruit.
Mould (a fungus) feeding on
producer
in the form of humus
consumer
etc ..... .
Figure 3. 1 The relat1onsh1p between producers, consumers and decomposers
Herbivores, carnivores and omnivores
herbivores >
Herbivores are organisms that feed only on plants. Examples are some insects
(like grasshoppers, locusts, butterflies, bees), some birds (such as seed-eating
and fruit-eating species) and some mammals (cows, horses, elephants, giraffes).
In water, herbivores may be very large like the manatee or very small like
a shrimp.
carnivores >
Carnivores are organisms that feed only on anima ls. They may hunt and
kill other animals for food. Examples include some insects (like the praying
mantis), some reptiles (such as snakes), some birds (eagles and hawks) and
some mammals (lions, dolphins and leopards).
lelulm1•li4-tl
Omnivores feed on both plants and animals. Examples are pigs and
humans.
Food chains
food chain >
A food chain is a simple diagram that shows how the food or nutrients (the
energy source) pass from one organism to another. For example:
leaf-+ caterpillar-+ small bird -+ hawk
The arrows show the movement of energy along the food chain.
The leaf is a part of a green plant that is photosynthesising and is a producer.
The caterpillar eats the leaf to get food (energy) to live and is thus a consumer.
The sma ll bird and the hawk are also consumers because they are getting their
food or energy from eating other organisms. Indirectly, their food comes from
the leaf, since the food made by the leaf is first taken into the caterpillar, then
into the sma ll bird as it feeds on the caterpillar and fina lly to the hawk. So all
the consumers in the food chain ultimately get their food from the producer.
We can also describe the food chain in terms of herbivores and carnivores.
Herbivores feed on the plants or producers and then the carnivores feed on the
herbivores. An omnivore may feed on the producer or herbivore (and even
carnivore in some cases).
producer -+ herbivore -+ carnivore
(grass)\ (chi:ken) (mongoose)
omnivore
(h uman )
25
Herbivores can only feed on the producers and are called the primary
consumers. Carnivores which feed on herbivores are secondary consumers.
Tertiary consumers feed on the secondary consumers and so on.
producer --+ primary consumer --+ secondary consumer --+ tertiary --+ consumer
Example: waterweed
Producer
trophic level >
A food chain is composed of trophic levels.
--+
tadpoles --+ small fish --+ bigger fish
primary
secondary
tertiary
(1°ry)
(2°ry)
(3°ry)
consumer
consuITier
consumer
Each organisITI in the food chain represents a trophic level. The three food
chains below each consist of four trophic levels.
These are examples of terrestrial food chains.
Food chain I
leaf --+ caterpillar -+ toad -+ snake
Food chain II
grass --+ grasshopper -+ insect-eating bird --+ hawk
This is an example of an aquatic food chain.
Food chain ill
algae -+ sna il -+ leech -+ fish
Table 3.1 Shows how the organisms of these three different food chains can be
classified.
Food chain I Food chain II Food chain
Ill
Type of
feeder
Consumer level Trophic level
leaf
producer
producer
first trophic level ·
herbivore
primary
consumer
second trophic
level
carnivore
secondary
consumer
third trophic level
carnivore
tertiary consumer fourth trophic
level
grass
t
caterpillar
t
t
t
insect-eating leech
bird
t
snake
t
grasshopper snail
t
toad
algae
t
hawk
t
fish
Table 3. 1 Different ways to classify organisms in food chains
CHAPTER 4
All food chains have certain characteristics in common, as seen in table 3.1.
The number of trophic levels in a food chain is normally limited to four or five,
since the amount of energy being passed on gets smaller and smaller at each
level (d1apter 4).
Predators and prey
i•li§•F?U•li•-11
i!mlfJd
Animals also show predator/prey relationships. Predators are carnivores that
feed on other animals that are called their prey. Predators hunt, capture, kill
and eat other anima ls and those that are hunted and eaten are the prey. Food
chains therefore include predators. They are the higher order consumers.
rosebush -+ aphid -+ ladybird -+ spider -+ insectivorous bird
26
Prey
Predator
aphid
-+
ladybird
ladybird
-+
spider
spider
-+
bird
Table 3.2 Predator/prey relationships in the
rosebush food chain.
In this food chain, while the spider is a predator because it kills and eats the
ladybird, it is also prey to the insectivorous bird. The food chain shows three
predator/prey relationships(table 3 .2)
Animals that are prey have evolved to hide and escape predators, using
characteristics such as camouflage, mirrticry and speed. Predators, on the other
hand, have evolved characteristics to improve their chances of catching prey,
like speed, lures and traps.
When all these organisms die, decomposers return their nutrients to the'
plants through the soil, and the nutrients return to other feeding animals in
the food chains.
Food webs
A food chain shows one organism feeding on one other organism only, but
feeding relationships are more complex than this. One organism may feed on
a number of organisms and in turn may be eaten by a number of organisms.
The interlinking of a number of food chains is called a food web (figures 3.3
and 3.4) .
•?a7
\../'-)
From the food web shown in figure 3.3:
(i) name (a) two herbivores, and (b)
two carnivores.
(ii) give the name of an organism
which is
(a) a primary consumer;
(b} a secondary consumer;
(c) a producer;
(d) a tertiary consumer;
(e) both a secondary and tertiary
consumer.
(iii) name (a} two predators, and (b}
two prey.
(iv) name an organism found in:
(a) the first trophic level;
(b) the third trophic level.
~
IT:Q2
frog
rat
I
butterfly
caterpillar
hibiscus plant
grasshopper
snail
\)
mango tree
grass
Rgure 3.3 A terrestrial food web.
warbine
l
due'
_
-
cosf rob
\../'-)
Construct a food web seen in a (i}
marine habitat (ii) a tree (such as a
mango tree).
~
~ water beetle
mayfly nymph
/
water boatman
water-flea
~
pond weed
l
algae
Figure 3.4 A freshwater (aquatic) food web.
27
Decomposers and detritivores
decomposer >
CHAPTER 5
~
IT:Q3
\../'--)
Define the terms 'producer', 'consumer'
and 'decomposer' and give two named
examples of each.
All living organisms eventually die. Their bodies are composed of complex
compounds like carbohydrates, lipids and proteins that they stored when
they were alive. T\.vo groups of organisms called the decomposers and
detritivores obtain their food or energy from the remains of the dead
organisms. As they feed on the dead organisms they cause their decay or
decomposition (figure 3.5). They help in the recycling of nutrients (chapter 5)
since they return the nutrients trapped in the dead organisms back to the
environment. The nutrients become available again to living organisms.
Dead organism
fungi and bacteria
simple substances
complex compounds
(proteins, lipids,
- - - - - - - - - - - - • (carbon dioxide (CO:U.
carbohydrates, etc.)
compounds of ammonia
(NH:i) from the proteins)
carbon dioxide (C02) released into the air
as the fungi and bacteria respire
fungi and bacteria live
f
f
/
in the dead organism
SOIL
ammonia is released into the soil and
combines with substances in the soil
to form ammonium compounds
/
after some time the dead
organism is broken down
completely by the fungi
and bacteria
SOIL
Agure 3.5 A dead organism decays or decomposes as fungi and bacteria feed on it.
1n11 ..11i.9
saprophyte >
~
IT:Q~
\../'--)
Draw a diagram to show the feeding
relationship between a producer, a
consumer and a decomposer using
examples from your answer to ITQ3.
lullil!mH•i••U
28
Decomposers include bacteria and fungi. They secrete enzymes which break
down dead plants and animal material into a substance called humus. Humus
enriches and improves the structure of soils in which plants grow and from
which they derive nutrients. Imagine the build-up of dead plants and animals
on the Earth's surface if there were no decomposers. All the vital chemical
elements or nutrients trapped in these dead organisms would not be able to
return to living organisms or be recycled.
Detritivores also help in the removal and recycling of dead o rganisms by
feeding on small fragments of the dead material, which are called detritus.
Examples of detritivores include woodlice and earthworms.
Saprophyte is the name given to any organism that feeds on dead organic
material, so decomposers and detritivores are all saprophytes.
Special relationships
The environment supports a host of organisms all living together. But some
organisms live in very special relationships with each other. These relationships
may be advantageous to all the organisms involved but, sometimes, one
organism can cause harm to another.
Symbiosis describes any relationship that exists when different species of
organisms live together. There are three types of symbiosis:
• mutualism;
• commensalism;
• parasitism.
3 · Feeding Relationsl1ips between Organisrns
Mutual ism
In this kind of association,
CHAPTER 5
two organisms of different
species Live closely together
and both benefit. Here are
some examples.
• Some sea anemones
and hermit crabs - The
anemone attaches itself
to the shell used by the
hermit crab and obtains
scraps of food as the crab
feeds. The crab gains
protection from predators
as it is camouflaged by the
anemone and protected
Figure 3. 6 A hermit crab and sea anemone.
from preda tors by the
stinging tentacles (figure 3.6).
• Leguminous plants and the bacterium Rhizobium (chapter 5) -The
bacteria live inside swellings on the roots of the leguminous plants, like peas
and beans. These bacteria convert nitrogen gas into ammonia, which is then
con vened into arp.ino acids and used by the plants for growth. The plants
benefit because they can thrive in a LI types of soil, even soil where nitrate
is in short supply. The bacteria also benefit by having a place to live and an
e nergy supply which they ger from the plant.
• Egret and cow - The egret perches on th e cow's back as it feeds on insects
and aradmids, especially ticks that can harm the cow. The egret is obtaining
food and the cow benefits by having blood-sucking insects removed from
its body.
Commensalism
commensalism >
~
IT:QS
I../'-)
Using named examples, distinguish
between mutualism and
commensalism.
Commensalism is a
relationship between two
species in which one clearly
benefits and the other is
not harmed. Here are some
examples.
• Some orchids or ferns
on trees - The orchids
or fems are small plants
that grow high on tbe
tree to obtain sunligh t
for photosynthesis
(figure 3.7). They use the Rgure 3.7 An orchid growing on a tree.
tree for support but n ot as
a food source. The tree is not harmed, nor does it benefit.
• Egret and cow - When the egret walks behind the cow, it feeds o n insects
that fl y up as the cow sha kes the grass while it walks. The egret benefits but
the cow does not.
• Shark and remora - The remora attaches itself to the shark and moves
around with it. As the shark feeds, the remora also feeds on scraps of food
that are floating around. The remora obtains food wh ile the shark is not
harmed, but nor does it benefit.
29
Living Organisms in the Environment
Parasitism
l•l§liU-1H51J
ectoparasite >
endoparasite >
A parasite is an organism wh ich lives and feeds on or ins ide another
o rganism , which is called the host. The parasite gains while the host is harmed.
• Parasites wh ich live on the outer surface of their hosts are called
ectopa rasites. For example, ticks, lice, fleas a nd leeches feed on th e blood
of th eir h osts such as dogs, hwnans, cattle and fish (figure 3.8).
• Parasites that live within a h ost are called endoparasites . An example in
humans is th e o rganism which causes mala ria. A protozoan of the genus
P/asmodium enters the human bloodstream through the bite of an infected
female Anopheles mosquito. Once in th e body, the parasite multiplies,
ca using bo uts of fever, pain, shivering and sweatin g. Millio ns of people
die each year from malaria, although anti-malarial drugs like quinine and
choroquinine have been developed.
,,
Chapter summary
Figure 3.8 A leech sucks blood from a
human
•
•
•
•
•
•
•
•
•
•
•
•
•
•
The Sun is the ultimate source of energy for most life on Earth.
Plants make food and are called producers.
Animals eat plants or other animals and are called consumers.
A diagram which shows the sequence in which organisms feed on each other is
called a food chain .
A food web shows the interlinking of a number of food chains.
Decomposers feed on dead plants and animals.
Herbivores feed on plants alone.
Carnivores feed on animals alone.
Omnivores feed on both plants and animals.
Symbiosis describes relationships between two different species.
Mutualism describes a relationship where both species benefit.
Commensalism is when one species benefits and the other is not harmed but nor
does it benefit.
In a parasitic relationship, one species benefits at the expense of the other.
Predators are carnivores that feed on other animals which are called their prey.
II
II
ITQ1 (i) (a) Aphid, butterfly, hummingbird, beetle, caterpillar, grasshopper
or snail.
(b) Ladybird, frog, kiskedee, tarantula, rar. snake, mongoose or hawk.
(ii)
(a) Aphid, butterfly, beetle, hu mm ingbird, caterpilla r, grasshopper or
sna il
(b) Ladybird, frog, kiskedee, tarantula, rat
(c) Hibiscus, mango tree, grass
(d) Frog, snake, mo ngoose, hawk
(e) Frog, hawk
(i ii) (a) Ladybird, frog, kiskedee, tarantula, ra t, snake, mongoose or h awk
(b) Snake, frog, ladybird, kiskedee, ta rantula, rat hummingbird, aphid,
beetle, caterpillar, grasshopper o r snail
(1v)
(a) Hibiscus, mango or grass
(b) Ladybird, hawk, kiskedee, frog, tarantu la or rat
30
ITQ2
killer whale
'
(
penguin
seal
\.
J
fish
'
(
krill
zooplankton
\.
J
bachae
phytoplankton
mango tree
Foodweb for a marine habitat
Foodweb for a mango tree
ITQ3 A producer is an organism tha t produces or makes organic food. A
plant makes organic food during photosynthesis, so any plant is a producer.
Examples are mango tree and hibiscus plant, bu t you may have thought of
many others.
A consumer is an organism that eats or consumes organic food. Animals
cannot make their own food, so any animal is a consumer. Examples are
caterpillars and humans.
A decomposer is an organism that feeds on dead organic food (dead animals
and plants). The food is said to be decaying or rotting as the decomposer feeds
on it. Examples are bacteria, fungi.
ITQ4 hibiscus plant -+ caterpillar
bacteria/
Mutualism and commensalism are both relationships between two
species or partners that are beneficial or good. In mutualism, both partners
benefit. In commensalism, one partner benefits while the other, though not
benefitting from the relationship, is not harmed in any way.
An example of mutua lism is between the pigeon pea plant (leguminous
plant) and Rhizobium bacteria that live in swellings of its roots. The pigeon pea
plant gets amino acids for growth, and the bacteria obtain shelter and energy.
An example of commensalism is seen with sharks and remora
fish . The remora fish obtain food an d protection from the shark
which benefits nothing from the relationship and is also not harmed.
ITQ5
Examination-style questions
(i) Construct a food web from the information given in the table.
Animal
What it was seen doing
small moth
feeding on nectar of a flower (morning glory)
lizard
feeding on insects
small bird
with a lizard in its beak
spider
feeding on insects trapped in its web
small butterfly
feeding on the nectar of a flower (lxora)
31
(ii) Examine the food web constructed and describe three consequences of the removal
of the lizards.
(iii) Describe the relationship between:
(a) the moth and the morning glory;
(b) the spider and the moth.
(iv) Name one predator/prey relationship from the food web and describe:
{
(a) how the predator is adapted to catch its prey;
(b) any feature used by the prey to escape the predator.
2
(i)
Using named examples, describe a:
(a) parasite relationship;
(b) mutualistic relationship.
(ii) (a) Draw a food chain with four trophic levels. (Use named organisms.)
(b) Identify the producer.
(c) How does the organism in the fourth trophic level obtain energy from the Sun?
(d) Which organism is the primary consumer?
(iii) Which organism in the food chain is a:
(a) herbivore?
(b) carnivore?
(c) predator?
(d) prey?
(iv) Describe the role of the decomposers in the food chain.
(v) Copy the table below and use examples from these food chains to complete it.
root -+ earthworm - frog - fox
pondweed - mayfly nymph -+ water beetle
Stages of food chain
producer
primary consumer
predator
prey
herbivore
second trophic level
third trophic level
first trophic level
32
Two examples of organisms, one from each food chain
Eicosystem,
Habitat, Population,
Community
0
0
0
0
0
0
understand that the Sun is the ultimate source of energy for life on Earth
explain why food is the source of energy needed by living organisms
understand that respiration is the process by which energy is released from
food
describe pyramids of energy
d escribe pyramids of numbers
d escribe pyramids of biomass
food chain
plant makes food using
light energy from Sun - - - - ,
some energy passed on
energy lost due to
animal eats and obtains ~ ~espiration , in
food (chemical energy) - - - - - i
urine and faeces
I some energy passed on J
animal - - - - - - -
(
)
food - source of
energy for all organisms
feeding pyramids:
• energy
• numbers
• biomass
I
importance of photosynthesis
to food chains
All living organisms need energy to carry out life processes; for example your
body uses energy to grow, move, inhale and eat. The energy that your body
is using came from your food. U you made a food web for everything you eat,
you would find that all the energy you use was trapped by plants from tbe
Sun. Ultimately, all energy for life comes from the Sun.
Trapping the Sun's energy
Plants use the Sun's energy to make food during photosynthesis (chapter 9).
During photosynthesis carbon dioxide and water are combined to make
glucose and oxygen.
energy from the Sun
carbon dioxide + water-------+ oxygen + glucose
The glucose is then used to make other carbohydrates, lipids and protein s
and everything else the plant needs. These become the components of food
(chapter 13) for consumers. The term 'food' can thus be used for the term
'energy', beca use energy is released from food.
33
Living Organisms in the Environment
respiration >
~
IT:.Q·1
\_.)'...J
Why is the Sun considered to be the
ultimate source of energy for all life
on Earth?
So the energy in the light from the Sun is converted to chemical energy (as
glucose and other chemicals) in the plant. The chemical energy (as food) then
passes on to consumers as they feed on the plants (figure 4.1).
Respiration releases the energy trapped in the food so that it can be used
by the organism. Respiration also makes carbon dioxide and water.
Food (usually glucose) is ' burnt' during respiration by plants and animals
to release energy so that they can carry out all the processes necessary for life.
So, not all the energy gained by a plant is passed on to an animal that eats the
plant (figure 4.2). Likewise, not all the energy gained by an animal is passed on
to a predator (figure 4.3)
glucose+ oxygen-+ energy+ carbon dioxide+ water
energy from
Sun passed to
Plants ·
(photosynthesis)
make
food/chemical energy
l l
energy from
plants passed to
Animals
(when they feed on plants)
During respiration this
energy is made available to be
used for everyday activities.
Rgure 4. 1 Energy from the Sun is
used by plants and by animals.
Rest of energy
stored in plant
tissues. Passed
on to herbivores
when they feed
on plant
light energy
energy
taken in
energy
stored
energy
lost
Some energy changed
to heat during respiration,
for life processes.
Heat lost to the environment
Rgure 4.2 Only some of the energy taken up
by a plant can be passed on to a herbivore.
Energy passed
on to carnivore
when it eats
the COW
Rgure 4.3 Only some of the energy that an animal gains through eating can be passed on to a
predator.
34
How a plant gains and loses energy
~
IT:Q2
V'-'
What happens to the energy that a plant
gains during photosynthesis?
• A plant gains energy wh en it converts light energy to chemical energy
during photosynthesis.
• It stores some of the energy by changing the glucose it made into other
chemicals.
• It uses up some of the food during respiration to release energy to grow and
carry out other llie processes. Some of the energy that is released is lost as
heat energy from the plant.
How an animal gains and loses energy
For each animal at each trophic level:
• energy is gained as the organ ism feed s;
• some of this energy is stored as tissue as the animal grows;
• some energy is lost as faeces and urine straight out of the animal's body;
• some of the stored energy is relea sed du ring respiration for the organism to
stay alive and some of that energy is lost as heat to th e envirom11ent.
~
IT:Q3
V'-'
What happens to the energy that an
animal obtains?
Movement of energy through a food chain
Energy flow through a food chain or web is related to the movement of food
through the chain. Figure 4.4 shows the movement of energy through a
food chain.
Energy lost as
heat due to
respiration
~l
PLANT
Energy stored
in tissue
-
Energy lost as
heat due to
respiration
Energy lost as
heat due to
respiration
Energy lost as
heat due to
respiration
l
l
l
HERBIVORE or
PRIMARY
CONSUMER
CARNIVORE or
SECONDARY
CONSUMER
CARNIVORE or
TERTIARY
CONSUMER
Energy stored
In tis_sue
-
Energy stored
in tissue
--·---------,
!
!
!
Energy lost
in urine
and faeces
Energy lost
in urine
and faeces
Energy lost
in urine
and faeces
Figure 4.4 Movement of energy through a food chain.
~
IT:Q~
V'-'
How is energy transferred through a
food chain?
~
IT:QS
V'-'
What is the importance of respiration in
a food chain?
Figure 4.4 shows that energy is lost at every step in the food chain. This means
there is less energy at each level for the animals in tha t level than in the level
below. The length of a food chain is limited by the energy loss at each level.
There will come a point when there is not enough energy to support another
level. There are usually not more than five steps in any food chain.
When the plants and animals die, the energy stored in the dead bodies is
passed on to the detritivores and decomposers as they feed. They also feed on
the urine and faeces made by animals.
35
Living Organisms in the Environment
CHAPTER 5
l•n•1uh-S-»
productivity >
Unlike energy, the elemencs of which organisms are made, such as carbon
and nitrogen, are recycled (chapter 5).
Energy is not recycled, it moves through and out of the food chains. Energy
enters a food chain as light energy from the Sun, and is lost from every trophic
level as hear energy ro the environment. Its flow is non-cycl ical, which means
that the energy cannot be returned to a living organism.
The length of a food chain depends on the energy in the biomass availabJe
at each level. Ultimately this depends on how much energy is being trapped
by the producers (their productivity). If the whole ecosystem is highly
productive, then the food chains will be longer because there w ill be more
energy entering at the producer level of the chain. If there is on ly a small
amount of energy being trapped by the producers, then they can support only
a few trophic levels (figure 4.5) . Ecosystems in eq uatorial regions are generally
more prod uctive tha n those in higher latitudes because they get more light
(figure 4.6).
fJl!I
Productivity of
ecosystem
is high
plant
fJl!I
Prod uctivity of
ecosystem
is low
plant
fJl!I
energy loss
-
energy loss
fJlt energy loss
-
~
energy loss
-
Figure 4.5 The productivity of the producers in an ecosystem limits the length of food chains that
can be supported
(a)
(b)
Figure 4. 6 (al Ecosystem of high productivity. (b) Ecosystem of low product1v1ty
Crop plants are mass-harvested for human consumption. If these plants are
eaten directly by humans, a lot more energy can be obtained by the humans
than if the plants were fed to other animals and those animals then eaten by
h umans (figures 4.7 and 4.8).
36
•
f/11
energy loss
-"
energy
~
energy loss
energy loss
energy
energy
~
energy
HUMANS
Figure 4. 7 Efficient use of food chain for energy by
humans.
f/11
energy
OTHER
ANIMAL
-
HUMANS
Figure 4.8 Inefficient use of food chain; a lot of energy is lost that could be available to
humans.
Pyramids of energy
pyramid of energy >
A pyram id of energy is a good way of showing the energy relationships
between organisms in different trophic levels. Figure 4. 9 shows the pyramid of
energy for a simple food chain . Each block in the pyramid shows the amount
of energy available to the next trophic level.
Using figure 4.9 as an example, 90 000 units of energy are available to the
grasshoppers. The grasshoppers consume that energy as food and lose some
of it to the environment as heat during respiration and activity, and some of
it as faeces. That leaves only 15 000 units for the insect-eating birds. The birds
consume that energy and lose some of it to the environment in faeces and as
heat. So only 2000 units are available to the next level, the cats. The cats lose
energy to the environment as faeces and as heat, leaving only 100 units of
energy in their bodies. This is not enough to support another trophic level, so
there are only four trophic levels in this chain.
grass ---+ grasshopper ---+ insect-eating bird ---+ cat
TERTIARY
CONSUMER
SECONDARY
CONSUMER
PRIMARY
CONSUMER
100
units of energy
2000
units of energy
15 000
r--___.__ , _ ___ - - --- - -
PRODUCER
A pyramid - each block gets
smaller as you go up
90000
unit s of energy
Pyramid of energy
Figure 4.9 A pyramid of energy shows that less and less energy is available to higher trophic
levels in a food chain.
Pyramids of numbers
pyramid of numbers >
A pyramid of n u mbers is like a pyramid of energy but shows the numbers
of all the organisms at each trophic level of a food chain within a given area .
Look at the pyramid in figure 4.10 (overleaf). The pyramid shows that, within
the area being studied there were 80 leaves. On these leaves, 8 caterpillars
were feeding. Tvvo birds were seen feeding on the caterpillars and one cat ate
both birds.
Ecosystems usually contain a large number of sma ll organisms and a smaller
number of large animals. Predators are usually larger than their prey and must
eat a number of them to stay alive.
37
Ll:ving Or-ganisms in the Environment
1O leaves
grasshopper --....___
10 leaves - - - - - - - - - - - grasshopper - - ---...,.
_ __,.
• bird
grasshopper --------------•~
1O leaves
10 leaves - - - - - - - - - - - • grasshopper
101eaves - - - - - - - - - - - •
10 leaves - - - - - - - - - - - •
~
~
cat
Each cat eats 2 birds
a day
10 leaves - - - - - - - - - - - •
101eaves - - - - - - - - - - - •
Each grasshopper eats
10 leaves each day
cat
bird
grasshopper
leaves
Figure 4.10 A pyramid of numbers is obtained by counting all the individuals at each trophic level.
With this type of ecological pyramid, no allowance is made for the size
of the organism. Each cat and ea ch caterpillar is each counted as one. So
sometimes we can see different shapes in pyramids of numbers (figure 4.11 ).
One tree may be eaten by many caterpillars, though we could have counted
each leaf separately to get a ' normal' pyramid shape. One dog is host to many
ticks, and each tick may have several parasites, but in this case each 'predator'
is actually smaller than its 'prey'.
Figure 4.11
pyramid of biomass )
hawk
parasites
on ticks
small
bird
ticks
caterpillar
dog
Some pyramids of numbers are of different shapes.
Pyramids of biomass
Instead of estimating the numbers of organisms at each trophic level we can
estimate their biomass or dry weight. From this we can construct a pyramid
showing the biomass of organisms at a given time in each trophic level. The
width of the boxes indicates the relative amounts of biomass present at each
trophic level.
At the start of the food chain in figure 4.12 is a large biomass of green
leaves. The p yramid shows that a large amount of plant material supports a
smaller mass of herbivores and an even smaller mass of carnivores.
mass of
tertiary
consumers
mass of
secondary
consumers
mass of
primary
consumers
mass of producers
Rgure 4. 12 A pyramid of biomass.
38
Bioaccumulation
Pesticides can spread through the environment in a food chain. Pesticides (such
as fungicides, herbicides and insecticides) are chemicals that are toxic to some
organisms. They work in one of two ways, on contact or once the chemical has
entered the organism. A grasshopper feeding on plants sprayed with insecticide
will only need to take in a small amount to kill it.
But this can harm other animals in the food chain. For example, a bird
feeding on the grasshoppers will accumulate in its body all the insecticide
that the grasshoppers have ingested. Remember that the bird will eat a large
number of grasshoppers every day. So the bird may end up with levels of
insecticide high enough to poison it or harm it in some way. A hawk or other
predator feeding on the small birds could end up with even higher levels
of pesticide in its body, again enough to poison or harm it. This is called
bioaccumulation or biological magnification.
DDT (dichlorodiphenyltrichloroethane)
DDT provides a well-known example of bioaccumulation (figure 4.13). It is
a very effective insecticide that was used in many countries in the 1950s and
1960s to control mosquitoes, which carry malaria, and to control other insect
pests. However, DDT is stored in fatty tissue so predators absorb the chemical
when they eat prey that contains it. Levels of DDT that accumulate in the
bodies of top predators may be enough to kill them or to harm them in other
ways. In a study of ospreys (North American birds) adult birds were found
to contain 8 million times more DDT than organisms at the bottom of the
food chain. These high concentrations did not kill the birds, but caused the
females to lay eggs with very thin shells. Many eggs broke and so numbers of
these birds dropped rapidly. Since 1972 the use of DDT has been banned in
many countries.
DDT accumulates
in the top consumers
fish eats herbivore
and accumulates DDT
124 ppm DDT
5 ppm DDT
herbivore eats
phytoplankton and
accumulates DDT
1 ppm DDT
Producer 0.0025 ppm DDT
DDT enters
phytoplankton
run-off from agricultural land
carries a dilute solution of
pesticides, e.g. DDT
Figure 4. 13 Pesticides like DDT accumulate In the tissues of each trophic level of a food chain.
39
- - Living Orgar:iisms In :the£nvir_o11rn_~~t
_
r
Chapter summary
• Energy from the Sun is used by plants to make food during photosynthesis.
• The equation for photosynthesis is:
carbon dioxide + water + light energy -+ glucose (food) + oxygen
• The energy that is stored in a plant is passed on to other organisms when they feed
on the plant.
• Respiration releases energy in plants and animals for life and growth.
• The equation for respiration is:
food (glucose) + oxygen -+ energy + carbon dioxide + water
I •
Most of the energy released in respiration is lost as heat to the environment and
cannot be passed on to the next trophic level.
• A pyramid of energy shows that less and less energy is passed on to the higher
trophic levels of a food chain.
• A pyramid of numbers shows.the number of organisms found in each trophic level of
a food chain .
• If the dry mass of the organisms at each tropic level of a food chain is measured, a
pyramid of biomass can be produced.
The energy from the Sun is used by plants or producers to make
organic food that is used directly and indirectly by all animals, including
humans. Withou t the Sun, plants would die so there would be no food for the
animals. They would also die and life, as w e kn ow it, would cease to exist.
ITQ2 A plan t stores som e of the energy in its tissues as it grows and uses
som e en ergy to stay alive. Some energy is lost as heat en ergy. Som e en ergy is
thus lost to the environment and some is kept in th e plant's body.
ITQ3 An animal uses some of the energy from respiration to stay alive.
Much of the energy is lost to the environment as heat . The animal may use up
more energy than a plant sin ce it is more active. It also stores some energy as
ch emical energy in its tissues as it grows.
ITQ4 Energy is transferred from one trophic or feeding level to another
when an organism feeds. En ergy is transferred in the form of food. Th e food
is n eeded for respiration which makes energy available to the organism. So
energy moves through a food ch ain when the organisms eat.
ITQS Some of the ene rgy tha t is released during respiration is lost to
the en vironment in the form of heat from the organism. Respiration is
important in a food chain because at each level in th e food chain en ergy
is lost. Only a proportion of the energy entering one trophic level is stored
in the organism 's body and is thus available to the next trophic level.
ITQ1
Examination-style questions
grass
(i)
grasshopper
bi re
Copy the diagram above and, using arrows, annotate it to show the movement of
energy into and out of each organism.
(ii) What is the importance of the following in a food chain:
(a) respiration?
(b) photosynthesis?
40
(c} digestion?
(iii} How is light energy converted to chemical energy?
(iv} Most animals spend a great percentage of their day looking for food. Why must
animals eat food?
(v) On the TV programme Sesame Street, there is a story about a boy who ate the Sun.
What do you think of this story? Give details.
2
(
Food chain A
grass --+ cow --+ tick --+ egret
Food chain B
grass --+ grasshopper --+ izard
(i}
Construct possible pyramids of numbers for food chains A and B. In each case,
discuss the shape of the pyramid.
(ii} Construct possible pyramids of energy for the same two food chains, A and B. Discuss
the shapes of the pyramids.
cat
bird
grasshopper
I
leaves
I
(iii} Look at the pyramid of energy above. Why do leaves contain the greatest amount of
energy?
(iv} What happens to the energy that is not passed on to the grasshoppers?
(v} What will happen to the cats if all the grasshoppers were killed by the use of
insecticide?
41
0
0
0
0
0
explain the carbon cycle
understand what is meant by the greenhouse effect and global warming
explain the importance of nitrogen to plants and animals
explain the nitrogen cycle
describe the causes and effects of acid rain
atoms in
animals
atoms in
plants
,..-
carbon
carbon hydrogen
hydrogen
oxygen
oxygen
.-+-- nitrogen - - - - - - - - - - - nitrogen _ ......_
others
others
biogeochemical cycles
atoms in the
environment
carbon
hydrogen
oxygen
- - - - - - - - - - nitrogen _.i_ _ _ _ _ _ _ _ _.,
others
(
greenhouse effect
)
acid rain
leaching
global warming
Biogeochemical cycles
Living organisms are made u p of different kinds of atoms. The most common
atoms are carbon, hydrogen and oxygen, with nitrogen following closely
behind. Smaller amounts of other atoms, such as iron, calcium and sodium, are
also found in living organisms.
These atoms bond together to form larger structures such as protein,
carbohydrates and lipids. These larger structures are then arranged in particular
ways to make up all the tissues needed to build a living organism. All living
organisms are, in essence, complex structures of organic molecules. If we look
at a person, we see skin, hair and nails - it is difficult to imagine that basically
we are just atoms of carbon, hydrogen, oxygen and nitrogen.
A carbon atom that was present in Einstein's
body could be present in your body right now.
biogeo chemical cycles >
Remember that carbon is found in carbon dioxide
(C0 2) , carbohydrates, lipids and proteins, since
carbon is an integral part of those compounds.
As an animal grows from birth to adulthood, the growing tissues come from
the food it eats. The animal increases its store of these atoms as it eats and
m uscle, bone and all the tissues that make up the organism increase in mass.
Then, when the organism dies, the body is broken down or decomposed, and
the atoms are released back into the environment.
The atoms become pan of the soil as the organism 's decomposed body
becomes mixed into the soil. They may then be taken up by plants and built.
into the plant's tissues as the plant absorbs them from the soil with water.
These plants are then eaten by animals and the atoms thus become part of an .
animal once again.
The cycling processed by which these essential atoms are released and
reused in nature are called biogeochemical cycles. The carbon and nitrogen
cycles are examples of such cycles.
The carbon cycle
The carbon cycle shows how c;arbon atoms are passed from one organism to
another and to their environment as they live, breathe, eat, die and decay. The
numbers of the following paragraphs refer to numbers in figures 5.1 and 5.2.
carbon dioxide (CO:z)
in the air (0.04%)
photosynthesis
organic
compounds
in green
plants
respiration
combustion
respiration
eaten by animals
------....i
death and decay
death and decay
fossilisation
organic
compounds
in bacteria
and fungi
..........
-..,;.;_~
fossilisation
organic
compounds
in fossil
fuels
~~------------'
Figure 5. 1 The carbon cycle shown 1n d1agrammat1c form
Equation for respiration:
food (glucose) + oxygen -+ energy +
carbon dioxide + water
1
.~
2
What atoms are living organisms
made up of?
(ii) How do they obtain these
components?
(iii) What happens to these
components after the organism
dies?
(iv) What is a biogeochemical cycle?
3
\./'-I
(i)
4
5
6
The atmosphere contains about 0.04% carbon dioxide. During
photosynthesis, plants use carbon dioxide from the atmosphere to make
carbohydrates, proteins and lipids. This is the first source of carbon in living
organisms - as a part of the plant's body.
Animals then obtain their supply of carbon by eating plants or other
animals that have eaten plants.
As plants and animals respire, molecules of carbon dioxide are released
back into the atmosphere.
Waste materials from living organisms (like urine and faeces) and their
dead bodies (all organisms die) , are used as food sources by decomposers.
Decomposers, like bacteria and fungi, feed on dead organic matter. Carbon
atoms then become incorporated into the bodies of the decomposers.
Respiration of the decomposers releases carbon dioxide into the
atmosphere.
In waterlogged soils where oxygen is in short supply, decomposers are
not able to break down tissues completely in dead bodies and the remains
43
Livir1g Organisms in lhe Environment
lt•1"1§!1(!tfUflJ
7
accumulate. For example, in the Carboniferous period (about 290 million
years ago) huge areas of waterlogged swamps covered many parts of the
world. When the swamp plants died, partially decomposed plant material
accumulated and eventually turned to coal, a solid fossil fuel. Oil and
natural gas are liquid fossil fuels that formed in a similar way from the
remains of plants and animals that died in oceans. Fossil fuels contain a
large proportion of carbon.
The burning of fossil fuels (combustion) releases carbon dioxide into the
atmosphere.
l~ndioxide
in~the air
photosynthesis
Z combustion
..
gas
coal
decomposers
in the soil
respiration
of decomposers
Figure 5.2 The carbon cycle in more detail.
~
l'.T:Q2
\..AJ
(i) What is the importance of
photosynthesis in the carbon
cycle?
(ii) What is the importance of
respiration in the carbon cycle?
(iii) What is combustion?
(iv) What role do decomposers play in
the carbon cycle?
44
And so the cycle continues, carbon dioxide in the atmosphere is taken up by
plants, which are eaten by anin1als, and returned to the atmosphere through
respiration, decomposition or combustion of fossi l fuels.
Note the importance of plants in this cycle. Without plants, the carbon stays
in the atmosphere and cannot be reused and incorporated into the bodies of
animals. If there were no plants, there wou ld be no animals.
The human effect on the carbon cycle
Figure 5.3 shows how the level of carbon dioxide in the air has been rising.
The rise in human population has been supported by an increase in
manufacturing and other types of industries. Since the Industrial Revolution,
humans have been burning fossil fuels to release energy for machines. This has
added carbon dioxide to the air at an alarmingly fast rate. The carbon was locked
away in the solid or liquid forms of fossil fu el for millions of years. Increased
combustion of these fossil fuels increases the carbon dioxide concentration
in the air. Increased concentration of carbon dioxide in the atmosphere is
associated with the environmental problem known as global warming.
- - -
-
-
-
-
-----
-
-
5 --The Cycling of ~utrients
-
The Industrial Revolution is a term used to describe the time when people
started to make and use machines to do a lot of their work. It began about 200
years ago. Machines need energy to make them work, and most of this energy
comes from burning fossil fuels.
7
Carbon emission from burning of fossil fuels
(billion tonnes)
370
6
360
5
350
4
340
3
330
2
320
Atmospheric carbon dioxide
(parts per million)
310
300
0
290
1840
1860
1880
1900
1920
1940
1960
1980
2000
'-~--'--~--'-~-'-~~'--~-'---~-'-~--'-~-----'
~840
1860
1880
1900
Year
1920
1940
1960
1980
2000
Year
Figure 5.3 The levels of carbon dioxide in the atmosphere over the last 160 years.
The greenhouse effect and global warming
greenhouse gases >
greenhouse effect >
global warming >
When heat from the Sun reaches the Earth's surface much of it bounces
straight back into the atmosphere (figure 5.4). Within the Earth's atmosphere
there are gases like carbon dioxide and methane that absorb some of the
escaping heat and send it back to the Earth's surface, keeping it trapped around
the Earth. They act like a greenhouse around the Earth and thus are called
greenhou se gases.
This is a natural process which helps keep the surface of the Earth warm.
Without this natural greenhouse effect, the Earth would be too cold for most
of the organisms living on it.
A problem arises when the proportions of these gases in the atmosphere
increase . They bounce more of the heat back to the Earth's surface. This is
called the 'enhanced' greenhouse effect. As a result the temperature of the
Earth increases, which is known as global warming.
infrared radiation
(heat) radiated
back towards space
absorbed by
'greenhouse gases'
to space
incoming solar
radiation (ultraviolet,
visible and infrared)
reradiated
into space
atmosphere heated
- raising Earth's
temperature
reflection
from clouds
Earth
Figure 5.4 Some solar radiation that reaches the Earth is absorbed by the atmosphere rather than going back out to space.
45
Carbon dioxide concentration in the Earth's atmosphere has increased
by about 20 % over the last 100 years. This effect has also been worsened by
deforestation. Trees (forests) remove carbon dioxide from the atmosphere
during photosynthesis, but large areas of forests are being cut down.
It is not proven that higher carbon dioxide levels cause temperature
increase, but scientific research suggests that the two may be associated.
Some people think tha t global warming might cause the Earth's temperature
to rise between 1.5 °C and 4.5 °C by the end of the 2 1st century.
Possible effects of global warming
• The polar ice caps may melt which could cause sea levels all over the world
to rise significantly. Many millions of people now live in lowland areas and
these may be flooded, driving people from their h omes.
• Fertile, crop-producing land would be lost by flooding.
• The distribution of organisms over the face of the Earth may change as land
floods and temperature and rainfall patterns change.
• Changes in the amount of land and sea could change weather patterns. This
could increase rainfall in some places and increase periods of drought in
others. Natural storms like hurricanes and typhoons may be more severe.
• Cold countries may become more temperate and fertile.
~
IJ:Q3
\.../'-J
Why are the carbon dioxide levels
in the atmosphere rising?
(ii) What might be some consequences
of this rise?
(i)
We must be very careful not to say that every example of extreme weather
is due to global warming. There have always been variations in climate over
the years and over centuries. Also, we must be careful not to make unjustified
assumptions about fu ture changes. For example, on the island of Svalbard in
the Arctic Ocean, one of the glaciers is retreating, but a neighbouring glacier
has advanced by more than a mile in seven years. Some sea levels are said to
be lower now than in the 18th century - for example mean sea level in the
Cook Islands has apparently dropped by about 20 cm in 200 years. Globally,
mean sea level is rising at about 3 mm per year. So although global warming
is a reality, and many experts attribute this to the enhanced greenhouse effect,
we should not be too quick to predict catastrophe.
The nitrogen cycle
About 79 % of the air around us is nitrogen gas. This gas is very unreactive - it
passes in and ou t of animal's bodies unchanged when they breathe. However,
nitrogen is an essential component of biological molecules such as proteins and
DNA. Muscle is composed of long strands of protein and DNA is the m olecule
in each nucleus of a cell which contains the information about how to build
that cell and make it work.
Plants manufacture protein by absorbing nitrogen from the soil mostly as
nitrate ions. These are combined with carbon, hydrogen and oxygen taken
from glucose that was made during photosynthesis. The elements are then
arra nged in another way as they combine with the nitrogen, to make the
building blocks for proteins and DNA.
Remember that glucose is made during photosynthesis and is composed of
carbon, hydrogen and oxygen.
Animals obtain their nitrogen from the protein in their diet, through
eating plants or other animals. The protein they eat is digested, absorbed
and reused as needed in the feeding animal. That is, the nitrogen obtained
from the protein of a piece of plant material or meat can be used to build
growing muscles, make DNA, enzym es and other proteins, and everything else
requiring nitrogen.
The numbers of the following paragraphs refer to numbers in figure 5.5.
46
-
_
_
_ _
-
-
_
=- -_
5 /ftle Cycling ~ot, Nutrients
-
nitrogen in the air
nitrogen-fixing
bacteria
lightning
denitrifying
bacteria ·
animal protein
plants
eaten
nitrogen
oxide
in root nodules
Rhizobium
and decay
ammonium
compounds
plant protein
nitrifying bacteria
Nitrosomonas
rain
(acid rain)
nitrates
absorbed
in soil
Clostridium
nitrifying
bacteria
Nitrobacter
nitrates in the soil
nitrites
in soil
~1
leaching
of the soil
fertilisers
Figure 5.5 The nitrogen cycle shown in diagrammatic form.
nitrogen fixation >
I
2
nitrification >
3
denitrification >
4
5
Nitrogen fixation - This occurs in nitrogen-fixing bacteria that convert
nitrogen gas in the air to nitrate. Some of these bacteria, like Azotobacter
and Clostridium, live in in the soil and convert the nitrogen gas found in the
air in the soil to nitrate. Plants cannot absorb nitrogen gas, only substances
that contain it, like nitrates. So nitrogen-fixing bacteria thus make nitrogen
available to plants in a form they can absorb. Plants use the nitrogen from
nitrates in the soil to make proteins and DNA.
Other kinds of nitrogen-fixing bacteria, called Rhizobium, live in the roots
of legumes (plants of the pea family). There, nitrogen gas is converted to
nitrates and used directly inside the plant to make protein.
Decay - When plants and animals die, their bodies are decomposed by
decomposers to make ammonium compounds in the soil. Animal wastes,
like faeces and urine, are also decomposed by bacteria living freely in
the soil.
Nitrification - The ammonium compounds formed during decay are
converted to nitrites and then nitrates. The processes that lead to the
formation of nitrates in the soil are called nitrification and are carried
out by nitrifying bacteria like Nitrosomonas and Nitrobacter. Plants take up
n itrate ions from the soil and make proteins.
Denitrification - The nitrogen cycle is completed by denitrifying bacteria.
They convert nitrates in the soil back to nitrogen gas. The activities of these
bacteria reduce soil fertility, since they take nitrates out of the soil which
the plants need to grow well.
Lightning - This provides energy to convert a little nitrogen to nitrogen
oxides which dissolve in rain to form nitrates.
47
_
6
1@'30!.t•iJ
7
-~ ~-=
-
-
_-= ~ =_·_ ;;_~-:_~c ~~-.
-
.- Living Organisms ,in the E~w!ror~!])~_ml'._ _
-
-
Fertilisers - To make crops grow better, we add artificial and natural
fertilisers to the soil to increase the levels of nitrates.
Leaching - As rain water passes through the soil on its way to the rivers,
lakes or seas, it carries with it dissolved nitrates and other soil nutrients. So
the nitrates can be washed out of the soil. This is called leaching (figure 5.6).
~
IJ:Q'1
L)'...I
Copy and complete this table.
Process in
Importance Examples
nitrogen cycle
of bacteria
involved
river
nitrogen
fixation
soil water to river
takes nutrients with if
decay
Agure 5.6 Diagram showing how n1trates can be leached from soil.
nitrification
denitrification
CHAPTER 3
The nitrogen cyde is thus essential to life as nitrogen is a vital component of
every living organism (figure 5.7).
This biogeod1emical cycle allows nitrogen to be used over and over by
living organisms. Nitrogen atoms cannot be created and there is only a certain
amounc on Earth. The importance of bacteria should be noted because they
are an integral part of this cycle. Nitrifying bacteria can be considered 'good'
bacteria, without which living organisms would slowly become extinct. The
relationship be tween the plants and the nitrogen-fixing bacteria is an exampl e
of mutualism (chapter 3).
nitrogen in
the air
~
protein 1n
animals
nitrogenfixing
_bacteria
denrtrifying
bacteria
lightning
nitrogen fixation
Rhizoblum
nitrates in soil
N1trobacter
t
nitrites in soil
ammonium
compounds
In soil
Agure 5.7 The nitrogen cycle in more detail.
48
'
5 · The Cyclin~ of Nutri~nts
Acid rain
Ft;l•li:O.U
Combustion of fossil fuels in industry and from motor vehicles releases acidic
gases sud1 as sulfur dioxide and nitrogen dioxide. These gases dissolve in
atmospheric water vapour in clouds and later fall as acid rain (figure 5.8).
Sulfur dioxide dissolves in atmospheric water to give, eventually, dilute sulfuric
acid. Oxides of nitrogen dissolve to form dilute nitric acid.
oxides of sulfur and nitrogen
from pollution dissolve in water
in the cloud to make acid rain
acid pollutant s
from vehicles, power
stations and industry
pH of rain
4-5
pH of rain
5-7
Figure 5.8 The formation of acid rain.
pH is a measure of how acidic or how alkaline a
solution is. ApH of 7 is neutral. A solution with a
pH less than this is acidic. If it has a pH above 7,
it is alkaline.
The acid clouds may be carried hundreds of miles away from the source of the
pollution by air currents. It has been recorded that rain with a pH as low as 4
has fallen over Scandinavia, Germany and Canada.
• Acid rain may kill plants and
trees. Some forests, like the Black
Forest in Germany, have been
severely damaged (figure 5.9) .
But it has been found that acid
rain enhances the growth of pine
forests in Scandinavia.
• Acid rain also dissolves some
compounds of poisonous m etals
thus introducin g them into
lakes and rivers. This poisons
organisms living in the water.
Rgure 5.9 These trees have been killed by acid
About 400 lakes in Norway are
rain.
now rendered fishless because of
acid rain.
• In cities. stone (statues and carvings) and metal structures have been
damaged because of erosion due to acid ra in.
Governments are trying to reduce acid rain by introducing regulations th at
demand th.at industries do not release atmosph eric pollutants. The design of
engines for motor vehicles is also important to reduce the amount of pollutant
gases that they make.
49
'Y
Chapter summary
• Living organisms are built up from single atoms, mostly carbon, hydrogen, oxygen,
with some nitrogen, iron, calcium, sodium, sulfur and other elements.
• Biogeochemical cycles show how materials are reused in nature.
• The carbon cycle shows how carbon passes between the air, soil, plants and animals
and back again.
• The greenhouse effect is an important natural process, caused by greenhouse gases
in the atmosphere that absorb heat energy from the Sun and keep the surface of the
Earth warm enough for life as we know it.
• Increasing levels of carbon dioxide in the air could lead to global warming which
could affect sea levels and weather, with devastating consequences.
• The nitrogen cycle shows how nitrogen passes between air, soil, plants and animals
and back again. Bacteria are very important in this cycle.
• Acid rain forms when acidic gases such as sulfur dioxide and nitrogen dioxide
dissolve in atmospheric water vapour. It can be very damaging to life.
(i) A Living organism is composed of different forms of proteins,
carbohydrates and lipids. These are made up of atoms of carbon, hydrogen,
oxygen, nitrogen and other atoms such as sodium, calcium and iron. (ii)
An animal obtains these components when it feeds. Food is organic and
contains carbon, hydrogen, oxygen, nitrogen, sodium, calcium and iron, etc.
Food is ingested, digested, absorbed into blood and transported to all parts of
the body to build tissues. Plants take in simple inorganic molecules, carbon
dioxide and water from the atmosphere, and nitrates form the soil to build
their tissues. (iii) The large organic molecules in dead bodies are broken
down by decomposers and detritivores into their smaller components. Then
the components can return to the environment and be used again by other
organism s. They are recycled through living tissue in different organisms in
food chains. (iv) A biogeochernical cycle is a cycling process by which an atom
is released and reused in nature .
ITQ2 (i) Photosynthesis is an important part of the carbon cycle because
it is the only means by which carbon from the air is taken into an organism.
Plants take in carbon dioxide and turn the carbon into glucose and other
chemicals in the plant's tissues . When animals eat the plant, the carbon atoms
can then become part of the animal's tissues. (ii) Respiration is the means
by which carbon atoms get back into the air (a s carbon dioxide) from living
organisms. (iii) Combustion is the burning of fu els, a process which uses
oxygen. When fuels, such as wood, gas and coal, are burnt, carbon dioxide is
produced, thus returning carbon atoms to the air. (iv) Dead plants and animals
have carbon molecules, in carbohydrates, proteins and fats, trapped in their
bodies. Decomposers feed on the dead bodies and release the carbon to the
environment as carbon dioxide when they respire.
ITQ3 (i) Carbon dioxide levels in the atmosphere are rising because of
the vast amount of combustion of fossil fuels to release energy, especially in
industry. An increase in human population leads to a greater demand for
energy. Widespread deforestation adds to the problem. (ii) Global warming
(or the enhanced greenhouse effect) which could lead to higher temperatures,
melting of polar ice caps, flooding and changes in weather patterns.
ITQ1
50
ITQ4
Process in nitrogen
cycle
Importance
Examples of
bacteria involved
Nitrogen fixation
Nitrogen gas is converted to nitrates in the soil and Azotobacter
absorbed by plants; or to amino acids in the root
Rhizobium
nodules and used by the plant to make protein.
Decay
Tissues of plants and animals are broken down and Decay bacteria
their components can be reused. They are broken
down to ammonium compounds.
Nitrification
Ammonium compounds are converted to a more
usable form, nitrates. Nitrates are absorbed by
plants and used to make proteins.
Nitrosomonas
Nitrobacter
Denitrification
Nitrates are converted back to nitrogen gas in
the air.
Denitrifying bacteria
Examination-style questions
(i) Using only an annotated diagram, describe the carbon cycle.
(ii) In the carbon cycle, carbon 'moves' as it becomes incorporated into the bodies of
organisms or is released into the environment during various processes. Copy and
complete the table below to show the movement of carbon in the processes listed.
Movement of carbon
Process
From
To
respiration in an animal
combustion of coal
photosynthesis
decomposition
(iii) State three ways human activities add carbon to the atmosphere.
(iv) State four possible effects of global warming.
2
(i)
Copy and complete the diagram of the nitrogen cycle shown below.
nitrogen in the air
c
ammonium compounds
A
nitrate In soil
(ii) Describe what happens at A, B and C.
(iii) How are some plants like the garden pea able to survive in soil deficient in nitrates?
(iv) Describe how nitrates are leached from the soil.
(v) Describe an example of symbiosis as seen in the nitrogen cycle.
(vi) Nitrogen is a vital component of every living organism. Describe its importance.
51
Aopulation Grovvth,
Natural Resources
and their Limits
0
0
0
0
0
understand that factors affect the growth of natural populations
understand why humans are not subject to the same constraints as other
organisms
describe various resources and their limits
understand the advantage and difficulties of recycling manufactured materials
consider biodegradable and non-biodegradable materials
population growth
(
1
population growth of humans
natural population growth
I
depletion of
i i"'
renewable
resources - (
non-renewable
manufactured
materials - - - -· recycle
r
biodegradable
'
non-biodegradable
11
reuse
I
reduce
Growth of natural populations
A population is composed of all the members of the same species living
together in the same place. Many populations live together as a community
occupying the same habitat. A population size may grow or decline depending
on condjtions at the time. If food is rearuly available, or there is adequate
space, then the population may grow (the number of individuals or members
of the species may increase).
Consider a population colonising a new habitat in which conditions are
initially ideal.
l At first, there are few reproducing individuals and population growth rate
is slow.
2 Then, since there is an abundant food supply, no competitors, no predators
or rusease, population growth rapidly reaches its maximum rate. Birth rate
exceeds death rate and the population size doubles at regular intervals. This
phase is called the exponential growth phase or log phase.
3 Exponential growth cannot. and does not, go on forever. Eventually
the population growth slows down. This is because of various factors in
the environment sud1 as lack of food or space, increase in numbers of
predators, increased competition or an increase in the incidence of disease.
4
sigmoid growth curve >
The population growth rate slows down and stops and the population size
remains fairly constant.
Figure 6. 1 shows the typical growth curve resulting from steps 1-4 above . It is
called a sigmoid growth curve (or S curve).
little
growth
rapid
growth
growth
slows
down
3
2
no growth, population
size is constant
---
4
''
''
Growth parameter
(e.g. number of
individuals In the
population)
\,- - A population may decline,
for example through sudden
disease, a serious change in
the environment or an
increase in predation.
(An example of this is humans
over-fishing a lake.)
Figure 6. 1 A typical growth curve.
Factors which reduce population size
carrying capacity >
QSb
l:t:Q-1
V'-1
What is meant by 'an environment can
carry a certain number of organisms of
a population?'
The maximum population size that can be sustained over a period of time by
the environment is called the carrying capacity of the en vironment. The
environment has enough space, food and whatever is needed to sustain or
'carry' a certain number of individuals. Some individuals die from disease or
predation (eaten by p redators). However, the death rate is more or less equal
to the birth rate as the population stabilises. Disease and predators help to keep
the population size 'in check' or constant or stable.
This will continue until there is a major change in the en vironment. For
example, a natural disease may develop in a popula tion that could wipe ou t or
kill most of the individuals. The popula tion size would then decrease drastically
(figure 6.2).
population size
increases
plenty of suitable space
few predators
able to avoid predators
good food supply
good water supply
ability to resist disease
suitable abiotic conditions
~--------- (e.g. light, soil type, ideal temperature)
population size
poor food supply
many predators present
inability to avoid
predators
population size
decreases
inadequate water supply
susceptible to disease
unsuitable abiotic conditions
(e.g. extreme temperatures, poor soil)
Figure 6.2 Some of the factors affecting population size.
Alterna tively, another organism may arrive in a habitat. It may be 'fitter' (more
able to adapt to small environmental changes), or a better competitor for space
and food, or it may reproduce at a faster rate than already existing populations.
53
Living Organisms in the Environment
~
IT:Q2
l..l'V
How is it possible for the planet Earth
to carry all of the different kinds of
animals and plants known to exist
on it?
This organism could ' take over' the habitat as its population size increases
causing others to decrease. Such an organism is called an invasive species.
Or, a natural disaster cou ld drastically reduce population size as many
individuals are killed, damaged or left homeless. For example, a fire blazing
through a forest could kill many of the organ isms there.
Growth of the human population
Humans are subject to the same
constraints as other organisms. They
need space for homes and adequate
food fo r th eir families . They are a lso
9
susceptible to many types of disease:
8
hereditary, deficiency, physiological and
7
Assuming an average of
6
pathogenic. Pathogenic diseases can be
2.6 children per woman
5
considered to be predators of humans.
4
At present, it is estimated that there
Assuming an average of
3
2.1 children per woman
are
about 7.2 billion peop le on Earth.
2
The
human population growth curve in
1
o ~~~~~~~~~~~~~~~~~~~
figure 6.3 shows that the population is
1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050
now doubling abour every 44 years.
Human population growth depends
Figure 6.3 The human population growth curve 1950- 2050.
on th e carrying capacity of th e Earth, or
the maximum number of people that the Earth could sustain over a long time.
Uni red Nation analysts predict that rhe world population may stabilise at about
12 billion in abo ut 120 years' time. Although humans are subject to the same
constra ints as other populations. they have actively worked on overcoming chem.
• Space - Humans have developed the equipment to move into and inhabit
most places in the world. Forests are cleared, coastal ;-va ters are filled and
developed for h ouses, and deseRs are made inhabitable. Some apartment
blocks are over JOO storeys h igh, to increase the possible living space.
Some people live permanently in boats on rivers and coasts. Humans need
space for h omes and also for factories and industries to support their needs
(figure 6.4).
• Food - Humans practise agriculture, which is the mass production of
food. Farming techniques and. more recently, developments in genetic
engineering, have increased agricultural and livestock ou tputs .
• Disease - Humans are constantly studying diseases, their causes,
symptoms, prevention and cures. Prenatal and postnaral care, and well developed immunisation programmes, prevent the death of millions of
children. Education about disease. technology to prolong life, development
Agure 6.4 Humans can adapt how they
of vaccina tions and gen etic engineering help preven t dea th from disease.
live in order to create more space.
• Predators - Humans invented gunpowder, which gave them an advantage
over all other animals, even those much larger and fiercer than themselves.
Humans no longer have any effective predator.
12
11
10
Population (billions)
~
IT:Q3
l..l'V
The activities of humans can cause the
sizes of populations of other organisms
to change. Using examples of animals
or plants, discuss how humans can
cause these population increases and
population decreases.
54
Some environmentalists believe that we need to do something now to curb
our population growth because of tl1e way we are exploiting the environment.
Imagine ha ving to feed 7.2 billion people every day. They say that food
resources may be used up, but there is still an abundance of food in the world.
However, agriculrural practices encourage pathogens, pests a nd parasites
to fl ourish . Others point o ut that as a population becomes more advanced,
popu lation growth slows naturall y.
For the moment, disease is still the greatest controlling factor on human
morta lity (death rate). Even with all our resea rch and technology, there is
still a prevale nce of disease. In developing countries, such as Africa, Cen tral
6 · Population Growth, Natural Resources and their Limits
~
IT:Q~
V'-J
Discuss four ways humans have
'conquered disease'.
America and India, overcrowding and poor living conditions and medical care
have led to prevalence of infectious diseases. In more developed countries, like
USA, Canada, Japan and the UK, a far smaller percentage of people die from
infectious disease. Most deaths in these areas are due to degenerative diseases
(those that get worse with time) , some of which are social and self-inflicted
in nature. Smoking can cause harm in a number of ways (cancer, brond1itis,
asthma). Misusing drugs like alcohol and heroin may lead to the development
of physical and mental disease. Eating large quantities of salty and fatty foods
puts people at risk of becoming obese and then at risk of obesity-related
diseases (diabetes, hypertension, heart disease). People in developed countries
generally live longer than those in less-developed countries, and so there is a
greater prevalence of diseases related to old age.
Population growth is a function of how many individuals that are born
survive to adulthood and reproduction. Birth rate and death rate are therefore
important controlling factors . In natural populations, these are not usually
under the control of the individual, but in humans we have a greatly reduced
death rate. We can also do something that very few other species can do:
control birth rate. In many developed counh·ies, birth rate has fa ll en to
around the same level as the death rate because of the use of contraception,
so population numbers in those countries are stabilising. In a few countries,
population size is actually falling. But there are still large areas of the world
where population size in increasing rapidly.
Resources and their limits
~
IT:QS
V'-J
Name two renewable resources and
two non-renewable resources.
renewable resource
non-renewa e resource >
Figure 6.5 The solar energy panel provides
a renewable electricity supply to the house.
Resources are features of the environment that can be used by human society.
There are many different types of resource whid1 indude:
• mineral resources like bauxite and other metal ores;
• soil resources for agriculture;
• biotic resources, like fish and plants for food and other purposes;
• water;
• fuel and other energy resources, like petroleum and natural gas.
Resources can also be class ified as renewable or non-renewable. A
renewable resource is one which can be reused or quickly replaced. Nonrenewable resources are in limited supply and once they are used up, they are
gone forever.
• Mineral resources are non-renewable: once they have been removed from
the ground they cannot be replaced.
• Soil resources remain renewable so long as the soil is cared for properly, but
if damaged by pollution or washed away by rainfall, soil is non-renewable.
• Biotic resources (including for food and timber for paper) are renewable so
long as they are cared for and managed properly.
• Water resources are renewable so long as we prevent the water from
becoming contaminated with pollution.
• Fuel resources based on fossil fuels (e.g. oU, coal and natural gas) are
non-renewable; others (e.g. wind, sunlight and water) are renewable
(figure 6.5).
Energy resources
Some form of energy is used for every form of human activity. In the past,
renewable energy sources like wind, water and firewood were used. Today,
most energy is derived from fossil fuels, like coal, oil and natural gas.
55
-
-
-.
-
--Liv
Jna:.Ol1c-1c:\r.i.i$r'llllai,i_
r:t~tt~ ~E"rn.v11JQl1~fil)lj
_-~
~ ----~~;;t__
- ~---- --
-
·=
_
_
-
_- -----=--_ --~=. ·
At present, the m ost impo rtant commercial energy resources in the
Caribbean are oil and natural gas which are fou nd m a inly in and aro und
Trinidad an d Tobago (figure 6.6).
L liquified natural gas plant
R oil refinery
c cement plant
.
• Point Usas
II oilfield
oil
.coal
gas field
•
•
oilfield with gas
natural gas
nuclear energy
gas pipeline
firewood and
biomass energy
hydroelectric,
geothermal, etc.
(a)
(b)
Figure 6.6 (a) On-shore and in-shore gas and oil fields of Trinidad; Large oil and gas fields are also found to the north-west and east
of Trinidad (b) Percentage share of Trinidad and Tobago energy source.
Local mineral resources
Bauxite from Kwakwani is transported
to Everton by barge for processing.
Bauxite from ltunl is transported to
Linden by rail. Bauxite and alumina
from Linden and Everton are exported
by ship.
Baux ite is a red clay, an ore from wh ich alumin ium is
obta ined. Bauxite is important in th e econ omies of Guyana
and Jama ica (figure 6.7). Alumin ium and its alloys are u sed
in the m anufacture of a ircra ft, trains, buses, cooking foil
an d man y other item s. Ba ux ite mining uses a large area of
land. In Jamaica, there are regu lation s which en sure th at:
• land rema ins in agricultural use until mining begin s;
• after mining, land is restored fo r oth er u ses.
When land is cleared for mining, the topsoil is removed
and p reserved for later use since it con tains most of the
nutrients and organic m a tter. After m ining, the land is
smoothed, reshaped and th e topsoil replaced. Fertilisers
can be added . The reclaimed land can be used for pasture,
h o using o r small-scale farming.
Reducing resource consumption
o processing plant
bauxite bearing area
.& Berbice Deepwater Facility
e
mining area
•
alumina plant (closed)
-
rail transport of Bauxite
-
water transport of Bauxite
Figure 6.7 The bauxite industry of Guyana.
56
By definition, n on -ren ewable resources will eventually
run o ut if w e continue to u se them . In order to preserve as
much of these resources as p ossible for future gen eration s,
people are being tau gh t to:
• re use;
• reduce;
• recycle.
This is particularly important in rela tion to discarded
m anu factured materials such as paper, glass, metals,
plastics and textiles. Human s are th e o nly species to use
th ese materials.
biodegradable '>
These manufactured materials are used at home, school offices and factories
and after a while they are discarded because they are worn out, used up or
no longer needed. The average composition of domestic waste is shown in
figure 6.8.
When discarded into the environment, some of these materials break
down naturally into simpler, usually harmless forms, by the action of
microorganisms. These are called biodegradable materials, and include
organic material, paper, some textiles and plastics.
Non-biodegradable materials, such as metals, glass and other kinds of
plastic, cannot be broken down or take a very long time to do so. As a result,
these wastes accumulate in the environment, leading to all kinds of pollution
of soil and water. The useful life of a fast-food package is often minutes, but it
may persist in the environment for years or centuries.
Reuse
H•lui•M•iH
Some types of waste can be reused in the same or other ways. For example,
tins and jars can be reused as eontainers, soda bottles may be returned to the
company for refilling and organic waste can be made into compost . Compost
is used as a natural fertiliser and soil conditioner (figure 6. 9, overleaf).
Reduce
Table 6.1 list some manufactured materials together with their sources and
uses. By simply reducing the accumulation of these manufactured materials,
the amount of discarded waste will be reduced, and less pollution will take
place. We can do this by buying only what is needed and choosing products
that are not over-packaged.
thers
~
textiles
7 .3%
5.5%
Manufactured
material
Source
Uses
paper
pulp from wood
writing, printing, wrapping
glass
molten mixture of soda ash,
silica.sand and lime
bottles, windows, spectacles, drinking
utensils, containers, ornaments
metals
iron, gold, tin, aluminium
cars, ships, buildings, containers,
electrical appliances, cables (and
many others)
plastics
petroleum
bottles, bags, containers, kitchen
utensils, cases for appliances, fibres
organics
26.7%
paper
19.7%
Table 6. 1 Some manufactured materials, their sources and uses.
Figure 6.8 Pie chart showing the average
composition of domestic waste.
57
Living Organisms in the Environment
(a)
(b)
Figure 6.9 Recycling in the Caribbean. (a) Collecting glass for recycling. (bl Collecting plastic for recycling.
Recycle
This is the process of collecting materials from the waste stream, separating
them by type, remaking them into new products, and marketing and reusing
the materials as new products.
Advantages of recycling
• Resources will not be used up as quickly, so there will be more for later
generations.
• Less land is needed for disposal of waste.
• Less pollution of soil and water occurs as waste decomposes.
• Less toxic waste is generated.
• Harm to animals is prevented (for example, plastic bags and glass are a
danger to animals).
• In many cases, less energy is used to recycle than to make a new product.
Difficulties of recycling
Collection of recyclables is rime-consuming. Each household must sort and h ave
suitable containers for rubbish and recyclables. The recyclables must be further
separated into glass, metal, plastic and so on, and placed in separate containers.
A problem is that recycle bins or containers must be provided and placed at
strategic p laces that are accessible to all. People must be educated about the
importance of separating their garbage and how to separate their garbage.
The recyclable materials must then be transported to recycling factories by
trucks or vans. Money must be spent on vehicles, maintenance of the vehicles
and gas. This uses fuel resources which must be taken into account when
trying to judge whether it is worthwhile recycling a material.
Tonnes of recyclables are collected weekly and there mu st be vast amounts
of storage space. There must also be space for the recycling facto ries and for
storage of the new product (figure 6.10) .
58
The waste for recycling is put
into a box for collection or
taken to a recycling depot
..
- -~
!(~)'
~
J,
~
~
((~)'
metal is compacted
P.E.T. is flattened, baled
l P.E.T. plastic
metal
for shipping to pu r chaser s at the r ec y cl i ng l l ant
glass
These mater i als are
glass is crushed
I
It is separated into
different materials
ca ~ ~
Mater i a l s are repro c essed to make new products in factories
I
...- - - - - - - - - ·......
~ ~~ 0 11 .....- - •....._ _ _ _ _ _ ___._
'
• new bottles
• fibre glass
• road building materials
• sewer pipes
J
• newsprint
• boxboard
• insulation
• cat litter
• roofing felt
• egg trays
REDUCE WASTE
• new cans
• tin plating
• new Iron and steel
• cars
• insulation
• clothing
• new P.E.T. containers
• other metal items
SAVE OUR RESOURCES
Figure 6.10 Recycling of household waste.
Ideas for making less waste
Shopping and the en vironment
Define these terms associated with
preserving and conserving the
environment: (i) reuse (ii) reduce
(iii) recycle.
• R educe - Buy only what you need. Can you make do with what you have
already? Buy long-lasting goods whenever you can afford them - you may
save in the long run. Consumer magazines can h elp you make informed
choices.
• R ecycle - Choose containers that can be recycled (such as cans, glass and
recyclable plastic) and recycle them. If you can, buy drinks in returnable
bottles.
• Avoid d isposables - The 'throw-away convenience' of some products may
not be worth the environmental cost. Paper plates and cups, throwaway
lighters and razors, and disposable diapers are handy but why not buy the
sorts you can use and use again?
• Avoid product s that are hazardous t o the e nvironment - Baking soda
can be used to scrub out tubs and sink; warm water and vinegar can be used
to dean windows; twice-weekly boiling water rinses keep drains open - and
if they do clog, use a metal 'snake' or a plunger to unblock them.
~
Re ducing waste
~
l:[Q6
\./"-'
l:tQ7
\./"-'
What are some advantages of reusing?
~
l:tQ8
\./"-'
What are the difficulties of recycling?
• Save and reuse things like string, gift-wrap, shopping bags.
• Give magazines and books to friends, hospitals, doctors' offices.
• Help nursery schools; they love to have egg cartons, yogurt containers, toilet
paper rolls, apple baskets.
• Give old clothes or furniture to charitable organisations such as Goodwill,
The Salvation Army, Saint Vincent de Paul.
59
• Cut down on food waste; 20% of food we buy ends up as garbage. Keep
track of what you have and use groceries while they are still fresh .
• Repair broken toys, appliances, fu rniture instead of bu ying new ones.
• Start a compost heap with kitch en and yard waste. You can use things like
banana peel, shells, coffee grou nds, leaves, grass clippings. You will reduce
your garbage by a third and make a good soil conditioner for your garden .
'7
Chapter summary
• A population is composed of all the members of the same species living together in
the same place.
• The population grows if food is readily available and there is adequate space.
• Many factors like disease, predation, competition, availability of food and space keep
a population size constant.
• A typical growth curve is sigmoid in shape (S-shaped).
• The maximum population size .that can be sustained in an area is called the carrying
capacity of that area.
• Humans, though subject to the same constraints as other organisms, have devised
many ways to overcome such constraints and, as a result, human population growth
is still increasing.
• Humans can make use of many natural resources such as minerals, biotic resources,
water, soil and fuel.
• Resources can be defined as being renewable and non-renewable.
• A renewable resource can be reused.
• A non-renewable resource is limited in supply and once used up is no longer available
for use.
• Oil and natural gas are important resources in Trinidad and Tobago.
• In Guyana and Jamaica, bauxite mining is important.
• Manufactured materials like paper, plastic, textures and metals are used by humans.
These materials can be biodegradable or non-biodegradable.
• Biodegradable materials can be broken down and recycled back into the environment.
• Non-biodegradable materials accumulate in the environment.
• People are being taught to reduce, reuse and recycle these materials.
• There are many advantages to recycling.
• There are also many difficulties involving in recycling.
ITQ1
An en vironment has a certain amount of space; this will support
only a specific amount of organisms, depending on how they use it. It can
also provide food for a specific numbe r of organisms. Man y offspring m ay be
produ ced, but some will be eaten by predators and some may die of disease.
At an y time, the en vironment will make it possible for some to live a nd so the
size of the population remains m ore or less constant unless there is a change
to th e environment. This constant point is called the carrying capacity for the
population in that environment.
ITQ2 Earth h as many different environments in which a ctiversity of
organism s exists. Animals and plants show adaptations for living in the
differen t habitats and changing environments. Natural disasters, diseases and
predators help to keep popu lation sizes under control. As long as there is
physical space and food for all these organisms, they will survive on Earth.
60
ITQ3 Animals and plants that humans use for food are encouraged to grow,
by creating ideal conditions in which they can live, and removing their pests
and predators.
Humans will cause population decreases by taking too much of a population
of plant or animal for food or other purposes, such as over-fishing of whales
for oil; dearance of an area of natural animal and plant populations so that the
area can be used for human purposes, such as housing, industry or growing
food crops; or accidentally by introducing a species from one environment to'
another where it outcompetes the natural populations.
ITQ4 The invention of vaccines and immunisation against deadly diseases
prevents thousands from dying each year.
Diseases that prevent couples from having children have been researched
and studied and now many couples who would have been childless can have
children of their own.
Many more babies are born daily because of technology, drugs and
healthcare services. The baby and mother are treated and cared for during the
pregnancy, at birth and after birth.
Many people live longer because of the research and technology applied to
the treatment and cure of diseases like pneumonia and cancer.
ITQ5 (i) Renewable resources: forest trees and fish. (You may have
mentioned others.)
(ii) Non-renewable resources: fossil fuels and precious metals (e.g. gold and
silver). (You may have mentioned others.)
ITQ6 (i) Reuse - find another use for a product which has already beed
used, so that there is no waste to pollute the environment.
(ii) Reduce - decrease the amount of products being used, so that there is less
to pollute the environment.
(iii) Recycle - utilise an already-used product in the manufacture of another
product that will be used again. This reduces the amount of pollution in the
environment.
ITQ7 Advantages of reusing include:
• less waste is generated;
• there is a reduction in the rate at which the resource which makes the
product is used, so the resource is not depleted as quickly;
• it allows for less pollution of the environment;
• fewer organisms will be affected by pollution.
ITQ8 The difficulties of recycling include:
• it is expensive;
• the public may not cooperate, for example in separating their garbage;
• waste may not be generated in large enough amounts and rates to keep the
recycling plant functioning;
• recycling plants cover a large area, so there is often not enough land
available for the plant.
61
Examination-style questions
(i) List four factors that could lead to an increase in population size.
(ii) The graph below shows a typical sigmoid growth curve.
Number of individuals
in the population
Time
(a) Describe each phase of growth.
(b) What factors influence the carrying capacity of the environment?
(c) A disease developed that wiped out all the individuals of the population. Copy the
graph above and continue the line to show how the population size is affected.
Population size
Time
(iii) The growth curve above shows the growth of the population of humans over the last
two centuries.
(a) How is this curve different from the typical sigmoid growth curve of a population?
(b) humans are not subject to the same constraints as other populations. Describe
how humans has overcome two factors that keep other populations 'in check'.
(c) What are some social and economic consequences of over-population by
humans?
(d) What are some implications to the environment of human over-population?
62
2
Explain the following terms giving examples of each:
(a) renewable resources;
(b) non-renewable resources;
(c) biodegradable waste.
(ii) In an effort to reduce the production of waste, people are being taught to (a) reduce,
(b) reuse, and (c) recycle. Explain each of these terms using examples.
3
(i) Describe the impact of agriculture on the environment.
(ii) (a) What is compost?
(b) Every home should practice backyard composting. What do you think of this
statement? What are some advantages to the environment of composting?
(iii) Discuss some difficulties of recycling.
(i)
9ihe Effects of
Human Activity on
the Environment
0
0
0
0
0
0
0
understand that human activities have great effects on the environment
describe the origin and effects of air, soil and water pollution
discuss deforestation and its consequences on the environment
understand the impact of industrialisation
understand the impact of human activities on marine and wetland environments
discuss current and future trends regarding climate change
understand how the environment can be conserved and restored
human activities
')
(
destruction of
the environment
industrialisation
deforestation
pollution
II
climate change
111
soil
marine
I
wetland
11
water
I
air
Humans and the environment
The planet Earth is a beautiful and green place brimming with life-s usta ining
water and ideal for life as we know it (figure 7.1).
Millions of different species of plants and animals inhabit the Earth, living in
balance w ith each other and the various reso urces that they use.
One species, Homo sapiens (humans) is able ro dominate life on Earth.
Humans have been able to use their intellectual abilities to 'conquer' th e
Earth, to exploit all kinds of environments and harness its natural resources
for their own use. Humans are very
successful, as seen by their great
population size; some parts of the
world are very densely popu lated by
humans (figure 7.2).
The human environment is
where humans live. Th e whole Earth
can be considered as the human
environment since humans can
be found almost everywhere. Th e
Earth itself and other living species,
plants and animals, make up the
Rgure 7.2 The human population is increasing.
environment for humans.
63
CHAPTER 6
~
l'.'f:Q·1
L/'--J
List three reasons why it is believed
that humans are 'successful'.
Q9:.,
l'.'f:Q2
L/'--J
Food, disease, predators and space are
all factors that control population size
and keep populations in check or at a
constant number. List three practices
of food production that have helped
humans to feed billions of people
worldwide.
Humans have been able to overcome those factors which naturally keep
populations in check, as we saw in the chapter 6. Each year, nearly 100 million
people are added to the Earth's population. This increase in population has led
to many effects on the environment.
• Humans are con stantly looking for new space, and have taken over areas
already inhabited by other species. They need space for homes, industries,
agriculture and other activities. A5 a result, many other species are losing
their living space and are becoming extinct. Changing the use of the lana for
human purposes changes its suitability for other species and they die out . .
• Humans are constantly producing waste from their various activities and
this has led to all kinds of pollution of land, sea and air.
• The great increase in human population size, together with the
developmen t of global travel and communications, leads to a greater need
for factories and industries. The impact of industrialisation includes the
generation of more waste and increasing use of natural resources on an ever
larger and more dangerous scale.
• Although humans do not live in water, their activities have polluted the
seas, over-fished marine life, caused oil spills and other disasters, and led to
severe stress on marine environments all over the world.
• More humans means more carbon dioxide in the atmosphere; many people
consider this is leading to global warming. The release of other chemicals is
also though t to cause depletion of the ozone layer which protects us from
harmful ultraviolet radiation.
• Human use and management of crops and food species changes the balance
of nature. In trying to control pests, many natural populations may be
destroyed. The development of genetic engineering makes these possibilities
and the risks of affecting th e environment even greater.
·
Endangered and vulnerable organisms
biodiversity >
endemic species /
There is an extraordinary variety of life on Earth. Biodiversity refers to this
biological diversity of the millions of microorganisms, plants and animals that
inhabit the Earth. Th e Caribbean islands, like most places, have a rich heritage
of biodiversity. In particular, th ere are a large number of endemic species
which are only found in a single geographic area, maybe just on one island.
People are concerned over the rapid decline of the Earth's biodiversity.
Extinction can be seen as a natural process - as environments change naturally
over time, some organisms will not be as well suited to the environment and
will die out. However, human activities have increased the rate of extinction
to several hun dred times greater than the natural rate. For example, there are
believed to be less than 1000 giant pandas in the wild in China. Since 1974, their
bamboo forests h ave died out at an alarming rate. This is part of the natural life
cycle of the bamboo, but increased population of the area by humans has made
the possibility of the panda becoming extinct much more likely.
We now classify organisms that are at risk for extinction as follows:
• endangered species are species whose numbers have been reduced to the
point that the survival of the species is unlikely;
• vulnerable species are those that may become endangered in the near
future because their populations are decreasing at alarming rates;
• extinct species are no longer known to exist.
Much research is being done on endangered species, to find ways to save
them from extinction. The International Union for the Conservation of Nature
(IUCN) regularly publishes lists of endangered organisms.
64
Reasons for increasing extinction rates
The increased rate of extinction is the result of many kinds of human activity:
• habitat destruction, including deforestation;
• pollution;
• introduction of more competitive species;
• hunting or cropping more than the population can sustain.
Habitat destruction
The manatee is also called sea cow because it
grazes on plants that grow on the sea bed.
Habitat destruction is the leading cause of species extinction around the world.
For example, all species of gorilla and many of the other apes are endangered
because they Uve in areas where human population is increasing. Many
large predators, such as tigers, and large herbivores, such as the West Indian
manatee, are also enda ngered because they need space that competes with
humans's need for space.
Deforestation
(a)
Deforestation is of particular concern at present. Large areas of rainforest are
being destroyed, to provide hardwood timbers and to create space for roads
and mining. These forests are not only important for their contribution to
carbon dioxide removal in the carbon cycle, but contain thousands of species
that cou ld easily become extinct.
Introducing competitive species
(b)
The introduction of more competitive species has a major e[fecr on endemic
island species. For example rats, cats, dogs and mongoose have ca used the
decline of many Caribbean species, especia lly reptiles and birds that are killed
or lose their eggs through predation by the new species.
Hunting
(C)
Hunting may directly cause the extinction of a species, for example, the
Tasmanian Wolf may have been hunted to extinction in Australia by the
middle of the last century, and the Dodo is a famous example of extinction
through hunting which happened around 1680. The polar bear and black
bear are killed for their fur and are under threat of extinction from hunters.
In addition, food fish, like populations of tuna, shark and card, are over-fished
and are at risk.
Hunting may also indirectly affect other species. For example, drift nets
are enormous nets used for commercial fishing. The nets trap and kill many
creatures apart from fish, especially dolphins, porpoises, sharks and turtles.
Today, many animals are at risk in the Caribbean (figure 7.3). These include
many birds, like the West Indian Whistling-Duck, the West Indian Flamingo,
the Barbuda Warbler and the Cayman Parrot. Of the reptiles, the Hawksbill
Turtle, the Leatherback Turtle and the Loggerhead Turtle are all at risk. The
American Crocodile, the Cuban Tree Boa and many iguanas are also at risk.
Reducing the risk of extinction
Rgure 7.3 Endangered species
in the Caribbean. (a) Whistling duck
(b) Leatherback turtle (c) Manatee.
There are ways to reduce the risk of extinction of other species. Wildlife
parks and reserves set aside land where the activities of humans are strictly
controlled. This can help to increase the numbers of endangered species and
prevent extinction. Zoos often specialise in looking after particular animals.
However, there are many problems in the breeding of anima ls in captivity.
65
__::_Livin9 Orgenisms ir:t t~'l°' ~nvjr_~r,iu),~1J: __
_ _ _ -::-.: _
-
_
_
_
0
Although much research is being done on maimaining the Earth's
biocliversity, we need to be sensitive to the needs of all the species living
around us and the effect that we are having on them.
Other effects of human activity
Shortage of water
Most living organisms must have a daily supply of water to live. Humans often
use more water than is strictly necessary and the shortage of fresh water is now
a worldwide problem. A number of factors working together have resulted in
this water sh ortage problem.
• Deforestation - This can remove large areas of densely growing trees,
like rainforests. Water is transferred to the atmosphere by evaporation
and transpiration by plants. This is an important part of the water cycle as
it leads to the formation of rain. Rain falling into rivers, lakes and dams
provide our supply of water. Removing large areas of trees can change the
pattern of rainfall ail around the area and possibly beyond.
• Industrialisation - Industry uses a lot of water most often simply to cool
equipment. For example, water ensures the constant functioning of the
iron, steel and oil industries.
• Pollution - Water pollution results in less water being suitable for drinkjng.
Each individual needs water for hygiene and food production. Billions of
inclividuals use and waste water every day, though much of this can be
recycled.
• Depletion of ground water - Much water is trapped in lakes
underground after it has seeped through the soil and rocks above. These
lakes are known as aquifers and we get a lot of our water from these. It
can take many years, even hundreds or thousands of years, for the water
to seep into them, so they can be used up faster than they are replerushed
by rainfall.
Over 90% of the Earth's water is salt water, which we cannot drink but which
could be desalted and made available for use by humans. Desalination plants
convert salt water of the oceans and seas into drinkable water. However,
desalination plants are costly to install.
At national level, efforts co reduce pollution (especially of the rivers,
lakes and seas) may result in increased water supplies, but also many simple,
everyday practices could add up to conserve water and reduce shortages.
These include:
• turning off taps while brushing teeth;
• fixing leaks in water pipes irnmeillately;
• recycling-reusing water when possible;
• minimising use of water in the garden;
• not having over-long showers;
• using a bucked instead of a hose to wash cars;
• being mindful of how valuable a commodity water is.
Pollution
Rgure 7.4 Chemical pollution from an
oil refinery.
66
Poilution is the contamination of land, water or air by the discharge of harmful
substances (figure 7.4). Humans are constantly polluting the environment.
Tables 7.1, 7.2 and 7.3 describe the origin of these pollutants and the effects on
the environment and on humans.
Pollutants
Origin
Control of pollutant
non-biodegradable
waste
household and industry Harmful substances
Careful removal of
(e.g. mercury, lead,
can accumulate on land toxic materials from
plastics, cyanide)
and enter air and water, waste to be disposed.
where they can poison Replacement with nonliving organisms.
toxic alternatives where
possible.
Insecticides and
herbicides
agriculture (e.g. DDl)
Effects
Accumulate in
organisms through food
chains, even killing top
consumers. May cause
mutation. May cause
eutrophication in rivers
and lakes. May upset
the balance of food
chains.
Replacement with
less toxic alternatives.
Replacement with
biological control.
Table 7.1 Land pollution.
biological control >
Biological control is the use of living organisms to control pests, often in
horticulture and agriculture. Introducing a predator or parasite of a pest can
greatly reduce the popula tion size of the pest to the point where the level
of damage is economically acceptable. However, great care must be taken to
make sure the introduced predator or parasite does not become a pest itself by
damaging populations of other organisms in that environment as happened
when the cane toad was introduced to Australia.
Pollutants
Origin
Effects
oil
spilled from
tankers or offshore rigs
Forms 'slicks' on the sea which Legislation to prevent cleaning
blocks oxygen and light, killing of tankers near land, and
marine life. Stops birds flying reduce the risk of loss from
and feeding. Ruins beaches. Is rigs. Spills can be localised
toxic to some marine life. Clogs with floating booms and
respiratory systems of fish.
dispersed with detergent. The
dispersed material may still be
harmful to marine life.
hot water
power stations
Changes the temperature of
the habitat which results in
death or migration of marine
life, especially death of coral.
Some organisms may flourish.
Cool the water before it is
released into the environment.
(Some of this heat can be used
to heat or power local homes.)
organic waste untreated
sewage from
housing, ships,
farms
Bacteria multiply and use
up oxygen. Can lead to
eutrophication of water. Can
cause disease.
Treat all sewage to remove the
biological risk before release
into the environment.
mineral
salts (e.g.
phosphate,
sulfate and
nitrate ions)
Eutrophication as increased
Use detergents which contain
nutrients in water encourage
minimal amounts of these
algal growth. Light is blocked substances. Use fertilisers in
because the growth is so thick. controlled amounts, only as
Algae die resulting in rapid
needed, to reduce leaching into
growth of anaerobic bacteria. water systems.
Oxygen used up so other
organisms die.
detergents,
fertilisers in
sewage and
water from
housing and
farms.
Control of pollutant
(continued)
67
Pollutants
Origin
toxic
chemicals
(e.g. organic
mercury
acid wastes,
heavy-metal
products)
industrial plants May be toxic to aquatic
organisms. Concentrated in
organisms as they move up
food chains. May change
the behaviour of aquatic
organisms.
Effects
Control of pollutant
Screen all wastes from
industrial processes to remove
toxic materials before release
to environment.
Table 7.2 Water pollution.
Pollutants
Origin
Effects
carbon dioxide burning fossil Builds up in the atmosphere
fuels, increased trapping heat which could lead
human
to global warming.
population
(deforestation
increases
problem)
car exhaust
Carbon monoxide combines
Control CO by use of more
more readily with haemoglobin efficient engines and catalytic
than oxygen does. Causes
converters. Use lead-free fuel.
headaches, unconsciousness,
death. Lead may cause mental
retardation.
smoke
burning fossil
fuels
Combines with fog to form
smog. Particles cause
respiratory disorders, increase
the risk of lung cancer.
Agure 7.5 This vehicle is run on biogas.
l"·@@t•W
biochemical oxygen demand >
68
For energy, use renewable
energy resources. For
vehicles, use mass transport
where possible, use biogas
replacements for fossil fuel.
carbon
monoxide
(CO), lead
sulfur dioxide burning fossil
fuels
Biogas is a fuel made from the fermentation of
waste plant products, such as sugar cane after
sugar extraction. In Brazil and parts of the US,
this is now being used to fuel vehicles instead
of gasoline (figure 7.5).
Control of pollutant
Cleaning of waste gases
from industrial processes can
remove these and prevent their
release into the environment.
Dissolves in rain water forming Cleaning ('scrubbing') of waste
acid rain. Affects plant growth, gases from industrial processes
damages leaves, corrodes
can remove sulfur dioxide and
surfaces of rocks and buildings, prevent its release into the
causes the death of fish and
environment.
plant life. Crop yields may be
reduced. Aggravates asthma.
Table 7.3 Air pollution.
Sewage treatment
Sewage consists of liquid and solid waste from urine and faeces, warer from
domestic use and industrial waste.
When raw sewage is discharged into rivers and sea, bacte ria in the water
decompose the organic matter in the sewage. These aerobic bacteria multiply
rapidly and need large amounts of oxygen dissolved in the water. This is called
biochem ical oxygen dem and (BOD). The release of nutrients by the bacteria
into the water encourages the rapid growth of algae. The algae add oxygen
to the environment as they photosynthesise. But they are a problem because
they blanket the surface of the water and restrict the entry of oxygen from the
atmosphere. They also restrict the entry of light and this causes submerged
plants to die thus adding to the organic matter available to the bacteria. When
all this takes too much oxygen from the water, other aerobic organisms like
7 · The Effects of Human Activity on the Environment
eutrophication >
domestic sewage
plants and fish cannot respire and so die. The decomposition of the dead
material and sewage by anaerobic bacteria continues.
This process, whereby large amounts of nutrients are added to a water
system and lead to the death of many of the organisms living in it, is known
as eutrophication.
To prevent pollution of water, raw sewage must be treated to remove solid
waste and other harmful substances, and decomposed aerobically before it is
disposed of into the rivers and the sea. Most sewage works use a biological
method of sewage treatment (figure 7.6).
water drainage from streets
Grit tank
Large tanks where grit, stones
and other heavy objects
sink to the bottom.
Coarse screen
Has wire nets to strain
out solid litter.
Aeration tank
Air is bubbled through the liquor
to encourage growth of aerobic
bacteria. These bacteria
decompose organic waste into
harmless substances and
carbon dioxide.
industrial sewage
liquid sewage
Primary sedimentation tank
Ughter matter such as faeces
settles to form sludge.
Sludge digester
Sludge undergoes anaerobic
treatment to form methane gas
(biogas) which is a good fuel.
Residual matter is dried
and used as a fertiliser.
Biological filter
The liquor is sprinkled onto large
tanks from a rotating arm. The
liquid sewage percolates down
t hrough a bed of stones covered
with a film of aerobic microbes
(bacteria and protozoa) which
digest the organic matter
in the sewage.
Effluent
• Discharged Into the river
and sea.
• Used to water plants.
• Used for flushing toilets.
II
Rgure 7. 6 The sewage treatment process.
Deforestation
Figure 7.7 Forest clearance.
Every week, at least 1 million acres of forest are cleared or degraded
worldwide. Although a forest is a renewable resource, removal at that rate is
much greater than the rate at which the trees can be replaced. Forests are not
being managed and maintained, but are being exploited in a destructive way
(figure 7.7). Rainforests are being cleared for farming, timber, mining, largescale cattle ranching, housing and industry.
When a small area is cleared, the forest recovers quite quickly, but when
large areas are cleared, there are many consequences on the environment.
• Soil erosion - Deforested slopes encourage surface run-off during
rainfall. When the forest is in place, it intercepts the rain water and lets
it trickle slowly to the soil. When the canopy of trees and smaller plants
is removed, rain falls directly on the soil causing erosion of the topsoil as
it runs off the surface of the land. The soil below is not as fertile, so will
69
- Living Orga"lsms in the E9vironrnent
•
•
~
ll!Q3
•
V'-'
(i) What is deforestation?
(ii) Why do people practise
deforestation?
(iii) What are two consequences of
deforestation?
~
•
_ __
-
_
not be able to sustain growth as well as the lost topsoil. The land can be
permanently damaged.
Soil degradation - If the land is cleared for agriculture, the soil becomes
infertile due to the removal of minerals by the crops. Leaching also occurs
which removes minerals that would otherwise have been taken in by
the trees.
Increased flooding -The increased run-off takes silt with it which blocks
rivers and causes flooding in low-lying areas. Flash floods also occur because
of the increased run-off.
Species destruction - The plants removed may become extinct. The
habitats of many organisms are destroyed, and the food chains that
dependent on those plants will break down Many organisms, plants and
animals, may become extinct.
Destruction of natural resources - Many crop plants originated as
rainforest species (cocoa, banana, rubber). Many forest plants also produce
medicinal drugs. Disease-resistant varieties of plants are usually found in
the wild. If we destroy these forests we may lose these resources before we
have even learned about them.
ll!Q~
V'-'
Look back through this chapter
and make a list of the results of
industrialisation.
~
ll!Q5
V'-'
For each item on your answer to ITQ4,
give an example of how humans are
attempting to reduce the impact of
industrialisation on the environment.
99:>
ll!Q6
V'-'
(i) What is industrialisation?
(ii) Discuss one advantage and one
disadvantage of industrialisation.
Industrialisation
Industrialisation is a sign of human success. The word industry is used to cover
all forms of economic activity: primary (farming, fishing, mining and forestry);
secondary (manufacturing and construction); tertiary (back-up services such as
administration, retailing and transport); and quaternary (high technology and
information services).
Industry requires a workforce and thus provides jobs for people who can
enjoy a 'good ' standard of living. It generates income for the country which
can be spent on improving education, healthcare and public utilities for
its people.
There is, however, a price to be paid for industrialisation. If not managed
properly, it can lead to serious environmental consequences (discussed above)
including pollution of land, air and water, water shortages and deforestation.
Industrialisation is two-sided. On one side, we see successful humans
harnessing resources and living a comfortable life. On the other side, we see
widespread destruction of the environment. The Earth is our only home and
we should take care of it.
Impact of human activities on marine and
wetland environments
Water is important to us. We love to go to the beach, snorkel, lie by the river,
fish and do many other activities which involve wa ter. On the physiological
side, over 75% of the human body is water. We cannot exist without water
and die faster from dehydration than from starvation. Other living organisms
depend on water as much as, or even more than, we do .. Our planet is able to
sustain life because of the presence of water.
Yet many human activities lead to a hotter and drier Earth, and to pollution
and the destruction of aquatic environments. Belwo are examples' of the
specific effects of human activity in marine environments in the Caribbean.
70
_ -
.~
IJ'-.)
Humans do not live in water, yet their
activities and practices have affected
the marine environment. Describe two
effects on the marine environment that
humans have had, and how they were
brought about.
~
IT:Q8
IJ'-.)
Why are coral reefs important to
Caribbean people?
~
IT:Q9
IJ'-.)
Discuss two reasons why mangrove
swamps should be conserved and
protected.
__ 7 · The §t(ects of ir-lll!.mar'1_Activity on the.~Enviroi1rnent
Some effects of human activities in the
Caribbean
• Destruction of mangrove swainps - Using the swamps as dumping
grounds or for building rice farms or other development, leads to many
problems, such as:
- nursery grounds for all kinds of fish are affected;
- pollution of water with toxic materials, or those wruch cause
eutrophication;
- pollution of water with human and animal waste can spread diseases like
cholera and diarrhoea;
- breeding grounds and nesting and roosting grounds for birds are reduced;
- the natural habitat of many invertebrates, like oysters and crabs, is
destroyed;
- money generated from eco-tourism (tourists visiting the area to see the
wildlife) is reduced;
- money generated from fishing crabs, oysters and other local fish is
reduced.
• Over-fishing - In the seas of the Carinbbean this is a serious problem.
Much money is spent on catching fish and too little on managing and
producing them.
• Destruction of coral reefs - This occurs by:
- collecting coral for sale;
- dynamiting for fish;
pollution with raw sewage, garbage, industrial and kitchen waste;
- pollution with hot water which kills the coral organisms;
- pollution with insecticides and fertilisers;
- smothering with silt from soil erosion;
- smothering with red mud ba uxite waste, dust and cement from
construction;
- removal to allow the building of harbours, channels, etc.;
- damage from anchors;
- damage by visitors to the reef.
• Damage to wetland environments - this occurs by:
- allocation for rice and other farming;
- fertilisers and other dangerous chemicals in the water;
- n oise pollution from use of heavy rice equipment;
- damage by visitors to the wetlands;
- pollution from visitors;
- hunting of animal s;
- noise pollution from hunting;
collection of animals for sale;
- squatters or development of housing settlements;
- over-fishing.
71
The coral reef is a natural resource important to the Caribbean islands and, as
such, needs LO be conserved. Damage such as that shown in figure 7.8 is to be
avoided if at all possible.
Rgure 7.8 Coral reef smothered by land run-off.
Impact of increase in greenhouse gases
Global climate change has already had observable effects on the environment.
Effects that scientists have predkted are now occurring. These changes are
largely due to an increase in the levels of greenhouse gases; they include:
• increase in Earth 's average temperature;
• changes in the pattern and amount of rainfall;
• reduction in ice and snow cover;
• rise in sea level;
• increase in the acidity of the oceans.
Conservation and restoration of the
environment
conservation >
sustainable >
Since humans are responsible for widespread destruction of the environment
on the Earth, they should take responsibility for the widespread restoration
and conservation needed to 'heal' this damage to our planeL. We need to
manage the environments that we live in and the resources that we use in a
sustainable way. That means using them in a way that they are not damaged
and depleted, so they are available for future generations . There are many
ways that this can be done.
Reduce pollution
• Replace fossil fuels with alternative, non-polluting energy sources like solar
energy, wind energy, wave energy, biogas and hydroelectricity.
• Treat all sewage.
• Use unleaded petrol and catalytic converters on vehicles to reduce all
emissions of pollu tants in exhaust gases.
• Replace harmful insecticides and herbicides with biological control or
biodegradable insecticides.
72
• Use cleaners of all exhaust gases from industry.
• Improve effluent release standards of industries to purify, treat and reduce
effluent release.
• Use recyclable materials at home and in industry; for example, paper and
biodegradable plastics rather than plastics, which are not biodegradable.
• Ban the disposal of garbage in rivers, swamps and seas.
Conserve natural resources
•
•
•
•
Recycle resources such as glass, metal and paper.
Use alternative energy sources.
Replace renewable resources, such as forests.
Manage food species, plants and animals, in a sustainable way by imposing
closed seasons and strict restrictions on how heavily populations are cropped.
• Limit deforestation to a rate at which forest recovery can be maintained.
Protect endangered species
• Ban the killing of species in danger of extinction, such as turtles and the
West Indian manatee.
• Set up breeding programmes for species in danger of extinction.
• Set up National Parks to provide areas for species to live and breed
undisturbed by human activity.
Conserve soil
• Replant trees immediately after harvesting to prevent run-off when it rains.
• Use crop rotation to maintain a balance of soil nutrients; different crops
remove different minerals from the soil .
• Use natural rather than artificial fertilisers to preserve soil structure, but
only as needed so as to prevent eutrophication of nearby water sources.
• Use terracing and contour ploughing around hillsides to prevent erosion by
soil run-off when it rains.
• Prevent over-grazing by animals like cows and sheep that remove plants
and their roots which hold the soil when it rains and prevent erosion.
Preserve clean water
• Prevent eutrophication by treating sewage properly and using only as much
fertiliser as is needed on farm land.
Improve land used in mining
• Replace vegetation as soon as possible after mining has finished .
• Fill the mined areas with soil and use for farming, housing or industry, so
that new areas do not need to be used.
Eanh is home not only for humans, but for millions of species of plants and
animals. The Earth can successfully 'carry' all these organisms when there is
balance in population size and the natural cycles can take place efficiently. It is
our responsibility to maintain that balance.
73
ITQ1
(i) They have inhabited most places on Earth and continue to colonise
new areas.
(ii) They have been able to overcome many natural diseases.
(iii) They mass-produce food, and so do not have to search for food each day.
ITQ2 (i) Agricu lture - mass cultivation of plants that can be used as food.
(ii) Livestock production - mass production of animals (cows, chickens) and
their prod ucts, (eggs, milk) that can be used as food.
(iii) Use of tech nology to intensify production to increase the yield (e.g. the
use of artificial selection) an d, in the future, possibly increasing use of genetic.
engineering to speed this up.
ITQ3 (i) Deforestation is the removal of a large number of trees from an
area.
(ii)
• For quarrying - to obtain gravel, soil, sand, etc. for building.
• To clear land to build homes.
• To provide lumber for housing, furniture, etc.
• To plant crops or for ranching.
(iii) Any of the consequences mentioned on pages 69- 70 wou ld be
approrpiate.
ITQ4 Your list should include examples for each of the following: pollution
of land, air and water, water shortages and deforestation (see tables 7. 1-7.3).
ITQ5 Your answer should include examples for each of the fo llowing:
control of pollution of land, air and water, water shortages and deforestation
(see tables 7. 1-7.3).
ITQ6 (i) Ind ustrialisation is th e spread of industries. As a coun try develops,
it becomes more industrialised.
(ii) As more industries develop, fewer foreign products are imported, so more
money is generated by the country and more jobs are available. This is the
major advantage of industrialisation.
A major disadvantage is that as industrialisation increases, damage to the
environment is more likely.
ITQ7
(i) Hot water from power stations is poured into the sea, changing the
temperature and thus the environment of marine life. Plants and animals may
not be able to adapt fast enough and are killed.
(ii) Oil spills from tankers form a layer of oil on the surface covering many
miles of ocean. This can have disastrous effects on the marine environment as
shown in table 7.2.
ITQS Coral reefs have many important functions.
74
• As a to urist attraction - A lot of money is generated from to urists who wish
to visit the area to see the reefs.
• As a source of job opportunities in tourism and conservation .
• In preserving bioctiversity - Man y different species live in the reefs.
• As a spawning ground - Many species of fi sh breed in coral reef areas,
including fish that w e use for food.
• In protecting the coastline from erosion - The reefs absorb bursts of wave
energy, especially during a storm.
• As a sensitive inclicator of global environmental changes - Cora ls are very
sen sitive to environrnentaJ conclitions and any change results in a chan ge in
the population of corals.
ITQ9 Mangrove swamps are spawning grounds for large fish and ensure the
continuation of man y fish species.
Mangrove swamps support bioctiversity: there are many species that live in
that one ecosystem.
Examination-style·questions
(i) Humans are constantly looking for and occupying new space.
(a) List some reasons why humans needs new space constantly.
(b) Suggest three consequences of occupying new space constantly.
(c) Discuss the greenhouse effect with particular reference to the over-population of
humans.
(ii) (a) What is a pollutant? Give some examples.
(b) Account for the presence of lead as a pollutant in the atmosphere.
(c) How can lead pollution be controlled?
(d) Describe the causes and effects of eutrophication.
(iii) (a) List four effects of sulfur dioxide pollution.
(b) Account for the presence of chlorofluorocarbons in the atmosphere.
(c) What are some of the effects of the build-up of these pollutants?
2
(i) What is deforestation and why is it practised?
(ii) State some consequences of deforestation.
(iii) State some consequences of industrialisation.
(iv) Why are conservation efforts so important?
75
Section B:
Life Processes and
Disease
0
0
0
0
0
0
draw diagrams to show the structure of typical plant and animal c ells
understand the functions of the cell wall, cell membrane, cytoplasm,
mitochondrion, chloroplast, nucleus and vacuole
compare plant and animal cells
understand that most microbes are unicellular
understand why specialisation is important in multicellular organisms
understand how some substances move into and out of cells
plant
animal
microbes - bacteria,
Amoeba
)
l
cell - basic
unit of life
1
(
microscope
tissue
'
organ
calculating size
of cells
6 image seen Is 400 times bigger
than the actual specimen
system
--- - -- 1'5 light passes through eyepiece lens,
I
magnification x10
organism
movement into
and out of cell
diffusion
osmosis
Why we need microscopes
4 light passes through lens,
r:a.1----'~--- magnification x40
~_....l~;;nr;::,:;;;:~;--- 3 light passes through the slide
(specimen)
2 light passes through the filter
and condenser
l light reflects on mirror
and travels up to the eyepiece
Th e cell is the basic un it of life. A cell cannot be
viewed by the naked eye since it is too small. It
can on ly be seen w ith a mi croscope. Cells are thus
described as being m icroscopic.
A microscope is used to produce a magnified
image of an object. There are different kinds of
microscopes, for example light and e lectron. When
looking through the microscope at a piece of tissue,
separate cells can be distinguished which would
not have been seen with the naked eye. How much
you ca n see w ith a microscope depends on h ow
powerful its magnification is. A light microscope
typically magnifies between l 0 and 400 times real
size (figu re 8.1). An electron microscope is more
powerful and can magnify tens of thousands of times
actual size.
8 ·Cells
Calculating the size of cells
~
IT:Q·1
V'-J
What is the purpose of a microscope?
The actual size of an object in a photograph can easily be calculated from the
image and the magnification given. If the length of the object in the ph oto is
measured as Z, and the magnification is given as xlOO, that m eans the object is
100 times larger than in real life. So, the actual size of the object is Z-;-100.
Plant and animal cells
Syllabus reference C1.1
--<+--
Plant and animal cells have the same basic structure but each has its own
characteristics that make it typically plant or typically animal.
The structures found within a cell are called the cell organelles. Th ey
have different functions and, as they work together, they keep the cell (and
therefore the organism) alive. Figure 8.2 shows diagrams of typical plant and
animal cells; figure 8.3 shows plant cell. Table 8.1 describes the functions of
some cell organelles.
- - nucleus contains -------\r----1
chromosomes which
carry genetic Information
chloroplast
-""-tt-- - - mitochondrion ----l~!lii.
starch grain
glycogen
granule
Plant
cell
0
Animal
cell
Rgure 8.2 Typical plant and animal cells.
.~
Rgure 8.3 Photomicrograph of a plant cell
(magnification x5000). Compare this with
the plant cell drawn in figure 8.2
Organelle
Function
cell wall
prevents bursting of a plant cell and gives it a fixed shape
cell membrane
Measure the width of the largest
chloroplast in the cell in figure 8.3,
and calculate its actual size using the
magnification given.
a selectively permeable barrier which controls exchange between the cell
and its environment
cytoplasm
site of many of the chemical reactions of life
nucleus
controls the activities of the cell, contains chromosomes
.~
vv
chromosome
carries genetic information in the form of DNA
mitochondrion
site of energy production
V'-J
Make a list of (i) all the organelles
which are found in both plant and
animal cells and (ii) organelles which
are only found in plant cells.
permanent vacuole important during exchange of water and minerals, and stores various
substances including waste products
chloroplast
where photosynthesis takes place
Table 8. 1 The functions of some cell organelles. (Organelles shown in green are only found in
plant cells.)
79
Life Processes and Disease
Table 8.2 describes differences between plant and animal cells in more detail.
.~
U'-J
Plant cell
Animal cell
Name two organelles found in a plant
cell but not in an animal cell. What is
the importance of these two organelles
to a plant cell?
Cytoplasm is surrounded by a cell membrane as Cytoplasm is surrounded by a cell membrane
well as a cell wall.
only.
Chloroplasts are present.
Chloroplasts are absent.
.~
V'--1
Carbohydrates are stored as starch.
Carbohydrates are stored as glycogen.
A large, permanent vacuole is present in most
plant cells. It has a definite, fixed shape.
Many small, temporary vacuoles are present at
a time. These have no fixed shape.
(i)
Distinguish between cell wall and
cell membrane.
(ii) Distinguish between
mitochondrion and chloroplast.
Cytoplasm is pushed to the edges of the cell by Cytoplasm is present throughout the cell.
the vacuole, so it is normally confined to a thin
layer.
Table 8.2 The main differences between plant and animal cells.
Unicellular microbes
Microbes are microscopic organisms (microorganisms) that cannot be seen
by the naked eye, only by using a microscope. Most, but not all, are singlecelled organisms, and are so tiny that millions could fit in the eye of a needle.
Microbes are everywhere, in the air we breathe, the ground we walk on and in
the food we eat. They are even inside us. They include:
• viruses
• bacteria
• protozoa.
Viruses
These are very small and can only be seen with an electron microscope. They
are not made of cells an d are sometimes referred to as virus particles or virions.
They cannot be killed by antibiotics such as penicillin. Examples of diseases
they cause include influenza, common cold, measles, mumps, german measles
(Rubella), smallpox, chickenpox, HIV (can lead to AIDS) and rabies.
Bacteria
glycogen granules,
lipid droplets
mesosome·
cell surface membrane
~
photosynthetic
membranes'
• = not pesent in all bacteria
Rgure 8.4 Diagram of a bacterium.
80
~~ small
i=~
\ _ ]
. .·
circular DNA
ribosomes
Bacteria are single-celled
organisms (Figure 8.4). Many
of us refer to them as 'germs',
but some are very useful. For
example, they decompose dead
organisms and digest cellulose.
Examples of diseases they cause
include cholera, tubercu losis,
septicaemia (blood poisoning),
pneumonia and gastroenteritis.
S·Cells
Protozoa
These are generally single-celled organisms (figure 8.5). Amoeba is very
common and can be found in back-yard ponds and drains. Examples of
diseases they cause include malaria, sleeping sickness and dysentery
peeudopodium (false foot) is sent out
in the direction of the food particle
the food particle is engulfed
enzymes are secreted into the food
vacuole and the food is digested
nutrients are absorbed into the
cytoplasm of the amoeba
unwanted (undigested) substances are
released from the amoeba into the
enviroment
Figure 8.5 Movement and feeding in Amoeba.
Cell specialisation in multicellular
organisms
Organisms can be described as unicellular or multicellular. Unicellular
organisms like Amoeba (animal) and Chiarella (plant) are just one cell in size.
Multicellular organisms, like all the larger animals and plants are made up of
many (sometimes millions) of cells.
The cells of unicellular organisms (e.g. Amoeba and bacteria) are
independent but are still able to carry out all characteristics of life. Multicellular
organisms, however, are made up of millions of cells. These cells work together
and are often dependent on each other to carry out all the characteristics
of life.
81
Life Processes and Disease
In multicellular organisms, each
cell has the same basic structure,
but there are variations in the
nucleus
design. Within a single organism,
such as a human, there are great
differences between the cells.
transmits
Each type of cell is specialised to,
nerve pulses
carry out a particular function
well. For example, a muscle cell
striations in cells
can shorten o r lengthen
is concerned with contraction of
the muscle, while a nerve cell
it---~ these cells
is specialised to transmit nerve
insulate the
impulses (figure 8.6) .
nerve cell
In a multicellular organism,
cells are arranged in groups to
lt'!lflll!l""i:!P.!:i."1"(#-1 form tissues. A tissu e is a structure
made up of many similar or
identical cells which are adapted
to perform one specific function.
Skeletal muscle cells
Nerve cell
Muscle cells make up muscle tissue
make up a muscle fibre
and all these cells are concerned
with the muscle function
of contraction.
Several different kinds of
Figure 8.6 Specialised cells that are found in nerves and muscle.
tissue may be grouped to form an
organ . For example, intestines
contain epithelial tissue and muscle tissue and a blood supply (figure 8.7). In
animals, organs form parts of even larger functional units called systems. The
digestive system is made up of several organs, including the stomach, intestines
and liver.
Epithelial cells
CELLS
® (j) (ii)
~@ e
l
Cells mass
together to form
an epithelial tissue.
1.mm.1~·+1.TIJ
1
epidermal cells
-TI~~
TISSUE
palisade
The epithelial
and smooth
muscle tissues
combine together
in the wall
of an organ
such as the
intestine.
l
leaf
ORGAN
in an organ
such as the leaf.
epidermal tissue
epid ermal cells
TISSUE
I
Cellsmass
together to form
smooth muscle
~~
tissue.
r
CELLS
Muscle cells
Figure 8. 7 Tissues in the intestine.
82
Rgure 8.8 Grouping of cells to form tissues in the organ of a leaf.
Cells in plants are also grouped into tissues, and tissues grouped into organs
(figure 8.8). Table 8.3 shows examples of tissues, organs and systems that are
found in plants and animals.
8 ·Cells
Structure
Examples in plants
Examples in animals
tissue
palisade mesophyll (chapter 9)
nerve tissue (chapter 18)
phloem tissue (chapter 14)
muscle tissue (chapter 17)
xylem tissue (chapter 14)
CHAPTERS 9, 10, 12, 14, 17, 18
organ
leaf, root
stomach, lung, brain , eye
system
(not organised into systems)
digestive system (chapter 10)
respiratory system (chapter 12)
nervous system (chapter 18)
Table 8.3 Examples of tissues, organs and s stems in plants and animals.
~
ll:Q6
V'-'
Give an example of each of the
following: cell, tissue, organ, system.
~
ll:Q7
V'-'
Distinguish between unicellular and
multicellular organisms, giving two
examples of each.
A healthy organism is made up of all these parts working efficiently together,
enabling it to do many things at the same time, such as use its energy source
and make the energy available for movement, reproduction, growth, response
and excretion. A total breakdown in the normal functioning of any one of
these systems can lead to the death of the organism, such as a heart attack
when the circulatory system breaks down.
Most animals are either predator or prey in food chains. A healthy organism
has all its systems functioning efficiently and so is able to survive in the
environment or wild. Unhealthy organisms may be unable to capture food or
fall prey to predators more easily. Survival is for the fittest, meaning that an
organism with all its systems functioning efficiently and continuously has an
advantage for survival - an advantage for life.
Movement of substances into and .out of
cells
1@3i§U.ht1
Substances moving out of
~
the cell. (These were made
, '\
by the cell and are important, ~
like hormones and enzymes.)
Q
All kinds of reactions take place within a cell. The organelles within a cell
require many different substances to carry out these reactions. Waste products
are formed during these reactions and must be removed. The substances,
needed and produced, must pass into and out ·of the cell.
There is thus a constant movement of substances into and out of cells.
• Substances needed by the cell, like glucose and oxygen, must pass into the
cell.
• Substances produced by the cell must pass out of the cell. These may be
waste products, like carbon dioxide and urea, or substances needed by
another cell, like enzymes. This is called secretion .
substances moving
into cell
~
Substances can be taken in within small
vesicles made from the cell membrane.
Amoeba takes its food in this way.
Substances can also be released from cells
when vesicles containing the substance
join with the cell membrane (figure 8.9).
Hormones are released from cells like this.
Substances may also enter and leave
cells as individual molecules. They do this
by various mechanisms including diffusion.
Water enters and leaves cells by osmosis.
Figure B. 9 Diagram showing substances moving into and out of a cell in small vesicles.
83
Life Processes and Disease
Movement by diffusion
l'!Dill@•hU
concentration gradient >
Practical activity
SBA 8.1: Diffusion in a solution,
page 341
permeable >
Diffusion is the movement of molecules from a region of high concentration
of those molecules to a region of lower concentration of those molecules.
Diffusion can happen in gases and in liquids.
A diffusion gradient or concentration gradient occurs when there is
a difference in the number of molecules, or the concentration of molecules
between the two regions. For example, when a drop of dye is added to ·
water, the dye molecules move around and between the water molecules
and eventually are spread evenly, even when not stirred. In other words, the
dye molecules move from where they are plentiful to where they are not so
plentiful. We say these diffuse (figure 8.10) .
Substances can also diffuse across membranes if the concentrations are
different on both sides and the membrane is permeable to those molecu les
(figure 8. 11 ).
Figure 8.10 Over time, the dye molecules diffuse so they are evenly spread throughout the
solution.
•
•
molecules at
a higher
concentration
e
e
molecules at
a lower
concentration
-
molecules at
the same
concentration
+-+-+on both sides
•
•
more molecules move from
left to right than from right to left
no net movement of molecules
Figure 8. 11
Diffusion can occur across permeable cell membranes.
Some examples of diffusion in the human body
• After a meal, the end-products of digestion are at a high concentration
in the gut. They diffuse down their concentration gradient into th e blood
where they are at a lower concentration (figure 8.12).
84
8 ·Cells
blood rich +-•••••m~;K~ll!l~•Klin~ZI···-- blood capillary
in the endproducts of
digestion
ileum o f the gut
end-products of digestion
at a high concentration
Figure 8.12 Diffusion of small food molecules from gut to blood.
blood rich
in oxygen (02)
oxygen ata
higher concentration
in the alveolus
/
• Diffusion occurs in the lungs (figure 8.13 ). Carbon dioxide diffuses from
the blood where it is at high concentration into the lungs w here its
concentra tion is lower. Oxygen diffuses in the other direction because it has
a higher concentration in the lungs and a lower concentration in the blood.
• When the blood gets near the celJs, the oxygen concentration in the blood is
higher than in the cells. The blood came from the lungs where it picked up
oxygen. The oxygen concentration in the cell is low, since the o xygen that
was in the cell was used for respiration. The oxygen in the blood diffuses
into the cell, where it can be used for energy production during respiration
.(figure 8. 14).
concentration gradient
-
higher concentration
of glucose in the gut
blood capillary
Figure 8. 13 Diffusion of gases between
the lungs and the blood.
;;:JE.-<---
lower concentration
in the blood
blood capillary
one cell thick
many ways - more
surface area, more diffusion
________.,
f ----lOOCly cells oxygen used up
during respiration
and its concentration
is low
Figure 8. 14 Diffusion of oxygen from blood into cells.
Figure 8.15 Adaptations that help to speed up the rate of diffusion.
• In the cells, carbon dioxide builds up as a waste product of respira tion. It is
at a higher concentration than in the blood. Thus it diffu ses ou t of the cell
and into the blood.
• Other wastes made by cells, such as ammonia, are at a higher concentration
in the cell than in the blood. They also diffuse out of the cell to the blood
and are taken away and expelled from the body.
Diffusion is a very slow process unless there is a large concentration gradient
over a short distance. Tissues like the lungs and smaIJ intestine are especiaIJy
adapted to maximise the rate (figure 8.15). Adaptations include:
• keeping the difference between the concentration on each side as high as
possible (maintaining a steep concentration gradient);
85
Life Processes and Disease
• having a large surface area to volume ratio so that molecules have as Large a
surface area of cells as possible to diffuse through;
• being very thin and thus minimising the distance over which diffusion must
take place.
Movement by osmosis
Practical activity
SBA 8.2: Some effects of osmosis,
page 342
Osmosis is a special kind of diffusion. It is the diffusion of water molecules
across a selectively permeable membrane. Cell membranes are all selectively
permeable membranes. ' Selectively permeable' means that water and some
substances can pass through the membrane but other substances do not.
Osmosis in plant cells
11"1-l(.]el!M
milt-WM
When a plant cell is put into a solution which has the same concentration as
the cell contents (isotonic), some water molecules will move into the cell
through the cell membrane and some will move out. There is no concentration
gradient so the movements each way are the same and balance each other out.
We say there is no net movement, or net flow, or water (figure 8.16).
•
..0..
..
• concentration of solution
outside isotonic with
(same as) inside cell
• no net flow of water
•! ·
• outside hypotonic to
(less concentrated)
inside cell
• net flow of water
into cell
• cell is turgid
·'·- ·· : ~
• outside hypertonic to
(more concentrated)
inside cell
• net flow of water out
of the cell
• cell membrane pulls
away from cell wall
• cell is flaccid
Figure 8.16 The effect of different concentrations of solution on a plant cell.
liW•r•H•liiiM When a plant cell is put into a solution that is less concentrated (hypotonic)
liiii•il••
hypertonic >
86
than the cell contents, there is a greater concentration of water molecules
outside than inside . Some water molecules move out of the cell but more move
into the cell, so there is a net flow of water into the cell . The cell becomes full
of water and is described as being turgid .
When a plant cell is put into a solution that is more concentrated
(hypertonic) than the cell contents, there are fewer water molecules outside
than inside. A few water molecules move into the cell but many more move
a ·Cells
1!@13!elJ
out of it, so there is a net flow of water out of the cell. The cell loses water and
is described as being flaccid . Flaccid cell s are easy to distinguish un der the
microscope beca use the cell membran e an d contents pull away from the cell
wall.
Osmosis in animal cells
~
11!Q8
vv
An animal cell placed in water will
burst. Explain fully why a plant cell will
not burst when placed in water.
An anima l cell h as no cell wa ll like a plant cell, so hypotonic and h ypertonic
solutions have different effects. In a h ypotonic (dilute) solution there is a net
flow of wa ter into che cell. With no strong cell wa ll to prevent th e membrane
from stretching too far, it even tually bursts. In a h ypertonic (concentra ted)
solution there is a net flow of water out of the cell and the whole cell shrinks
(figure 8.17) .
•·
,,
• cell in hypotonic
solution
• net flow of water
into cell
• no strong cell wall
so cell bursts
• cell in isotonic
solution
• no net movement
of water
• cell in hypertonic
solution
• net flow of water
out of cell
• cell loses water
and shrinks
Figure B. 17 The effect of different concentrations of solution on an animal cell .
CHAPTER 16 ~
It is important for cells to be protected from large changes in con centration of
the solutions aro und them . Animal bodies ha ve complex m echanisms to do
this called osmoregulation and homeostasis (ch apter 16).
rChapter summary
• The cell is the basic unit of life.
• A cell contains smaller parts called organelles.
• The nucleus, cell membrane, cytoplasm and mitochondrion are some organelles
found in typical plant and animal cells.
• Plant cells also contain cell walls, chloroplasts and large central vacuoles.
• Most microbes are unicellular.
87
Life Processes and Disease
•
•
•
•
•
•
•
•
•
•
Cells in multicellular organisms are often specialised for a particular function.
A group of specialised cells that have the same function is called a tissue.
An organ is a group of different tissues that work together.
Organs working together make up a system.
Systems coordinate with each other and work together in a living organism.
Many substances can move into and out of a cell through the cell membrane which i~
selectively permeable.
Diffusion is the movement of a substance from a high concentration to a low
concentration.
Osmosis is the movement of water across a selectively permeable membrane from a
solution where there is a high concentration of water molecules to a solution where
the concentration of water molecules is lower.
Diffusion and osmosis occur at many places in a living organism.
Different concentrations of solution have different effects on plant and animal cells. ,.
II..
ITQ1
A microscope is an instrument used to produce a magnified image of
an obj ect . Organisms and objects that cannot be seen by the naked eye may be
visible under a microscope.
ITQ2 The measured width of the chloroplast in the photograph is
14 mm (or 14 x 10- 3 m ). The magnifica tion is x5000 . This means that
the measured size is 5000 times large r than in reality. So the actual size is
(14 7 5000) x 10- 3 m = 0 .0028 x 10- 3 m (or 2.8 x 10-6 m or 2 .8 µm ).
ITQ3 (i) Plant a nd a nimal cells have: cell membrane, nucleus, cytoplasm,
mitochondria, small vacuoles.
(ii) Plant cells have a cell wall*, chloroplasts, large central vacuole. (*Fungal
cells and som e bacteria also have cell walls,bu t these have a completely
different structure from those in plants.)
ITQ4 The plant cell wall has protective an d structural functions. It p rotects
the plant by protecting each plant cell from bursting when the plant takes up
w ater. It also helps to support stems and leaves of the plant when th e cells are
full of wa ter, because plants have no skeleton like many animals.
The chloroplast con tains the pigmen t chloroph yll which collects the light
energy of the Sun. Chloroplasts are the sites of photosynthesis, so animals do
n ot need them .
The large plant vacuole is importan t during exchange of wa ter and minerals,
and stores various substances including waste products.
ITQS
(i) The cell membrane is a partially permeable barrier th at controls
the passage of substances into and ou t of the cell whereas the cell wall provides
support and protection and allows the free passage of wa ter.
(ii) Th e mitochondrion is the site of respiration during which en ergy is
released from sugar. All cells have mhocd1ondria. The chloroplast is the site of
ph otosynth esis where sugar is made. Chloroplasts are found only in plant cells.
ITQ6 Cell: e.g. mu scle cell .
Tissue: an y group of on e kind of cell w orking together e.g. muscle cells in
muscle tissue.
Organ: any group of tissues working together e.g. stomach , m ade up of
secretory tissue, muscle tissue and other tissues; leaf, made of palisa de tissue,
xylem tissue.
System : any group of one kind of organs working together e.g. digestive
system, made up of stomach, liver, intestines and other organs.
88
8·Cells
ITQ7
A unicellular organism is an organism that h as only one cell. This
small organism shows all the characteristics of We and lives an independ ent
life. For exa mple, Amoeba and Chlorella . A multicellular organism is made up
of man y cells. These cells work together, and the organism is able to show all
the characteristics of life. For example, a human and a worm (there are many
other examples you co uld have chosen ).
ITQ8 A plant cell has a cellulose cell wall around the cell membrane.
The wall is strong and cannot stretch. When placed in water, th e cell will
take up water, but the cell membrane wilJ n ot burst because th e cellulose
cell wall stops it stretching to bursting point. An animal cell does not
have a cellulose cell wall and so can stretch to the point w here it bursts.
Examination-style questions
1
(i) The drawing below was constructed by a biology student after viewing a slide under
the microscope. The drawing made was magnified 2500 times. What is the actual size
of the cell labelled A?
( C) I C) I C) J
A
(ii) The figure below shows how a section of a root or stem is mounted for microscopic
investigation.
/
I
Explain why it is necessary to cut a very thin section of the material which is to be
observed under the microscope.
(iii) (a) Name two types of microscope.
(b) Why are cells described as being microscopic?
2
(i) Make labelled drawings of typical plant and animal cells.
(ii) Use a table to compare typical plant and animal cells.
(iii) Give one advantage of being multicellular.
(iv) Name one difference between a tissue and an organ.
(v) Give one named example of:
(a) a tissue;
(b) an organ to be found in:
•
•
an animal;
a plant.
89
Life Processes and Disease
3
The figure below shows onion rings A, B, C and D before and after immersion in water and
a salt solution.
onion ring A
0
onion ring before
immersion in water
onion ring C
0
onion ring before
immersion in salt solution
onion ring B
onion ring D
0
onion ring after immersion
in water
0
onion ring after immersion
in salt solution
(i) Copy and complete the table below to show the measurements of the rings.
Onion ring
Outer diameter
Inner diameter
Mean diameter
A
B
c
D
(ii) (a) Using measurements.from the table, describe what happened to the onion ring
placed in:
• water;
• salt solution.
(b) Explain fully the results seen in:
• water;
• salt solution.
(iii) (a) What process is taking place?
(b) Give an example of the occurrence of this process in living organisms.
(iv) Describe two examples of diffusion as it occurs in living organisms.
90
P. hotosynthesis
0
understand the difference between heterotrophic, autotrophic and saprophytic
nutrition
0
0
describe photosynthesis in green plants
0
explain how environmental factors affect the rate of photosynthesis
relate the structure of the leaf of a flowering plant to its function in
photosynthesis
photosynthesis
autotrophic nutrition
inorganic substances
converted to
organic substances
(
heterotrophic
nutrition - animals
saprophytic
nutrition
leaf structures
limiting factors - light,
temperature, carbon dioxide;
water
1
conditions
adaptations for
photosynthesis
Plants are the food supply for animals
Th e relationship between autotrophs, heterotrophs and sproph yres is sh own
in figure 9. 1.
AUTOTROPH
HETEROTROPH
'self-feeders'
e.g. plants that make
their own food
during photosynthesis
feed on other organisms
e.g. consumers that
feed on plants and
other animals
SAPROPHYTE
feed on dead organic
material
e.g. decomposers that
feed on the dead
autotrophs and
heterotrophs
/
Figure 9.1 Relationships of autotrophs, heterotrophs and saprophytes.
91
Life Processes and Disease
In the study of food chains we saw that plants are producers and are at the
heterotroph >
QSb
start of almost all food chains. Animals are consumers and feed on the plants or
on other animals. Plants do not eat, yet they are full of food. They are rich in
carbohydrates, fats and proteins. This is because they are able to manufacture
their own food. We call them autotrophs (self-feeders) because they are able to
make organic substances (glucose) from simple inorganic substances (carbon
dioxide and water). This process is called photosynthesis and requires light
from the Sun to provide the energy needed to carry it out. From glucose, the
plant makes all the other carbohydrates, fats and proteins it needs.
.
Consumers feed on the organic substances made by the plants. Consumers
are h eterotrophs (other or different feeders). Heterotrophic nutrition is
the intake of complex organic substances when animals feed. Autotrophic
nutrition is the intake of simple inorganic substances by plants during
photosynthesis and must occur before heterotrophic nutrition (figure 9.2).
C02
IT:.Q-1
l./'-J
Distinguish between an autotroph and a
heterotroph.
~
IT:.Q2
l./'-J
Why must autotrophic nutrition occur
before heterotrophic nutrition?
~
IT:.Q3
l./'-J
Why is saprophytic nutrition important?
Autotrophic nutrition
Heterotrophic nutrition
...__ _. .
~ I plants take in inorganic
H20
substances and make
inorganic
organic substances
substances
animals take in organic
substances when
they feed
'
Figure 9.2 Autotrophic nutrition must occur before heterotrophic nutrition can occur. Food chains
start with plants, then animals feed on the plants.
When plants and animals die, saprophytes feed on the dead bodies which
are full of organic substances such as carbohydrates, fats and proteins.
Saprophytes are also called decomposers and they are very important to the
cycling of these materials back to the earth, from where they are then available
to plants again.
Photosynthesis
Practical activity
SBA 9.2: Is light needed for
photosynthesis? page 344
Photosynthesis can be summarised in words or by the simple equation:
light
carbon dioxide + water _ _ _ __, glucose + oxygen
chlorophyll
photosynthesis equation >
light
6C0 2 + 6H 2 0
C6 H 12 0 6 + 60 2
chlorophyll
light-dep endent stage )
light-independent stage >
Chlorophyll is a complex green pigment. At the centre of a chlorophyll
molecule is a single atom of magnesium chemicaly bonded to four atom s of
nitrogen. Without supplies of nitrogen, a plant cannot make chlorophyll and so
cannot photosynthesise successfully.
Experiments show that there are two main stages in photosynthesis
(figure 9.3), namely:
• the light-dependent stage
• the light-independent stage
Light-dependent stage
Chloroplasts are organelles seen in green plants cells. They contain the green
pigment chlorophyll which 'traps' the light energy from the Sun. The energy
is used to 'split' water (Hp) into hydrogen and oxygen. The oxygen is a waste
product and diffuses out of the leaf.
92
9 · Photosynthesis
Light-independent stage
The h ydrogen then combines with carbon dioxide (COJ to make glucose
(C6 H 12 0 6 ). This stage of photosynthesis does not n eed light and can h appen
when it is dark.
~
3~chlorophyl
, .•diffuses out of the leaf
O><Jlgen / /
,/'/
water
hydrogen
light -dependent stage
~
/
carbon dioxide
diffuses into the leaf
glucose
light-independent stage
Figure 9.3 Light-dependent and light-independent stages of photosynthesis.
The organ specialised for photosynthesis is the leaf. The transverse section
of a leaf reveals many cells, a rranged in a manner that is ideally suited for
photosynthesis.
Adaptations of the leaf for photosynthesis
Practical activity
SBA 9.3: Is chlorophyll needed for
photosynthesis? page 345
lfU.),ifiiOJ
palisade cell >
Leaves a re adapted to carry out
photosynth esis in a number of ways
(figures 9.4 and 9.5).
• They are generally broad and flat with
a large surface area to a bsorb a lot of
light and carbon dioxide.
• They lie at 90° to the sunlight and are
spaced around th e stem to ca tch as
much light as possible.
Rgure 9.4 How leaves catch as much
• The leaves are thin to allow light
sunlight as possible.
and carbon dioxide to reach all cells
ra pidly.
• Stomata (small holes) are present in the lower epidermis to allow gases to
get in and out easily. (One h ole is a stom a. Stomata is the plural. )
• Air spaces around the cells in the lower half of th e leaf allow carbon dioxide
to get to the chloroplasts as quickly as possible.
• Chloroplasts are most numerous in cells in the palisade layer, which is in
the top part of th e leaf, closest to the sunligh t.
• Xylem vessels transport wa ter to the leaf cells.
• Phloem sieve tubes carry away the food made in th e leaf cells to the rest of
the plant.
• A waxy cuticle p revents water Joss form both surfaces of the leaf; it is
transparent to le t light through .
93
Life Processes and Disease
the leaf is cut at
A-B and magnified
B
\
A
veins - run
throughout leaf
B
stoma
epidermis
magnification of
this small section
(a transverse section)
upper epid ermis
palisade layer
air space
xylem vessels
vein -~:::.....~f------1._....._.....
spongy layer
i.,..o;r;.,,""' ~f---- p hloem tubes
cell of lower
epidermis - no
chlorop lasts
lower epid ermis
guard cellthickened - - - - - - "
inner wall
stoma
Figure 9.5 A section of a leaf.
Guard cells
-
epidermal
cell
guard cell
CHAPTER 14
94
A stoma is surrounded by a pair of specialised
(turgid)
epidermal cells called guard cells. The gua rd
cells vary the size of the opening of the stoma
stoma open
by changing their shape, thu s the size of
the stomata! pore is regulated by the guard
cell. The stoma is the route by which water
is lost from the plant during transpiration
(chapter 14), and also by which the gaseous
___.____ guard cell
exchange necessary for photosynthesis
(flaccid)
occurs. By controlling stomata! opening a nd
closing, a plant controls the balance between
stoma
the need to conserve water and the need to
closed
exch ange gases.
Stomata! opening varies as a result of
ch an ges in the turgidity of the guard cells
Figure 9.6 The guard cells control the
(figure 9.6)
opening and closing of the stomata! pore.
9 · Photosynthesis
~
IT:Q:.t
\../'-.I
Why do you think that the stomata of
some desert plants close during the
day?
• when they are turgid, the stoma opens;
• when they are flaccid, the stoma d oses.
The following observations have been made:
• most stomata open during the day and close at night;
• stomata generally dose when a plant suffers water stress, or when
transpiration rate exceeds the rate of water absorption by the roots;
• the stomata of some desert plants close during the day and open at night.
How everything gets to the chloroplast
Practical activity
SBA 9.4: Is carbon dioxide needed for
photosynthesis? page 346
Photosynthesis takes place in the chloroplasts of specia li sed leaf cells. The
following numbered paragraphs refer to Figure 9.7.
light from the Sun
~
IT:QS
\../'-.I
Describe how carbon dioxide gas in the
atmosphere gets to a photosynthesising
cell inside a leaf.
typical
photosynthesising cell-~.......
(chlorophyll is present
in the chloroplasts)
water travels to the
v~...,..._f::;!M--f-- leaf via the xylem, from
the soil surrounding
the roots
ti"t---i"t1r>--nt!t---
C02 used up during
photosynthesis
• Its concentration is
thus low in the cell
•
carbon dioxide in the
air surrounding the leaf
-
-+1"'.ll'tt---
• C02 in the air space.
Its concentration is
higher than in the cell
• C02 diffuses into the
cell from the air space
C02
Rgure 9.8 Carbon dioxide diffuses down
its concentration gradient into the leaf.
Rgure 9.7 All the requirements for photosynthesis must get to all the photosynthesising cells.
1
rrr.:a_- the leaves are thin
and flat and lie
at right angles to
the Sun's rays
~...--..--:::;;::--~ xylem vessel in
~
IT:Q6
the stem
transports water
\../'-.I
Look at the tomato plant and describe
four ways in which the plant is adapted
for photosynthesis.
leaves are
spread around
the stem
2
Ca rbon dioxide diffuses from
the surrounding air into
the stomata or pores on the
underside of the leaf. It moves
into the air space su rrounding
the mesophyll cells, and then
into the cells themselves. As
the carbon dioxide is used
up during photosynthesis, its
concentration drops. There is
thus a greater concentration of
carbon dioxide outside the cells
than inside and carbon dioxide
dilfuses into them (figure 9.8).
Water moves by osmosis from
the soil into the roots of the
plant. It then travels up the
xylem vessel in the stem and
into the leaves. From the
95
Life Processes and Disease
3
4
xylem in the leaf. water moves by osmosis to the palisade cells where it is
used during photosynthesis.
Light rays pass into the leaf from all around, especially from above.
Chloroplasts are found mainly in the palisade cells where the chlorophyll
can easily intercept and trap the light energy.
Within the chloroplasts the light energy splits the water which then reacts
with the carbon dioxide .
Products of photosynthesis
Practical activity
SBA 9.5: Is oxygen produced during
photosynthesis? page 347
.tt"t--+'ttt---;tt.~ • Oxygen is produced
during photosynthesis
• Its concentration is
therefore high in the
cell
--"=t....H-- • Oxygen diffuses into
the air space where its
concentration is lower
• Oxygen diffuses out of
the cell through stomata
02
Figure 9.9 Oxygen moves out of a leaf.
limiting factor >
The glucose produced during photosynthesis is used in several ways.
• It is broken down during respiration to release energy so the plant can carry
out all the processes of life.
• It is converted to starch and stored in the leaf to be used in the night when
the plant is not photosynthesising.
• It is converted to sucrose and transported to other parts of the plant. It can
then be converted to other carbohydrates, lipids and proteins and used for
growth, or it can be converted to starch and stored, as in potatoes .
Oxygen is a waste product of photosynthesis. The cells in the leaf will use some
for respiration, but the rest of the oxygen is not needed by the plant. Inside the
leaf, photosynthesis is taking place and oxygen is being produced. It is thus at
higher concentration inside the leaf than oucside. So oxygen diffu ses out of the
leaf through the stomata (figure 9.9).
Limiting factors in photosynthesis
Photosynthesis is a chemical reaction, and the rate at which a reaction can
happen depends on how fast the chemicals that are reacting can get together.
In photosynthesis, a plant requires water, carbon d ioxide and light. If
any one of these is in short supply, the rate of the reaction will slow down.
For example, a plant may have sufficient carbon dioxide and water, but not
enough light for photosynthesis to take place at its maximum rate. Light is
then said to be the limiting factor, since the rate of photosynthesis is limited
by the amount of light. The reaction will take place at a rate that is limited by
the factor which is a t its least favourable value (light, in this example). Water,
light and carbon dioxide may all be limiting factors for photosynthesis at
different times.
The limiting factors which affect photosynthesis are:
• temperature;
• light intensity;
• carbon dioxide concentration;
• availability of water.
Temperature
CHAPTER 10
96
The rate of a reaction increases as temperature increases. With heat, the
molecules move about and come together faster.
Photosynthesis also involves a series of enzyme-catalysed reactions.
Enzymes have an optimum temperature or temperature at which they work
best (chapter 10), so this w ill also affect the rate of the reaction.
Temperature is often the limiting factor on the rate of photosynthesis in cool
seasons in temperate regions.
9 · Photosynthesis
Carbon dioxide concentration
The concemrarion of carbon dioxide is re latively low in the atmosphere. So
carbon dioxide is us ually the limiting fa ctor when cemperature and light levels
are high. Commercial growers who grow their crops in large greenhouses often
pump in extra carbon diox ide to increa se the rate of photosynthesis in the
crops (figure 9.10).
Light intensity
The amount of light in the e nvironment varies grea tl y between night and day.
Light is usually the limiting fa ctor from dusk until dawn (figu re 9.10).
Rate of photosynthesis
rate slows down, some ractor 1s limiting the rate
0.13% C02 at 30 °C
-
areater C02 concentration rate increases
0.03%'C02 at 30°C
~
co_
rate of photosynthesis slows down because of
concentration - C02 is the hm1t1ng factor, not light
\./'-I
Which factor will most likely be limiting
photosynthesis in each of these cases?
(i) Middle of the day after plenty of
rain in Jamaica.
(ii) Cool autumn day in Britain.
(iii) Dry season in Australia.
+------ rate or photosynthesis increases as hyht 1ntens1ty
increases - light Is the limiting factor
Light intensity
Rgure 9.10 How light and carbon dioxide may limit the rate of photosynthesis
Availability of water
The ava ilability of water varies in the environment. If the soil is dry, wa ter may
be the limiring factor on photosynthesis.
Etiolation
mmmm.],p
Cf the plant cannot get sunlight, for
example it is shaded by a rock or anoth er
plant, it cannot photosynthesis. Without
photosynthesis it cannot make food.
But this does not mean that it cannot
continue to grow. For a short while, it can
use some of the food stored w ithin the
plant to grow and lengthen. This gives it
a chance to get som e leaves into the light
a nd so start to photosynth esise again.
The form o f growth a plan t shows
wh en it is out of light is different from
n ormal. All the energy is u sed to make
long thin cells, so the stem becomes
e lo ngated and thin, and leaves are kept
very small. Th e stems and leaves are also
pale yellow as n o chJorophyll is made.
This fom1 of growth is called etiolation
(figure 9.11). If it does not reach light
Figure 9. 11 The et1olated plants on the
quickJy the plant will run o ut or rood
nght have long thm, white stems and small
reserves and die.
yellow leaves
97
Life Processes and Disease
.. _
-
An autotroph is an organism that is able to make its own food (organic
substances) from simple substances (inorganic substances) . A plant is an
autotroph - when it photosynthesises it makes glucose from carbon dioxide
and water.
A heterotroph is an organism that takes in organic food when it feeds. It
must have a supply of organic food since it cannot manufacture it for itself.
ITQ2 Autotrophs make organic food which is eaten by heterotrophs.
Autotrophic nutrition must therefore take place first so that heterotrophs can
have something co eat.
ITQ3 Saprophytic nutrition is important for the recycling of nutrients in the
environment. Nutrients trapped in an organism are made available when that
organism dies. Saprophytes can digest cellu lose and lignin and can decompose
all plant remains.
ITQ4 Some desert plants close their stomata during the day to p revent loss
of coo much water from the leaf when it is hot. They open their stomata at
night to exchange gases for photosynthesis. (They have a special mechanism
which allows them to trap the energy from sunlight during the day and
store it. until the stom ata open at nigh t and the energy can be used to make
glucose.)
ITQ5 Carbon dioxide is in the atmosphere around the leaf and gets to the
photosynthesising cell by diffusion. A photosynthesising cell uses carbon
dioxide, and so the ca rbon dioxide concentration decreases within the cell.
Carbon dioxide diffu ses into the cell from the surrounding air space where its
concentration is greater. The carbon dioxide concentration is thus lowered in
the air space. Carbon dioxide _from the atmosphere can now diffuse into the air
space through the stomata.
ITQ6 •
The leaves are spread around the stem and lie at right angles to
the Sun's rays so that they can intercept as m ud1 light as possible.
• Leaves are green because the cells contain chlorophyll. This captures light
energy which is needed in photosynthesis.
• Xylem vessels in the stem transport water to the leaf.
• The leaves are thin and flat so gases can diffuse in and out as quickly as
possible.
ITQ7
(i)
Carbon dioxide
(ii) Temperature
(iii) Water
ITQ1
98
9 · Photosynthesis
Examination-style questions
The diagram below shows a transverse section of a leaf as seen under a microscope.
(i) Label the parts A to F.
(ii) Which cell is most actively photosynthesising?
(iii) (a) Write the equation that summarises the process of photosynthesis.
(b) From the equation, identity three factors/conditions necessary for photosynthesis
to take place.
(c) Describe how two of these factors reach a typical photosynthesising cell.
(d) Describe the role of the cell labelled E.
2
(i)
Define:
(a) autotrophic nutrition;
(b) heterotrophic nutrition.
(c) saprophytic nutrition
(ii) Photosynlliesis"ls summarised in one equation, but described as two stages (a) lightdependent, and (b) light-independent. Describe the two stages of photosynthesis.
(iii) List five ways a plant is adapted for photosynthesis.
3
The diagram below shows a leaf in its actual size.
(i) Making a drawing of the leaf.
(ii) Write a heading for the drawing.
(iii) Calculate the magnification of your drawing.
(iv) Label the parts of the leaf.
99
./ understand the importance of minerals in plant nutrition
./
understand the importance of a balanced diet to humans
0
describe food tests for carbohydrates, proteins and fats
./
relate a balanced diet to age, sex and activity of an individual
./ explain the meaning of the term 'malnutrition'
./ describe hypertension and diabetes
./ describe health problems associated with food additives
0
describe the role and structure of teeth
f?
understand the action of enzymes
Z, understand how the alimentary canal of humans works
./) describe what happens to the products of digestion
age
minerals in plants
pregnancy
food additives
diet
balanced diet
malnutrition
sex
alimentary system
I
activity
ingestion
physical digestion
- teeth
chemical digestion
- enzymes
}
I
digestion
absorption
villus
I
assimilation
liver
egestion
constipation
All organ isms, plan ts and animals, must be supplied with a source of energy
fo r metabolism. This energy is used for ma intenance, growth, and repair of
their bodies to sustain thei r lives. Plants (autotrophs) are able to make their
own food using energy tram the Sun. They take in only very simple inorganic
substances like water, carbon d ioxide and also magnesium and nitrate ions.
Nitrogen and magnesium are basic components of chlorophyll. Choprophyll
allows a plant to grow more rapidly and produce large amounts of succulent
green leaves. These minerals also strengthen and support the roots thus
enabling p lants to take in more water and nutrients from the soil. Nitrogen is
10 · Feeding and Digestion
also important in the formation of proteins. Animals (heterotrophs) can only
obtain energy when they feed on other living organisms made up of complex
materials such as carbohydrates, proteins and lipids.
Diet
l!l@IJ
balanced diet >
IOeliM
~
IT:.Q-1
vv
Define the terms 'diet' and
'balanced diet'.
To maintain their bodies in good hea lth, anima ls need various materials. These
include carbohydrates, proteins, lipids, vitamins and minerals. Animals eat food
that contain these materials or nutrients. The term 'diet' is used to describe the
quantity and quality of food eaten (i.e. which nutrients and how much of each
is present in the food being eaten every day).
A balanced diet is a diet which has the quality and proportions of
nutrients needed to maintain good health. This includes water and fibre.
Water is essential because around 70% of our body mass is water. If we do not
get enough water, systems in the body soon stop functioning properly. Fibre, or
roughage, is the tough fibres that come from plant material. We cannot digest
and absorb them, but they an; essential to the healthy working of the gut.
Without enough fibre, we soon suffer from constipation. Eventually this can
lead to bowel disease.
Some nutrients that are needed are organic and some are inorganic
(table 10.1).
Organic nutrients
Inorganic nutrients
Carbohydrates
Minerals
contain carbon (C), hydrogen (H) and oxygen (0) calcium, iron, potassium, sodium, iodine,
phosphorus
Proteins
contain C, H, Oand also nitrogen (N) and small
amounts of sulfur (S)
Lipids
contain C, H and 0
Vitamins
contain C, H and Oand other essential elements
Table 10. 1 The organic and inorganic nutrients needed by living organisms.
Organic nutrients
Figure 10.1 Three-dimensional ball-andstick model of a glucose molecule.
monosaccharide >
disaccharide >
These are required in the diet in relatively large amounts (tables 10.2 and 10.3,
overleaf).
Carboh ydrates are compounds of carbon, hydrogen and oxygen in the
radio 1 C: 2 H: 1 0. An example is glucose. Figure 10.l shows a baJJ-and-stick
model of a molecule of glucose. It can also exist as a ring formed from five
carbon atoms and one oxygen atom. The sixth carbon atom in a - CH 2 0H group
is attached to a ring carbon.
Compounds with one such ring structure are called monosaccharides .
The formula can be shortened to a symbol which can be either
or, for
diagrams, just • .
Glucose and fructose are examples of monosaccharides. Monosaccharides
are often called simple sugars.
Two monosaccharides can combine to form a disaccharide (figure 10.2,
overleaf). This happens in a condensation reaction as a water molecule is
removed. Disaccharides can be broken back down to monosaccharides by
hydrolysis which is a chemical reaction involving recombination with water.
0
101
Life Processes and Disease
Monosaccharides and most disaccharides reduce Benedict's solution to an
orange/red compound. Sucrose is the only common disaccharide which
does not react in this way. This provides a distinguishing test for sucrose.
Disaccharides are called complex sugars.
H
O H
HO H I H
20
HO
OH
condensation (water removed)!
HO
monosaccharides
OH
j hydrolysis (water added)
H: OoO
:H
j
H~ O\oO o001
0oO :H
condensation!
/
dlsaccharide
hydrolysis
polysaccharide
Figure 10.2 D1saccharide molecules are made when two monosaccharide molecules join
together. Polysacchande molecules are made of many monosacchande molecules.
Organic nutrient Major groups
Carbohydrate
Protein
Structure
Characteristics
Importance
monosaccharide (e.g.
glucose, fructose)
five carbon atoms and an
oxygen atom form a ring
called simple sugars
small molecules, soluble,
sweet taste
major energy source
disaccharide (e.g.
maltose, sucrose)
two rings join together
called complex sugars
soluble, sweet taste
major energy source
polysaccharide (e.g.
starch, cellulose,
glycogen)
many rings join together
long chains of simple sugar
(glucose) joined together
insoluble and do not have a
sweet taste
starch is used as the energy store
in plant cells and as a food source ·
for animals
cellulose is found in plant cell
walls
glycogen is used as the energy
store in animals cells
a difference in the order of
amino acids in the chain
results in different protein
there are millions of
proteins, some soluble e.g.
haemoglobin, red pigment in
blood), and some insoluble
(e.g. keratin, from which hair
and nails are made).
used for making new cells, growth
and damaged parts of the body
antibodies, hormones and enzymes
are also proteins
insoluble in water
secondary energy supply after
carbohydrates have been used up
important for storage (oils in seeds)
also function as insulation (fat
under skin) especially for animals
living in cold regions
foods like butter, oils and nuts are
rich in lipids
JlD
made up of long chains of
amino acids
there are about 20 different
amino acids
they can be arranged in the
protein chain in any order
/
(
·-o- ~
~
·-~
Upids
(fats and oils)
four moelcules (three fatty
acids and one glycerol)
joined together
--
[E ff
glycerol
fatty ac ids
(continued)
102
10 · Feeding and Digestion
Organic nutrient Major groups
Vitamins
Structure
A, B, C, D, Eand K
each vitmain has many
funcitons
Characteristics
Importance
small amounts needed for
good health
A - aids vision in dim light
B- asissts in respiraiton
C- keeps tiossues helathy
D- aids absopriton of calcuim
K- aids in blood clotting
Table 10.2 The major organic nutrient groups.
Vitamin
Sources
Functions
Symptoms of deficiency
A
carrots, spinach, egg yolk, cod liver oil,
butter
keeps skin and mucous membranes
healthy, aids vision in dim light
dry skin, mucous membranes
degenerate, poor night vision
B1
liver, rice, cereals, whole wheat flour,
yeast
helps in respiration
beriberi - muscles become weak and
painful, nervous system affected
B6
leafy vegetables, eggs, liver, fish, kidney
helps in metabolism
depression and irritability
c
citrus fruits, green vegetables
keeps tissues healthy
scurvy - guns bleed, wounds take
longer to heal, heart failure
D
egg yolk, dairy products, cod liver oil,
also made by the action of sunlight on
the skin
controls calcium and phosphorus
absorption, important in bone and tooth
formation
rickets - growing bones do not calcify,
results in 'bow' legs in young children,
and 'knock-knee' in older children
Table 10.3 Some vitamins needed by humans for healthy growth.
polysaccharide >
NB Both Benedict's and Fehling's solutions
contain copper sulfate. Reducing sugars reduce
the copper(ll) ions (CU2• ) present in the copper
sulfate to insoluble red-brown copper(I) oxide
which contains cu• ions and is a precipitate.
Practical activity
SBA 10.1: Which food groups are
present in a food sample? page 348
Substance to be tested
Many monosaccharides can be joined to fo rm or syn thesise a very large
molecule called a p o lysacch aride. Since condensation (deh ydration) reactions
are involved in the synthesis of these polymers, these reactions can be
called dehydration synthesis. Starch, cellulose and glycogen are examples of
polysaccharides. They can form very large molecules.
Food tests
Table 10.4 sh ows the standard tests which can be made on a sample of food to
indicate each of the main food grou ps.
Test
Observations
3
Reducing sugars - all
monosaccharides (e.g.
glucose, fructose) and some
disaccharides (e.g. maltose)
(i) Benedict's test: 2 cm of the solution to be tested
The initial blue colour of the mixture turns green and
3
is put into a test-tube. 2 cm of Benedict's solution is
then yellow and may form a brick-red precipitate.
then added. The mixture is shaken and brought gently to
the boil.
(ii) Fehling's test: 2 cm3 of the solution to be tested is Same as Benedict's test.
put into a test-tube. 1 cm3 of Fehling's A is added. 1 cm 3
of Fehling's B is then added. The mixture is shaken and
brought gently to the boil.
Non-reducing sugars
(e.g. sucrose)
1 cm3 of the solution is put into a test-tube and 1 cm 3 of A red-brown precipitate results as the sucrose is
dilute hydrochloric acid (HCI) is also added. The mixture hydrolysed to fructose and glucose by the acid. Fructose
is bolled for 1 minute. 1 cm 3 of aqueous NaOH (NaOH
and glucose are reducing sugars, so Benedict's test then
solution) is added, followed by 2 cm3 of Benedict's
can be carried out.
solution. The mixture is then shaken and boiled gently.
Starch
2 cm3 of 1% starch solution is added to a test-tube. A
few drops of iodine in potassium iodide (12KI) solution is
added.
A blue-black precipitate results.
(continued)
103
Life Processes and Disease
Substance to be tested
Test
Observations
Protein
Biuret test: 2 cm3 of protein solution is put into a testtube, 2 cm3 of 5% potassium hydroxide (KOH) is then
added. The mixture is stirred and 2 drops of 1% copper
sulfate (CuSOJ is added.
A mauve or purple colour slowly develops.
Fats
Ethanol test: 2 cm 3 of fat solution or oil is put into a
A cloudy white suspension can be seen when the water
test-tube. 2 cm3-of absolute ethanol is then added.
is added.
The mixture is shake~ vigorously and 3 cm3 of water
is added.
Grease spot test: a drop of the sample is dropped onto A permanent translucent spot is seen on the paper.
a piece of paper.
Table 10.4 Tests for the main food groups.
Inorganic nutrients
trace element >
~
ll:.Q2
l../V
Give three named examples of foods
which can be eaten to obtain (i) organic
nutrients (ii) inorganic nutrients.
Minerals are inorganic nutrients that are required in small amounts for good
health and development. Some are required in only trace (very small) amounts
for good health and thus are called trace elements . Table 10.5 shows some
mineral elements required by plants and table 10.6 shows some minerals
required by humans.
Element
One function
Deficiency effects
nitrogen (N) (absorbed as necessary for proteins
nitrates)
small yellow leaves and poor
growth
magnesium (Mg)
necessary for chlorophyll
leaves yellow between the veins
iron (Fe)
necessary for chlorophyll
new leaves yellow between veins
calcium (Ca)
necessary for cell walls
poor stunted growth, leaves
yellow, terminal buds die
potassium (K)
maintains the salt balance in cells yellow/brown edges on leaves,
edges wither, plant dies early
sulfur (S)
makes proteins
young leaves small, thin, yellow
between green veins
phosphorus (P)
makes some proteins
poor growth, small reddish-brown
leaves
Table 10.5 Some elements needed by plants for healthy growth.
Mineral
Sources
Functions
calcium
milk, cheese
formation of bones and brittle bones and teeth
teeth
iron
red meat, green leafy
vegetables
formation of
haemoglobin
Symptoms of deficiency
anaemia - tiredness, lack of
energy because of a reduction
in the number of red blood cells
(continued)
104
Ingredients: sugar, enriched bleach flour
(wheat flour, niacin, reduced iron, thiamine
mononitrate, riboflavin, folate) food
starch-modified, partially hydrogenated
soybean and cottonseed oils, leavening
(sodium bicarbonate, sodium aluminium
phosphate), emulsifier (propylene glycol
monoester, monoglyceride, sodium
stearoyl lactylate), salt, natural and artificial
flavours, citric acid, guar gum, xanthan
gum, isolated soy protein, whey.
Blueberries: blueberries, water.
Agure 10.3 There are many additives in
the ingredients of manufactured food as
seen in this list of ingredients for a blueberry
muffin mix.
Mineral
Sources
iodine
sea foods, iodised table formation of the
salt
hormone thyroxin
goitre (adults) - reduced
metabolic rate, swelling of the
thyroid gland
cretinism (children) - physical
and mental retardation
phosphorus
meat, fish
brittle bones and teeth
Functions
combine with calcium
in the formation of
bones and teeth
Symptoms of deficiency
Table 10.6 Some elements needed by humans for healthy growth.
Food additives
Many additives a re used in preparing food, for many different reasons
(figure 10.3) . Food additives may be natural or artificial. Common natural
additives include sugar, corn syrup and pepper. Common artificia l additives
are some flavours and sweeteners. The major groups of additives include the
following.
Dyes and colourings
These are purely cosmetic and rarely add nutritional va lu e. Tartazine is used to
give a yellow colour to foods and drinks, for example, orange juice, fish fingers.
It does, however, h ave some adverse effects as it is associa ted with:
• h yperactivity in children;
• a llergic reactions;
• adverse efiects on asthmatics.
Preservatives
These make food less susceptible to bacterial infection, so food can be kept for
longer periods of time in tins. packets, spreads and bottles without spoiling. When
food is produced and packaged it may travel thousands of miles, over several
months, before it is used. The health of the general population has improved
because preservatives reduce the risk of bacterial poisoning. They are perhaps
the most easily justified additive, but only make up l % of a ll additives used.
Synthetic flavourings
During preparation, food can lose some of its flavour, so these are added to
improve or even ch ange the flavour.
Flavour enhancers and sweeteners
Saccharin is often used to sweeten prepared foods. Monosodium gl utamate
(MSG, Ali-jo-moto, Vet-sin) is a commonly used flavour enhancer found in
processed foods including soups, fast foods and Chinese foods. Young children
and pregnant and lactating women are advised not to eat foods containing
MSG as it may be related to asthma, attention deficit disorder, acute headaches,
extreme mood swings, depression and paranoia.
Propellants
Carbon dioxide and nitrous oxide may each be used to form an aerosol, forcing
food out of contain ers.
105
Life Processes and Disease
Acids
These are added to give a sour taste to prepared food.
Firming agents
Aluminium sa lts are used to retain crispness; gums increase the thickness of
sauces and soups.
A balanced diet
41% staples
(a) cereal grains
(b) starchy fruits,
roots and tubers
21% legumes
and nuts
11 % dark green
leafy and/or
yellow
.. #
i'if ~
vegetables
11%
it/
11 % food from
f fruits
animals
Rgure 10.4 Pie chart showing the relative
proportions of foods in a balanced diet.
~
ll!Q3
V'--J
Describe a meal which includes all the
nutrients necessary for good health.
We ca11 group all the foods available to humans into six food groups.
• Staple foods -These include cereal grain (e.g. rice), cornmeal, wheat flour,
oats, sta rchy fruits, roots, tubers.
• Peas and beans (legumes) - These include red beans, pigeon peas, black
eyed peas, broa d beans.
• Dark green, leafy vegeables and yellow vegetables - Cabbage, pak
choi, lettuce, spinach are leafy examples; pumpkin and carrot are examples
of yellow vegetables.
• Foods from animals - Fish, poultry, meat, milk, eggs, cheese are all food s
from animals.
• Fruits - Citrus fruits, bananas, apples are all examples.
• Fats - These include oils, butter, margarine and food with a high proportion
of fat such as ca kes, biscuits.
Figure 10.4 shows th e components of a balanced di et. Each block represents a
food group and the size of the block indicates the proportion of the ctiet which.
that food group should constitute.
Balanced diet related to age, sex and activity of
an individual
Nutritional requirements vary with age, sex and activity.
Energy requirement
Energy requirements are generaJJ y greater for men (figure 10.5). They
usually have more muscle, relatively less fat and weigh more than women.
In women, the energy requirements are
higher during the last three months of
12 000 - Energy (kcal per day)
emae •
mae •
pregnancy. Extra energy is needed for
growth
of the fe tus and deposition of fat
10 000 in preparation for breast feeding. This
requires extra energy because the energy
8000 needed by the baby for rapid growth
in
early postnatal life comes from its
6000
mother's milk.
Energy requirements for a growing
4000 individual increase up to about the age of
18 years, when the energy requirements
2000
are the greatest. The requirement for
energy then decreases as the person
0 1-3 I 7-10 I 15-10 I 23-26 I 31-34 I 39-42 I 47-50 I 60-64 I 75+
gets older.
4-6
11- 14
19--22
27-30
35-38
43-46
51-59
65-74
Physical activity of an individual
Age (years)
varies with both occupation and leisure.
Rgure 10.5 Ener requirements for men and women vary as they get older
Some people are mostly sedentary
1
106
10 · Feeding and Digestion
(sitting for much of the time, such as in an office) and others are very active.
Energy req uirements for different levels of activity can vary greatly.
Protein requirement
Men require more protein than wo men from around the age of 11 years
onwa rds. This is when the muscle-to-fat ratio starts to differ because of the
development of secondar y sexual characteristics. Women start to store fat
in their hips and breasts and men develop more muscle, especia lly on their
shoulders and legs. Extra protein is required by women during pregnancy and
breastfeeding.
Requirements of minerals and vitamins
Mineral intake is especially important during pregnancy and lactation. The
mother's diet must con tain sufficient iron, calcium, vitamin C, folic acid, and
everything needed to make the baby's tissues inccluding blood, bone and
muscle. Extra folic acid may be given to the mother to red uce the risk of spina
bifida in the baby.
Malnutrition
malnutrition >
Malnutrition means bad nutrition, and can be applied to under-eating, overea ting and bad eating habits. Malnutrition is the cause of many diseases like
deficiency diseases, obesity, hea rt diseases and anorexia. Education on ba lanced
di et and good health is very important in preventing the occurrence of many
diseases.
Under-eating
Figure 10.6 A child suffering from
kwash1orkor and marasmus.
fht•W&WIJ
Starvation is one kind of under-eating and is most often associated with
developing countries. It means not eating enough food to supply the energy
requirements for daily activHies. Also, not enough protein and vitamins are
eaten which are necessary for growth, development, resistance to infecti on and
a healthy life. Marasmus and kwashiorkor are common conditions ca used by
under-eating (figure 10.6).
Some signs and symptoms of marasmus and kwash.iorkor:
• very underweight (less than 60 % fo r age);
• thin muscles, thin a rms and legs;
• redu ced growth may lead to reduced mental development;
• reduced resistance to infection;
• sometimes swelling of the body tissues with fluid (oedema);
• shru nken features giving the face the appearance of an o ld person;
• hair becomes thin, sparse and easily removed;
• rough skin;
• little interest in surrou ndings.
Anorexia is another kind of under-eating but is associated with developed
countries. It is the voluntary refu sa l to ea r and is most commonly found in
teenage girls, though teenage boys can also get this illness. It is as much a
psychological illness as a physical one, because the refusa l to eat is based on
a poor self-image. The patient continues to think that they are fat even when
they are underweight. Recovery requires treatment for the psychological
condition as well as an improved diet.
107
Life Processes and Disease
Obesity
FMMIMJ
r;rrmmm
CHAPTER 13
Obesity results from over-eatin g, especially of fatty foods, a nd a lack of
exercise. Excess fat accumulates in the body and body mass increases to well
above norma l (figure 10.7). Obese people are predisposed to many diseases
like diabetes (see below), hypertension (high blood pressure, chapter 13 ),
coronary heart disease, arthritis, cancer and stroke. Over-earing can be
prevented by earing sensibly, and engaging in regular aerobic exercise.
Heart diseases and cardiovascular disease
corona
heart disease >
Some diseases of the heart and cardiovascular system develop slowly after
years of living on a diet of fatty foods and not much exercise. Atherosclerosis
is a disease of blood vessels . It is a thickening of the inner layers of artery
walls, even tu a lly the artery may become blocked. If the affected artery is the
coronary artery, the heart muscle is not supplied with food and oxygen and
char part of the hean dies. This could result in a heart anack (coronary heart
disease). A similar blockage in a blood vessel in the brain results in a stroke.
The rough surface of the thickened wall could also encourage formation of a
blood clot which may block blood vessels.
Diabetes
Rgure 10.1 A person 1s described as
'obese· if they weigh at least 20% more than
the average for someone their height.
holozoic nutrition >
Diabetes is a group of metabolic diseases in which a person has high blood
sugar, either because rhe pancreas does not produce enough insulin, or the
body cells do not respond to the insulin that is produced. Management of
diabetes concentrates on keeping blood sugar levels as close to normal as
possible, which can usua ll y be accomplished with diet, exercise and appropriate
medication. Obesity, high blood pressure and lack of regu lar exercise accelerate
the harmful effects of diabetes.
Holozoic nutrition
Mammals, including humans, feed by taking in or ingesting organic food. This
particular type of heterotrophic nutrition is termed holozoic nutrition, and
includes ingestion, digestion, absorption, assimilation and egestion.
• Ingestion - The act of taking in food (into the mouth in humans).
• Digestion - The process of breaking down large, complex, insoluble
material into sma ll, simple, soluble molecules. The teeth physically break
the food into pieces, and enzymes then chemically break down the large
molecules into smaller ones.
• Absorption -The diffusion of soluble fo od molecules (glucose, amino
acids, fatty acids, glycerol, vitamins, minerals and water) into the
bloodstream.
• Assimilation - When these food molecules are taken from the blood and
used by the body cells for respiration, growth and development.
• Egestion - The process by w hich the undigested part of rhe good is
removed from lhe body. It is also known as defecation.
Digestion
The physical action of teeth
physical digestion >
108
Teeth h elp with the physical breakdown or mechanical breakdown of food.
This is ca lled physical digestion. The structure of a typical tooth is shown in
figure 10.8.
10 · Feeding and Digestion
I
-~---- enamel (hard material)
crown
~
gum
-----
root
-
-
- - - -- pulp cavity (contains
blood vessels and
nerve endings)
- - - - - cement (holds the
tooth in the bone)
- - - - - jaw bone
- - - - - - - nerve
Rgure 10.8 A section through a tooth showing the general structure.
Mammals differ from other animals in that they have more than one type
of tooth. In humans, there are four kinds and Table 10.7 summarises their
structures and functions. Figure 10. 9 shows the position of the different teeth
in the mouth.
Type
incisor
canine
Shape
Function
chisel-shaped for cutting
1 root
pointed or dagger-shaped
1 root
cutting food
biting off bits of food
grasping and tearing food
(well developed in carnivores for tearing
flesh)
premolar
flat with cusps or bumps on crush and grind food
the fairly broad surface
2 pointed cusps
2 roots
molar
flat, with cusps on the
broad surface
4 or 5 cusps
2 or 3 roots
large back teeth to crush and grind food
Table 10.7 The shape and function of human teeth.
mJU:lrffimlJ
Milk t eeth are the first set of teeth in humans. They appear singly or in pairs
from the time a child is approximately 3 months old. By age 3 years, most
children have about 20 teeth. These begin to fall out when a child is about 7
years old.
109
Life Processes and Disease
permanent teeth >
wisdom teeth >
Permanent teeth are
the teeth which replace
the ones that have fallen
out. An additional 12 new
teeth also erupt which
make up the complete
set of permanent teeth by
about age 17. Most adults
have 8 incisors, 4 canines,
8 premolars and 12 molars.
The 4 molars at the end of
the jaw are the last set to
grow through the gum and
are called wisdom teeth.
molars,
Q:ioot-'T--1::>,._,..,r--duct from
salivary gland
The u se of fluorides
Figure 10.9 There are four types of teeth in humans.
The use of fluorides in
toothpaste or in water
supplies helps to prevent tooth decay in humans. Fluorides are compounds of
the element fluorine which improve resistance to tooth decay by hardening the
enamel. When permanent teeth are developing in children, the use of fluorides
is effective in helping these 'new' teeth resist decay.
Compounds of fluorine can act as serious pollutants in the environment. In
the production and extraction of aluminium from bauxite, sodium aluminium
fluoride (Na 3AIF 3 ) is used to lower the melting temperature of alumina from
2050 °C to 950 °C, so that less energy is used. The exhaust gases from the
manufacture of aluminium then contains fluorides. Fluorides seem to affect
trees, and on grass they can enter food chains. The teeth and bones of grazing
animals are affected badly.
Although fluoride provides resistance to tooth decay in humans, an excess
in the environment can be harmful. Also fluorides can be dangerous to young
children and they should never swallow fl uoridated toothpaste.
The chemical action of enzymes in digestion
Despite the action of teeth in breaking down food physically, food must
also be chemically broken down. Chemical digestion involves enzymes .
Enzymes are organic catalysts, which means they speed up chemical reactions
occurring in living cells. During digestion, enzymes speed up the rate at which
the large, insoluble food molecules are broken down into small, soluble
food molecules.
chemical digestion
Practica] activity
SBA 10.2: The action of an enzyme,
enzymes (amylase)
polysaccharides
page 349
disaccharides + monosaccharides
en zymes (protease)
proteins
amino acids
enzymes (lipase)
lipids------+ fatty acids +glycerol
£?.Sb
IT:Q4'
V'--1
Define the terms 'physical digestion'
and 'chemical digestion'.
110
There are thousands of enzymes bu t all have similar properties.
• They are all proteins.
• Each enzyme is specific for the type of chemical reaction it speeds up.
• They are required in small amounts.
• They are inhibited or prevented from working by poisons like cyanide and
arsenic.
10 ·Feeding and Digestion
• They work best at a particular
temperature called the optimum
temperature (Figure 10.10).
• They are denatured or destroyed by high
temperatures.
• They work best at a particular pH, called
the optimum pH (Figure 10.11 ).
optimum temperature
- enzyme works best
at this temperature
Rate of reaction
rate increases as the
The substance that the enzyme breaks
mm;rmm down is called the substrate and the
1.u.1.rmu:tJ
substances that are made are known as the
products.
Digestion and
absorption along the
alimentary canal
.--<3-- - pH at which
enzyme works best
lower pH
optimum pH
for enzyme
I
enzyme breaks down - at higher temperature
20
30
40
50
60
Temperature ("C)
Figure 10. 1O The effects of
temperature on an enzyme-catalysed
reaction. The activity of the enzyme is
small below 20 °C, rises steadily to a
maximum near 50 °C, then falls sharply.
The alimentary canal (gut) is a long
muscular tube, which extends from the mouth to the anus (figure 10.12).
It consists of the major parts of the digestive system w here digestion and
absorption of food take place.
higher pH
Rate of reaction
gall bladder - -- - bile duct - ---=--+
optimum pH
of pepsin
!\
2
4
small J duodenum
intestineC leum
6
8
10
pH
caecum - - - - - appendix ---.-- - - - - --
• pepsin works best at pH 2.5
• trypsin works best at pH 8.0
• most enzymes in cells work
best at pH 7.2
Figure 10. 11 The effects of pH on an
enzyme-catalysed reaction. The activity of
the enzyme rises sharply near the optimum
pH and falls just as sharply as that pH 1s
exceeded.
ft'tlMU
salivary am lase >
Figure 10.12 The human alimentary canal.
The mouth
Digestion begins in the mou th, after food is ingested using the hands, lips and
tongue. The teeth break the food down into smaller pieces. This is done with
the help of saliva, which moistens the food. Saliva is secreted from the salivary
glands and is a mixture of water, mucus and salivary amylase . The water
111
Life Processes and Disease
and mucus soften the food, while the enzyme salivary amylase begins to digest
the starch in the food. The mucus also helps food to move easil y a long the
alimentary ca nal.
Salivary amylase breaks down the bonds in starch by h ydrol ysis, and
so hydrolyses sta rch into smaller and sma ller cha in s, eventua lly to gl ucose
molecules (fig ure l 0. J 3).
glucose
•••••••••••••
!
amylase
starch - long
chain of glucose
addition of water
(hydrolysis)
maltase
•• •t• •• •t• •t• •••
bond
broken
bond
broken
I
smaller chains
bond
broken
eventually, all the bonds will be broken
•••••••••••••
"'
glucose
Figure 10.13 Starch is broken down to glucose by the enzyme amylase.
IWlill"-IJ
So both physica l digestion and chemical iligestion occur in the mouth. The
tong ue churns food a nd rolls it into a bolus, or a ba ll -like structure, which is
then swa llowed.
The oesophagus
oesophagus >
G!It!IG'UW
When food is swallowed it enrers rhe oesopha gus. The trachea, or windpipe,
which opens to the lungs lies to the front of the oesophagus. If yo u press your
hands gently on your throat, yo u can feel the rings of cartilage of the trachea .
The oesophagus is directly behind this.
When food is swallowed, it is prevented from going into the trachea by a
small, flap-like structure ca lled the epiglottis, which covers the trachea as you
swallow (figure 10.14). It is therefore impossible to swallow and inhale at the
same time. 1Ty it!
food
bolus goes Into
the oesophagus
air can go
.._,....,.,..____,_ into the trachea
oesophagus
Figure 1O. 14 The epiglottis stops food entering the trachea when you swallow
112
trachea
closed
10 ·Feeding and Digestion
l•MMflM!O.fJ
However, if a person is eating while talking and laughing, the food can
become stuck in the trachea. The Heimlich manoeuvre, which forces air rapidly
out of the lungs, can be applied to remove the stuck food (figure 10.15).
The oesophagus is a muscular tube and food moves down it by peristalsis.
This is a wave of muscle contraction that moves downward and squeezes the
food into the stomach .
(b) clasp both hands
around the waist
(a) give five sharp slaps
between the
shoulder blades
(c) pull sharply upwards
and below the ribs
Rgure 10.15 The Heimlich manoeuvre.
The stomach
oesophagus
muscles contract, narrowing
L ....- - - the oesophagus and pushing
the bolus down
bolus is pushed
down and into
the oesophagus
The muscular wa lls of the stomach rela x and contract to
churn the food as it arrives. Food is mixed with enzymes,
mucus and hydrochloric acid. This mixture is called chyme.
The stomach walls are dotted with pits leading to gastric
juice glands that secrete gastric juice into the stomach
(figure 10.17).
pits in the stomach
wall secrete gastric juices
Figure 10.16 A bolus moves down the oesophagus to
the stomach by peristalsis.
part of the
stomach wall
magnified
~=:::::..~
'
~
Figure 10. 17 Gastric juice pours out of pits in the stomach wall.
Gastric juice consists of:
• mucus;
• hydrochloric acid;
• pepsin.
H§elelhU
Digestions of proteins begins in the stomach as the long protein chains are
broken down b y the enzyme pepsin into amino acids. Hydrochloric acid
provides the acidk medium in which pepsin works most efficiently. It also kills
any pathogens that may have entered the body with the food.
The stomachs of young mammals produce the enzyme rennin. which
curdles or dots the milk that they get from their mother. The milk proteins
113
Life Processes and Disease
l!XEM%U are then broken down by pepsin into shorter polypeptides and then into
amino acids.
After one or two hours in the stomach, small amounts of chyme pass
into the next region of the alimentary canal, the duodenum as the sphincter
muscles at the bottom of the stomach relax and open.
Peptic ulcers
A peptic ulcer is a hole or 'sore' in the stomach lining. It used to be thought
that excessive secretions of hydrochloric acid and pepsin damaged the stomach
wall and caused these ulcers . But recent research has shown them to be caused
by the presence of Helicobacter pylori, a species of bacterium that ljves in the gut.
Some patients have been successfully treated with antibiotics; others have been
successfully treated with a drug which suppresses the production of stomach
acid.
The duodenum
duodenum >
emulsification >
pancreatic juice >
~
ll:QS
V"...J
Describe, giving examples, the role of
enzymes in digestion.
~
ll:Q6
V"...J
Copy and complete this table.
Part of alimentary canal
mouth
stomach
duodenum
Importance
The duodenum is the first region of the small intestine. It receives chyme
from the stomach and secretions from the gall bladder and pancreas. Bile,
which is produced by liver cells and stored in the gall bladder, breaks down
large lumps of fat into tiny droplets. This process, called emulsification,
increases the surface area of the fats making it much easier for the enzyme
lipase to digest the fat.
Pancreatic juice is secreted from the pancreas and contains many
enzymes.
• Amylase continues the digestion of starch into maltose before it can be
digested into glucose.
• Lipase digest fats or lipids into fatty acids and glycerol.
• Trypsin is a protease (an enzyme which digests protein) that breaks down
long protein d1ains into shorter ones (polypeptides) so that they can be
broken down into amino acids by other proteases.
These emymes work best in a neutral environment, but the chyme, which
came from the stomach is aciillc because it contains hydrochloric acid.
Pancreatic juice also contains sodium hydrogencarbonate which neutralises
the hydrochloric acid so the pH of the mixture increases to pH 7- 8, which is
optimum for pancreatic enzymes. Bile also contains bile pigments which are
waste products from the liver that need to be excreted.
The food is now fully broken down physically and chemically into the endproducts of digestion.
The ileum
llt:JilulJ The ileum is the second part of the small intestine and is the site of absorption
in the alimentary canal. By the time food reaches the ile um, it has been broken
down into glucose, fatty acids, glycerol, amino acids, vitamins, minerals and
water. These nutrients are small enough to be absorbed and used by the body.
The structure of the ileum has many adaptations which make it good for
absorption.
• It is about 6 metres long and has a large surface area .
• There are folds and ridges that are invaginations in the intestinal walls that
increase the surface area even more for efficient absorption of nutrients
mlllJ
(figure 10.18) . They have villi (finger-like projections) on their surfaces.
They are covered with epithelial cells which themselves have microscopic
ml!ijM!WfB
folds on their surface, called microvilli. These further increase the surface
area for absorption.
114
10 ·Feeding and Digestion
1Fmirm10
• The epithelial cells have large numbers of mitochondria, which provide the
energy fo r transport of the nutrients from the ileum to the blood.
• Each villus has a good blood supply in the form of a dense network of
capillaries that transport those nutrients that do not diffuse across and
require energy away from the ileum to the liver for processing.
• Ea ch villu s contains a lacteal, or lymph capillary, whid1 absorbs fatty acids
from the digestion of fat.
r.-- - - - villus wall. one cell
thick - diffusion of food
molecules can occur
readily
1a---
-T"--<-- - capillary network - food
molecules are absorbed
into the blood
-=---1--~r-- lacteal -
larger food
molecules (fatty acids)
are absorbed here
1----++-----+-- Small
intestine
large
Intestine
Figure 1O. 19 The arrangement of the
intestines in humans.
Figure 10.18 (a) The wall of the ileum is made up of villi that increase the surface area. (b)
Diagrammatic section through a villus.
The colon
lb@t:t•»
mt.htJ
After most of the nutrients have been absorbed into the blood in the ileum,
the remaining intestinal contents, now called faeces , continue to move
slowly along the colon, or large intestine. The main fun ction of the colon is to
rea bsorb water from the faeces into the bloodstream so that water loss from the
body is mininlised. Th e arrangement of the small and large intestine in humans
enables a very long tube to be packed into a very small space (figure 10.19).
The rectum
Faeces con sist of undigested cellulose and plant fibre, dead bacteria and
intestinal cells scra ped off the gut walls. The faeces are stored temporarily in
115
Life Processes and Disease
li4+Jil!uQ
l#le!IW
the rectum. As faeces accumulate, pressure increases in the rectum which
results in a desire to defecate, or expel faeces through the anus .
About 24 hours after earing, food has traversed the length of the alimantary
canal. most of the nutrients have been absorbed, and the undigested part is
ready to be expelled .
Constipation
constipation >
~
IJ:Q7
\..A-I
Describe the route taken by a bolus
from the mouth to the anus.
Constipation results from poor earing habits. A diet lacking fibre can lead to a
blockage of the alimentary canal. Egestion of undigested waste material cannot
then occur normally.
Constipation sometimes results in haemorrhoids, which are protrusions
of tissues through the anus because of forced 'pushing'. Constipation also
increases the chance of developing colon cancer. Dietary fibre, the undigestible
pan of food from plants (mainly cellulose), aids peristalsis and prevents
constipation (figure I 0.20).
(a)
(b)
water reabsorption
occurs in colon
-
undigested food with fibre is bulky
and pushed easily along the colon
I
peristalsis does not take place
readily - undigested food has no fibre
-
stored temporarily in
the rectum then egested
peristalsis
rectum
anus
water reabsorption occurs
~·~1111!!!!!!1!1. . . . . .~~~~~~~~~0
faeces stays in colon and forms
a hard solid mass that is
difficult to move - this is constipation
Figure 10.20 Dietary fibres help to prevent constipation . (a) The faeces containing fibre stay bulky
and soft and are easy to egest. (b) Without fibre, the faeces become hard and solid and are difficult
to get rid ot.
Assimilation
assimilation >
Assimilation is the process of incorporating and making use of the digested
food into the body. These absorbed food molecules may be sto red by the body
for future use, broken down to produce energy or used for growth, repair and
to maintain good health .
Monosaccharides {glucose)
This is taken to the liver, then to the rest of the body where:
• it is used in respiration;
• excess amounts are converted into glycogen in the liver, and stored in liver
a nd muscle cells;
• excess amounts are converted to fat and stored under the skin or around
organs.
Amino acids
These are taken to the liver and then to the rest of the body where:
• they are u sed by the body cells for growth and repair;
116
10 · Feeding and Digestion
• they are used to make hormones and enzymes;
• excess amounts are converted to glycogen or fat;
• excess amounts are broken down, or deaminated, in the liver and converted
to urea to be excreted by the kidneys.
Fatty acids
Fat molecules are carried by the lymph to the blood and are:
• stored u nder the skin and around the organs;
• used to form new membranes in cells and organelles;
• used for respiration in some circumstances.
Functions of the liver
The liver is one of the most important organs in the body as it has many
functions that are essential to keeping the body healthy.
• Carbohydrate metabolism - Excess glucose is stored up as glycogen and
reconverted to glucose when blood sugar levels fall. Excess carbohydrate
may also be converted to fat .
• Lipid meta bolism - Excess cholesterol is excreted into the bile and
removed from the body.
• Protein m e tabolism - Excess amino acids are broken down to form
ammonia and then converted to the less toxic substance, urea. Urea is
transported to the kidneys by the blood and excreted in urine.
• Production of bile - Bile salts are produced and temporarily stored in the
gall bladder. They then travel to the duodenum to aid in digestion.
• Storage o f vitamins - A number of vitamins are stored in the liver and
released if the diet is deficient in vitamins.
• Storage of minerals - The liver also acts as a store for some essential
minerals, such as iron and potassium. (This is why .liver is a nutritious food.)
They can be released into the body if the diet lacks these minerals.
• Synthesis of p lasma proteins - These important proteins are found in
blood plasma. For example, prothrombin and fibrinogen are needed for
blood dotting.
• D e toxification - Toxic materials absorbed from the intestines are stored,
broken down or removed by the liver.
• Breakdown of red blood cells - Red blood cells are broken down (they
live only for three months) and the iron components may be stored, reused
or excreted as bile pigments.
• Production of h eat - A lot of metabolic activity occurs in the liver,
which requires a considerable amount of energy. Much of the energy from
respiration is lost as heat, so the liver generates a lot of heat. In mamma ls
(including humans) and birds, the liver also plays an important role in
keeping the body at the right temperature inside.
Chapter summary
..
• A balanced diet is important for good health.
• A balanced diet has appropriate proportions of carbohydrate, proteins, lipids, vitamins
and minerals. Water and fibre are also important.
• Plants need minerals for healthy growth.
~
117
Life Processes and Disease
r
• Ingestion in humans is the intake of food using the mouth, hands and lips.
• Physical digestion involves breakdown of food by teeth, and chemical digestion is the
breakdown of food by enzymes.
• In humans, there are four different kinds of teeth: incisors, canines, premolars and molars:
- incisors are chisel-shaped and are used for biting food;
- canines are dagger-shaped and are used to tear or rip food;
- premolars and molars are used to chew food into small pieces.
• Enzymes are biological catalysts: they speed up the chemical breakdown of food.
• Food is broken down from insoluble to soluble substances by enzymes.
• Digestion takes place in the mouth, stomach and duodenum.
• Absorption is the movement of the end-products of digestion into blood. It occurs in
the ileum.
• The ileum has several adaptations for absorption, such as a large surface area
provided by the villi.
• The food is assimilated when the body cells make use of it.
• The liver has many important functions relating to the assimilation of food.
ITQ1 (i) Diet is the quan ti ty and quality of food eaten every day by an
individual.
(iii) A balanced diet has the quantity and quality of food needed to maintain
good health.
ITQ2 (i) Organic nutrients can be found in food such as chicken, bread, livei:.
(ii) Foods which contain inorganic nutrients include: lettu ce, liver, banana.
ITQ3 Your a nswer needs to includ e an example from each food group. For
example:
• Staple foods
rice
• Peas and beans
red beans
• Dark green leafy vegetables
salad leaves, spinach
• Food from animals
chicken
• Frui.t
orange juice
• Fats
oil for cooking
ITQ4 Physical digestion is the mechanical breakdown of food into small
pieces by the teeth.
Ch emical digestion is th e breakdown of food by enzymes into soluble
compounds.
ITQS Enzymes speed up the breakdown of food molecules into their respective
end-products. Enzymes are not used up themselves. Some examples are:
• am ylase, which breaks down starch eventually to glucose;
• pepsin, which breaks down proteins into polypeptides;
• lipase, which con verts lipids into fatty acids and glycerol.
ITQ6
Part of alimentary Importance
canal
Mouth
Food is moistened and lubricated. Physical digestion takes place. The
conversion of starch to maltose (chemical digestion) begins.
Stomach
Acid contents kill bacteria in food. Food is churned into chyme. In babies,
curdling of the milk occurs. In adults, protein digestion begins in the
stomach as proteins are converted to polypeptides.
(continued)
118
10 · Feeding and Digestion
Part of alimentary Importance
canal
Duodenum
Chemical digestion takes place here.The enzymes amylase, trypsin, and
lipase are secreted. They break down starch to maltose, which is further
broken down into glucose and fructose. Polypeptides are broken down to
amino acids. Lipids are broken down to fatty acids and glycerol.
ITQ7 mouth ..... oesophagus --+ stomach ..... duodenum ..... ileum ..... colon .....
rectum ..... anus
Examination-style questions
(i)
The starch test can be summarised in a series of stages:
1 A leaf is dipped in boiling water for 10 seconds.
2 The leaf is immersed in ethanol which is placed in a water bath at 80 °c.
3 The leaf is then dipped. in tap water.
4 The leaf is tested with iodine.
(a) Why was the leaf dipped in boiling water?
(b) What is the role of ethanol?
(c) Describe the iodine test for starch.
(d) A starch test was performed on a leaf and positive results were seen. What
interpretations can be suggested about activities in the leaf?
(ii) Explain the meaning of the term 'destarched ' as it refers to a leaf. Give details of the
process by which a leaf is destarched.
(iii) Describe an investigation to show that plants need C02 for photosynthesis.
2
(i) Five main processes occur in holozoic nutrition. Define each in the order in which they
occur.
(ii) Give two functions of the tongue during eating.
(iii) Describe how food moves down the oesophagus.
{iv) Name the enzyme found in saliva and describe its action.
3
(i)
List the functions of these substances in the stomach:
(a) mucus {b) hydrochloric acid (c) the enzyme pepsin.
(ii) A peptic ulcer is a damage to the stomach wall. It can be very painful and is easily
infected.
(a) How can the stomach all be damaged? Give details of how ulcers are formed.
(b) Why is an ulcer painful?
(c) Why is an ulcer easily infected?
(iii) What are the products of digestion of:
{a) starch? (b) lipids? (c) protein?
4
(i)
Explain how the structure of the wall of the small intestine is adapted for its function
of absorption.
(ii) The table below refers to some enzymes involved in digestion of food in the digestive
system. Copy and complete the table.
Name of enzyme
Site of production
Production of reaction
Fatty acids and glycerol
Salivary gland
Stomach wall
Maltase
-------
119
Life Processes and Disease
(iii) The diagrams below show different types of teeth found in a human mouth. Copy and
complete the table below to show the type and function of each tooth.
c
B
A
Tooth
A
c
B
Type of tooth
Function of tooth
5
(i) List the components of a balanced diet.
(ii) Define (a) obesity (b) malnutrition;
(c) deficiency disease (d) food additive.
(iii) Vitamins and minerals are essential to a healthy life. Explain why:
(a) pregnant women must include calcium and iron in their diet;
(b) it is recommended that we eat an orange a day.
(iv) Nutritional requirements vary with age, sex and activity. Describe the nutritional
requirements of:
(a) a 19-year-old male who plays competitive football;
(b) a 19-year-old female who loves to read.
6
The figure below shows the graphs obtained from an investigation into an enzymecontrolled reaction. Each represents an experiment performed to study the time taken for
the enzyme to break down the substance. Graph 1 shows the time taken under different
temperature conditions with the reaction at a constant pH of 6.7. Graph 2 shows the time
taken under different pH conditions at a c~nstant temperature of 40 °C.
Graph 1
Graph 2
at a constant pH 6.7
at a constant temperature of 40°C
16
14
12
10
Time (minutes)
8
.J.....-__ --
6
4
2
00
10
120
20
30
40
50
Temperature (°C)
60
70
2
3
4
5
Temperature {°C)
6
7
8
10 · Feeding and Digestion
Study the graphs and answer the following.
(i)
(a) At what temperature did the reaction occur in the shortest time?
(b) At what pH did the reaction occur in the shortest time?
(ii) In graph 1:
(a) Why did the reaction slow down at higher temperatures?
(b) What effect on the reaction rates is shown by a steady increase from low to
medium temperatures?
7
An experiment was carried out to investigate the effect of temperature on the rate of
an enzyme-controlled reaction. The concentration of enzymes and substrate were kept
constant at all the temperatures investigated. The results are shown in the table below.
Temperature {°C )
Rate of reaction (mg of products per unit time)
5
0.3
10
0.5
15
0.9
20
1.4
25
2
30
2.7
35
3.3
40
3.6
45
3.6
50
2.3
55
0.9
60
0
(i) Plot the results on graph paper.
(ii) Interpret and explain them as fully as you can.
(iii) If the enzyme used was amylase, name the substrate used in the experiment.
(iv) If the enzyme used was amylase, what effect would pH have on its activity?
8
The table below shows the activity on an enzyme in relation to pH.
pH
4.5
5.5
6.5
7.5
Units of enzyme activity
3.1
9.6
14.5
10.1
(i) At which pH is most activity seen?
(ii) At which pH is least activity seen?
(iii) What is the optimum pHfor this enzyme?
(iv) Give an example of an enzyme that might give these results.
(v) Give examples of enzymes that would not be expected to give these results.
121
fl
I
fl
describe the process of aerobic respiration
0
distinguish between aerobic and anaerobic respiration
I
describe the uses of anaerobic respiration to humans
0
understand simple investigations that show the products of respiration
understand that respiration takes place at the level of the cell
understand the function of ATP
respiration
aerobic
anaerobic
r
mitochondrion
humans
'
bacteria
yeast
ADP~ATP
oxygen
debt
alcohol
production
bread
production
yoghurt
production
Aerobic respiration
Respiration is the process by which the energy in food is made available for
a cell to do the work necessary to keep it a li ve (figure 11. 1). When oxygen is
used in the reaction , we call it aerobic respiration . The process is cata lysed by
enzymes and is also ca lled cell ular. internal or tissue respiration.
energy for building up materials
food
respiration
....,... energy
I
energy for contraction
I
I
I
Some of the uses of
the energy made by
a cell.
I
I
I
I
..
I
I
organism Is
alive when all
the cells are
alive and working
/
can move
can grow
can reproduce
Some of the activities
of an organism.
They all require energy.
can respond
Figure 11.1 An organism 1s alive when all its cells are respiring
11 · Respiration
How do food and oxygen get to respiring cells?
~
IT:Q-1
V'--1
What is the purpose of respiration?
~
IT:Q2
V'--1
When do animal cells and plant cells
respire?
A respiring cell needs both food and oxgen (figure 11.2 )
• Food - In animals, food eaten is digested and absorbed into the
bloodstream. The end-products of digestion eventually reach all the body
cells. In plants, the food made in photosynthesis in the leaves travels around
in phloem tubes and eventually reaches all body cells.
• Oxygen - In vertebrates, oxygen comes from the air that is inhaled into
the lungs. It diffuses into the bloodstream and is transported to all the bod y.
cells. In plants, some of the oxygen comes from photosynthesis and some
through diffusion in through the leaves and other parts of the plant.
blood rich in 0 2 is taken
to all body cells
blood rich in glucose
is taken to all body cells
•
body cell
where respiration
occurs
blood rich in
C02 is taken to
lungs to get rid of C02
Figure 11.2 A respiring cell in a mammal is supplied with food and oxygen.
Product and waste product of aerobic respiration
Practical activities
SBA 11 .1: Is carbon dioxide produced
during respiration? page 350
SBA 11.2: Is heat produced during
respiration? page 351
SBA 11.3: Is oxygen used up during
respiration? page 352
In both plants and anima ls, the type of food from which energy is released is
usually glucose. Energy is released when glu cose combines with oxygen (the
oxidation of glucose). Carbon dioxide is a waste product of this reaction. In
vertebrates, carbon dioxide diffuses back into the bloodstream , to be taken to
the lungs and exhaled out of the body. In plants, it is used for photosynthesis
during daylight.
How does aerobic respiration occur?
respiration equation >
~
IT:Q3
V'--1
What is the important product of
respiration? What are the waste
products of respiration?
r!u:IJ
Respiration or cellular respiration occurs in a series of steps, each of which is
catalysed by enzymes. The overall process can be summarised in words or by
the respiration equation below:
glucose + oxygen -+ energy + carbon dioxide + water
C6 H 12 0 6 + 60 2 -+ energy +
6C0 2
+ 6H2 0
During aerobic respiration, glucose is broken down completely into carbon
dioxide and water.
At each step in the breakdown of glucose, energy is released. This is used
to con vert a d1emi cal called ade nosine diphosphate (ADP) into adenosine
triphospbate (A T P ). Ead1 molecule of ATP acts as a little 'packet' of energy.
The energy can be stored and used later when needed.
There are m an y advantages of storing and using energy in small packe ts
like this.
• The energy ca n be released from ATP wherever and whenever it is required
by a cell.
123
Life Processes and Disease
• The energy can be released rapidly.
• Energy is not wasted. A large amount of energy is released by oxidising
one glucose molecule and ma ny ATP molecules are formed. A cell may not
require very much energy a t on ce. By storing the energy in small packets
in ATP molecu les, the cell can use sm all amounts of energy as required
(figure 11.3).
• The energy can be used to drive many different chemical reactions rapidly.
• Energy can be stored as ATP in one part of a cell and transpo rted and used
elsewhere without causing reactions in between .
adenosine
(
ADP
r"'"--•: energy \..+ATP
c
ATP
ADP
oxidation ,. . . . _ _
" energy
(
.
of
ATP
glucose
1""'' - - • . energy
,....,_...,.
.energy
high energy bond
ADP
I
ADP
(.
ATP
the energy from the
breakdown of glucose is
stored in this high energy bond
ATP
ATP is a packet of energy!
Rgure 11.3 The oxidation of glucose results in the formation of many molecules at ATP.
Ene rgy production and utilisation are very effici ently and carefully controll ed
by the cell.
Where does aerobic respiration occur?
mitochondrion >
~
ll:Qll
Respiration occurs in an organelle called the mitochondrion (figu re 11.4).
Mitochondria are present in all cells, animal and plant, and are sometimes
referred to as the 'power houses' of the cell.
The en ergy stored in ATP (aden osine triphosphate) is released when it is
converted back to ADP (adenosine diphosphate).
v......i
Where does respiration occur?
co2 transported
to lungs
~
11:Q5
v......i
Give three reasons why it is
advantageous to store energy in
small packets.
0 2 transported
to cell
--+- - energy is released
during respiration in
the mitochondrion
_ _ _...,. energy ('' -"'-)
ATP
+
energy used
by the cell
+
p
ADP
+
p
+ phosphate
Figure 11.4 Energy can be released from ATP made during respiration in the mitochondrion.
124
11 · Respiration
Anaerobic respiration
anaerobic respiration >
Respiration can also occur without oxygen and this type of respira tion is called
anaerobic r espiration. Both anaerobic and ae robic respiration involve the
breakdown of glucose (figure 11.5). However, in anaerobic respiration, it is n ot
completely broken down.
(a) Plant and animal cells
can respire aerobically.
ID1.
>
~
"
'
"
'"""' 0
oxygen
oxygen ~ Q /
/
glucose
water
I) energy
•
. / water
oa<bon dioxide
carbon dioxide
(bl Animal and plant cells can respire
anaerobically but do so in different ways.
glucose - - -..
GJ '.::
glucose
Figure 11.5 Cells can respire anaerobically and aerobically.
~
IT:Q6
l/"-.J
Give two examples of organisms that
respire aerobically, and two that respire
anaerobically.
One mole (mot) of a chemical contains 6 x 1022
molecules of that substance.
Habitats such as stagnant ponds and deep underground have no oxygen.
Organisms living there have adapted to survive without oxygen; the y must
respire anaerobically all the time. These organisms indude some worms, some
bacteria and some fungi. Parasites that live inside other organisms, such as the
gut parasite tapeworm and bacteria, also live in conditions that lack oxygen.
They must also respire anaerobically.
Many living cells that normally respire aerobically can also respire
anaerobically if oxygen is lacking. Animal and plant cells do this in different
ways (table 11. 1).
Aerobic respiration
Anaerobic respiration
uses oxygen
does not use oxygen
• in plants and animals:
C6H1206 + 602 -+ energy + 6H20 + 6C02
water and carbon dioxide are waste products
• in animal cells:
C6H1206 -+ energy + 2C3H603
lactic acid is the waste product
• in plant cells:
C6H1206 -+ energy + 2C2H50H + 2C02
ethanol and carbon dioxide are waste products
large amounts of energy produced (2880 kJ per small amounts of energy are produced (150 kJ
mole for the breakdown of glucose)
per mole for breakdown of glucose in animals
and 21OkJ per mole in plants)
glucose is broken down completely to inorganic glucose is not broken down completely molecules
ethanol and lactic acid are organic molecules
that still contain useful energy
occurs in the mitochondria of the cell
occurs in the cytoplasm of the cell
Table 11.1 Differences between aerobic and anaerobic respiration.
125
Life Processes and Disease
Anaerobic respiration in humans
Human cells respire normally aerobically. However, during strenuous exercise,
muscle ce lls need much more energy for the extra work that they are doing.
The breathing rate and heart rate increase in an attempt to get more oxygen
to these cells. Sweating occurs to help lose some of the extra energy as heat.
With increased respiration, a lot of heat is produced which is lost from the skin
(chapter 19). After a period of sustained exercise, the oxygen supply becomes
inadequate, even with panting for air and the increased heart rate. The muscl~
cells then respire anaerobically.
Energy is still produced when cells respire anaerobically, although it is a
much sma ller amount for ead1 molecule of glucose. This means that they ca n
continue to do work (contract and relax).
CHAPTER 19
anaerobic respiration
Figure 11.6 The build-up of lactic
acid 1n muscle cells after strenuous
exercise can be painful
lactic acid + energy
glucose
in muscle cells
UillU@@t•D
ltfU[1!i!:il
~
IT:Q7
V'-1
Humans respire mostly aerobically.
When do humans respire anaerobically?
oxygen debt >
Lactic acid is a waste product of this reaction. It builds up in the muscles and
causes them to ache (fi gure 11.6). This is often called fatigue . After exercise,
the body has to get rid of the lactic acid as quickly as possible. This is done
by using oxygen to change it back to a chemical like glucose so that it can be
broken down completely in aerobic respiration. When anaerobic respiration
occurs in muscles it is in addition to aerobic respiration and not in place of it.
A person continues to 'breathe hard ' or pant for some time after exercise as
oxygen is needed to get rid of the lactic acid. The oxygen required to get rid of
the lactic acid is called the oxygen debt (figure 11. 7).
~
cell during
__ _. used for contraction etc.
anaerobic respirat~ energy (smaller amount) - - - - -
IT:Q8
V'-1
Q
What is alcoholic fermentation and
what are two of its uses?
~O
'
Y
Q
O
C
~lactic
e.g. muscle cells,
during prolonged
strenuous exercise
alcoholic fermentation >
sugar
fermentation
• sugar from barley seeds
• cane sugar or molasses
after some
time
1
ethanol + carbon dioxide
fermentation
fermentation
t
series of reactions
leading to breakdown to
C02 + H20
Figure 11 . 7 The oxygen debt is the oxygen needed to break down the lactic
acid formed during exercise.
Anaerobic respiration in yeast
rum
During anaerobic respiration in yeast ethanol and carbon
dioxide are produced as waste products. Ethanol is an alcohol
and the process is known as alcoholic fermentation .
Yeast is very important in the making of alcohol and bread
(figure 11.8). The ethanol can be produced in many ways to
make a wide range of alcoholic drinks, including beer and wine,
which are enjoyed by humans.
The production of carbon dioxide is used in bread-making
to make dough rise. The carbon dioxide produced by the yeast
as it respires accumulates inside the dough in small pockets.
The dough is seen to get bigger or rise as the gas expands with
warmth. Ethanol is also produced but in small quantities - it
evaporates when the bread is baking in the oven.
• dough rises as bubbles of C02
get caught in the dough
• baking kills the yeast and
evaporates the ethanol
126
acid
beer
• flour and yeast dough, after kneading flour has starch which is broken down
to maltose
• yeast uses the maltose as a source of
sugar and fermentation occurs
Agure 71 .B Uses of fermentation.
I
11 · Respiration
~
IT:Q9
\.../'-I
Sometimes bacteria can be found
in canned foods or tins, despite the
fact that the cans and tins are sealed
so that no air can enter. How is this
possible?
Anaerobic respiration in bacteria
Some bacteria also respire anaerobically. Like animal cells, they make lacti c
acid as a waste product. We m ake use of this in th e manufacture of yoghurt
and cheese (figure 11.9).
milk contains lactose
'
pasteurisation
heat treatment (90°C) to kill disease-causing organisms
'
inoculation
cooled to 40°C and a 'starter' culture of bacteria added
e.g. Lactobaci//us bulgaris
'
fermentation
incubated in 1arge vats (40 ° C for about 5 hours)lactose converted to lactic acid producing natural yoghurt
'
'
'
cool, add fruits, etc.
package and distribute
at 4.5 ° C the bacteria remain alive but no more
fermentation occurs at this temperature
store at 2 ° C
Figure 11.9 The manufacture of yoghurt depends on the anaerobic respiration of Lactobacillus
bacteria.
I
I
• Anaerobic respiration releases a small amount of energy without the use of oxygen .
• Humans usually respire aerobically but their muscle cells can respire anaerobically
during prolonged exercise.
• Lactic acid is produced during anaerobic respiration in animals and creates an
oxygen debt which has to be repaid.
• Anaerobic respiration in yeast produces ethanol which is used in the alcohol industry
and carbon dioxide which is used in making bread.
• Anaerobic respiration in bacteria is used in the making of yoghurt and cheese.
127
Life Processes and Disease
Du ring respiration, the energy from the food eaten by an organism is
made available. This en ergy can be used to carry o ut all the processes of life:
m ovem ent, growth, reproduction, and so on .
ITQ2 Animal cells respire all th e time because th e animal is in constant need
of en ergy. Plane cells also respire all the time. During the day, while sunlight is
available, plants also photosynthesise, but they never stop respiring.
ITQ3 The important product of respiration is energy, which an organism
n eeds to carry ou t th e characteristics of life. The waste products of respiration
are carbon dioxide and water.
ITQ4 Respiration occurs in the mitoch ondria of cells.
ITQ5 Energy is released only when necessary; only as mu ch energy as is
needed is used; energy is released rapidly when it is needed.
ITQ6 Organism s that respire aerobically include humans and birds (there
are m an y others). Organisms that respire anaerobicaIJy include yeast and
tapeworms inside the intestine. Yeast can also respire aerobically if it has access
to oxygen .
ITQ7 Human muscle cells use anaerobic respira tion during prolonged
exercise, when oxygen cannot be supplied fa st enough for sufficient aerobic
respiration to take place. As a result, energy is produced to do the work
n ecessar y when exercising, although less en ergy is produced from each glucose
molecule than in aerobic respiration.
ITQ8 Alcoholic fermentation occurs when yeast respires anaerobically
to produce ethanol. This process is important in the bread, beer and win e
industries.
ITQ9 The bacteria tha t are fo und in cans and tins respire anaerobically. This
means they do no t need oxygen to release energy for all their living processes.
So the fact that there is no air in the ca n does not affect them ; th ey can live in
that environm ent.
ITQ1
Examination-style questions
{i)
Respiration is described as a characteristic of life. What is the importance of
respiration to plants and animals?
(ii) Although respiration occurs in a series of steps, it can be summarised in an equation.
{a) Write the equation.
(b) Describe how energy is made and stored.
(c) Discuss three advantages of storing energy in this way.
(iii) A form 2 student remarked that she had not eaten any food for breakfast or lunch and
that she felt 'weak'. Explain to her why she is feeling weak and why it is important not
to skip meals.
2
128
{i) Using a table, outline the differences and similarities between anaerobic and aerobic
respiration.
{ii) Explain the importance of anaerobic respiration in humans.
{iii) Define:
{a) oxygen debt;
{b) alcoholic fermentation.
{iv) Outline the importance of anaerobic respiration in:
{a) the bread-making industry;
{b) the alcohol industry.
(v) Describe how yoghurt is made.
11 ·Respiration
3
Diagrams A and B below show investigations to demonstrate the products of respiration
and photosynthesis.
A
0
0
0
0
0
0
0
0
0
B
0
~
(i)
Copy the diagrams and, using annotated labels only, complete diagram:
(a) A to show how carbon dioxide is produced during respiration;
(b) B to show that oxygen is produced during photosynthesis.
(ii) The diagrams below are investigations to show that oxygen is used up during
respiration.
(a) What is the importance of soda lime?
(b) How does the investigation show that oxygen is being used up?
(c) Calculate the rate at which oxygen is being used up.
{d) What would you see if more organisms were put in the flask and what would this
indicate about the total amount of respiration?
at the start
capillary oil drop
tube
----------- -
wiregauze
after 30 minutes
I" '" I"' ""'l""""'l""""'I I
small animals,
e.g. woodlice
or millipedes
129
G aseous Exchange
0
understand the function and mechanisms of breathing and gaseous exchange
in humans
0
0
0
0
understand the function and mechanisms of gaseous exchange in plants
identify characteristics common to gaseous exchange surfaces
discuss the effects of cigarette smoking in humans
understand marijuana addiction
gaseous exchange
I
r
respiratory system
'
respiratory surface
rcigarette
smoking
inhalation
exhalation
lungs
humans
leaf
plant
gill
fish
Amoeba
cell membrane
characteristics
thin
large surface area
rich blood supply
constantly moving
transport medium
~
lltQ·1
V'-..J
(i) What is gaseous exchange?
(ii) List two places where it occurs in
the human body.
Importance of gaseous exchange in
humans
Respiring cells need a continuous supply of oxygen. They must also be able to
get rid of the carbon ctioxide that is being produced constantly. The blood is the
means by which oxygen and carbon dioxide are transported to and from cells.
At some point, blood has to pick up oxygen and give off carbon dioxide, that is,
exchan ge these two gases. In humans, gaseous exchange takes place in th e
lungs (figure 12. 1).
12 ·Gaseous Exchange
mouth, nose
air inhaled - has
more oxygen
than air exhaled
blood rich in oxygen flows to the body cells
respiring body cell
uses oxygen ,
produces f
carbon dioxide
air exhaled has more carbon
dioxide than the
air inhaled
GASEOUS EXCHANGE
oxygen net diffusion
}
into the blood
blood vessels
carbon dioxide net
in the lungs
diffusion out of the blood
____/
~
._...._..._
blood rich in carbon dioxide flows towards the lungs
Figure 12. 1 The role of the lungs in exchanging gases with the environment.
Mechanism of gaseous exchange
in humans
FWl:Z•l!IJ
The human respiratory system is involved in the exchange of gases in humans.
The lungs are very important and are made up of many tiny air spaces or air
sacs called alveoli (figure 12.2) .
rib - l'----
-1----,F---
-
trachea opens to mouth and nose
-+--r---
larynx (voice box)
----r
internal intercostal muscle -+----~
Figure 12.2 The human respiratory system.
131
Life Processes and Disease
l!iB9•!¥1J
Air enters the nose and/or mouth and moves down the trachea (windpipe).
The trachea is supported by C-shaped rings of cartilage so that it is kept 'open' a t
all times. The trachea then divides into two bronchi, the right and left. These a re
also supported by rings of cartilage. Each bronchus branches into smaller and
sma ller tubes called bronchioles. At the end of each bronchiole are the many
tiny sacs called alveoli (figure 12.3). Gaseous exchange occurs in the alveoli.
bronc hiole >
leU.letijUll'-11
ring of cartilage, supports
the soft tissue of the trachea
and keeps the trachea 'open'
so that air can pass easily
bronchus branches into
smaller and smaller branches
~
1:r.Q2
V'--J
What is the importance of the rings of
cartilage in the wall of the trachea?
~
alveolus or air sac found
at the end
l:r.Q3
V'--J
Describe the passage taken by an
oxygen molecule from the air to a
capillary in the lungs.
site of
gaseous exchange
Figure 12.3 The route taken by air into and out of the lungs.
The walls of th e alveoli are the gaseous exchange surfaces or the respiratory
surfaces. The smallest blood vessels, capilJaries, are closely wrapped around
each alveolus (figure 12.4). Blood is thus brought to and taken away from each
alveolus. Oxygen diffuses across the walls of the alveolus into the capillary and
the bl ood in the capilla ry becomes oxygenated. Carbon dioxide diffuses from
the capillary into the alveolus and is exhal ed out of the body. The walls of the
alveolus and capillary are very thin (onl y one cell across) so that diffusion can
occu r readily (figure 12.5).
capillary, transporting blood that has
little oxygen (deoxygenated
blood) to and from the alveolus - blood has
high concentration of carbon dioxide
capillary transporting oxygenated
blood from lungs blood has low concentration
of carbon dioxide
t
deoxygenatecl blood
air
~--"i.--- capillary
(the wall is
one cell thick)
alveolus (the wall is
one cell thick)
section of one alveolus
network of capillaries surrounding
alveolus - gases are exchanged here
Figure 12.4 The blood supply to one alveolus.
132
flow of blood in capillary
Figure 12.5 Gaseous exchange between an alveolus and the blood
in a capillary.
12 ·Gaseous Exchange
~
l:fQ~
\.../'--)
list the difference between the blood in
the capillary coming to, and the blood
leaving, the alveolus in figure 12.5.
mm
inspiration )
The continuous exchange of gases in the lungs is extremely important. Body
cells can obtain a constant supply of oxygen for respiration and the carbon
dioxide that is constantly being produced is exhaled out of the body.
Gaseous exchange also occurs at the level of the cells. Here oxygen leaves
the blood and diffuses into the cells. Carbon dioxide moves in the opposite
direction (figure 12.1).
The trachea is Lined with mucus, a slimy substance which traps and holdsr
dust and microorganisms. The tra chea is also lined with microscopic hair-like
extensions called cilia. These beat in a wave-like manner, moving the mucus
containing dust and microorganisms upwards and out of the lungs.
Pathogens can enter the lungs with air as it is breathed in. The mucus and
cilia afford some protection by trapping and moving them out of the lungs.
If an irritating substance like dust is breathed in, this can stimulate a sneeze
during which the irritant is ejected out of the lungs.
The other parts of the respiratory system, namely the ribs, intercostal
musdes and diaphragm, are also involved in gaseous exchange. They help
to move air in and out of the lungs. Breathing in is called inspiration and
breathing out is called expiration. Table 12.1 compares the constituents
of inspired and expir ed air. Table 12.2 (overleaf) compares inspiration
with expiration.
Constituent
gases
Inspired Expired air
air
Reason for difference
oxygen
21%
16%
some of the oxygen is used by the cells of the body
during respiration
carbon dioxide 0.04%
4%
carbon dioxide is made by the cells and is transported
by blood to the lungs
nitrogen
78%
not used
78%
water content variable
usually higher the alveolar surface has a thin film of moisture to aid
than when
gaseous exchange, and some of this evaporates
inspired
temperature
usually higher air is warmed by the body heat while within the body
than when
inspired
variable
Table 12.1 A comparison of inspired and expired air.
133
Life Processes and Disease
Inspiration
Expiration
• External intercostal muscles contract (internal intercostals relax) and
the ribcage is raised.
• The muscles of the diaphragm contract and the diaphragm moves
downwards.
• Internal intercostal muscles contract (external intercostals relax) and
the ribcage is lowered.
• The diaphragm muscles relax and the diaphragm moves upwards.
air in
air out
ribs move up
and out
diaphragm contracts
(moves down)
vertebral
diaphragm recoils
upwards
volume Increased
volume decreased
air in
air out
sternum moves
upwards and
forwards
diaphragm contracts
sternum moves
downwards and
backwards
diaphragm recoils
• These two movements increase the volume of the thorax.
• These two movements decrease the volume of the thorax.
• The pressure inside the thorax is lowered to below atmospheric
pressure. This pushes air into the lungs so they expand.
• The pressure inside the thorax increases which squeezed the lungs.
• •Air rushes into the lungs through the mouth/nose and trachea.
• Air is pushed out of the lungs. It passes out through the trachea and
the mouth or nose, out of the body.
Table 12.2 A comparison of inspiration and expiration.
134
12 · Gaseous Exchange
Importance and mechanism of gase~us
exchange in plants
CHAPTERS
X
~
IT:Q5
vv
What is breathing and why is it
important?
(ii) Which muscles are involved in
breathing in humans?
(i)
~
The leaf is the respiratory surface or gaseous exchange surface. There are tiny
pores called stomata on the underside of the leaf through which the gases pass.
From the air space inside the leaf, the gases diffuse into and out of the plant
cell. The gases move down their concen tration gradients (chapter 8).
During the day, plants photosynthesise and need carbon dioxide. Oxygen is
a waste product and must be removed. Plants respire all the time but, during
the day, photosynthesis is also being carried out. More oxygen is made in
photosynthesis than is used up in respiration and more carbon dioxide is used
than is made. So there is a net flow of oxygen out of the leaf and a net flow of
carbon dioxide into it.
At night photosynthesis stops because there is no light but respiration
continues. Oxygen moves into the leaf and carbon dioxide moves out
figure 12.6).
Day
IT:Q6
Night
vv
Which gases leave and enter a leaf at:
(i) 12 noon?
(ii) 12 midnight?
• respiration occurs
• no light, therefore no photosynthesis
6C02 + 6H20 -+ CsH120 5 + 602
photosynthesis equation
C5H120e + 602 -+ energy + 6H~ + 6C02
respiration equation
Figure 12.6 The net flow of gases diffusing in and out of a leaf during the day and at night is
different.
Characteristics common to gaseous
exchange surfaces
gaseous exchange surface >
Gaseous exchange or respiratory surfa ces are those surfaces where the
exchange of oxygen and carbon dioxide occur. These surfaces must have
certain characteristics that encourage:
• a lot of gaseous exchange to take place;
• gaseous exchange to take place quickly;
• gaseous exchange to take place continuously.
This means that organisms respiring aerobically can get a constant supply of
oxygen and remove carbon dioxide. Without oxygen, ce lls die and carbon
dioxide, if allowed to accumulate in cells, could poison and kill them.
135
Life Processes and Disease
Adaptations for efficient gaseous exchange
Large surface area
For gaseous exchange to take place quickly and in large amounts, respira tory
surfaces must have a large surface area or a large area over which the exchange
of gases can occur (figures 12.7, 12.8 and l2.9).
blood brought to the
alveolus - it is low in 0 2
and high in C02
blood taken away it is rich in 0 2
and low in C02
thin wall of capillary -
layer of moisture - oxygen dissolves in
this moisture and there is always
a high concentration of oxygen
next to the capillary
blood flows constantly
lungs, highly folded
to Increase surface area
Figure 12.7 Adaptations of the lungs in humans for efficient gaseous exchange.
stiff gill rakers, which filter out food
particles from water as it passes over them;
the food particles are then swallowed
bony gill bar,
supporting the gill
leaf is thin and flat for
large surface area
I
oxygen leaving leaf is
0 2 blown away, leaving a
low concentration
around the leaves
)
wind
soft, dark red gill lamellae, where
gas exchange takes place -
'" 7
g<eatly ""''""'""
,,.----,.......~-,IF-~...,..-.,
blood capillaries - bring blood
to pick up 0 2 and lose C02 ,
take away blood rich In
0 2 and low in C02
leaf is about
4-5 cells
thick
spongy
mesophyll
water flowing around gills
Figure 12.B Adaptations of the lamellae on the gill of a fish for
efficient gaseous exchange.
136
Agure 12.9 Adaptations of leaves on a plant for efficient
gaseous exchange.
12 ·Gaseous Exchange
- - .. ..
flow of water brings
more02
thin membrane
small volume relative to
large surface area
..
flow of water takes
C02 away
..
movement of water
Figure 12 10 The unicellular Amoeba
needs no special organ for gaseous
exchange. It is so small that the gases can
be exchanged efficiently across its cell
membrane.
~
IT:Q7
V'-...J
What is the respiratory surface for each
of the following organisms: a human, a
fish, a plant, Amoeba?
In humans, the lungs are made up of thousands of sacs called alveoli,
which, if laid out side by side, would cover a tennis court. In fish, gill lamellae,
which are part of the gills, form the respiratory surface. There are thousands of
lamellae in each gill creating a large surface area (or exchange.
In plants, the respiratory surface is the leaf. Leaves are thin and flat to
create the largest area possible for gaseous exchange. On a tree, the thousands
of broad flat leaves show what a large surface area is available for gaseous
exchange.
Protozoan s, Like Amoeba, are microscopic unicellular organisms. Their
surface area to volume ratio is alreay large. Gaseous exchange occurs across the
cell membrane by diffusion and, because the cell is so small, the entire body of
Amoeba can be supplied with oxygen (figure 12.10).
Thin surface for gaseous exchange
For gaseous exchange to take place quickly, the respiratory surfaces must be
thin so that diffusion of the gases can take place rapidly.
In humans, the walls of the alveoli and capillaries are just one cell across.
The walls of the alveoli are also moist, so that the gases dissolve in the moisture
before they diffuse. In fish, the lamellae and capillaries are also one cell across
and diffusion can thus readily occur across the gills.
Air spaces inside leaves ensure that the gases can get dose to most of the
cells into and out of which they must diffuse.
The cell membranes of protozoans are very thin and diffusion readily
occurs.
Constantly moving transport medium
For gaseous exchange to take place continuously, the medium which brings
the gases to the respiratory surface must be constantly moving. This ensures
that a concentration gradient is always maintained and diffusion will take
place constantly. For example, in humans and in fish there is a rich blood
supply constantly flowing past the respiratory surface. In humans, breathing
continuously refreshes the air in the lungs; in fish, water is continuously forced
across the gills.
In plants, the wind blows or moves the gases away from the leaves ensuring
that a concentration gradient is always maintained and that diffusion occurs
readily.
In unicellular protozoans, the water around the organism constantly takes
away and supplies the gases which dissolve easily in water.
The effects of smoking
Tobacco may be the cause of over 3 million deaths a year, worldwide. Death
from cigarette smoking comes mainly from lung cancer, but heart disease is
also associated with smoking. The products of cigarette smoke, (whether the
smoke is directly from smoking a cigarette or from inhaling another person's
cigarette smoke) include nicotine, tar and (Like car exhaust fumes) carbon
monoxide.
Nicotine
• Makes cigarettes highly addictive.
• Reduces air flow in and out of the lungs.
• Paralyses the cilia lining the trachea, so they cannot remove dirt and
bacteria.
137
Life Processes and Disease
• Raises blood pressure.
• Raises heart rate.
• lncreases the risk of osteoporosis.
Osteoporosis is the loss of calcium carbonate from the bones which can happen
in older people. It makes the bones brittle, so they break more easily and are
more difficult to heal.
Tar
•
•
•
•
Sticks to cells in the lungs.
Causes the development of cancer.
Damages lung tissue.
Breaks down the alveoli, thus decreasing the surface area for gaseous
exchange.
• Causes bronchitis or inilammation of the lining of the air passages.
• Causes 'smokers cough'.
Carbon monoxide
•
•
•
•
•
Combines irreversibly with haemoglobin in the blood.
Causes less oxygen to be transported by blood.
Reduces the smoker's ability to take strenuous exercise.
Causes breathlessness.
If a pregnant woman smokes, carbon monoxide gets into the blood of the
fetus and combines with the haemoglobin. Less oxygen gets to the growing
tissues, resulting in a baby with a lower birth-weight; this is associated with
greater risk of health problems during and after birth. ·
Although studies show that there is a connection between cigarette smoking
and lung cancer, m illions of people worldwide continue to smoke. A large
percentage of smokers are young people who become addicted very quickly
and continue to smoke throughout their lives. Statistics show that 25 % of
smokers die of lung cancer. Figure I 2.11 shows the effects of smoking on
human lungs.
(a)
(b)
Figure 12.11 A normal lung (a) and a cancerous lung (b) . The cancerous lung came from a heavy
smoker
138
12 · Gaseous Exchange
Marijuana addiction
This is a green or grey mix of dried shredded flowers and leaves of the hemp
plant Cannabis sativa - also called by many, many other names including pot,
herb, ganja and weed. The active ingredient is THC (tetrahydrocannabinol)
which provides to the 'high' that users experience when they smoke the drug.
The short-term effects of marijuana can include:
• problems with memory and learning;
• distorted perception;
• difficulty in thinking;
• difficulty in problem-solving;
• loss of coordination;
• increased heart rate;
• anxiety;
• panic attacks.
Marijuana smoke is unfiltered, users inhale more deeply and hold the smoke
in the lungs. The effects on the lungs are thus greater than those caused by
tobacco smoke because more tar and more carbon monoxide are inhaled.
139
Life Processes and Disease
ITQ1 (i)
Gaseous exchange is the exchange of gases, in particular oxygen
and carbon moxide.
(ii) In the lungs, where gases are exchanged between the alveoli and blood.
In the tissues, where gases are exchanged between the blood and cells.
ITQ2 These are complete rings which keep the trachea open. They also
support the trachea.
ITQ3 nose -+ trachea -+ bronchus -+ bronchiole -+ alveolus -+ capillary
ITQ4 Blood in the capillary approaching the alveolus contains a higher
concentration of carbon moxide and lower concentration of oxygen than blood
leaving the alveolus.
ITQS (i) Breathing is the process whereby air is pushed into the lungs by
atmosph eric pressure and expelled from the lungs by muscular contraction.
It is important because it brings a supply of oxygen, wh ich is needed for
respiration, and it also takes away carbon dioxide, a waste gas.
(ii) The muscles involved in breathing are: the diaphragm muscles and the
external and internal intercostal muscles.
ITQ6 (i) At noon, oxygen is leaving the plant and carbon moxide is entering
the leaf because photosynthesis is happening at a much faster rate than
respiration can use the oxygen or produce carbon dioxide.
(ii) At midnight, there is no light so photosynthesis cannot take place.
Respiration is the only process that is occurring, so carbon moxide is leaving
the plant and oxygen is being taken in.
ITQ7 Human respiratory surface is the alveolus;
fish - gill; plant - leaf; Amoeba - cell membrane.
Examination-style questions
(i)
Inhalation and exhalation are movements that ventilate the lungs. The diagram below
shows the ribs and diaphragm.
(a) Copy the diagram and use arrows to show the movements of the diaphragm, the
ribs and air during exhalation.
(b) Explain fully how the volume of the thorax is increased by giving details of
contraction and relaxation of muscles involved in raising of the ribs and lowering
of the diaphragm.
140
12 · Gaseous Exchange
(ii) List three ways inhaled air differs from exhaled air.
(iii) A boa constrictor kills its prey by squeezing it to death. This is termed 'asphyxiation'.
Explain how asphyxiation results in death.
2
(i)
Define the following terms:
(a) gaseous exchange;
(b) respiratory surface.
(
(ii) List three characteristics of respiratory surfaces. Describe how the lungs of humans
are adapted in these three ways to increase the rate of gaseous exchange.
(iii) The nicotine found in tobacco smoke can prevent the beating of cilia in the trachea.
Suggest how this contributes to the development of lung diseases.
(iv) List two effects of each of the following products of cigarette smoke:
(a) nicotine (b) tars.
(V) How are plants adapted to exchange gases efficiently by diffusion?
3
The apparatus shown in the diagram below is used to investigate the chemicals in
cigarette smoke.
air
outlet
-
lighted
cigarette
cotton wool
(i)
After some time, the cotton wool turns black and appears oily.
(a) What are the black particles trapped in the cotton wool?
(b) What chemical causes the oily appearance?
(ii) Describe and explain the colour change of the litmus paper.
(iii) If a cigarette with a filter is used, what difference in the appearance of the cotton wool
would you expect?
(iv) One of the gases in cigarette smoke is carbon monoxide. What is the effect of carbon
monoxide on the body?
(v) How do chemicals in cigarette affect the cilia in the trachea?
(vi) Name two respiratory diseases that may be caused by prolonged smoking.
141
liransport and
Defence in Animals
./) understand why there is a need for a transport system in multicellular organisms
Q)
Q)
Q)
Q)
Q)
understand why certain materials must be transported in animals
describe the circulatory system of humans
relate the structure of the heart to its function
relate the structure of blood vessels to their function
describe the composition and functions of blood
./) understand how and why blood clots
./) understand blood groups and their importance in blood transfusion
Q) understand the nature and danger of hypertension
/
describe the role of blood in defending the body against disease
./) explain how the principles of immunisation are used in the control of
communicable diseases
plasma
haemoglobin
red blood cells
blood
white blood cells
platelets -
.
hypertension -
transport system
in humans
-
heart
clotting
action of
- { heart
heartbeat
(
functions
t
take important
substances
to cells
blood vessels
]
\
t
take waste
products
away from cells
arteries
veins
capillaries
The need for a transport system
Large mu lticellul ar animals, like human s, have a large volume in re lation to
Lhe ir surface area. Substances would therefore take a long time to diff use from
the air into the body and would get to cells deep in the body at a much slower
than th e rate at w hi ch th ey are needed by the cells.
Imagine oxygen diffus ing into th e skin of an organ ism. It may not be able to
get to all the cells of the skjn, far less the cells of organs inside the body. Oxygen
would have to pass th rough m illions of cells to get to the liver. Also, the skin is
13 · Transport and Defence in Animals
~
IT:Q-1
V-...J
A unicellular organism like Amoeba
does not have a transport system and
a multicellular organism like a human
cannot live without one. Explain why
this is so.
CHAPTERS 10, 11 , 12, 16, 18
X
~
IT:Q2
V-...J
Name two substances which must be
transported to a cell and explain why
each substance is needed.
circulatory system >
a to ugh waterproof layer and may also be covered with hairs, fur and feathers.
It is impossible for oxygen to diffuse to cells inside the body of a m ammal or
other la rge organism. In an y organism larger than a few cells, any substance
needed by a cell within the bocy must be speciaDy transported to the cell.
A transport system is necessary to get important and needed substances
to every single cell and also to transport waste or toxic substan ces away from
every cell. Just to stay alive, a m ulticellular organism requ ires a con stant
supply of substances like oxygen and glucose to all its cells. When active, the~e
substances are required in even greater amounts.
Table 13. l shows some of the substan ces which need to be transported in
animals.
Substance to
be transported
Transported from
Transported to
dissolved food
(chapter 1O)
ileum where it is absorbed
cells of the body - to be used for
respiration, stored, converted to other
materials, etc.
nitrogenous
waste
(chapter 16)
cells where produced
kidneys to be excreted
oxygen
(chapter 12)
lungs where it diffuses into the
blood
body cells to be used for respiration
carbon dioxide
{chapter 11)
body cells where it is produced in
respiration
lungs to be excreted
hormones
(chapter 18)
endocrine glands where they are
produced
organs where their effects are needed
white blood
cells including
antibodies
marrow of bones where they are
produced
where there are infections or invasions by
microorganisms
Table 13. 1 Some substances which are transported in animals.
The circulatory system of humans
Blood is the m eans by which substances travel to and from cells. These
substances dissolve in blood, w hich is mainly water and diffused into th e cells
where they are n eeded. The blood is transported around the body in blood
vessels. The heart h elps to push blood a ro und the body.This transport system is
called a circulatory system. Most substances dissolve in the plasma, but the
red blood cells are specialised to transpo rt oxygen .
The circula tory system is made up of three parts:
• the heart, which is a pump;
• th e blood, w hich is the fluid being pumped a nd contains all the ma terials to
be transported around the body;
• the blood vessels (like pipes) through which blood flows to get to and from
the cells, these are the arteries, veins and capillaries.
The structure of the heart
The heart pumps blood so tha t it can get around the body. It pushes blood
forcibly thus ca using it to be constantly m oving in the blood vessels. The
walls of th e hea rt are made of a special type of muscle, ca lled cardiac m uscle.
143
Life Processes and Disease
cardiac muscle )
fliill!ull
i@nrmlm
Cardiac muscle contracts and relaxes regu larly and constantly throughout
life. It never grows tired. But it may stop working iI it is not supplied with the
substances it needs to release energy - oxygen and glucose. These are supplied
via the coronary circulation.
The mammalian heart is divided into a right side and left side (figure 13. l ).
Each side has two parts or chambers:
• the atrium, which receives blood;
• the ventricle, which pumps blood away.
(a)
left pulmonary
artery
right
pulmonary ~--­
veins
left pulmonary
(b)
_ ____ left pulmonary
artery
r~======!=
::;;;;.---left pulmonary
vein
:"r-- - - left atrium
't--- - - semilunar valves
---"~--
- tricuspid valve --~~---==
vena cava from - - - - - i 4 - lower part of body
I
-
bicuspid valve
-tendon, holds
the valve in place
left ventricle
r
Agure 13.1 The heart: (a) showing its blood supply and (b) in section.
The action of the heart
Deoxygenated blood, that is blood coming from the body cells w here some of
the oxygen bas been used in respiration, flows into the right atrium through
the vena cava . This blood is also rich in carbon dioxide made during respiration
in the cells. The blood must now be tran sported to the lungs wh ere it can load
up with more oxygen and offload the excess carbon dioxide.
144
13 ·Transport and Defence in Animals
tricuspid valve }
bicuspid valve }
~
l:f:Q3
\_,)'...J
The heart beats continuously for years.
How is heart muscle nourished and
supplied with oxygen and glucose?
From the right atrium, blood passes through the tricuspid valve into the
right ventride. The walls of the ventricle contract and the blood is pushed into
the pulmonary artery and travels to the lungs. There, gases are exchanged.
Excess carbon dioxide leaves the blood and diffu ses into the lungs, and oxygen
moves into the blood from the alveoli.
Oxygen-rid1 blood returns from the lungs via the pulmonary veins and
flows into the left atrium. It passes through the bicuspid valve and flows
into the left ventricle. The thicker muscular walls of the left ventricle contract
strongly and blood is pushed forcefully into the aorta and all the way around
the body. Blood therefore flows through the heart twice in one circuit of the
body (figure 13.2)
deoxygenated
blood from head
deoxygenated -+-- 1 -- - - - + blood to the lungs
deoxygenated
blood from body
J-- ,oxygenated blood to
head and body
oxygenated
blood
to the body
Figure 13.2 Blood flows through the heart twice in one circulation
atrioventricular valves >
semi-lunar valves >
Q9;,
l:tQ~
\_,)'...J
Describe the route taken by a red blood
cell from the vena cava to the aorta.
Valves prevent the back-flow of blood in the heart. The bicuspid and
tricuspid valve, known as the atrioventricular valves, ensure that blood
flows in one direction through the heart only. Tendons attached to the walls of
the heart hold them in place. When the ventricles contract, blood pushes back
on these valves, forcing them shut. So the blood can only move forward into
the pulmonary arteries and aorta .
Semi-lunar valves are found at the start of the pulmonary artery and
aorta . They prevent the back-flow of blood into the ventricles when they relax.
Heartbeat
The heart 'beats' when the muscles of the heart contract and relax. The re
are three phases to a heart beat. The sound s heard - 'lub dub' - are the
sounds made by the valves closing and blood hitting the valves. The 'lub'
sound is made during ventricular systole as blood is forced against the closed
tricuspid and bicuspid valves. The 'dub' sound is made during ventricular
diastole when blood impacts on the d osed semi-lunar valves in the aorta and
pulmonary artery. The third stage, diastole, when blood flows into the empty
atria and ventricles, makes n o sound (figure 13.3).
The rate of heartbeat is controlled by the ' pacemake r', which is found in the
mu scle between the ventricles. It has its own na tural rhythm of stimulating
145
Life Processes and Disease
con tractions, which is usually around 70- 80 beats per minute. This can be
speeded up by h ormones such as adrenalin, and by activity.
from lungs
atria and ventricles
relax (diastole)
Diastole - when all the muscles of the
heart relax and blood flows into the heart
atria contract
(systole)
Atrial systole - the muscles of the atria
contract and force blood into the ventricles
~
I
ventricles contract
(systole)
1+I
,I ...._
Ventricular systole - the muscles of the ventricles
contract and push blood out of the heart
Agure 13. 3 The three phases of a heartbeat.
~
l:t!QS
V'-1
List the three main stages of the
heartbeat and explain the importance
of each.
FUC§W
l!hl·lllblt'B
m1eu
Blood vessels
Blood flows through blood vessels to get to all parts of the body from the heart
and then from the body back to the heart. There are three kinds of blood
vessel:
• arteries (and arterioles) whlch carry blood away from the heart;
• capillaries which are tiny vessels that pass close to all body cells;
• veins, (and venules) which carry blood back to the heart.
An artery branches into smaller and smaller vessels called arterioles. These
branch into even smaller and smaller vessels, until the vessels are very small
and the walls are only one cell thick. These tiny vessels are ca lled capillaries.
Capillaries flow in between the cells of the organs and the exchange of
substances food, oxygen, wastes, etc. takes place at this level.
Capillaries then join up to form larger and larger vessels called venules,
which then join to form veins which carry blood back to the heart.
Fiigures 13.4 ansd 13.5 show the relationships between the three types of
blood vessel. Table 13.2 compares arteries, veins and capillaries.
146
13 ·Transport and Defence in Animals
arteriole from artery
Rgure 13. 4 The relationship between arterioles, capillaries and venules.
cells give out
waste products
cells take in
Deoxygenated blood
full of waste products
goes to the heart. then
to the lungs and gut to
collect oxygen and food.
Diffusion occurs across
the capillary network.
Oxygenated blood full of food
and other useful substances goes
to the cells.
Figure 13.5 A network of capillaries surround all the cells of tissues
Capillaries
Arteries
wall composed of a
single layer of cells
fibrous layer
muscle and
elastic layer
.,
smalllumen ~
Veins
fibrous layer
lumen and red
blood cells
pass in single file
endothelium ___/one cell thick
• thick elastic walls to withstand the hgh
pressure of blood and absorb some of
the energy of the pulse
• walls one cell across - thin enough for
diffusion to take place easily
• thin elastic walls (do not have to withstand high
pressure)
(continued)
147
Life Processes and Disease
Arteries
Capillaries
Veins
• carry blood away from the heart
• carry blood to the cells of the tissues
and organs
• carry blood towards the heart
• blood pressure is high
• blood pressure decreases along the
length of the capillaries
• blood at low pressure
• blood flows rapidly in pulses created by • blood flow is smooth and slow
contractions of the ventricles (this is the
pulse you can feel most easily at your
wrist)
• smooth and slow flow - the large lumen offers little
resistance
• carry oxygenated blood, except the
pulmonary artery
• as it flows through a capillary network • carry deoxygenated blood, except the pulmonary vein
the blood loses oxygen to body cells and
gains carbon dioxide
• lie deep within the body
• run through the tissues
• lie close to the body surface
• no valves present
• no valves
• valves prevent the back-flow of blood because the
'push' of the heart is not felt here
flow
of blood
l
blood can flow
in one
direction only
valve open
valve closed
• blood can flow in one direction only
~
ll'.Q6
\...l'-1
Describe two differences between
blood leaving an arteriole and blood
entering a venule, having passed across
a capillary network.
lfl•l•f?M
G#•€•1f§kkU
coronary arteries >
CHAPTER 16
Table 13.2 The main differences between arteries, capillaries and veins.
The circulation
Blood leaves the left side of the heart at a high pressure and flows through the
aorta , the largest artery, to all parts of the body. When the capillaries reach
the body cells, the blood gjves up food and oxygen and picks up wastes, such
as carbon dioxide and urea. Deoxygenated blood returns to the heart via the
veins whid1 collect into a main vein called the vena cava. From the right side
of the heart, blood flows to the lungs to be oxygenated, then back to the left
side of the heart. This flow is repeated continuously. The tissues of the heart
itself are supplied with oxygen by the coronary arteries .
In its circulation throughout the body, blood picks up food (such as glucose
and amino acids) from the gut, hormones from endocrine glands, and other
vital substances. It also drops off waste products to be excreted, like urea and
carbon dioxide, at sites where the body an get rid of them. that is the kidneys
(chapter 16) and the lungs (figure 13.6).
.~
\...l'-1
Why does the aorta have the thickest
walls of all the vessels in the
circulatory system?
148
~
(1~8
(i) What is the pulse?
(ii) What is the pulse rate?
13 ·Transport and Defence in Animals
----
-
jugular and - ----,;-7.,._...a..
subclavian veins
- carotid artery
(to head)
carotid and
subclavian
arteries
head and arms
subclavian artery
(to arms)
1
subclavian vein
pulmonary -~----,f----3it::....:
vein
1
pulmonary -+-..___.,,,
artery
vein
pulmonary artery--r--..,,,
(to lungs)
1--'ilft--
hepatic portal
vein (liver)
. -- -----'-
- --
renal artery
(to kidney)
hepat ic -f-~~
mesenteric ---~E="
artery
(to gut)
Iliac - 1---- -vein
arteries
vein
•- - - --
-hepatic
artery
Iliac
artery
(to feet)
Iliac vein
deoxygenated blood
pulmonary circulation -
oxygenated blood -
systemic circulation -
~
deoxygenated blood
11!09
oxygenated blood -
l../'-J
Describe the route taken by a red blood
cell from the renal vein to the hepatic
vein.
Rgure 13.6 The circulatory system in humans.
Blood
l~O
l../'-J
Describe the differences in composition
between blood:
(i) in the renal artery and the renal vein
(ii) in the pulmonary artery and
pulmonary vein. blood plasma >
red blood cells
trunk and
legs
white blood cells >
Blood is the medium by which substances or materia ls are transported. It is
made up of about:
• 55 % blood p lasma;
•
45 % blood cells.
The blood plasma is about 90% water and most of the substances which
must be transported are dissolved in it. This includes dissolved food (glucose,
amino acids, fatty acids and glycerol), carbon dioxide (as the bicarbonate ion),
nitrogenous wastes, hormones and mineral salts (as ions such as Na+, K+, Cl+).
The blood cells are of two main types, red and white. There are also
fragments of cells called platelets.
Table 13.3 (overleaf) summarises the structure and function of blood cells.
149
Life Processes and Disease
Blood cell
Function
Red blood cells or erythrocytes
• biconcave disc shape (squeezed in from both sides)
gives large surface area for diffusion
• have no nucleus so only live for 3-4 months
• new cells constantly made in the bone marrow and
destroyed in the liver and spleen
• contain the red pigment haemoglobin which combines
with and releases oxygen readily
• 1 mm3 of blood contains about 5 million of these cells
contains
haemoglobin,
a red pigment
which contains
iron; no nucleus
transport oxygen combined with haemoglobin,
from the lungs to tissues where the oxygen is
given up readily
t
White blood cells or leucocytes
• two main types: phagocytes and lymphocytes
Phagocytes
• move like Amoeba by pseudopodia - can move through
the capillary walls to sites of infection
• formed in bone marrow
engulf disease-causing organisms at sites of
infection
Lymphocytes
• produce antibodies
• formed in lymph nodes and spleen
produce antibodies that kill pathogens by causing
them to clump together, or neutralise their toxins
Platelets or thrombocytes
• cell fragments
• no nucleus
• formed in bone marrow of lone bones
help blood to clot to prevent loss
~
Table 13.3 Structure and function of blood cells
ll':Q·1 1
V"-J
Protection of the body is one of the
functions of blood. List two components
of blood concerned with protection and
explain how each works.
~
ll':Q-12
V"-J
Describe the process that leads to
blood clotting after a cut to a blood
vessel.
Carriage of oxygen and carbon dioxide in
the blood
The respirato ry gases, oxygen and ca rbo n dioxide, are transported aroun d the
body in the blood. Most of the carbon dioxide is transported in solution in
blood plasma as h ydrogen carbonate ions. Oxygen is carried by the molecule
haemoglobin, which is found inside red blood cells. Haemoglobin is a protein
that is combined with iron - this gives it its red colour. Each m olecule of
haemoglobin combines reversibly with up to four molecu les of oxygen.
haemoglobin + oxygen -+ oxyhaemoglobin
The oxygen is readily given up in the body tissues wh ere oxygen levels are low.
The body cells can then use th e oxygen for respiration .
oxyhaem oglobin -+ haemoglobin + oxygen
Red blood cells are so full of haemoglobin that there is no space for a nucleus.
That is why th ey only survive for 3-4 mon ths, after which th ey are cleaned out
of the blood by the liver.
150
13 • Transport and Defence in Animals
Blood clotting
HH•M•E®U When the skin is cue and a small blood vessel is broken , a blood clot ronns
haemorrhage >
to prevent further blood loss (figure 13. 7). A series or reactions cake place at
the site of the cut vessel which results in the formation of fibrin, an insoluble
fibrous protein which traps blood cells and pl ugs the gap (figure 13.8).
The dot a lso prevents the entry of disease-causing organisms. Loss of blood
from a vessel is called a haemorrhage, and losing a lot of blood could result in
death. In this case, a blood transfusion can be given to replace blood and save
the person's life.
(a)
disease-causing
organisms may enter
no more loss of blood,
pathogens have a
barrier once more
I
~ssofblood
clot
The cut is sealed
with a blood clot
A cut vessel
(b)
platelets exposed to air In damaged tissue
l
calcium ions
vitamin K
prothrombin - - - - - - - - - - - thrombin
(inactive protein
(active)
in the blood)
1
fibrinogen ----"--+~ fibrin insoluble fibres
(inactive protein
that trap red blood
in the blood)
cells and form a clot
Figure 13. 7 The formation of a blood clot.
Blood groups
Figure 13.8 Red blood cells trapped In
fibrin.
Ft.1e1.111
l(§lff i•U§ellJ
During a blood transfusio n, a person is given another person's blood. Early
attempts at transfusion worked in some cases, but in many they resulted in
death. We now know that for a transfusion to be successful, the two sets of
blood must be compatible - able to mix wirht each other without the red cells
sticking together..
Th ere are four blood groups, known as A, B, AB and 0. These groups are
based on proteins, ca lled antigens, that are present on the surface of red blood
cells. For example if an tigen A is present on all the red blood cells of a person,
that person is said to have blood group A.
There are also antibodies present in the blood plasma. These are associa ted
with the antigens. So a person with b lood group A, fo r example, has antigen A
(A) on their red cell and and antibody anti-B (b) in their plasma (table l 3.4).
During a transfusion it is important to note:
• the protein (or antigen) on the red blood cell of the donor;
• the type of antibody present in th e plasma of the recipient.
If the antibody matches the antigen, the red blood cells stick together and
transfusion will not be successfu I.
151
Life Processes and Disease
Table 13.4 shows the success of transfusion for all the blood groups. A tick
means that this combination of donor and recipient will make a successfu l
transfusion; a cross indicates that this combination will lead to a reaction
(potentially fatal) in the recipient.
Donor's blood type
Recipient's
blood type
~
IT:.Q·1 3
v-..;
State whether these transfusions
are possible:
• donor AB, recipient O
• donor AB, recipient A
• donor O, recipient A
• donor B, recipient A
• donor B, recipient B
A
B
AB
0
(A)
(8)
(A) B
none
" "
"
"
.I
.I
A
(b)
B
(a)
AB
none
.I
0
(a) (b1
" "
t
antibody
present
.I
.I
.I
.I
+-
antigen present
.I
.I
+- universal recipient: blood
group AB
t
universal donor: blood group 0
Table 13.4 The success or failure of blood transfusions between different blood groups.
Hypertension
hypertension >
EmlDJ
~
IT:.Q-1 4
v-..;
(i) What is hypertension?
(ii) What factors in a person's life may
increase the chances of suffering
from hypertension?
152
High blood press ure is when the pressure caused by the blood pushing against
the inside walls of the main arteries is high . Persistent high blood pressure is
called h yp er tension .
Capillaries are tiny blood vessels, with walls that are one cell across. Blood
flowing at a high pressure can cause these vessels to burst. If a vessel in the
brain burst, then a portion of the brain becomes damaged from a lack of
oxygen . This is called a stroke and can resu lt in paralysis or even death.
Capillaries in other important organs like the kidneys may burst because
of high blood pressure. This could lead to shutdown of the organ (e.g. kidney
failure) and can have serious consequences on the body.
Hypertension can develop without symptoms or signs and is sometimes
called the 'silent killer'. It is linked with a number of factors such as:
• high levels of emotional stress;
• lack of exercise;
• obesity;
• tobacco smoking;
• high alcohol intake;
• high blood cholesterol levels.
All these factors are influ enced by lifestyle, and can be controlled by changing
lifestyle. A h ea lthy lifestyle, that includes regular exercise, no smoking, low
intake of fat, salt and alcohol, can prevent the development of hypertension.
13 · Transport and Defence in Animals
The role of blood in defending the body
against disease
physical barrier >
phagocytes >
Microorganism s are all around us. These microscopic o rganisms (viru ses,
bacteria, etc.) are in the air we breathe, in the food we eat, on everything we
tou ch and all over our bod ies.
The skin is the body's first Line of defence (figure 13. 9) . It acts as a physical
barrier. When there are breaks in this barrier, such as cuts or sores, the
body reacts to produce blood clots and a m eshwork of fibrous scar tissue. The
opening is thus blocked, which prevents pathogens (microorganisms that can
cause disease) from entering the body.
Sometimes the white blood cells called phagocytes move out of the blood
and to the infected areas. There they engulf the invading microorganisms,
killing and removing them from the body before they can cause disease. This is
our second line of defence (figure 13. 10).
wax in the auditory
canal traps dust
and other particles
- - - tears contain a mild antiseptic
- - - hairs in the nose trap dust
and other particles
trachea lined with mucus
and cilia to move dust
and other particles out of the lungs
skin -a
physical barrier
stomach produces hydrochloric
acid which can kill microorganisms
vagina - mucus moves out constantly
break in the skin - a clot forms
Figure 13.9 The skin is our first line of defence. Any openings in the skin have special means of
expelling dust which carries many disease-causing organisms.
bacterium within the
~ phagocyte - it is killed
and digested
8
G
Figure 13. 10 White blood cells
(phagocytes) are our second line of
defence. They leave the blood and
migrate to a site of infection
phagocyte engulfing
bacterium
phagocyte moves toward
site of infection
blood capilliary
153
Life Processes and Disease
Immune response
lymphocyte >
lmJOitimWJ
The phagocytes can cope with any small, non-specific invasion by pathogens.
U more dangerous, specific pathogens enter, then an immune response is
activated. In this case, another kind of white blood cell, called lymphocytes,
recognise the specific pathogen and mobilise other lymphocytes to make
antibodies to attack, disarm, destroy and remove these pathogens.
1m1u.14,u Antigens and antibodies
immune response >
memory lymphocytes >
natural immunity >
Anything that is foreign or different and causes antibody formation is called
an antigen. This is our third line of defence against disease. When antigens,
such as the measles virus, enter the body, lymphocytes recognise them and
start to produce specific antibodies on a large scale to destroy the viruses. The
immune response is very specific - only the antibodies for that particular
antigen are made.
To defend the body against disease, antibodies act in a number of ways:
• they cause the antigens to dump together resulting in their death and easy
removaJ by the phagocytes;
• they neutralise toxins produced by the antigens;
• they prevent the antigen from entering body cells.
Recognition of antigens and production of the specific antibodies against them
takes time. During that time, the antigens will have produced symptoms of
the disease. Once the antibodies are produced, the antigens or the toxins
they produce are destroyed or neutralised and the symptoms disappear. The
antibodies then gradually disappear from the blood, but they leave behind
speciaJ memory lymphocytes. If the specific antigen invades a second time,
the memory lymphocytes immediately recognise them, and rapidly make large
amounts of the specific antibody. This time, the antigens are destroyed before
symptoms develop, and the person is said to be immune to that disease. This
happens naturally and is called natural immunity (figure 13.11) .
Antibody concentration
in the blood
first infection
second infection
slow build-up of
antibodies gives
pathogens time
to cause disease
0
10
20
30
large amount of antibodies made
1--- - immediately, pathogen destroyed
before symptoms develop - person
is said to be immune to that disease
40
50
60
70
80
90
Time in days
Agure 13. 11 Immunity 1s a rapid large increase of antibodies in the blood
1?ot.s
V"...J
We are surrounded by pathogens. How
is the body protected from infection?
154
There are two types of naturaJ immunity.
• Actively acqu ired immunity - When the body has already experienced
an infection by a pathogen or antigen, as described above, the lymphocytes
produce large quantities of antibodies to fight the disease before symptoms
develop a second time.
• P assively acquired immunity - Antibodies can pass across the placenta
providing a newborn baby with immunity against diseases that the mother's
13 ·Transport and Defence in Animals
body is immune to. Also, antibodies present in breast milk help to protect
the baby against antigens.
Immunisation and the control of communicable
diseases
vaccination >
~
IT:Q·1 6
\....)'-/
Explain what is meant by a vaccine.
artificial immunity >
1~7
\....)'-/
Copy and complete the table.
Natural
immunity
Artificial
immunity
Active
Passive
Immunisation provides immunity to communicable diseases. This is achjeved
by injecting, or administering orally, small amounts of dead or weakened
(attenuated) antigens into the body. This is called vaccination . The body is
stimu lated to produce antibodies.
One example is the MMR vaccine given at around 2 years of age or
younger to protect children against measles, mumps and rubella. DTP vaccines,
administered at any age, protect against diphtheria, tetanus and pertussis
(whooping cough)
Smallpox has been eradjcated because of immunjsation programmes.
Vaccines against tuberculosis (TB) and hepatitis B have also been developed,
but there are still not vaccines against diseases such as cancers, leprosy, malaria
and AIDS, despite much research. The World Health Organization (WHO)
Expanded Program of Immunisation (EPI) aims to extend immurusation to
children all over the world, especially in developing countries so that d1ildren
can be immunised at no cost to their parents. Immunisation is known as
artificial immunity.
There are two types of artificia l immunity,
• Actively acquired - This is by vaccination at a suitable time in the person's
life, when they are not infected with the antigen. The vaccine used contains
treated antigens which cannot cause the disease, but which can stinrnlate
the body to make antibodies. Immunity is obta in ed because if the real
antigen should enter the body, antibodies are immediately and rapidly
produced to destroy il. This happens before symptoms develop and the
person is said to be immune to that disease.
• Passively acquired - The vaccine contains ready-made antibodies whid1
provide immediate relief by destroying the antigens. Thls is given when the
person has been infected with the antigens and has no previous immunity.
The importance of immunisation or vaccination is seen when children are
protected from dangerous diseases like polio, measles, mumps, tetanus
and whooping cough (figure 13.12). Thls is achieved in a programme of
immunisation where often a second, booster injection is given. This stin1ulates
a much quicker production of antibodies which is longer lasting and whlch
protects the chiJd from the disease for a considerable time.
~
IT:Q·1 8
\....)'-/
Explain the meaning of the term
'immunisation' and give one advantage
of immunisation.
(a)
(b)
(C)
Rgure 13. 12 (a) Mumps and (b) chickenpox are common childhood diseases. In some children
they can cause long-term damage. (c) Poliomyelitis can cause life-long damage to the body even
after the infection has gone.
155
Life Processes and Disease
~
Chapter summary
• Large multicellular organisms have a small surface area-to-volume ratio. This means
that they need transport systems to carry substances to and from cells around the
II
body.
• A cell needs nutrients, oxygen and other substances to stay alive.
t
• Waste products are produced and need to be removed from cells so they do not
damage them.
• The transport system of humans is composed of a pump (heart) a transport medium
(blood) and vessels (blood vessels) through which blood flows. This is the circulatory
system.
• The structure of the heart is suited to its function as a pump.
• Blood passes through the heart twice for each time it circulates the body; after one of
these passes through the heart blood goes to the lungs for the exchange of gases.
• There are three kinds of blood vessel: arteries, veins and capillaries.
• Blood is composed of plasma, blood cells and platelets.
• Plasma is mainly water with the substances being transported dissolved in it.
• There are two types of blood cell; red blood cells transport oxygen and white blood
cells protect the body against pathogens.
• Platelets help blood to clot; this is important to prevent blood loss.
• For a successful blood transfusion, the donor's and the recipient's blood groups
must match because if the antigens and antibodies in their blood react together, the
transfusion will not be successful.
• Hypertension is persistent high blood pressure, which is dangerous to health.
• White blood cells protect the body against pathogens.
• Phagocytes can leave the bloodstream, gather at sites of infection and engulf and kill
pathogens.
• The body has three lines of defence against infection: the skin (and blood clotting),
phagocytes and the immune system.
• In the immune system, lymphocytes form antibodies which are specific for the
pathogen.
• After an infection, memory cells remain in the blood, which recognise the pathogen
again quickly. A second infection does not result in symptoms of the disease because
the production of antibodies is much faster and greater.
• A person is immune to a disease if, on infection with the disease, no symptoms
develop.
-
156
13 · Transport and Defence in Animals
ITQ1
In the unicellular organism, the surface area to volume ratio is large,
which means that there is a lot of surface area for the volume of the organism.
Diffusion can occur fast enough across the cell membrane and get to all pans of
the cell for all life processes to happen effectively.
In a multicellular organism, for each cell to get a supply of oxygen and
everything else it needs as fast as it needs it, a transport system is necessary ,
because the surface area is not large enough in proportion to the volume for
diffusion from the external environment to be effective.
ITQ2 (i) Oxygen is used in respiration, which in tum provides the body
with energy.
(ii) Glucose is oxidised during respiration to provide the body w ith energy.
(You may h ave chosen other substances.)
ITQ3 Heart muscle has its own set of blood vessels, called the coronary
arteries and coronary veins. The coronary arteries supply it with glucose and
oxygen needed for respiration.
ITQ4 vena cava -+ right auricle -+ right ventricle -+ pulmonary artery-+
lungs -+ pulmonary vein -+ left ventricle -+ aorta
ITQS Atrial systole - pushes blood from the atria into the ventricles.
Ventricular systole - pushes blood out of the heart, so that it can be pumped
to the lungs through the pulmonary artery, and through the aorta to all parts
of the body.
Diastole - allows blood from the body to collect in the atria, before it is
forced into the ventricles by contraction of the muscles around the atria.
ITQ6 Blood leaving arteriole:
• has a lot of oxygen in it as the arteriole carries oxygenated blood to body cells;
• is rich in glucose, hormones, water, vitamins, etc. , which will be used by the
cells for different purposes .
Blood entering venule:
• h as less oxygen, as some has been used by the cells in contact with the
capillary network;
• has less of other substances, as the blood has been depleted of these when
passing through the capillary network
• has more carbon dioxide and other waste products from cells.
ITQ7 The aorta receives blood at the highest pressure from the contraction
of the muscles of the left ventricle. As the blood enters the aorta, its thick
muscular walls are stretched but do not burst.
ITQS (i) Each heartbeat results in a surge of blood, which can be felt as
the arterioles stretch to accommodate blood flowing at a high pressure. Each
heartbeat results in one pulse.
(ii) The pulse rate shows the rate at which the heart is beating because ead1 .
heartbeat is felt as one pulse.
ITQ9 renal vein -+ vena cava -+ heart -+ lungs -+ heart -+ aorta -+ hepatic
artery -+ live r -+ hepatic vein
l
i
mesenreric artery -+ gut -+ hepatic portal vein
ITQ 10 (i)
Renal artery
Renal vein
rich in oxygen
little oxygen present
little carbon dioxide present
rich in carbon dioxide
rich in glucose
little glucose present
157
Life Processes and Disease
(ii)
Pulmonary artery
Pulmonary vein
rich in carbon dioxide
little carbon dioxide
little oxygen present
rich in oxygen
ITQ11 Platelets are involved in blood dotting, which prevents entry of
pathogens when there is a cut on the skin.
White blood cells destroy foreign bodies that might harm the organism.
ITQ12 On exposure to air, platelets in the blood, in the presence of calcium
ions and vitamin K, cause prothrombin, an inactive blood protein, to be
converted to thrombin. The presence of thrombin causes the conversion of
fibrinogen, another inactive blood protein, into fibrin. Fibrin is made up of
insoluble fibres that trap red blood cells and form a clot.
ITQ13
• donor AB, recipient 0: no
• donor AB, recipient A: no
• donor 0 , recipient A: yes
• donor B, recipient A: no
• donor B, recipient B: yes
ITQ14 (i) Hypertension is prolonged high blood pressure.
(ii) Factors that contribute to the chances of suffering from hypertension are:
• a genetic predisposition (having a relative who suffers from the disease );
• smoking;
• obesity;
• diet that contains many fatty foods;
• no exercise;
• old age.
ITQ15 The body ha s three lines of defence against infection:
• the skin is a physical barrier and openings in the skin have special
mechanisms, such as blood clotting, to keep pathogens from entering the body;
• if pathogens get into the body through a wound, phagocytes migrate to this
site and 'eat' the invading microorganisms;
• antibodies are produced to seek out antigens (foreign invaders like bacteria)
that have entered the body, and destroy them or neutralise their effects. They
are completely destroyed at this point.
ITQ16 A vaccine is a substance injected into the body. It contains antigens
which cause the immune response, or antibodies which protect the body.
ITQ17
.
Natural immunity
Artificial immunity
Active
Antigens enter the body naturally
and bring about the immune
response
Antigens are introduced in a vaccine
to the body and the immune
response is generated
Passive
Antibodies enter the body naturally Antibodies are introduced in a
and protect the body against disease vaccine to the body so the body is
protected
ITQ18 Immunisation is a programme of dispensing vaccines for various
diseases. The act of introducing the vaccine to a person is also immunisation.
One advantage is protection against disease.
158
13 • Transport and Defence in Animals
Examination-style questions
The functions of blood include transport of substances and protection against blood loss
and infection
(i) Describe the transport of a named substance from the site where it is picked up by
blood to a named body cell.
(ii) Describe how a blood clot forms and how the clot protects the body against blood loss
and infection.
2
(i)
Make a labelled drawing of a transverse section of the heart. Use arrows to show the
movement of blood through the heart.
(ii) Describe the role of the heart in the circulatory system.
(iii) Explain why the muscles of the left ventricle are thicker than those of the right.
(iv) Explain the effects on the heart if the coronary artery becomes blocked.
3
(i) Compare the structure of an artery with that of a vein.
(ii) How does the structure of an artery related to its role as a blood vessel?
(iii) Describe how a glucose molecule moves:
(a) from the heart to a capillary next to a body cell;
(b) from the capillary into the cell.
(iv) Compare the composition of blood as it enters and leaves the lungs.
A blood vessel in the brain may burst, resulting in a condition called a stroke. Major
strokes can result in severe paralysis or even death. Minor stokes may occur without
symptoms.
4
(i)
Suggest a likely consequence of the bursting of a blood vessel in the brain and how
this could result in paralysis or even death.
(ii) Suggest reasons why some strokes occur without symptoms.
159
•
0
0
0
0
0
0
0
0
0
Plants
describe the movement of substances in plants
understand the structure of xylem vessels, sieve tubes and companion cells
understand how the structure of xylem vessels suits them for their function
describe the movement of water through a plant
describe the processes involved in transpiration
describe the effect of external factors on transpiration
discuss adaptations in plants to conserve water
understand the function of phloem in the transport of substances in plants
explain how the structure of the phloem is suitable for its function
transport in plants
vascular bundle
f
\
xylem
phloem
I
I
uptake of
water from soil
translocation movement of food
water in soil
around root hairs
food
storage
across cells of
root to xylem
perennating
organs
I
movement
through xylem
I
movement
through eel lls of leaf } transpiration -
potometer
movement through
stomata to air
The importance of transport in plants
There is much activity going on inside a plant, but it is difficult to imagine that
j ust by looking at one. Th e main activity is photosynthesis. During daylight,
14 · Transport in Plants
all the leaves of a plant are actively photosynthesising and therefore need all
the substances necessary to carry out this process. Transport in plants is thus
rela ted to photosynthesis as substances are transported to and away from
leaves (figure 14. 1).
li;il';' - - - - water may travel
up to 1000 ft against
gravity without a
pump I
root extends {
further out below
the soil than the
branches and
leaves above
Rgure 14.1 Transport In plants.
Photosynthesis is summarised by the equation:
light
carbon dioxide + water ----+ glucose + oxygen
chlorophyll
• The gases carbon dioxide and oxygen move between the atmosphere and
the leaf. The leaves are thin, broad and flat and cover a wide surface area so
that diffusion is adequate to transport these gases.
• Light rays from the Sun pass into the leaf and get to all the
photosynthesising cells.
• Chlorophyll is p resent in the leaf cells.
• Water must be transported from the soil through the roots to the leaf.
Dissolved salts are present in the water.
• Some of the manufactured food is transported away from the leaves to be
used and/or stored in other pans of the plant.
~
l:fQ1
V'-'
Use a table to show the substances
that are transported in a plant. Indicate
where the substance is transported
from and to, and its importance to the
plant.
xylem vessels >
phloem tubes >
Transport systems of plants
The transport system of plants is much simpler than that seen in animals.
There is no pump (heart) or specialised transport medium (blood). Ir is made
up of two types of transport vessel:
• xylem vessels, which carry water and minerals;
• phloem tubes, which carry food materials that the plant has made.
Structure of xylem vessels
llrffilhll
Xylem vessels are long, very narrow, tubes formed from columns of elongated
cell s that are joined end to end. The end walls of the cells have disappeared, so
a long, open tube is formed . These cells are all dead and con ta in no cytoplasm
or nuclei (figure 14.2). The cell walls become thickened with tough lignin .
Lignin is very strong and so xylem vessels help to support the plant by
keeping them upright. Wood is composed almost entirely of lignified xylem.
1.61
Life Processes and Disease
space (no
cytoplasm)
where water
passes
cB
thick cell
wall
containing
lignin
t
gap where
end walls
of two cells
have been
lost
transverse section
longitudinal section
Figure 14.2 Transverse and longitudinal sections through xylem tissue.
Structure of phloem tubes
..1@t:llelff100
sieve tube element >
companion cell >
Phloem tubes are also made up of cells joined end to end. However these end
walls do not break down completely, but become perforated with small holes .
These perforated end walls are called sieve plates. Each cell, called a sieve
tube element, contains living cytoplasm, but no nucleus. The cell wa lls do not
contain lignin. Each sieve tube element has a companion cell next to it. The
companion cell has a nucleus which probably controls both cells (figure 14.3).
The end walls of the two cells are
not completely broken down.
This is called a sieve plate and
has small holes.
companion
cell
I
sieve
plate
transverse section
'-··
Companion cell containing a
nucleus and cytoplasm;
found next to a sieve
tube element.
sieve plate
sieve plate
._#----l'*'i!.,...=--i.;;+-~-fl!"il!-~• ~
-
section cut
through phloem
H+- - cytoplasm - seen
as strands
cell wall does not
contain lignin
·-·
Transverse section
of these cells.
Companion cells are seen
when the section runs
through the sieve plate.
longitudinal section
(a)
(b)
Figure 14.3 (a) Transverse and longitudinal sections of a sieve tube element and a companion cell. (b) Longitudinal section through a phloem tube
and transverse section across it.
162
14 ·Transport in Plants
Vascular bundles
vascular bundles >
Vascular bundles are made up of bundles of xylem vessels and phloem tubes
close together. The arrangement of these bundles in roots and shoots is shown
in figures 14.4, 14.5 and 14.6.
phloem
xylem
xylem is made
up of xylem vessels
which run the length
of the stem, trunk,
branch, etc.
a number of
xylem vessels
lie close together
phloem is made up
of phloem tubes
which run the length
of the stem, trunk,
branch, etc.
I
I
made up of a
number of
xylem vessels
xylem
phloem ~
vascular bundle
I
made up of a
number of
phloem vessels
Agure 14.4 Transverse section of a root of a
dicotyledonous plant.
xylem
phloem
J
vascular
bundle
Figure 14.5 Transverse section of a stem of a
dicotyledonous plant.
Figure 14.6 Diagram relating the
transverse section to the longitudinal section
of a stem.
Movement of water through a plant
~
ll:Q2
V'-1
How are xylem vessels and phloem
tubes arranged in a vascular
bundle?
(ii) Explain how the structure of the
(a) xylem and (b) the phloem are
suited to their function.
The movement of water th rough a plant can be broken down into five stages
(Figure 14.7). The numbers in the following text relate to numbers in the
figure).
(i)
~
ll:Q3
V'-1
(i)
What are the functions of vascular
bundles?
(ii) Draw a sketch to show how they
are arranged in the stem of a
dicotyledonous plant.
Figure 14.7 Diagram showing the movement or water through a plant.
163
Life Processes and Disease
1
2
3
4
Practical activity
SBA 14.1: The rate of transpiration,
page 353
CHAPTER9
X
~
IT:.Q~
V'-....1
Describe the route taken by a water
molecule from the soil to the air as it
passes through a plant.
5
Absorption of water by the root hair cells.
Movement of water across the root cortex to the xylem.
Movement of water up the xylem.
Movement of water across the leaf cells.
Movement of water from the leaves.
Evaporation of water from the leaves
Stomata are found on the underside of leaves (chapter 9). Just inside the
stomata are the leaf cells which contain and are surrounded by water. The
concentration of water molecules inside the cells is higher than in the air space,
and higher there than outside the leaf. So some of the water evaporates from
the cells into the air space and diffuses out of the leaf through the stomata,
down the concentration gradient (figure 14.8).
Figure 14.8 Diagram showing how water evaporates from cells around the air space and diffuses
out of the stoma.
transpiration >
All the cells of the leaf
obtain water by osmosiS ---+-++from the xylem.
Water evaporates -~~__,
from the cells around
the air space.
Transpiration is the loss of water by evaporation from the surface of leaves.
This constant loss of water from the leaves creates a 'pull' of water through
the plant. During the day, water is also constantly being taken up from the top
of the xylem vessels to supply the photosynthesising cells in the leaves. This
reduces the pressure at the top of the xylem vessels, and water thus flows up
to the top because the pressure below is greater. This constant flow of water
through the plant is known as the transpiration stream.
The conversion of liquid water into
watervapour as it lea ves the cells and
enters the air space requires heat. Using
Water moves from
heat to convert water into water vapour
cell to cell by osmosis.
helps to cool the plant.
Water moves out
n.~~+:.._ of the xylem to
surrounding cells.
Movement of water
within the leaf
As water evaporates from the
surfaces of cells near the air spaces,
its concentration in those cells
Water diffuses out
(A in figure 14.9)) is lowered. Its
of the plant. -+-__.,•
concentration in the adjacent cells (B)
is now higher than in the A cells. This
Rgure 14.9 Diagram showing the movement of water from the xylem, through the cells of the resu lts in the movement of water from
leaf, to the air space and then out of the leaf as water vapour.
the B cells to the A cells by osmosis.
164
14 ·Transport in Plants
~
IT:QS
Water is drawn through all the cells of the leaf by osmosis as it moves
towards the air space and then out of the leaf.
Describe how water travels from the
xylem in a leaf to an air space.
Movement of water up the xylem
\../'-I
lmlet4il•leN
m.t¥UeleM
~
IT:Q6
\../'-I
List the processes by which water
travels up the xylem.
-
glass tube
-
water moves
higher up a
narrow tube
Water moves up and through the xylem vessels because of three factors.
• Capillarity - When a thin straw is placed in a glass of water, the water
rises a little up the straw (figure 14.10). This is due to attraction between r
the water molecules and the walls of the straw, which is called adhesion.
Water molecules tend to stick together, which is known as cohesion. Thus;
water molecules stick together and to surfaces of narrow tubes and the
water rises up the tube, which is called capillarity. The narrower the straw,
the higher the water will rise. Xylem vessels are extremely narrow and the
attraction between the water molecules and the xylem walls is great.
• Root pressure - Water constantly moves into root cells by osmosis because
the presence of sugars and other dissolved substances in the root means
that the water concentration can never be as high in root cells as in the soil.
Water absorbed into the plant from the soil creates a pressure in the root
xylem. The pressure there is greater than in the leaf xylem because water
is being pulled out of the leaf xylem by transpiration. So water moves from
the high pressure in the roots up the xylem vessels in the stem to the low
pressure in the leaves (figure 14.11 ).
• Transpiration pull - The flow in the system is mainly by cohesive forces
holding water molecules together and the loss of water by evaporation in
the upper areas of a plant creating a tension that 'pulls' water upwards. This
is the transpiration pull.
a lot of w ater coming
from the roots creates a
lower pressure in this
region since water is
lost at the top
xylem, made up of
narrow xylem vessels
\' rf+--+--r--H----r- water molecules
are attracted to
,_
the walls of the tube
water
Figure 14. 1O Water moves up narrow
tubes.
Figure 74. 11
Low pressure at the top, high pressure below and water is pushed up.
Movement of water across the root cortex
Water moves between the cortex cells of the roots by osmosis (figure 14.12,
overleaf). As water enters the xylem, the cells next to the xylem now have a
lower concentration of water. Water then moves into those cells from adjacent
cells. These cells now have a lower concentration of water and water flows
into them by osmosis. In this way, water moves from the root hair cells to
the xylem.
165
Life Processes and Disease
cortex cells
xylem vessels
t
t
1 water moves into the
xylem and is pulled up
r--.
~*
- ----'2 water moves from these
these cells (B) have-----'
more water than cells A
and so water moves by
osmosis to those cells
cells into the xylem and so
these cells have less water
than the ones next to them
Agure 14.12 Water moves between all the cells of the root cortex by osmosis.
Absorption of water by the root hair cells
~
l:W:Q7
V'-1
Describe how water travels from the
soil to the xylem vessel in the root.
The soil particles are surrounded by a film of water which contains some
dissolved salts. Inside the root cells, there are sugars and other dissolved
substances at a much higher concentration. So water is continuously moving
into the root cells by osmosis (figure 14.13).
The root hair cells extend into the surrounding soil and the surface area for
absorption is thus increased.
soil particle
cortex cells
water moves from the root hair cells
to the cortex cells and so water is
pulled into the root hairs
xylem vessels
water moves across
these cells to the xylem
Agure 14.13 Water moves into the root hair cells.
Transpiration
Transpiration is the evaporation of water from a plant. It is important beause:
• it pulls water up to the leaves for photosynthesis;
• the moving water carries dissolved mineral salts up to the leaves;
• the evaporation of water cools the plant.
166
14 ·Transport in Plants
transpiration rate >
• The rate at which a plant takes up water depends on the rate at which
it is lost from the plant, called the transpiration rate. The faster the
transpiration rate, the faster the plant takes up water. Environmental
factors affect the transpiration rate.
• Temperature - With high temperatures, as on a hot day, evaporation
occurs rapidly. Transpiration rate increases as temperature increases.
• Humidity - With high humidity, the air is almost saturated with water r
vapour. So the concentration gradient of water between the air spaces and
the outside air is low and the rate of evaporation of water through the
stomata is slow. Transpiration decreases as humidity increa ses
(figure 14. 14).
• Air movement (wind) - In windy conditions, water vapour is carried
rapidly away from the leaves and the rate of transpiration is fast. During still
conditions, the water vapour remains around the leaves and transpiration is
slow. Transpiration increases as wind speed increases (figure 14.15) .
• Light intensity - During bright light, the stomata are fully opened. This
may be to supply carbon dioxide for photosynthesis. With stomata fully
open, the rate of transpiration can be high. With dim light, the stomata
almost close and transpiration is slow.
LJ
HO
o/
i?JwH
,O
H0
H.,Q .,,,,,.---.
~ H· 0
As water molecules
H,O Q < diffuse out, they are taken
away by wind currents.
11 0
The concentration of water
molecules outside will
always be small and so there
~n
::)
Agure 14.14 High humidity means that the
concentration gradient of water molecules inside
compared to outside the plant is low.
~
IT:Q8
l../'-1
(i) What is transpiration pull?
(ii) What is the transpiration stream?
(iii) What is transpiration?
xerophytes >
mesophytes >
hydrophytes >
water molecules
taken away by
wind currents
0
"'II be oot ootw""' d;Ho•oo.
Figure 14. 15 Windy days result in more
rapid transpiration.
When there is very little water in the soil, the stomata almost close. This
reduces the rate of transpiration to conserve water. The plant cells become
flaccid and the plant wilts as the water lost in transpiration cannot be replaced.
Adaptations in plants to conserve water
Plants need water for their existence. Transpiration occurs constantly, so a
supply of water from the environment is vital. Plants that live in places where
water is in short supply are called xerophytes. They show striking adaptations
which:
• reduce the transpiration rate;
• m aximise water uptake from the environment.
Other plants are grouped into three categories.
• Mesophytes are plants that live in areas where water is readily available.
• Hydrophytes are plants that live in very wet, freshwater environments
such as ponds, lakes and rivers.
167
Life Processes and Disease
haloph es >
• Halophytes are plants Lhat live in water with a high concentration of salt,
such as in salt marshes, swa mps or areas close to th e sea.
Xerophytes may have any of the following fea tures:
• fine spine-like leaves to reduce the number of stomata and so reduce
transpiration;
• thickened stems or leaves capable of storing la rge amounts of water;
• an extensive root system to absorb water quickJy when it rains;
• a thick epiderm is covered with a thick waxy cuticle to reduce water loss and
reflect light and infra -red radiation (so the plant remains cooler);
• the ability to trap carbon dfoxide at n ight so that the stom ata can be closed
during the da y;
• other features such as sunken stomata, rolled leaves and interlocking hairs.
Table 14.1 compares the adaptations of a xerophyte (e.g. cactus) and a
h ydrophyte (e.g. water lily) to the environments in which th ey live.
Xerophyte
Hydrophyte
Description of
environment
Very hot, sunlight intense as few or no Still, fresh water from 15 cm to 2 m
clouds, no larger shade trees, soil hot deep
and dry
Description of
leaves
Small spikes, not green, usually black Broad, flat, green, lie on surface of
or grey in colour
water, stomata on upper surface
Description of
stems
Thick, green, with thick cuticle
Colourless, entirely under water and
extending to roots in mud at bottom
Table 14. 1 Comparison of a xerophyte and a hydrophyte
Uptake and movement of mineral salts
Mineral salts are absorbed by the root hairs as ions dissolved in soil water. They
are taken up using energy because the concentra tion inside the root is much
higher than outside. They are then carried throughout the plant in the xylem.
Transport of manufactured food
translocation >
168
The soluble product o f photosynthesis are sugars (ma inl y sucrose) and amino
acids. These are transported in the phloem tubes. The transpo rt of organic food
through a p lant is called translocation . This manufactured food is transported
from the leaves (called the source) to wherever it is needed (called the sink) for
respiration or storage.
14 ·Transport in Plants
Phloem and the movement of food
Plants rely on pressure gradients to move their phloem sap. The pressure- flow
hypothesis, also called the mass fl ow hypothesis, was proposed by Ernst Munch
in 1930 to explain h ow the phloem transports food (figure 14. 16).
leaf
pholem
sieve tube
sugar is made during
elements
photosynthesis ..._..;;;:_..__ _ _ _ _"
_ " )- - -
sugar lowers the
water potential
(increases the
concentration)
which draws in
water and raises
the pressure
L - - - L - --
roots
water
sink
sucrose solution
transported from
high to low pressure
sucrose enters the
roots and lowers
the pressure in
pholem as water
is lost
Figure 14. 16 The pressure-flow hypothesis.
1
IT:Q9
Sugar made during photosynthesis moves into the sieve tubes at the source
(leaf) which makes it more concentrated there.
2 Water then moves into the sieve tubes since it is now more concentrated.
3 The uptake of w ater causes the pressure to build up in the sieve tubes at
the source (leaf) which pushes the sap down.
4 Unloading of sugar at the sink (other parts of the plant) relieves the
pressure since water is also lost at the sink.
Sugar is thus translocated from the leaf to th e root and other parts of the plant
that are respiring, storing and using the sugar.
How are sugars transported in
the phloem?
Evidence that phloem translocates organic food
~
Radioisotopes
V...J
If a plant is supplied with carbon dioxide containing radioactive carbon it
~
V...J
IT:Q·1 0
What is translocation?
will make food containing radioactive carbon. If the source of radioactive
carbon is removed then, after a while, the radioactivity is detected only in the
phloem tubes. This means that the food which the leaves h ave made is being
transported in the phloem .
169
Life Processes and Disease
Ringing
The phloem tu bes in a woody stem are j ust underneath the bark. If a ring of
bark containing the phloem is removed, sugars accumulate above the ring,
resulting in a slightly swollen appearance (figure 14.1 7).
food cannot get
to lower regions
Figure 14. 17 Removing a nng of bark also
removes the phloem.
Using aphids
Aphids are insects that feed on plant juices by pushing their mouth pa rts
(stylets) into phloem tubes. If the mouthparts of a feeding insect are cu t off,
phloem sap keeps flowing out through the stylets (figure 14. 18). The sap can
be analysed and shows the presence of organic material.
~
(a)
(b)
l'.tQ·11
Mouthpart cut off and
left In the plant.
L.l'--1
Describe three ways in which the food
manufactured during photosynthesis is
used by a plant.
stylet
oozing 'food'
Mouthpart (stylet) of aphid penetrates
the phloem. It sucks 'food'; this is
how it obtains food for energy.
Aphids are parasites of plants.
Figure 14. 18 If the mouthparts of (a) a feeding aphid are cut off (b) they continue to ooze sap
fY
-
Chapter summary
•
•
•
•
•
•
•
•
•
•
•
All materials needed for photosynthesis must be transported to the leaves of a plant.
Water is transported from the soil.
Carbon dioxide diffuses in through the stomata.
The products of photosynthesis, manufactured food and oxygen, must be transported
from the leaf.
Manufactured food is transported in the phloem to various sites in a plant.
Oxygen diffuses out through the stomata.
The structure of the xylem is suited to its transport and support functions.
The structure of the phloem is suited to its transport function.
Transpiration is the evaporation of water from the leaves of a plant.
The rate of transpiration is influenced by many external factors.
Translocation is the transport of organic food through a plant.
ITQ1
Substance Taken from
Transported to
Importance to plant
Means of
transport
carbon
dioxide
air surrounding leaves all photosynthesising
cells
needed for
photosynthesis
diffusion
water
soil - water forms a
thin layer around soil
particles
needed for many
purposes including
photosynthesis
xylem
all cells
(continued)
170
14 ·Transport in Plants
Substance Taken from
Transported to
Importance to plant
Means of
transport
minerals
soil - present as
soluble ions in water
all cells
healthy growth
xylem
organic
food
(glucose)
leaf cells where it was all cells
made
all cells must respire to phloem
have energy for giving
processes
oxygen
leaf cells
oxygen produced during diffusion
photosynthesis and not
needed for respiration
must be removed
outside the leaf
ITQ2 (i) The xylem vessels are positioned together in the vascu lar bundles
in a region where only xylem vessels are found. Similarly, the phloem tubes
and their accompanying comparuon cells are positioned together in a part of
the vascular bundle where only these structures are found.
(ii)
(a) Xylem vessels are elongated, tubular and made up of dead cells
thus providing a water-proof vessel for the transport of water and absorbed
minerals.
(b) Phloem is also elongated and tubular but made up of living cells. Energy is
thus available for the transport of manufactured food.
ITQ3 (i) The vascular bundles consist of xylem vessels and phloem tubes.
The xylem vessels transport water containing dissolved minerals from the roots
to the leaves of the cell. The phloem tubes transport organic food from the
leaves where it is produced to all the cells of the plant.
(ii) Your sketch should look like figure 14.5.
ITQ4 soil - root hair cell - root cortex cells - xylem - palisade mesophyll
- air space - stoma - air
ITQ5 Water travels by osmosis out of the xylem and then travels across the
cells of the leaf to an air space by osmosis also. The water is moving down a
concentration gradient, from a high concentration of water molecules to a
lower concentration.
ITQ6 Water travels up the xylem by:
• root pressure;
• transpiration pull;
• capillarity, coh esion and adhesion.
ITQ7 Water moves by osmosis into the root hair cell from the soil. The
water then moves across the cells of the root cortex to the xylem. Th e water is
moving along a concentration gradient. As water travels up the xylem, more
water moves into the root from the soil .
ITQS (i) The flow in the xylem is mainly by cohesive forces holding water
molecules together and the loss of water by evaporation in the upper areas of
a plant creating a tension that 'pulls' water upwards. This is the transpiration
pull.
(ii) The water moving up the xylem is the transpiration stream.
(iii) Transpiration is the loss of water vapour from the leaves of a plant.
ITQ9 Sugar is transported as sucrose which loads into the phloem from the
leaf (source). This increases the concentration of the solution in the phloem,
which draws in water. This increases the pressure of the solu tion. The pressure
is lower at the roots and movement thus occurs from the leaf to the root. At
the root (sink), the pressure is lower because the sugar moves into the roots
thereby lowering the concentration of the solution, causing water to move our.
ITQ10 Translocation is the movement of manufactured food from the leaves
to all the cells of a plant.
171
Life Processes and Disease
ITQ11
• It is stored as starch in plant cells.
• It is used for respiration to release energy for use by plant cells.#
• It is used for the production of fruits and seeds during reprodu ction.
Examination-style questions
(i)
State the functions of:
(a) phloem;
(b) xylem.
(ii) Describe how aphids can be used to investigate the function of phloem.
(iii) Explain why it is necessary to water many potted plants at least once a day.
2
(i) Define transpiration.
(ii) State three environmental factors that affect the rate of transpiration.
(iii) Using an annotated diagram only, describe how the photometer can be used to
measure the rate of transpiration.
3
(i) Suggest three ways in which transport in plants differs from transport in animals.
(ii) Suggest two ways a xylem vessel is similar to an artery.
(iii) A plant may be 50 metres in height and does not have a pump to push water to
the leaves at the top. Describe how water travels in the xylem, from the soil to the
uppermost parts of a plant.
4
Two tubes A and B were set up as shown below. Both tubes were left indoors for 50
minutes and then taken outdoors for another 50 minutes. The tubes were weighed every
1Ominutes. The table shows the results obtained.
, ~·
cotton wool
- J..~
water
Tube A
Time (min.)
0
10
TubeB
20
30
40
50
60
70
80
90 100
Tube A (g)
305 294 285 272 262 250 220 206 184 150 120
Tube B (g)
280 280 280 279 279 279 278 278 278 278 278
(i) State the processes by which water was lost form (a) tube B, and (b) tube A
(ii) Explain the role of the cotton wool in the investigation.
(iii) Plot a graph of the results for both tubes A and B on the same page.
(iv) Explain fully, the differences seen between tubes A and B.
(v) Describe the differences seen for tube A between the first and second parts of the
investigation.
(vi) Explain fully the differences seen for tube A between the first and second parts of the
investigation.
172
Storage in Plants
and Animals
0
0
understand the importance of food storage in living organisms
identify some products stored and the sites of storage in plants
,/) draw and annotate stages in germinating seeds
ZJ describe the structure of a dicotyledonous seed
Q) describe the processes taking place within a seed during germination
,/) draw buds from plant storage organs
0
identify some products stored and the sites of storage in animals
food storage
importance
I
I
(
plants
roots
stems
leaves
'
animals
seeds
fruits
liver
develo~ment 1
of em~
fat
deposits
provide for
periods of
scarcity
vegetative
reproduction
overcome the
need for
continuous
food intake
Why do organisms store food?
Manufactured food (from photosynthesis using the Sun) is the source of
chemical energy for aU living organisms. Glucose, which is the chem ical
compound made during photosynthesis, is oxid ised to release energy. All living
things depend on this energy fo r life processes to take place. Some of this food,
however, is stored. Plants and animals store food in their bodies for the same
reasons, some of which are listed below:
• to overcome the need for contin u ous manufacture; during the night,
photosynthesis stops because there is no light;
• to overcome the need for continuous food intake; animals cannot eat
continuou sly because other activities are also important;
• to provide for periods of scarcity, like droughts and famines;
• to provide for special functions (muscle cells need their own store of food);
• to produce reproductive structures (fruits, seeds and embryos must store
food).
Food storage in plants
The food made by a plant during photosynthesis may be stored temporarily
as starch in the leaves. For longer periods of time, other parts of the plant
are used, such as roots, stems, fruits and seeds. Table 15.l (overleaf) lists the
importance of the various sites of food storage in a plant.
173
Life Processes and Disease
Site of storage
Importance of storage
Leaves
The cells of the leaf need to respire and there is a store of glucose as starch in starch grains.
cabbage
bokcho
Sometimes underground leaves are used to store food.
omon
garlic
leaf, swollen with food
-
bulbs e.g lily
Stems
Some stems can become swollen with stored food.
Some plants can protect themselves against unfavourable conditions of weather by reserving food in underground stems which
will be used to generate new plants.
harsh environmental
conditions
-food stored
in 'good' conditions
plant stores food
plant is still 'alive'
underground
good conditions again
- new growth seen
(continued)
174
15 · Storage in Plants and Animals
Site of storage
Importance of storage
Underground swollen stems are sometimes used to store food.
- - new shoot
growing
from rhizome
stem tuber - the tip
of an underground
stem is swollen
with food
~ _ y roots growing
r
rhizome - food stored
in an underground stem
from rhizome
' r-- roots
stem tubers, e.g. Potatc. ,
- -bud - grows into
new shoot
corm - the base of a
vertical stem becomes
swollen with food
rms e g eddo dasheen
Above-ground swollen stems are sometimes used to store food .
...._ __,.,__ swollen stem
stores food
sug
ne
(continued)
175
Life Processes and Disease
Site of storage
Importance of storage
Roots
Underground swollen roots are sometimes used to store food.
root tuber - tip of
root swollen with food
root tubers 1:;- 'd r
-
veet potato
tap root - swollen
main root
These swollen organs (like underground stems) are called perennating organs. They are filled with food stores built up in the
time of good growing conditions. They lie protected in the soil. The food store enables the plant to grow quickly when good
conditions arrive again.
Fruits
Most fruits are adapted to protect seeds and to help their dispersal. Succulent or juicy fruits store mainly sugars to attract
CHAPTER 21 animals that use the fruits as a food source. The animals help to disperse the seeds that are in the fruit (chapter 21).
fleshy edible
part of fruit
seeds
pumpKJr,
seed
arape
Seeds
Seeds contain a store of food for germination. The cotyledon(s) or endosperm of seeds store starch, protein and lipids. This store
is used up during germination as the embryo develops. The seed respires, using the stores to provide energy for growth and
development into a seedling. The stores are needed until the seedling develops leaves and can photosynthesise.
Table 15.1 Sites of food storage 1n pants.
176
15 · Storage in Plants and Animals
Germination
mu1 ..111m
1m.rmm
endosperm >
Germination is the growth of the seed into a seedling. The seed conta ins the
embryo which is made up of the plumule (grows into the shoot) and the
radide (grows into the root). The parent plant sends the embryo out into the
world with a store of food in the cotyledon and/or endosperm. The embryo
is protected by a tough testa (figure 15.1) .
~
IT:Q2
L)'....J
(i) What is a perennating organ?
(ii) Distinguish between a stem tuber
and a root tuber
(Iii) What is the importance of the food
stored in each of the following - a
fruit, a seed, a leaf and an above
ground stem?
hilum
- - --+--- micropyle (tiny hole)
micropyle
radicle
-
(a)
J
embryo
-+-- -- plumule
(b)
Agure 15. 1 A seed (a) in side view, (b) in section.
~
IT:Q3
L)'....J
(i) What is germination?
(ii) Describe the differences between
epigeal germination and hypogeal
germination.
In its inactive and dehydrated state, a seed can stay a seed for a long time. It
is said to be dormant. When conditions are favourable, germination begins
(figure 15.2). Germination requires three conditions:
• water - moves rapidly into the micropyle and to all the cells. Enzymes are
activated and starch is broken down to glucose for respiration;
• ox ygen - needed for respiration ;
• warmth - to provide the optimum temperature for enzymes.
The energy demands of a germinating seed are very Wgh. Energy is released
from the stored food by respiration and is used for growth of the rad icle and
plumule. The radicle grows down into the soil and the plumule grows upward
to develop into the shoot above ground. When the first leaves develop, the
seedling begins to photosynthesise to make its own food. It continues to grow
and develop more leaves and a root system until it is an adult plant ready to
produce flowers.
Epigeal g ermination - cotyledons brought above ground
cotyledons open, are green and photosynthesise
for a while
food store used
up as grows
Hypogeal g ermination - cotyledons remain below ground
leaves grow and begin
to photosynthesise -
leaves grow and
photosynthesise
_ plumule
iil
(a)
(b)
Figure 15.2 Germination.
177
Life Prq~esses a!1d .Diseas~
~
IT:Q't
V-...J
Why would a human being die after 10
minutes without oxygen but could go
for 5 days without food?
~
IT:QS
V-...J
How do humans become obese? Why
are wild animals never obese?
Food storage in animals
Animal cells also store glucose, bur nor as search. Animals store glucose
as glycogen in granules. Cells respire continuously and animals breathe
continuously for their supply of oxygen bur they do not feed concinuously for
their supply of glucose.
Fats
Triglycerides (fats) have a higher proportion of h ydrogen than either
carbohydrate or protein. This means fats are a more concencrated source of
energy than eicJ1er carbohydrate or prootein. One gram of fat yields twice the
amount of energy that a gram of carbohydratecan yield. In mammals, excess
fat is laid down for storage under the skin. When we eat excess food, we
become obese, 'fat'. Animals that live in cold conditions have a thick layer of
fat (blubber) under the skin which serves both as an energy store and provides
insulation for the extreme cold (figure 15.3).
Glycogen
As blood passes through the liver, the excess glucose (from a meal) is changed
to glycogen and stored. The liver is the main storage organ for glycogen.
Glycogen is also stored in the muscles where it can be qu ickly accessed for
muscle contraction. The liver also stores minerals (iron and potassium) and
the vitamins A, D and B12 • After a meal, vitamins, minerals and other nutrients
from the food pass from the intestine into the blood. This nutrient-rich blood
then passes through the liver where the vitamins and minerals in excess are
stored for times when they are lacking in the blood (figure 15.4).
hepatic vein
Rgure 15.3 Penguins and whales need
extra fat stores to stay warm in polar
conditions.
bile duct
~
IT:Q6
hepatic portal vein
from ileum
Rgure 15.4 Nutrient-rich blood travels directly to the liver from the Intestine.
V-...J
What is the importance of food stored
in:
(i) a seed
(ii) an egg
(iii) the liver
(iv) a fruit
(v) a tap root?
178
Eggs
Embryo birds and reptiles (snakes, turtles, alligators, etc.) develop inside a shell
from cJ1e time eggs are laid until they hatch (figure 15.5). The egg white is
made up of water and a protein called albumen. The yolk contains protein, far
and lecithin (a natural emulsifier).
15 ·Storage in Plants and Animals
yolk sac
stalk
amniotic cavity
allantoic cavity
chorionic cavity
yolk sac
Figure 15.5 The eggs of birds and reptiles store food for the developing embryo.
~
'I Chapter summary
•
•
•
•
•
•
•
•
•
•
Glucose is manufactured by plants during photosynthesis; some of it is stored
Plants and animals store food in their bodies
Plants store food in their leaves, stems, roots, fruits and seeds
Animals store glucose as glycogen for respiration; plants store glucose as starch
One gram of fat yields more energy than one gram of carbohydrate
Germination is the growth of a seed into a seedling
Water, oxygen and warmth are needed for germination
In animals, the liver is an important storage organ
Glycogen is stored in the liver and muscle of animals
Birds and reptiles store food in the eggs for development of the embryo into a
hatchling
So that food is available when needed.
To prevent shopping for every meal..
To have the choice to plan a healthy and balanced <lier.
ITQ2 (i) An organ which enables plants to survive adverse conclitions, such
as cold, extreme heat, lack of light or d rought.
(ii) A stem tuber is an underground stem swollen with food and a root tuber
is an underground swollen root.
(iii) To attract agents of dispersal for the seeds.
To store the energy needed for germination.
To store the energy needed for the reactions that take place in the leaf cells.
To help the plant survive adverse weather conclitions.
ITQ3 (i) Germination is the growth of a seed into a seedli ng.
(ii ) In epigeal germination, the cotyledon is brought above the ground; in
hypogeal germination the cotyledon remains underground.
ITQ1
179
Life Processes and D isease
ITQ4 Oxygen is not stored but food is; both are needed at every moment for
respiration.
ITQS Humans over-eat; wild animals have no fast-food outlets or groceries.
Wild animals hunt for every meal, humans may have passive lifestyles and
food is readily availableITQ6 (i) Food stored in a seed is used for germination of a seed into a
seedling.
(ii) An egg stores food for the developing embryo.
(iii) The liver stores glycogen, vitamins etc. so that when lacking in the cliet,
they are still available for metabolism.
(iv) Food stored in a fruit attracts animals to eat the fruit and so disperse the
seed (s).
(v) After adverse conditions, the tap root
generates a new plant using the stored food.
Examination-style questions
{i) List three reasons why living organisms may need to store food.
{ii) Copy and complete this table.
Storage organ in plant Importance
fruit
seed
root tuber
{iii) Discuss the importance of storing glucose in plant and animal cells.
2
The weight of a germinating seedling was measured over 7 days and recorded in the table
below.
Day
Weight in grams
1
10
2
10
3
6
4
4
5
12
6
15
7
20
{i) Plot a graph of the change in weight of the seedling over the 7 days.
{ii) Describe the changes seen in the graph.
{iii) Explain the changes seen in the graph.
{iv) Distinguish between epigeal and hypogeal germination.
3
180
{i)
Explain the importance of storage in:
{a) an animal cell
{b) the liver.
{ii) Use a diagram to show the importance of the hepatic portal vein.
{iii) What is the importance of food stored in {i) an egg and {ii) a seed?
Eixcretion,
Osmoregulation and
Homeostasis
Q) understand the importance of excretion in living organisms
Q) distinguish between excretion, egestion and secretion
Q) give examples of substances excreted by plants
Q) give examples of substances excreted from animals
Q) understand how substances are excreted from plants
Q) understand how substances are excreted from animals
Q) understand the structure of the excretory system
Q) relate the structure of the kidney to its excretory function
Q) relate the structure of the kidney to its osmoregulatory function
Q) understand homeostasis
Q) understand the control of blood glucose
Q) understand the control of body temperature
Q) understand the control of the amount of carbon dioxide in the body
protein - source of urea
excretion of metabolic
waste (especially
nitrogenous waste)
f
osmoregulation
(
homeostasis
control of
• amount of
water in body
• blood glucose
• body temperature
• C02 concentration
in blood
'
antidiuretic
hormone (ADH)
'
animals
plants
excretory
system
kidney
failure - dialysis
I
variation in
concentration
of urine
kidneys
I
pressure
filtration
I
nephrons
I
selective
reabsorption
L_ urine _ )
Metabolism
The sum total of all the chemica l reactions going on in ce!Js is known as
metabolism . Chemical reactions must occur in a!J li ving ce!Js, and therefore
181
Life Processes and Disease
i@iji§itelelJ
defecation >
~
l'.f:Q·
1
l..)'-.J
all living organisms, to susta in life. These metabolic reactions produce a range
of waste produces, called excretory products, which muse be eliminated from
the organism. The removal of the excretory products is called excretion. Many
of these excretory products are toxic and slow down metabolic reactions. If
these substances were allowed to accumu late in the body, they could damage
and kill body cells. They n eed to be continually removed.
Excretion must not be confused with the removal of faeces (defecation.)
during egestion in humans (figure 16. l ). Defecation or egestion is the removal
of undigested food but excretion is the getting rid of waste products produced
by cells during metabolism. Undigested food sin1ply passes through the
alin1entary system and is not absorbed into the cells of the body. It passes out
of the anus as faeces.
Excretion must also not be confused with secretion, which is the release of a
substance, such as a hormone, from cells (figure 16.1).
Explain the terms 'metabolism',
'excretion', 'egestion' and 'secretion'.
r ,Hf-- - -r---+-- secretion of female
homlones into blood
by the ovaries
~?""9---1-- excretion of urine
containing metabolic
waste by the urethra
excretion of urine
containing metabolic
waste by the urethra
secretion of male-;----------t~~
hormones into
blood by the
testes
Figure 16.1 The difference between egestion, secretion and excretion.
Excretory products in animals
Waste products of respiration
All cells respire co release energy which is used to do the work necessary to
keep the cell , and therefore the organism, alive. During respiration, carbon
dioxide is also produced. Carbon dioxide is dangerous to living tissue because
it increases the acidity of fluids which can affect other reactions. ln humans,
carbon dioxide is transported in the blood to the lungs and removed from
182
16 ·Excretion, Osmoregulation and Homeostasis
CHAPTER 12 ) {
CHAPTERS 10, 19
the lungs during exhalation (chapter 12). Other animals have similar ways of
removing the carbon dioxide.
Some of the energy produced during respiration is converted into heat
energy, the accumulation of which increases the temperature of the body.
At high temperatures, enzymes can be denatured (chapter 10) which means
reactions will stop. Excess heat is lost through the skin (chapter 19).
During exercise, when the rate of respiration is increased, the excretory
'
products of respiration are being produced at a faster rate. Breathing rate
increases to get rid of the excess carbon dioxide and sweating occurs to get rid .
of the excess heat faster.
Waste products from red blood cells
A red blood cell has a short life span of about three month s. After this
time, it is destroyed in the liver or spleen. The red blood cell is packed with
haemoglobin, a protein pigment which transports oxygen. The excess protein
portion is broken down into excess amino acids and reused by the body. The
iron is extracted, stored, and may be reused later. The remainder is broken
down into bile pigments and is later excreted by way of bile into the gut and
out with faeces.
Waste products of protein metabolism
Proteins are essential in the diet. However, proteins contain nitrogen and the
breakdown of protein that is not needed by the body produces nitrogenous
waste which is converted to urea (figure 16.2). Urea is removed by the kidneys
during the production of urine (discussed later in this chapter).
Excretory products in plants
Waste products of photosynthesis
CHAPTER9
X
Plants photosynthesise or manufacture food from inorganic compounds. This
food can then be used by the plant to make energy. During photosynthesis,
oxygen is produced as a waste product. It is lost from the leaves of the plant
through the stomata (chapter 9). Water is also a product of photosynthesis, but
this is either needed by the cells or lost from them in transpiration.
liver - the amino acid groups (NH2)
of the excess amino acids are
converted to ammonia (NH3, highly
toxic) and urea (non-toxic, soluble)
absorption of amino
acids into blood
kidneys filter urea out of blood
urine, containing urea
collects in bladder
Blood rich in amino acids is taken to the heart via the liver
and distributed to all parts of the body. The
amino acids are used during metabolism for
growth and repair of body organs.
Excretion of urea
Figure 16.2 Ingestion of protein leads to the excretion of urea.
183
Life Processes and Disease
Other plant wastes
~
IT:Q2
vv
Draw up a table to show how the
following excretory products are
produced and where they are
excreted. In animals: carbon dioxide,
heat, nitrogenous compounds;
in plants: oxygen.
Plants al so produce some nitrogenous wastes which are converted into
insoluble substances. Calcium oxalate is another insoluble waste product. These
wastes are stored in leaves, bark, flowers, fruits and seeds. When the plant
sheds these structures, the excretory products are removed. These products can
be poisonous to the plant but may be useful to humans as dyes, oils, perfumes
and for medicinal purposes. These waste products include tannins, resins, '
latexes, nicotine, caffeine, morphine and gums. Some waste products are stored
permanently by the plant, such as in the old xylem (hard wood)
·
The human excretory system
The kidney
The human excretory system includes a pair of bean -shaped organs, the
l3Gl114'IJ kidneys, which are positioned in the lower back region behind the intestines
(figure 16.3 ). The kidneys are the major excretory and osmoregulatory organs
osmoregulation > of mammals. Osmoregulation is the control of the amount of water in the
blood. Since the blood is constantly in close contact with all cells of the body,
this means that the kidneys control the amount of water in the body.
·' < - - ---'If - - - left kidney (slightly higher)
~l!llt---t---'----t-- renal artery takes blood
with wastes to the kidney
.JEL'----~--+-- renal vein takes
cleansed blood away
- t-,-=-=;,.,.-o---;- bladder - sac which
stores urine temporarily
sphincter muscle
controls the
release of urine ++~~+~~:.:..,ai~;_~
r~,~E;~~~~t- urethra tube leading
from the bladder
to the environment
Figure 16.3 The excretory system of humans.
The renal artery brings blood with nitrogenous and other waste products to
the kidneys to be cleansed. After passing through the kidneys, this cleansed
blood returns to the heart via the renal vein, while the nitrogenous and other
iilileIW
wastes flow down through the ureter as urine to the bladder to be stored. The
Hr:DAM• bladder stores urine temporarily before it is released into the environment via
lili§Jhli§M the urethra . Sphincter m uscles control the release of urine from the bladder.
Sense cells in the bladder walls are stimulated when the bladder fills,
triggering the desire to relax the sphincter muscles and contract the walls of
the bladder. When this happens, urine flows out of the bladder through the
urethra. Trying to hold back the release of urine requires conscious tightening
of the sphincter muscles which can be uncomfortable. Babies are not usually
~
IT:Q3
capable of controlling this muscle before the age of 2-3 years.
vv
Describe the function of each of the
When a person is said to be suffering from a 'weak bladder', that person
following: kidney, bladder, renal vein,
has to urinate frequently. In this case, it is really the sphincter muscJes that are
urethra, the bladder sphincter muscle.
weak and the bladder does not hold as much urine as it normally stores.
184
16 ·Excretion, Osmoregulation and Homeostasis
ii1¥J•h!i•hiJ
11@00
Figure 16.4 illustrates a longitudinal section through a kidney. The three
regions seen are the cortex, medulla and pelvis. Each kidney is made up of
thousands of tiny structures called nephrons. Each nephron spans the cortex
and medulla, the two outer regions. The pelvis, the innermost region, collects
urine from the collecting ducts. The nephrons all end at collecting ducts so that
urine, as it forms, flows through these collecting ducts and then out into the
pelvis. The urine then flows to the bladder through the ureter.
collecting duct Into
which urine from a
number of nephrons
flow
renal vein
glomerulus
Bowman's_. _- capsule
renal artery
cortex - made up of
Bowman's capsules
and convoluted
tubules of all the
nephrons
_..,..___ pelvis - collects
urine from all the
collecting ducts
medulla - contains - ......---loops of Henle and
collecting ducts which
open into the pelvis
(a)
ureter
(b)
Figure 16.4 (a) False-colour X-ray showing blood supply to kidney. (b) A simplified diagram of a
longitudinal section through a kidney, showing the position of the nephrons.
Bowman's capsule >
glomerulus >
The nephron and urine production
Bowman's capsule
arteriole from
renal artery
cortex
venule to
renal vein
-
J,.
collecting duct
The main regions of the human nephron
are shown in figure 16.5. It is basically
made up of a cup-shaped structure called
a Bowman's capsule and a long tubule
with clearly defined regions. These are
called the proximal convoluted tubule,
the loop of Henle, and distal convoluted
tubul e and the collecting duct. Each has
a very important role in the formation of
urine.
A mass of capillaries, called a
glomerulus, is enclosed by the
Bowman's capsule. The blood supply to
the glomerulus comes from the renal
artery which brings blood carrying
nitrogenou s and other waste products to
be cleansed.
Figure 16.5 Detailed structure of a nephron.
185
Life Processes and Disease
Pressure filtration
IOifEl'fll
The afferent arteriole whlch comes to the capsule has a bigger diameter than
the efferent arteriole leaving it. As a result, pressure builds up in the capillaries
of the glomerulus. As blood flows under this high pressure, the smaller
components of the blood plasma are pushed out into the surrounding cup-like
Bowman's capsule. This becomes the filtrate whlch contains water, glucose,
amino acids, vitamins, hormones, salts and urea, which are some of the small
compon ents of blood. Large molecules, such as plasma proteins, and blood cells
(erythrocytes and leucocytes) remain in the blood. The arteriole leaving the ·
capsule continues to flow through a network of capillaries whlch surrounds
the rest of the nephron as shown in figure 16.6. The filtrate flows into the
proximal convoluted tubule (figure 16.7).
High blood pressure can cause the capillaries of the glomerulus to burst thus
destroying the nephron which is the basic unit of the kidney. This can lead to
kidney failure.
efferent arteriole has
Bowman's
capsule
capillaries
pressure
builds up in the
glomerulus
filtrate minus glucose\ \
\
moves down to
loop of Henle
the~
Figure 16.6 Bowman's capsule.
Rgure 16.7 The proximal convoluted tubule
reabsorbs glucose from the filtrate.
Selective reabsorption
proximal convoluted tubule >
186
Selective reabsorption is the reabsorption of a substance in preference to others
that are present. This occurs in the region of the nephron called the proximal
convoluted tubule. Glucose is a small molecule, so it is a component of
the filtrate as it moves through the proximal convoluted tubule. Here it is
reabsorbed into the plasma of the capillaries that are wrapped around the
tubules. Glucose is not a waste product - it is needed by the body because it is a
source of energy. It is reabsorbed from the filtrate, which continues on into the
loop of Henle.
A person who has diabetes mellitus has glucose in the blood at such a high
level that it exceeds that which the kidneys can reabsorb and so glucose is
excreted in the urine. This condition is also known as sugar diabetes. The urine
of non-illabetics does not contain glucose since all is reabsorbed back into the
blood. The urine of a person with illabetes tests positively for reducing sugar
(glucose).
16 · Excretion, Osmoregulation and Homeostasis
Reabsorption of water
loop of Henle >
The filtrate now flows through the loop of Henle where water is reabsorbed
into the blood capillaries. The longer the loop of Henle, the more water is
reabsorbed. The filtrate continues to the distal convoluted tubule.
The kangaroo rat, a rodent which lives in deserts, has a very long loop of
Henle. Most of the water in the filtrate is thus reabsorbed and conserved by the
anima l. It is so good at this that the rat rarely has to drink water.
Selective reabsorption
distal convoluted tubule
collecting duct ,,
CHAPTER18
X
As the filtrate moves through the distal convoluted tubule and collecting
duct, reabsorption of salts and water occurs (figures 16.8 and 16.9). This
reabsorption, however, is controlled by h ormones and depends on the
concentration of solutes in the blood (chapter 18).
Urine
~
l:S:Q~
l.../'-J
Describe the route taken by a red blood
cell from the renal artery to the renal
vein.
~
l:S:QS
l.../'-J
Describe the route taken by the urea
molecule as it travels from the renal
artery to the external environment
(in urine).
The filtrate is now called urine, and contains the water, salts and urea that are
not needed by the body. The urine flows to the pelvis of the kidney from the
thousands of collecting ducts. It then travels, via the ureter, to the bladder to be
stored before urination.
filtrate from
filtrate with
less water
""-....
r+
blood leaves
with
more water
filtrate, water and salts
reabsorbed according to
the needs of the body
filtrate now called urine
flows to the peMs
then to the bladder
Figure 16.8 Water is reabsorbed from the
filtrate in the loop of Henle.
Figure 16.9 Reabsorption of salts and more
water occurs in the distal convoluted tubule
and collecting duct.
Table 16. 1 compares the composition of the renal artery with the renal vein
and sh ows the effect of the kidneys on 'cleansing' the blood.
Renal artery
Renal vein
• contains more water
• contains less water because some is lost with the urine
• contains a high concentration • contains little or no urea because all ls filtered and lost as
of urea
urine
• salt concentration is higher
Table 16. 1 Composition
of blood in the renal artery
and renal vein.
• salt concentration is lower
• more oxygen and less carbon • more carbon dioxide and less oxygen because kidney cells
dioxide
respire to stay alive and do their work
187
Life Processes and Disease
Describe the route taken by a glucose
molecule as it travels from the renal
artery to the renal vein.
l.A-J
Both the renal artery and the renal vein contain red blood cells and blood
proteins since these are coo large to be filtered out into the Bowman's
capsule. All glucose is reabsorbed apart from that used by the kidney cells for
respiration. The glucose content is thus lower in the renal vein than in the
renal artery.
~
Kidney failure and kidney transplants
~
IT:Q6
IT:Q7
l.A-J
Explain these terms: 'pressure
filtration', 'filtrate', 'selective
reabsorption', 'urine'.
kidney dialysis >
Kidneys sometimes fail as a result of damage or infection. If one kidney is lost. .
the remaining one can undertake the work necessary to remove metabolic waste
and keep the body healthy. However, loss of both kidneys is fataJ if not treated.
It is possible to transplant a kidney from one person (the donor) into the
patient (the recipient). The tissue of both persons, the donor and recipient,
must match closely since the body rejects anything that it 'perceives' to be
foreign or not itself.
A person suffering from kidney failure must have regular treatment on a
kidney machine which carries out dialysis (figure 16.10). Dialysis must take
place for many hours (up to 10 hours) every few days, to ensure the removaJ
of wastes and prevent the build-up of toxic compounds that could poison and
kilJ the body cells.
Dialysis is a method of separating particles of different size in blood
by passing the blood through a tube made from a selectively permeable
membrane. This tube is surrounded by a dialysis fluid that has the same
concentration as normal blood. Any substance in excess in the blood, such as
urea and salts, will diffuse out. Dialysis fluid leaving the machine will therefore
be rich in saJts and body wastes like urea.
(b)
heparin - prevents blood clotting
dialysis
fluid out
-
dialysis
fluid in
(a)
to heart
(cleansed
blood)
-..........~..,, cleansed blood
returned to patient
Figure 16.10 (a) A dialysis machine can do the job of the kidneys after kidney failure. (b) How the
dialysis machine works.
188
16 ·Excretion, Osmoregulation and Homeostasis
Osmoregulation
osmoregulation >
~
11~Q8
l/V
(i) Define osmoregulation.
(ii) Reabsorption of water occurs in
the loop of Henle, and in the distal
convoluted tubule and collecting
duct. How is reabsorption of water
different in the two areas?
The kidneys have a second important function - osmoregulation . They
regulate the concentration of body fluids. The amount of water and salts found
in the blood is never constant. Daily activities such as sweating and eating
cause the concentration to vary. The kidneys regulate the concentration of
blood by controlling the amount of water and salts that are reabsorbed into the
capillaries during selective reabsorption in the distal convoluted tubules and '
collecting ducts.
During its normal circulation, blood passes through the hypothalamus in
the brain. The h ypothalamus monitors the concentration of the blood and if
the blood is too concentrated - for example, from excessive sweating, ingesting
large amounts of salt or drinking too little water - the hypothalamus sends
a message to the pituitary gland. The pituitary gland is situated next to the
hypothalamus; when it receives the message, it secretes more antidiuretic
hormone (ADH) into the blood. ADH stimulates the walls of the distal
convoluted tubules and collecting ducts to reabsorb most of the water from
the filtrate. As a result, small amounts of concentrated urine are produced
(figure 16. 11 ).
Hypothalamus detects
solute concentration in blood
hypothalamus
If too high, sends message
to pituitary to secrete more ADH
If too low, sends message to
pituitary to secrete less ADH
ADH travels in blood to kidneys
ADH travels in blood to kidneys
More ADH makes distal
convoluted tubules and
collecting ducts more permeable
to water - more water reabsorbed
from filtrate
Less ADH makes distal
convoluted tubules and
collecting ducts less
permeable to water - less
water reabsorbed from filtrate
kidneys
Small amounts of
concentrated urine produced
Large amounts of
dilute urine produced
Figure 16. 11 The concentration of urine 1s controlled by the secretion of ADH by the pituitary
If the hypothalamus detects that the blood is too dilute - possibly due to
drinking large volumes of water, little sweating or low salt intake - less ADH
is released and little water is reabsorbed. In this case, large amounts of dilute
urine are produced.
Homeostasis
homeostasis >
Homeostasis is used to describe all the mechanisms by which a constant
internal environment is ma intained. While the external environment outside
the body may change, the internal environment inside the body must remain
189.
Life Processes and Disease
fairly constant otherwise all the reactions needed in living cells may be
disrupted . The body must detect any deviation from the normal and make
the necessary adjustments to return it to its normal condition as quickly as
possible. The temperature within the body and the composition of tissue fluid
which bathes the body cells must remain as steady as possible for the chemical
reactions that occur within these cells to proceed normally (figure 16.1 2).
substances to be
taken away enter
the capilliary
b lood flows
body cell
blood from
an arterio le
Figure 16.12 Body cells surrounded by tissue fluid and capillaries.
Tissue fluid must:
• be within a small range of pH (acidity);
• contain enough glucose for respiration and activity;
• contain enough oxygen for respiration;
• not contain high levels of carbon dioxide;
• not contain high levels of nitrogenous wastes;
• contain enough, but not too much, water;
• be within a small range of temperature;
• be specific in many other ways for body cells to function normally.
~
IT:Q9
vv
Define homeostasis and explain why it
is important.
Excretion and osmoregulation are examples of homeostasis. A build-up of
waste products could damage and even kill cells. Here are some examples of
how.
• Carbon dioxide causes the pH of the blood and tissue fluid to be lowered,
which then affects the rate at which chemical reactions can occur within
cells.
• Nitrogenous wastes are toxic to cells so they must be cleared from the blood
quickly.
• Too low a temperature makes chemical reactions too slow, and too high a
temperature denatures proteins, including enzymes.
• In extreme amounts, water causes body cells to malfunction.
Feedback
The body can detect changes in these factors in the blood and has mechanisms
to bring the levels back to a normal range. These mechanisms are called
feedback mechanisms because a change in the internal environment causes
a correction to happen which feeds back to the conditions in the internal
190
16 ·Excretion, Osmoregulation and Homeostasis
negative feedback >
~
environment. Such mechanisms are used to keep the internal environment
constant.
ll the internal environment is disturbed, the disturbance sets in motion
a sequence of events which tends to restore the system to its original state .
This is called negative feedback because it removes the effect of the change.
Examples of negative feedback can be seen in figures 16.1 3, 16.14, 16.15,
16. 16 and 16.17.
r::=
IT:Q-1 0
V'-1
In the regulation of carbon dioxide in
the blood, when does an increase in
carbon dioxide concentration come
about, and how is the concentration
brought back down to a normal level?
too moch - - - - - - • corrective mechanism
normal level
normal level
Rgure 16. 13 A typical feedback mechanism.
body fluids
too concentrated
high levels of ADH
kidneys reabsorb
most water
from the filtrate
• excessive sweating
• excessive salt intake
• low water intake
small amounts of
concentrated urine
produced
correct concentration
of body fluids
correct concentration
of body fluids
• little sweating
• low salt intake
• large water intake
large amount of dilute
urine produced
body fluids
too dilute
low levels of ADH
kidneys do not
reabsorb much
water from the filtrate
Rgure 16. 14 Osmoregulation: control of concentration or blood plasma and body fluids.
too much carbon
dioxide in the blood
_ _ _ _ _ _ _ _ _.,.
increases
breathing rate - - - - - - - -......
carbon dioxide
lost more rapidly
from lungs
e.g. exercise
normal level
of carbon dioxide
normal level
of carbon dioxide
carbon dioxide
lost less rapidly
from lungs
too little carbon
dioxide in the blood
breathing rate
reduced
Figure 16. 15 Control of the amount of carbon dioxide in the body.
191
Life Processes and Disease
• skin produces sweat
dilate
,__ _ _ _ _ _..,. body temperature _ _ _ _ _ _ _... •• skin
hairscapillaries
lie flat
~
rises above 37 °c
• respiration slows
• panting occurs
• fever
• exercise
• hot environment
body temperature drops
normal body
temperature (37 °C)
normal body
temperature (37 C) .
°
body temperature rises
• cold environment
body temperature
.....,,_ _ _ _ _ _..,.drops below 37 °c
• no sweat produced
• skin capillaries constrict
• hairs become erect
-------~
• shivering occurs
Figure 16.16 Control of body temp~rature.
~------+ (150
high glucose level - - - - - - - -...
mg/100 cm3)
pancreas secretes
insulin
• liver converts glucose
to glycogen and fat
• cells absorb glucose
such as after a meal
correct amount of
glucose in the blood
(90 mg/100 cm3
correct amount of
glucose in the blood
(90 mg/100 cm3
• liver converts glycogen,
fat and protein to glucose
• cells absorb less g lucose
such as fasting
low glucose level _ _ _ _ _ _ _ _...
(70 mg/100 cm3)
pancreas secretes
little insulin
Rgure 16.17 Control of blood glucose.
I
192
16 ·Excretion, Osmoregulation and Homeostasis
• Homeostasis is the term used to describe all the mechanisms by which a constant
internal environment is maintained.
• Feedback mechanisms are used during homeostasis.
• Feedback mechanisms are used to control blood glucose levels, water, body
temperature and the amount of carbon dioxide in the blood.
....
ITQ1 •
Metabolism is all the activities of a cell. These require certain
substrates and produce many useful products as well as some waste. The term
'metabolism' encompasses all these reactions at any given time in a cell.
• Excretion is the process by which cells and the organisms get rid of
metabolic waste.
• Egestion is the process by which undigested food in the alimentary canal is
leaves the body through the anus.
• Secretion is the process by which a chemical, such as a hormone, leaves a
gland; for example, the salivary gland secretes saliva into the mouth.
ITQ2
How produced
Where excreted
carbon dioxide
during respiration
from the lungs
heat
during respiration
through the skin
nitrogenous compounds
from breakdown of protein
from the kidneys
during photosynthesis
through the stomata
Excretory product
In animals
In plants
oxygen
The kidney is the organ of excretion of metabolic waste and excess
water from th e body.
• The bladder stores urine temporarily before excretion.
• The renal vein takes cleansed blood away from the kidneys .
• The urethra is the tube through which urine passes from the bladder to the
outside environment.
• The bladder sphincter muscle controls the release of urine from the body.
ITQ4 renal artery -+ afferent arteriole -+ glomerulus -+ efferent arteriole -+
renal capillary -+ renal vein
ITQS renal artery -+ afferent arteriole -+ glomerulus -+ Bowman's capsule
-+proximal convoluted tubule -+ loop of Henle -+ distal convoluted tubule -+
collecting duct -+ pelvis -+ ureter -+ bladder -+ urethra
ITQ6 renal artery -+ afferent arteriole -+ glomerulus -+ Bowman's capsule -+
proximal convoluted tubule -+ renal capillary -+ renal vein
ITQ7 •
Pressure filtration is the filtration of the smaller components of
blood into the Bowman's capsule. It occurs because of pressure that builds up
as blood flows from a wider vessel into a smaller vessel.
• The filtrate consists of the smaller compon ents of blood (urea, water, salt,
glucose, etc.) that are filtered into the Bowman's capsule and move along the
tubes of the nephron.
• Selective reabsorption is the reabsorption of a substance in preference to
others that are present. Glucose is selectively reabsorbed back into the blood
while other components of the filtrate continue along the nephron .
• Urine is the substance that collects in the bladder. It is m ade up of water,
salts and urea.
ITQ3 •
193
Life Processes and Disease
ITQ8 (i)
Omsoregulation is the maintainance of constant osmotic conditions
in the body. The regulation of the water content and solute concentration of
body fluids is important for cells to work efficiently
(ii)
Loop of Henle
Distal convoluted tubule and collecting duct
re~bsorption of water is automatic
reabsorption of water is controlled by
antidiuretic hormone (ADH)
the longer the loop of Henle, the more water is
reabsorbed
water reabsorbed according to needs of body
Homeostasis is the maintenance of a constant internal environment.
CeJls need a constant environment in which to function efficiently.
Homeostasis describes all the mechanisms that come into play to keep
the internal environment constant. For example, enzymes need a specific
temperature and pH to function efficiently.
ITQ10 During exercise, respiration increases and so does the concentration
of carbon dioxide because it is a waste product of respiration. Carbon dioxide
is transported to the lungs to be excreted. When there are increased amounts
of carbon dioxide in the blood, the heart beats faster, allowing blood to flow
faster to the lungs and therefore more carbon dioxide is excreted. The carbon
dioxide concentration is thus brought back to the normal level in the blood .
ITQ9
Examination-style questions
(i)
Define: (a)
excretion
(b) osmoregulation.
(ii) Using an annotated diagram only, describe how urine is formed in a nephron.
(iii) Describe how and why the volume and composition of urine changes:
(a) after strenuous exercise;
2
(i)
(b)
after drinking large volumes of water.
List three excretory products, besides nitrogenous waste, produced by animals.
(ii) List two excretory products produced by plants.
(iii) (a) Describe the production of nitrogenous waste in humans.
(b) Describe the excretion of nitrogenous waste in humans.
3
(i)
(a) Label the parts A, B, C, D, E, F and Gin the figure below.
(b) In each case state its role in excretion.
(c) List four differences between A and B.
f!
i------+--- A
+++---
-
-+-- B
1------+--- C
r._- - -I + - --
194
-
-
---+- F
--+- G
16 ·Excretion, Osmoregulation and Homeostasis
(ii) The kidneys are very important organs involved in the removal of toxic substances
which, if allowed to accumulate in the body, could be fatal.
(a) The body offers some physical protection of its internal organs. How are the
kidneys protected?
(b) Suggest two ways the kidneys may be damaged.
(iii) Describe how a dialysis machine works to cleanse blood during kidney failure.
4
(i) Define homeostasis.
(ii) The figure below shows some body cells and their supply of blood.
(a) List some differences between blood at A and B.
(b) Name the process occurring at C.
(c) Name the process occurring at D.
(d) Explain fully how the cell labelled Eis supplied with oxygen.
(e) Name the substance found in F.
(f) State three properties of F.
(g) State the importance of the properties listed in (g) above.
(h) Describe the mechanism by which one of these properties is regulated.
195
ovement
0
0
0
0
0
0
0
understand the importance of movement in animals
understand growth movement in plants
understand how external factors affect plant movement
describe the structure and function of the skeleton of humans
describe the mechanism of movement in a limb of humans
describe the long bones of a fore and hind limb
describe the cervical, thoracic and lumbar vertebrae
movement
I
r
r
plants
skeleton
auxin
___,__
,,
'
limbs
(
I
muscle -
tendons
'
vertebral
column+ skull
l
joints
I
(
hinge
'
animals
ligaments
'
r
'
phototropism
geotropism
vertebrae
• cervical
• thoracic
• lumbar
ball-and-socket
The importance of movement in animals
Most animals have to look actively for food and, to do this, they must move
from one place to another. Movement from one place to another is called
locomotion and it involves the expenditure of energy. There are a number of
reasons why animals move from one place to another and these include:
• to find food;
• to escape predators;
• to find a mate;
• to disperse offspring;
• to reduce competition;
• to avoid danger;
• to avoid waste products;
• to avoid extreme environmental conditions.
Animals move in many ways, which include flying, swimming, walking,
running and gliding. Each animal is adapted to move in its own special way.
For example, humans are adapted to walk or run from place to place.
17 · Movement
Movement in plants
Movement in plants can be demonstrated by a germinating seedling. When
a seed has germinated, it will grow into a seedling if all the conditions for
germination are met. Movement is seen when it grows. The shoot grows
towards a light source and the roots always grow downwards towards gravity
into the soil. This is related to nutrition in the plant as plants need light
and water for photosynthesis. Movement in plants is thus usually growth
movement. and when we study movement in plants we look at factors that
lii•l•ll•juiJ affect their growtJ1. Growth movements are called tropisms.
A few plants show another kind of movement apart from growth
movement. The sensitive plant (Mimosa pudica), for example, can fold its leaves
when touched (figure 17. l). Some plants like the hibiscus can fold their petals
at night. Insectivorous plants like the Venus flytrap can catch small insects by
moving a part of its body, and the pods of pigeon pea can curl and split when
dry to disperse the seeds, as a part of reproduction.
Figure 17. 1 Plant movements. (a) Mimosa pudica 'wilts' when touched. (b) The trap of a Venus
flytrap closes when an insect touches the sens1t1ve hairs on the surface.
Growth movement in plants
The most important plant movements are tropisms or growth movements.
Growth in response to the stimu lus of light is called phototropism , and
geotropism is growth in response to gravity. Growth in plants is controlled by
l:Uf3hQ the hormone, auxin. Auxin is made in the tips of roots and shoots which are
the growing parts of the plant. It diffuses to the region just behind the tip and
Practical activities there it causes growth (figure 17.2).
Light and gravity are examples of external factors (factors in the
SBA 17.1 : Does gravity affect plant
growth? page 354 environment) that affect growth in plants. The shoots of plants respond to light
SBA 17.2: The growth of a radicle, by gi·owing towards it. When a shoot is Lit from one side, a uxin breaks down
page 355 on the Light side and accumulates on the shaded side. This results in more
SBA 17.3: Does light affect plant growth on the shaded side so the shoot bends towards the light (figure 17.3,
growth? page 356 overleaf) . In a shoot whid1 is not upright, gravity causes the auxin to collect
on the lower side. This has the same effect as before, rn make the shoot grow
faster on that side, so it bends away from gravity.
phototropism >
geotropism >
more auxin produced
which diffuses down
Rgure 17.2 A shoot grows because of the hormone auxin.
197
Life Processes and Disease
more
auxin accumulated on
the shaded side
__
growth;;~
.. •:.·/(· .
.....
' '-"'-"'
.,
·") ' "
(
light
light
less growth
shoot grows
towards the light
shoot is
horizontal
less
grow~;~!:))
·~ore
auxins accumulate on the lower side due to gravity
growth
shoot grows upwards
~
IT:Q3
Figure 17.3 Shoots always grow towards light and upwards or against gravity.
Agar blocks were placed under cut tips
of shoots. The blocks were then placed
on growing shoots as seen. How will
each shoot grow?
However in roots, concentrations of auxins slow down growth. As in the
shoot, auxin accumulates on the lower side because the gravity, but in a root
the upper side will grow faster because it is less affected by the auxin. No matter
how a root is placed in the soil, it will always grow downwards (figure 17.4).
l.../'-J
gravity
TI
I!
gravity
l
l
l
agar block
root placed
horizontally
·.:.
·:·~
growing tip
l
l
~
gro~
more growth
less
·:'-..,
root grows
downwards
'(.
roots always grow downwards
or towards gravity
Figure 17.4 Roots always grow down
Simple investigations can show the effects of light and gravity on
germinating seedlings as shown in figure 17.5. They use agar blocks containing
auxin because the hormone can easily diffuse through the agar.
:·.,
shoot tip cut
and placed on an
agar absorbs
! : ~'i -------_.theauxin
..~
shoot tip cut off cut shoots are used
in investigation
agar block with auxin
placed on a cut shoot
- shoot will grow
/~
agar block with auxin
placed to one side
of a cut shoot
agar block with no
auxin results in
no growth
Figure 17.5 Investigations of growth in seedlings. Agar blocks which absorb auxin are used.
198
17 · Movement
Uses of plant hormones
· 1;rm;mmm
Pesticides are poisonous chemicals which kill pests. Some plants, especially
weeds, are described as being pests and herbicides are used to kill them or
remove them from the environment.
Synthetic plant hormones, for example auxin, can be used as a herbicide.
When present in excessive amounts, much more than produced naturally,
auxin can disrupt plant growth and so kill plants. 2,4-D and 2,3, 5-T are
examples of selective herbicides which kill broad-leaved plants. They stimulate
auxin production in the plants. The weed killer causes dicotyledons to grow so
fast that they cannot sustain their own growth and they die.
Some herbicides work because they are translocated throughout a plan t.
They are called systemic herbicides. They are translocated from the leaves,
where they were applied to the roots where they interfere with root function.
Because the root is killed, the whole plant dies.
The skeleton of humans
endoskeleton >
exoskeleton )
axial skeleton >
appendicular skeleton >
The skeleton of h umans is an endoskeleton , which means that it is inside
the body. All vertebrates have the same arrangement of endoskeleton, with
the bones inside and the muscles and other body tissues surrounding it. Some
invertebrates also have an endoskeleton, such as squid and octopus, but many
have an exoskeleton where the hard part is on the o utside. For example,
insects have a jointed exoskeleton made of chitin, and many molluscs, like
dams, have a hard calcified shell. Exoskeletons have an advantage in that they
can protect the whole of the body, but they also limit the size to which the
organism can grow.
The body of h umans is held upright by a skeleton which is made of bones
arranged as seen in figure 17.6 (overeaf).
The human skeleton can be divided into two parts: the axial skeleton,
which is the skull and vertebral column with the rib cage, and the
appen dicula r skeleton, which includes all the other bones, the fore and hind
limbs, and the pelvic and pectoral girdles.
Functions of the skeleton in humans
~
l'.T:Q'4
L.-1'-I
Name the bones found in the lower
limb, from the pelvic girdle to the toes.
~
l'.T:Q5
L.-1'-I
What is the importance of the blood
vessels and the marrow in a long bone?
• Protection of organs - The skull protects the brain, the vertebral column
protects the spinal cord and the ribs protect the lungs, heart and much of
the liver. Bones surround these delicate organs, forming cup-like structures
or tube-like structures in which the organs are housed.
• Support of the body - Humans are supported upright more than most
mammals and can stand on two feet. The skeleton acts Like a fra me
supporting the soft body parts. The limbs are separated by the width of the
girdles and this helps to keep the body stable.
• Movement - The skeleton is made up of a number of bones joined
together. Muscles, and other tissues such as tendons, can cause movement
of a single bone. The coordinated movement of many bones results in
walking, running and all the movement seen in a human.
• Manufactur e of red and white blood ce lls - These are made in the bone
marrow of th e pelvis, ribs, sternum and leg bones.
Structure of a long bone
The long bones are the femur, tibia and fibula of the hind limb and the
humerus, ulna and radius of the fore limb. The structure of the long bone is
shown in figure 17.7 (overleaf).
199
Life Processes and Disease
skull
cranium -
+---
shoulder girdle
(pectoral girdle}
~----clavicl e
thorax
upper limb
-+--
- - - humerus
metacarpals
phalanges
lower limb
-+--
-
femur
-+H--tibia
r + - - - fibula
the axial skeleton (skull and
vertebral column) is coloured
D
tarsals
"""M'•:i:--- metatarsals
phalanges
Figure 17. 6 The human skeleton.
The vertebral column
In humans, the vertebral column extends from the neck to tailbone or coccyx
~
rf:Q6
vv
Describe two functions of the vertebral
column.
200
(figure 17.8). It is made up of 33 bones called vertebrae. All vertebrae have
the same basic structure (figure 17.9). There are 7 neck or cervical vertebrae,
the first of which are the atlas and axis. The cervical vertebrae are followed by
12 thoracic vertebrae, then 5 lumbar vertebrae. The sacrum follows the lumber
vertebrae and is made of several vertebrae fused together. Finally, the tail
vertebrae are fused to form the coccyx.
17 · Movement
neural spine
~
,,.,,,.... in
anterior facet
cervical
epiphysis
J....- cartilage
spongy bone
(contains red
marrow)
Structure of a typical vertebra
thoracic
vertebrae (12)
-
-compact bone
marrow cavity
shaft
spinal cord runs
through the neural canal
blood vessel
lumbar
vertebrae (5)
three vertebrae interlock
to form part of the
vertebral column
sacral
vertebrae (fused)
epiphysis
coccyx_o_r _'ta
_i_I' - - - - -
Rgure 17.8 The vertebral column in humans.
Figure 17.7 The structure of a long bone.
v
~C
centrum
transverse process
~ertebrarterial canal (two small
holes in vertebra, one on either side)
Cervical vertebra - has two small holes apart from the large neural canal
neuraI canaI
\If
(}___neural spine (long)
transverse process (short) - facet - -
't- neural spine (short)
neural canal ~ '
facet
~
6
centrum big and - - well developed
~
rib
_/
-...- J
\
.,J-~
centrum ~
Thoracic vertebra - articulate with ribs as well as other vertebrae
~ transverse process (long)
)
Lumbar vertebra - has large centrum and long transverse processes
Figure 17.9 The cervical, thoracic and lumbar vertebrae in humans.
201
Cervical vertebrae
•
•
•
•
large neural canal because these vertebrae are closest to brain;
vertebraterial canals present;
shore neural spine;
short transverse processes.
Thoracic vertebrae
• neural canal smaller than cervical because further from brain;
• very long neural spine for attachment of back muscles;
• short transverse processes to accommodate rib bones on either side.
Lumbar vertebrae
•
•
•
•
centrum big and well developed to support weight of body;
neural canal small;
long, wide neural spine;
long transverse processes for muscle attacl1ment.
Table 17. l summarises the functions of the various surfaces and projections of
ead1 vertebra.
Part of vertebra
Function
neural canal
protects the spinal cord
neural spine
muscle attachment
transverse process
muscle attachment
facet
articulates with facets of adjacent vertebrae and allows slight movement
centrum
central rigid body of vertebra, discs of cartilage separate adjacent vertebrae
Table 17.1 The functions of the different parts of a human vertebra.
Movement in a limb of humans
Practical activity
SBA 17.4: Compare the movements of
tour animals, page 357
spongy
bone
compact
bone
articular cartilage
- functions as a
Movement in a limb is brought about by many tissues, such as muscles,
tendons, ligaments and bones, all working together. Bones are able to move
because of the presence of joints in the skeleton. A typical joint is seen in
figure 17. 10.
Bones are attached to each other by ligaments. They cannot move on
their own. Muscles are seen around the bones and move the bones when
they shorten (contract) and lengthen (relax). This is sh own in the simplified
diagram in figure 17.1 1.
muscle
ligament
synovial
membrane
contract
ligament
synovial fluid
- lubricates joint
reducing friction
during movement
Figure 17. 1O A typical joint.
202
contract
+-bone moved
to the left
Figure 17. 11 Bones are moved by muscles.
-
bone moved
to the right
antagonistic muscles >
l(ijet•l•hll
The muscles of the arm move the bones of the arm to flex or extend the arm
in the same way as seen in figure 17.12. The bones are attached to each other
by ligaments and attached to muscles by tendons. They have special names
(triceps and biceps) and contract or relax to move the bones. All the bones
of the body need muscles to help them move. Imagine the coordination of
contraction and relaxation of muscles needed to cup the fingers around a
,
bottle, and then move the bottle to the lips to cake a drink of water.
Movement is brought about by the contraction of antagonistic muscles .
Antagonistic muscles are pairs of muscles that always work together: when
one is contracting, the other is relaxing. They move many bones of the human
skeleton . In the joint of the upper arm, the triceps and biceps are antagonistic
muscles. They are attached to the bones by tendons which are non-elastic.
A muscle shortens when it contracts and is lengthened when it relaxes.
Movement of the bone is brought about when the muscles pull on the bones
(figure 17.12).
Flexing the arm
Extending the arm
/\~
tendons, attach r
muscle to bone
~
biceps muscle
(contracts)
(flexor muscle)
triceps muscle
(contracts)
(extensor muscle)
triceps muscle
(relaxes)
ulna
biceps muscle
(relaxes)
,.
arm bends or flexes
arm extends
Figure 17.12 Flexing and extending the arm.
flexor muscle >
extensor muscle >
When the biceps contracts (and triceps relax), it pulls the bones of the lower
arm upwards so the arm bends or flexes. The biceps is called a flexor muscle.
When the triceps contracts (and biceps relaxes), it pulls th e bones of the lower
arm so that the arm straightens or extends. The triceps is called an extensor
muscle.
Types of joint
There a re three types of joint:
• immovable joint;
• partially movable joint;
• movable joint.
E!UliiM
gliding joint >
l•M•llt.lleiH
Immovable joints are also called sutures. The bones are fu sed together
allowing no movem ent. Examples are joints of the cranium and pelvic girdle.
Partially movable joints allow some movement. Examples of joints between
the tarsals (ankle) and carpals (wrist). The bon es ca n slide over each other
producing the movements seen in the wrist and ankle. These are also called
gliding joints.
A partially movable joint also exists between the atlas and axis at the top
of the neck allowing some m ovement of the head in relation to the spine (e.g.
nodding or shaking). This is called a pivot joint.
203
synovial joint >
Moveable joints are also called synovialjoints. Synovial fluid in these joints
reduces friction allowing free movement of the bones. There are two types of
synovial joint (figure 17.13).
• Hinge joint - Allows movement in one plane; for example, elbow, knee
and finger joints. Bones of a hinge joint are capable of carrying heavy loads.
• Ball-and-socket joint - Allows movement in all planes; for example, the
shoulder and hip joints.
Hinge joint
Ball-and-socket Joint
one
plane
- - s o cket
• movement is restricted
to one p lane
• may be dislocated
• e.g. elbow, knee, fingers
• movement is allowed
in three planes
• easily dislocated
• e.g. pelvic girdle (hip), shoulder
Figure 17. 13 The hinge and ball-and-socket joints.
~
~
l:F:Q1'
l:F:Q9
(i) What is a joint?
(ii) What is the importance of joints?
Put these in the order they occur when extending the arm:
(a) the arm is pulled down.
(b) biceps muscle relax.
(c) ligaments stretch arm.
(d) muscles pull on radius and ulna.
(e) triceps muscle contract.
\../'-I
~
l:F:Q8
\../'-I
Name the structures found around a typical joint, giving a
reason why each is important.
\../'-I
~
l:F:Q·1 0
\../'-I
(i) What kind of joints are seen in the fingers?
(ii) What is the advantage of each finger having a number of
hinge joints, rather than one hinge joint?
204
17 · Movement
fl'
-
Chapter summary
• Movement is a characteristic of life.
• There are a number of reasons why animals move.
• Some plants can move some of their parts, but all plants show growth movement or
tropisms.
• During growth, plants respond to light (phototropism) and gravity (geotropism).
• The tips of the growing parts of a plant produce auxin, the hormone responsible for
growth in plants.
• The skeleton of humans has many functions, one of which is movement.
• The skeleton forms a framework inside the body of humans and is made up of the
axial and appendicular skeletons.
• The axial skeleton consists of the cranium and the vertebral column.
• The vertebral column is made up of many bones called vertebrae and includes the
cervical, thoracic and lumbar vertebrae.
• The appendicular skeleton consists of the limbs and rib cage.
• The skeleton is made up of many bones joined together; movement is seen at these
joints.
• Movement is brought about by muscles, tendons and ligaments at these joints.
• There are many kinds of joint: immovable, partially movable and movable joints.
Any two of the examples from the bullet list on page 000 is suitable.
A plant has to move (grow) towards the ligh t because light is
necessary for photosynthesis.
Some plants are able to close special leaves that trap small insects. These
plants need to acquire their protein from insects, because they live in nitratedeficient soil.
ITQ1
ITQ2
ITQ3
Pelvic girdle, femur, tibia and fibula, tarsals, metatarsals, phalanges.
The blood vessels bring nutrients and oxygen to the bone, since it is
alive and must respire. Also, these vessels take away waste produced by the
bone.
The marrow cavity is important for the production of red blood cells. Red
blood cells are constantly produced in the bone marrow.
ITQ6 The vertebral column holds the body upright and protects the spinal
cord.
ITQ7 (i) A joint is where two bones m eet. It is lubricated to reduce friction
when the two bones move.
(ii) Joints are important for movement. All movement takes place because
muscles contract and move the appropriate bones. The bones move from
where they are joined to another bone. Without joints, no movem ent would
not be possible (not movement of the entire body, nor movement of a part of
the body).
ITQ4
ITQS
205
~;.; :.- .... L~f~! ~.recesses and DiseC!_se ·
·
..
..
ITQ8
Structure
Importance
ligament
joins bone to bone, and can stretch as the bones move away from and towards
each other during movement
muscle
can contract or lengthen - because it is attached to bone, it can pull on (extend)
the bone, so muscles bring about movement
(
tendon
joins muscle to bone, is non-elastic, so the effect of the muscle contraction or·
relaxation can be applied to the bone
synovial fluid
fluid found in the joint which helps to reduce friction when bones move with
respect to one another.
ITQ9 1 - b and e (antagonistic muscles); 2 - d; 3 - c; 4 - a
ITQ10 (i) The fingers have hinge joints.
(ii) Having a number of hinge joints allows fingers to be curled around an
object.
Examination-style questions
(i) List the main functions of a vertebrate skeleton.
(ii) Make a labelled drawing of:
(a) a typical vertebra;
(b) a vertical section of a typical long bone.
(iii) The human skeleton, as is typical of mammalian skeletons, can be divided into two
components or parts. Name these parts and the bones included.
206
2
(i) Suggest some differences between movement in plants and animals.
(ii) Define:
(a) phototropism;
(b) geotropism.
(iii) Explain fully how plants respond to light.
(iv) How do plants growth substances differ from animal hormones?
(V) (a) Since the late 1980s, scientists have been conducting experiments on the effects
of space travel on seed germination. Why do you think there is an interest in such
studies?
(b) Experiments conducted on seeds in space yielded growing plants, but these
'extra-terrestrial' plants did not grow straight, they grew in all directions. Explain
what might have caused this to happen.
(c) Suggest ways of producing 'straight plants in space.
3
(i) Make a labelled drawing of a typical joint.
(ii) The exoskeleton of an insect lies outside the muscles that are attached to it. Like the
joints of the endoskeleton, the joints of an exoskeleton, provide an excellent means of
locomotion. The diagrams I and II below show joints seen in an insect and humans.
I - insect's limb
extensor muscle
II-human limb
A
E
c
(a)
(b)
(c)
(d)
Name the parts A, B, C, D, Eand F.
Using a diagram, show how the insect can flex or bend its leg.
Using a diagram, show how the human can bend the arm.
What name is given to muscles that work together to move a limb? Give
examples of these muscles as seen in the insect's limb and human's limb.
(iii) Describe the state of these muscles when:
(a) the insect's limb is extended or straightened.
(b) the human's limb is extended or straightened.
207
l·nritabi Iity, Sensitivity
and Coordination
0
0
0
0
0
0
0
0
0
0
define the terms 'stimulus' and 'response'
describe responses of green plant and invertebrates to stimuli
understand why responses to stimuli are important for survival of organisms
define the terms 'receptor' and 'effector'
identify the main sense organs and the stimuli to which they respond
describe the main sense organs
describe the nervous system
describe the endocrine system
explain a simple reflex action
distinguish between a cranial and spinal reflex
0
describe the functions of the main regions of the brain
0
discuss the physiological, social and economic effects of drug abuse
sense organs
eye
ear
nose
tongue
skin
receptor
stimulus
survival of
organism
'
nervous(system
spinal(chord
response
'
brain
effector
motor
sensory
relay
synapse
neurone
movement towards
or away
:
Irritability, Sensitivity and Coordination
Irritability
CHAPTER 1
1n chapter 1, we found that irritability is one of the seven d1aracteristics of
living things. It means that living organisms can respond to changes in their
internal environment and the world around them. These responses usually
increase their chances of survival.
Animals and plants react to changes in the environment, not only drastic
climate changes, but also simple everyday changes. For example, a snake
looking for food will move toward the scent of a rat, and the shoots of a
seedling will grow towards Ugbt.
Stimulus
Eihuii!ilO-fl
li%l•r•lli'--J#I
A stimulus is a change in the environment that an organism reacts or
responds to. It could be light, temperature, a texture, a chemical in the air
or moisture, a response is the d1ange in the organism brought about by the
stimulus (figures 18.1 and 18.2). The response to stirnuU is important for the
survival of organi sms.
Response of animals
Stimulus
Figure 18.2 This male moth has large
antennae that can sense just a few
molecules of a chemical attractant that a
female several miles away has released.
Q5b
IT:Q·1
l...A.J
(i) Define irritability.
(ii) Why is it important for the survival
of an animal?
Molecules from the rat are
in the air. The snake detects these as it
'tastes' the air with Its forked tongue.
Response
The snake moves towards
the rat. It is delicious food and
important to the survival of the snake.
Figure 18.1 A snake responds to the stimulus of food.
Table 18.1 shows some examples of stirn ulL the responses and the importance
to the organism of responding in this way.
Stimulus
Possible response
Importance to organism of response
chemical from
an organism
move towards organism
organism may be a potential mate or
potential prey
moisture in soil
move towards moist areas
prevent desiccation or dying, especially
for organisms without a waterproof
outer covering
light
move from light to darker areas
escape from predators since it is
harder to be seen in darker areas
cold
temperatures
move away from cold temperature
organism cannot survive In cold
temperatures, body not adapted
Table 18.1 Responses to some stimuli and the importance of those responses.
209
---
.
Life Processes and Disease
Response of green plants
CHAPTER 17
In chapter 17, we saw that seedlings respond to unilateral (one-directional)
stimuli of light and gravity. The roots grew in the direction of gravity and the
shoots grew towards light. Plants need water and minerals from the soil, so
the roots must grow down into the soil to reach them. Green plants, including
seedlings, also need light for photosynthesis. It is therefore important for the
survival of green plants to grow towards light (figure 18.3).
A plant in a room will grow towards the window where there is sunlight. A
seed may be taken into a cave by a bird or bat. It may germinate and then the
seedling will grow towards light and out of the ca ve's entrance or any other
opening. Otherwise, the plant will die for lack of food in the darkness.
Invertebrates, like millipedes, earthworms and wood li ce, need certain
conditions to survive. They respond to variations in light intensity, temperature
and moisture. The investigation illustrated in figure 18.4 shows that these
invertebrates respond by moving towards a cooler temperature, moist soil and
away from bright light. These responses ensure that they do not dehydrate and
are hidden from predators, that is, the responses help to ensure their survival.
It germinates and begins to grow
towards the light at the cave's
entrance. It could die in the darkness.
seed taken into a
cave by a bird or bat
It reaches the entrance where there
is light. It can now photosynthesise
efficiently and will survive.
Figure 18.3 A plant responds to the stimulus of light.
Ilght
dry soil
10 organisms, e.g. woodlice,
are placed in the apparatus
After a while they all move
towards the dark, moist areas.
Figure 18.4 Many small invertebrates respond to the stimuli of light and moisture.
~
ll'!Q2
V-...J
The senses of some animals are said to
be better developed than in a human.
Give two examples of animals like this,
and explain the importance of the sense
to the animal.
sense organs >
210
Unlike most humans, anima ls in the wild have to find food every day and
maybe avoid being food for another organism. They have to be very aware of
stimuli coming from their environment and be able to make the appropriate
response. More often than not, these everyday changes in the environment are
a matter of life or death.
The sense organs of humans
Humans have five senses: hearing, sight, smeU, ta ste and tou ch. In humans,
the main sense organs are the eyes, ears, nose, tongue and skin. A group of
sen se cells and other tissues fo rm a sense organ.
• Eye - At the back of the eye is the retina which is a layer of sensory cells that
respond to light. Impulses are sent from these ceUs to the brain by the optic
nerve so that d1anges in shape, colour, brightness and distance are detected.
:
Figure 18.5 Taste buds on a human
tongue.
Irritability, Sensitivity and Coordination
• Ears - Sensitive hairs in the inner ear respond to vibrations in the air (sound
waves). Impulses are sem from these hairs to the brain by the auditory
nerve so that changes in the quality, tone, pitch and loudness are detected.
• Nose - As air flows into the nose during breathing, chemica l molecules in
it touch sensitive hairs. These send messages to the brain so that changes in
scent are detected.
• Tongu e - Groups of receptor cells, called taste buds, respond to chemicals
in the food (figure 18.5 ). Different parts of the tongue are sensitive to
different flavours like salt, sweet, bitter and sour. These send m essages to
the brain so that changes in flavour of the food are detected.
• Skin - This is the largest organ of the body. Nerves ending as sensory cells
are scattered throughout the skin. These are sensitive to pain, touch, change
in temperature, light pressure and heavy pressure. They send in1pulses to
the brain so that it can detect what has been touched.
The nervous system
1.r411g.ur41
Practical atctivity
SBA 18.1 : Touch receptors in skin,
page 359
The ne rvous system is made up of neurones or nerve cells. Neurones transmit
electrical impulses to and from the brain. The nervous system is made up of:
• the central nervous system (CNS) whkh consists of the brain and spinal cord;
• the peripheral nervous system (PNS) whid1 consists of all the nerves outside
the central nervous system (figure 18.6).
central nervous
system (CNS)
cranial nerves
(from brain)
peripheral
nervous
system
(PNS)
~r++- spinal nerves
(from spinal
cord)
Rgure 18. 6 The nervous
system.
sensory neurone >
motor neurone >
relay neurone >
The peripheral nervous system forms a vast communication network linking
the reception of the stimuli to a response. Receptors receive stimuli from the
environment and responses are brought about by effectors.
Sensory neurones conduct impulses from receptors to the central n ervous
system. Motor neurones conduct in1pulses from the centra l. nervous system
to the effectors. Intermediate or relay neurones link sen sory and motor
neurones. They are found in the central nervous system (figure 18.7, overleaf).
211
Life Processes and Disease
dendron - carries impulses
towards the cell body
intermediate or
relay neurone
motor
neurone
sensory
neurone
node of Ranvier
Figure 18. 7 Motor, relay and sensory neurones.
.,____
-----
stimulus
sensory neurone
I
receptor
IITT-O~L
relay neurone
/
-
motor neurone
effector
brings
about response
Figure 18.8 The structures of the sensory, relay and motor neurones can be related to this typical
nervous pathway.
~
IT:Q3
V'-1
Describe the nervous system of
humans.
(ii) How do you respond to a stimulus?
(i)
212
Figure 18.8 is a typical pathway, from the s~ulu s touching the receptor to the
effector bringing about a response. The numbers in the following paragraphs
refer to figure 18.9.
1 The stimulus is, say, a hot object touching a pain receptor in the skin of the
hand.
2 A signal travels along the sensory neurone to the central nervous system
(CNS).
3 In the CNS, a relay neurone carries the signal through the brain.
4 The rela y neurone passes the signal to the motor neurone.
5 The signal travels along the motor neurone to the effector (biceps muscle)
which responds (contracts).
6 The hand is moved away from the hot object.
.
18 ·Irritability, Sensitivity and Coordination
contraction of the biceps
muscle moves hand away
from hot object
axon
dendron
-
CNS
spinal cord
to brain
stimulus
e.g. hot object
motor neurone conducts
nervous impulses from
CNS to the effector
sensory neurone conducts
nervous impulses from
receptor to CNS
Rgure 78.9 A typical pathway of receptor to effector.
~
l'.fQ~
V'-'
Describe a typical nervous pathway.
The nervous system is adapted to carry messages quickly between specific
locations in the body, so that quick responses can be made. Sometimes the
effector may be a gland. Endocrine glands are found throughout the body and
they regulate a wide range of activities, including heart rate, metabolism and
reproduction. Together, the nervous system and endocrine system co-ordinate
all of the body's activities.
The synapse
E'AhM"1¥il
Signals travel along neurones as electrical impulses, which are very fast.
However, there are millions of neurones in your body, and where the ends
of two neurones meet there is a small gap called a synapse (Figure 18.10).
Electrical impulses cannot cross th ese gaps, so they are converted to a chemical
signal in order to cross the synapse. As they reach the other neurone, they are
converted back into electrical impulses so that they can con tinue quickly on
their way.
A
sensory neurone
impulse arrives in
sensory neurone
cell
body
mltochondrlon
sensory
A~neurone
synapse
Figure 18.10 A synapse.
- - next nerve cell
message is transferred to
another nerve cell
B
213
Life Processes and Disease
~
Table 18.2 describes some receptors, effectors and responses in humans.
V'-1
Stimulus
l:T:QS
What is the receptor, the effector and
response of an animal when it sees and
moves towards a mate?
Receptor
Effector
Response
object moving towards retina of the eye
the face
receives and sends a
message to the brain
muscles of the neck
head turns away so the
object cannot hit the
face
very hot object which is nerve endings in
about to be picked up the skin sensitive to
temperature send a
message to the brain
muscles of the arm
hand pulls away from.
the hot object
chemicals from food
(smell) reach the nose
chemoreceptors in the salivary gland
nose send a message
to the brain
saliva secreted and
body prepares to digest
food
Table 18.2 Receptors, effectors and their responses in humans.
~
l:T:Q6
V'-1
(i)
What is a synapse?
All activity involves the coordination of the brain, spinal cord, sensory and
motor neurones. Stimuli are constantly being received, sent to the brain where
they are analysed and appropriate responses sent back (figure 18. 11).
(ii) Describe what happens at a
synapse.
1 Receptors in the skin (and face)
receive information and messages
are sent to the brain.
@ Brain receives and interprets
'-._. '
/
message: appropriate
response determined.
/
·!
/
-1
I\
Examples
3 Messages are sent from
the brain to the appropriate effector.
Jl
Touched on shoulder
nervous
Person turns around
Receptors in skin of shoulder ~ system ~ Effectors are muscles needed
to turn the body
Your name is called
Receptors in ears
nervous
Sees a friend
Receptors in eyes
nervous
system ~
~
system
Person stands up
Effectors are muscles
needed to stand up (legs)
Person walks towards friend
Effectors are muscles
needed to walk
Rgure 18. 11 Every day, millions of messages are received by the brain and appropriate
responses made. This Involves the coordination of sensory neurones, CNS and motor neurones.
214
~~~.l!!'itabil.!_ty, Sensitivity and Coordination
Reflex actions
reflex action >
Practical activity
SBA 18.2: Two reflex actions, page 360
~
IT:Q7
V-...J
What is the reflex action?
A reflex action is a rapid and automatic response to a stimulus. It does not
require conscious control (you do not think about doing it). Examples of reflex
actions are the knee jerk, sneezing, the pupil reflex and blinking. The pathway
between the receptor and effector is called the reflex arc. There are two kinds
of reflex:
1
• spinal reflexes are nerve impulses that pass through the spinal cord and do
not go to the brain (e.g. the knee jerk response, figures 18. 12 and 18.13 );
• cranial reflexes are reflexes in the head region (e.g. blinking and the
response of the pupil in the eye to light, figure 18.12).
(a) Simple (flow) diagram of the knee jerk reflex (spinal)
(b) Simple (flow) diagram of the pupil reflex (cranial)
bright light stimulus
stimulus received by
pressure receptors
at base of knee
.....I
sensory nerve
from receptors in eye
sensory nerve
to spinal cord
---~
r----~
motor nerve to leg
muscles (effector)
pupil gets smaller
in response to
bright light to
protect the retina
motor nerve to
muscles in iris
Rgure 18. 12 Simple diagrams of a spinal reflex and a cranial reflex.
2 stretch receptors detect
impulse causes the leg
muscles to contract. pulling
the foot forwards
the pressure on the tendons ::::~~~===f=.==~
9 sensory neurone
4 Impulse comes to the
CNS but does not go
to the b rain
knee cap
femur
1
st imulus - pressure
on tendons
---i- ---r- tibia
7
foot pulled
forwards - res ponse
Figure 18.13 Detailed description of the knee jerk spinal reflex.
215
Life Processes and Disease
The brain
~
IT:QS
\./'-I
A person who suffered brain
damage is now unable to see.
Explain how this could happen.
(ii} What consequences would result
from damage to the cerebellum of
the brain?
(i}
The brain is the most important part of the nervous system. It enables humans
to 'think' or 'reason', a skill which is supposedly lacking in most animals.
The brain has grey maner on the outside and white matter on the inside. It
is surrounded by tough membranes, called meninges, and cerebrospinal fluid
which cushion it from knocks. It is also surrounded by the bones of the skull.
Your brain is very well protected (figure 18.14) . Humans can perform compl ex
mental and physical activities co-ordinated by different areas of the brain
(figure 18.15). They receive stimuli from the environment and the brain brings
about the appropriate response.
(a)
(b)
meninges - the membranes
covering the brain
and spinal cord
~--
left cerebral
hemisphere
bone
cerebrospinal LM-....._,,....,__~
fluid
h<=;;;:;;;;;:;;:~~~~;:;;:::,~~c_~%-~'7'--fr hypothalamus
-
-11-.<--..,....::.+ - cerebellum
medulla oblong ata
dorsal root}
sp inal cord
ganglio n
ventral root
. 1
sp1na
nerve
Figure 18. 14 The brain (a) Section through the head. (b) External view of human brain.
motor areas
toot
cerebrum
leg
trunk
skin and
muscle
sensory areas receive
impulses from receptors
via sensory neurones
hypothalamus controls the - - -- .::...- - - body's internal environment
- homeostasis
pituitary gland - ----'=tendocrine gland,
secretes
several hormones
cerebellum controls
balance by coordinating
muscular activity
-~--- m edulla oblongata controls
involuntary muscular actions,
e.g. heartbeat, breathing,
swallowing , peristalsis,
blood pressure
Agure 18. 15 Functions of the various parts of the brain.
216
'°1.:;l
18 ·Ir r it a bility, Sensitivity and Coordination
The spinal cord is also composed of grey and white matter, but here the
white matter is on the outside and the grey matter on the inside (figure 18.16 )
back of body
ventral root
front of body
Figure 18.16 Cross-section of the spinal cord.
Autonomic nervous system
autonomic nervous system >
CHAPTER 16
~
IT:Q9
vv
Name six activities that occur
in the body while a person is
sleeping.
(ii) How is it possible for these
activities to take place?
(i)
The autonomic nervous system is the n ame given to all the nerves which
automatically control the normal functioning of internal organs like the heart
without conscious control. For example, your heart keeps beating, peristalsis
occurs, breathing occurs, pupils dilate and blood vessels constrict, without you
having to think about any of these responses - they occur even when you sleep.
The internal environment of the body must be kept stable (chapter 16).
Homeostasis, the maintenance of a constant internal environment, depends
on the autonomic nervous system. All cells, and th erefore tissues and organs,
function efficiently in certain conditions of temperature, pH and wate r. Any
change in these conditions must be remedied: for example, if there is a lack of
water, cells become dehydrated, so th e body responds to increase the amount
of water available. Animals and plants respond to internal changes in ways that
lead to stabilising the internal environment.
The endocrine system
In humans, the endocrine system consists of a number of glands called
endocrine gland >
endocrine glands. The endocrine system controls growth and developmen t.
A gland is a structure which secretes a specific chemical substance. In
humans, there are two types of gland: exocrine glands and endocrine glands
(figure 18. 17).
exocrine gland
endocr ine gland
(gland w ith a duct)
(ductless gland)
blood with
no secretion
secretions arrive
at target area
duct through which
secretions pass
blood with the secretion
flows to the target organ
Figure 18. 17 Exocrine and endocrine glands.
217
Life Processes and Disease
exocrine gland >
~
IT:Q-1 0
V"--1
Draw up a table to show the differences
between endocrine and exocrine
glands. Describe how they work and
give examples of the substances that
they secrete.
Exocrine glands transport their secretions by ducts to other parts of the body.
For example, salivary glands in the mouth secrete saliva via ducts into the
mouth; tea r glands by the eye secrete fluid which passes through ducts onto
the eye's surface. Endocrine glands secrete chemicals called hormones directly
into the bloodstream . These glands have a rich blood supply to collect the
hormone and transport it to its target organ.
The pancreas is an organ of the digestive system. It contains rwo types of
secretory cell. One type produces enzymes that make up pancreatic juice which
is secreted through a duct to the duodenum. Tbe type produces the hormone
insulin that diffuses into blood vessels which pass through the pancreas.
The pancreas is therefore a structure that is made up of both exocrine and
endocrine glands (figure 18. 18).
pancreas - some cells
make enzymes,
some make insulin
blood with no hormone
(insulin) flows to pancreas
enzymes in the gut
- blood rich in insulin
leaves the pancreas
Figure 18. 18 The pancreas contains both endocrine and exocrine glands.
Hormones help to control and coordinate many body activities, including
growth and development. They are produced by endocrine glands positioned in
specific areas of the body (figure 18.19).
- --+-- hypothalamus (manager)
pituitary (master gland)
ovary (female)
1--
r.,.--
-
tt-+- (progesterone, oestrogen)
---.,,c--
testis (male)
(testosterone)
Rgure 18. 19 The endocrine system in humans
Hormones are produced in very small amounts and travel through the body
in the bloodstream to target organs. Hormones influence the activities of these
target organs .
218
·
18 ·Irritability, Sensitivity and Coordination
The pituitary and the hypothalamus
hypothalamus >
~
IT:Q-11
V'-1
(i) What are hormones?
(ii) Name four different hormones
produced in humans.
Most, but not all, endocrine glands work under the influence of a single
master gland - the pitu itary, which is situated beneath the brain. The
hypoth a lamu s is situated close to the pituitary. While the h ypothalamus is
not an endocrine gland, it regulates the secretion of some of the pituitary gland
hormones. If the pituitary is thought of as the master gland of the endocrine
system, then the hypothalamus can be tho ught of as the manager. The
hormones produced by the pituitary and their effects are shown in Table 18.3.
Hormone
Functions
pituitary growth hormone
stimulates growth of the entire body: too much
causes gigantism; too little causes dwarfism
antidiuretic hormone (ADH)
stimulates the kidneys to reabsorb more water
from filtrate when the blood plasma becomes
too concentrated
other hormones: e.g. follicle stimulating
stimulate other glands such as the
hormone (FSH), luteinising hormone (LH), thyroid ovaries,thyroid, and testes into activity
stimulating hormone (TSH)
Table 18 3 Functions of the hormones produced by the pituitary.
Drugs and the effects of drug abuse
li!il[eiJ
A drug is any substance or chemical which alters the body's action, or
interferes with some aspect of the body's metabolism. It affects chemical
reactions in the body and ultimately, has effects on the brain. A drug can be
administered to the body in many ways:
• by injection;
• orally;
• applied to the skin;
• inhaled.
Medicinal use of drugs (prescription drugs)
Doctors assess the need for these drugs
very carefully, since many have side-effects.
However, some people abuse steroids,
diet pills, tranquillisers and antibiotics for
personal 'miracles', ignoring and sometimes
ignorant of the harmful effects. You should
take care to read all instructions on any
medicines that you use, or are prescribed by
your doctor to make sure you are aware of
the risks and side-effects (figure 18.20).
J
•
f f.dl.t-J d
P ror" ""'*<# de
Whar shou/d I avoid
.
t.ld··•
/uru: can mcrea I
/Wee while
increase rhe lrl..e~~h r It: "lllounr of Ml
OOd rhar YOU will
What arr th
.
• SI
' Poss1b/, sldr tHttts
owed hearrb (b
• Stomach Problear radycardi~
o d' h ems such as
Ou nut d ,,,, ,~ 81dpi::tru11"'' " ' '
rarr ea
nausea
vomiting
stomach are C b
111d1ges11on a a dominaf)
• fec/rng tired and
• skin problems suc~eak
as redness ~
Tell Your docto b
' '
r a out an 'd
,_: nor go away. Th
y sr e effect th ·
.
ese are not II h
'
o'..v Fo r more informati
a t e POSSib
~
on ask your doctor or
r (~~ :.?,~r _doctor for medir:ol , .,,.:
Figure 18.20 The side-effects of one
medicinal drug.
219
Life Processes and Disease
therapeutic drugs >
Medicinal drugs are widely u sed to diagnose, prevent and treat disease. These
include painkillers, antibiotics and vitamins which are described as being
t h e ra p e u tic d rugs.
Penicilljn is a common antibiotic, which is used for the treatment of
many bacteria l infections. Antibiotics save millions of lives each year, but are
sometimes used unnecessa rily and ineffectively to treat viral diseases. This
misuse can increase the risk of resistant strains of bacteria deve loping and
eventually serious bacterial diseases may become untrea ta ble.
Painkillers (analgesics) are very u seful but can be abused. Aspi rin is a
common painkiller which a lso reduces fever and inflammation. It works by
blocking the transmjssion of pain signals from the receptors to the spinal cord
and brain. However, it can cause irritation to the stomach waJls and is n ot
recommended fo r ch ildren as it may cause fata l brain and Uver damage. We
often resort to painkillers too easily, unmindfu l o{ the side-effects.
Many people drink coffee every morning, and some continue to consume
coffee all day. Caffeine is the drug found in coffee and is also added to some
soft drinks, incl uding many colas. It is a stimulant, making the user fee l more
alert and en ergetic. However; it is addictive and interferes with the proper
functioning of the central ne"rvous system. Caffeine also prevems ca lcium
absorption and can thus lead to weak bon es and teeth in the o lder years.
The use of diet pills, laxatives and diuretics is an unh ealth y and potentially
very dangerous way to lose weight. Some diet pills contain ephedrine w h ich
increases metabolism and makes the hea rt beat faster. This can lead to heart
palpitations, cardiac arrest, stroke, and death, even in an oth erwise healthy
person.
Steroids, which work similarly to some hormones, are used in the treatment
of asthma . However, th ey are sometimes abused by athletes and body-builders
to build up muscle, thus increasing strength and speed. The associated risks ·
include aggression, reduced sex drive and masculinisation of women.
Tranquilisers are sedatives that depress the nervous system , and are used in
the treatment of anxiety and stress. They are valuable drugs but over-u se ca n
make a person unmotivated and unable to cope with daily activities.
Abuse of drugs
psychoactive drugs '>
drug addiction !
CHAPTER 12
withdrawal symptoms \
Drug abuse refers to use of substances which may cause a person to become
dependent. These range from mild stimu lants like caffeine to powerful
chemica ls like narcotic drugs that can a lter mood and behaviour. Drugs
that interfere with the nervous system and cause change in menta l sta te
and behaviour are called psych oactive drugs . These include LSD, alcohol,
coca ine, nicotine and heroin. Use of these can lead to drug addiction, which
is the state of psychologica l dependence on the drug. Marijuana addiction is
discussed in chapter 12. Physical dependence occurs when the body adapts
to a drug and increases its tolerance to the drug's effects. This leads to using
larger doses of drug to achieve the origina l effect. Severe physica l withd rawa l
symptoms occur if the drug is not taken.
Alcohol
Euip'J;ml!+j
Alcohol is found in intoxicating beverages and is a depressant of the central
nervous system. In small amounts, its effect is to make the drinker more
sociable, more self-confident and to give a sense of weU-being and release from
anxiety. However, people abuse alcohol by repeatedl y drinking it in excessive
amounts. People who must drink alcohol every day to cope with life are
alcoholics: this dependence is classed as a disease ca ll ed alcoholism.
220
- - -- - -- - - - - -- - - --
-
- -
18 ·Irritability, Sensitivity and Coordination
Short-term effects of a lcohol abuse:
• slurred speech;
• impaired menta l function;
• loss of muscular coordination;
• increased excretion leading to dehydration;
• na usea and vomiting;
• possibl y vio lent or agg ressive behaviour;
• possibl e loss of conscio usness.
Lo ng-term effects of a lcohol abuse:
• physical and psychological dependence;
• severe physica l w ithdrawa l symptoms that in clude nausea, vomiti ng,
shaking, abdo minal cramps and pain, e n larged blood vesse ls in the face;
• sudde n discontinuation can lead to severe sbak.ing, hallucinations a nd
sometimes fatal convu lsions;
• malnutrition and risk of deficiency diseases;
• cirrhosis of the liver (wh en dead cells in the liver are replaced with fibrous
tissue);
• liver ca nce r;
• stomach ulcers as alcohol irritates the stomach lining ca using it to produce
excess gastric juice;
• corona ry heart disease and rugh blood press ure;
• a range of social, persona l and occupa tio nal problems.
Drinking during pregnancy can cause low birth weigh t, poor physical and
mental development in the fetu s, even fatal abnormalities; it can also lead to
miscarriage.
Cocaine
Cocaine has long been used by doctors as a local anaesthetic. However, it
is abu sed as a drug for the sense of euphoria or ' h igh ' it produces. It is a
stimulant, w hich helps in socia l situations. Tt can be very addictive, especia lly
as ' crack'.
Symptoms of cocaine a buse include:
• strange and violent behaviou r;
• hallucinations leading to schizophrenia, menta l illness and sometimes
death;
• increased blood pressure and heartbea t;
• lung and nasa l damage;
• red uced need for sleep.
Coca ine addiction is a worldwide problem. Many governments try to ed ucate
their people about th e dangers associated with cocaine, includ ing the murder
and corrup tio n wh ich ofte n follow its production and sa le. Ao addict's famil y
suffe rs emotiona lly, financially and socially. But a lot of mone y is involved in
th e illega l dru g trade a nd trafficking and the problem of addiction persists in
many parts of the world .
Social and economic implications of drug abuse
• loss o f working time which red uces th e productivity of the econom y and
causes loss o[ earn ings for th e country and reduced standard of li ving for its
people.
• loss of U(e due to overdose.
221
Life Processes and Disease
• Increased demands on hea lth services [or rreatment and sornerimes
pro longed and expensive care. Research for cures is a lso very expen sive.
• Increa sed crime and social unrest.
• Fam il y and personal neglect.
• A stimulus is a change in the environment that an organism reacts to.
• A response is the change in the organism brought about by the stimulus.
• Responding to stimuli is important for the survival of animals; responses may help to
find food, to escape predators and to find a mate.
• Green plants respond to the stimulus of light by growing towards it.
• Sense organs are organs that receive stimuli. In humans, the sense organs are the eyes,
ears, nose, tongue and skin. The eye responds to light; the ears respond to sound; the
nose and tongue respond to chemicals; the skin responds to pressure and temperature.
• The nervous system is responsible for receiving stimuli and coordinating a response.
• The nervous system is made up of the central and peripheral nervous systems.
• The central nervous system is composed of the brain and spinal cord.
• The peripheral nervous system is composed of all the other nerves.
• Sensory nerves carry impulses towards the central nervous system.
• Motor nerves carry impulses away from the central nervous system.
• The junction between two neurones is called a synapse.
• Receptors receive stimuli from the environment.
• An effector brings about a response to a stimulus. It is often a muscle.
• A reflex is an automatic response to a stimulus and does not require conscious control.
• The brain enables humans to perform complex mental and physical activities.
• The autonomic nervous system controls those responses that do not require
conscious control.
• Any substance which changes a body's action is a drug.
• Prescription drugs and drugs used for medicinal purposes can also be abused .
• Some drugs such as alcohol, cocaine and marijuana can lead to addiction or a state
of physiological dependence on the drug.
• Drug abuse has many social and economic implications for the family, community
and country.
222
··S:,,:_ . _. ~ ·.1~ ..· l~rjt?bility, Sensitivity and Coordination
ITQ1 (i) I rrita bility is th e ability of livi ng o rga nism s to respond the stimuH
co m in g from the enviro nment.
(ii) lrrira bility is importa nt because stimuli from the en vironm ent ca rry
informa tio n abo ut food, predators, co mpeti tors a nd so on. An o rga nism ma y
die q u ickly i[ it cann o t respond to this informa tio n .
ITQ2 Dogs have a very keen sen se o f sme ll w hich they use to hunr fo r l'ood.( A
rabbit has eyes at the sid es o [ its head, w h.ich give the ra bbit a bigger fi e ld o ( view
to see preda tors. Yo u may have tho ught of o the r examples - the re are ma n y.
ITQ3 (i) The nervo us system o f h uma ns co nsists of the brain, spina l co rd
and a n umbe r of ne rves that extend th ro ugho u t the bod y.
(ti) Senso ry ne rves d ecec1 stim u li from th e e nvi ro rune nt a nd m essages are
sent to the brain, which whe n processes a nd sto res che informatio n . Messages
are sent back to certai n o rgans in respon se to the stimuli .
ITQ4 stimulus - recep to r - sensory ne u ro ne - cen tra l ne rvous system mo ror ne uro ne - effector - respon se
ITQ5
Receptor
Effector
Response
eyes see the potential mate
muscles
animal moves towards the mate, showing courtship
behaviour, etc.
ITQ6 (i) A sy napse is the j unction between rwo ne rve cells.
(ii) Messages in the fo rm o f e lecrr ica l im pu lses a rrive at the e nd o f o ne nerve
cell. Thi s ca uses a che mical to cross th e junction be tween the two nerve cel ls.
On arrivaJ o f rhe ch emi ca l ar th e oth er n erve cell, electrica l imp ulses are
gene rated the re and the m essage is senr o n .
ITQ7
A re fl ex actio n is a respo nse to a stimu lus w itho u t conscio us
knowledge.
ITQ8 (i) The person m ust have received da mage co the regio n of the brain
respo nsible [or receiving a nd p rocessing info rmation comi ng from tbe eyes.
Even tho ugh the eyes may function perfectly, tbe bra in can no t receive o r
process signals from ch em so there is n o perceptio n o f seeing.
(i i) The cere be llu m is responsible for bala nce and coordina tio n o f muscle
activity. If rh e cerebeLlu m is dam aged, the person will not be able to sta nd,
wa lk, eat o r perfo rm activities chat involve the mu scle coordination .
ITQ9 (i) Respiratio n in a ll ce lls; bearing o r th e heart; brea th ing movements;
m ovem ent of food a long che aLim eora ry ca nal; movem e nt o f blood through o ut
the body; prod uctio n o[ urine by th e kidneys.
(ii) The a u tonom ic n ervous system is respo nsible fo r a ll these activi ties.
Messages a re sent to va rio us orga ns consta ntl y, ensurin g tha t they continu e to
do their j obs, e ve n during sleep .
ITQ10
Endocrine
Exocrine
gland lies next to a blood capillary
gland has a tube that connects to its site of action
hormone diffuses across membranes to the
blood and is transported by the blood to the
site of action (e.g. insulin and adrenalin)
chemical passes through the duct to the site of
action (e.g digestive juices and saliva)
ITQ11 (i) A h o rmo ne is a cl1e1nical messe nge r. II travels in the blood and has
its e ffect at a rarget site w here th e chem ica l brings abo u t a reaction.
(ii) lns u li n, ad re na li n, resterone, oestroge n
223
Life Processes and Disease
Examination-style questions
(i)
Explain the meaning of the terms:
(a) stimulus;
{b) response.
(ii) Describe fully a named response and explain why it may be important to the survival
of the organism .
·~
(iii) Copy and complete the table below.
Sense
organ
Stimulus to which An example of its importance (describe an everyday
it responds
activity that uses the sense organ and explain how
it is used)
eye
ear
nose
tongue
skin
{iv) A person deficie.nt in one sense organ is said to develop another sense to a greater
extent than normal. For example, a blind man is said to have a better sense of hearing.
{a) Suggest an explanation for this phenomenon in nature.
(b) Suggest two ways a person who has lost his/her sense of sight may be affected.
2
{i) The nervous system is made up of two parts. Name the parts and give a description of
each part.
(ii) Make a labelled drawing of a typical motor neurone.
(iii) List some differences between a motor neurone and a sensory neurone.
(iv) A child touches something hot, and pulls away her hand from the hot object. Describe
the pathway of this response through her nervous system , from the time the hot
object touches the receptors in her skin to the contraction of muscles as she pulls her
hand away.
3
(i)
Copy the figure below which shows a section of the human brain. Name the parts
labelled A, B, C, D and E.
(ii) All the activities of the body are controlled by the brain. Annotate your copy of the
figure to show the sites of control of these functions:
(a) intelligence
(b) hearing
(c) sight
(d) coordination of muscular activity.
224
9ihe Eye, the Ear and
the Skin
0
0
0
0
0
0
0
0
relate the structure of the human eye to its function as a sense organ
0
discuss skin care
understand sight d efects and their correction
relate the structure of the ear in humans to its function as a sense organ
understand how we hear
understand how the ear is used for balance
explain the terms poikilotherm and homeotherm
understand why temperature regulation is an example of ho meostasis
relate the structure of the human skin to its function in temperature regulation
and prot ection
sense organs
light
r
I
tongue
eye
I
sight
defects
I
sound
nose
'
pupil -
light
intensity
retina _
'
l
outer
ear
distance
homeotherm
middle
ear
J
l
behaviour .
skin
ear
accommodation
lens -
poikilotherm
J
conserve heat
lose heat
inner
ear
r
optic nerve
to brain
r
ear sac
balance
I
\
semicircular
canals
skin care
'
hearing
I
cochlea
Our s urviva l, ind eed o ur very existen ce, dep end s o n o ur reactio ns to stim ul i
co rning from th e en vironmen t. We feel, bea r, see, taste and sm e ll o ur
su rro un dings every Uving m o ment. The ma in sense o rga ns in hu mans a re tJ1 e
skin , ea rs, eyes, ton g ue a nd nose (table 19. l ).
Sense organ Stimulus to which it responds
tongue
Taste buds on the tongue are composed of sensory cells. Chemicals dissolved in
moisture in the mouth are detected by these cells. The taste buds on the tongue
are sensitive to four different tastes - sweet, sour, salt and bitter. Messages are
sent to the brain to determine the taste.
nose
Sensory cells line the nasal passage. These cells detect chemicals in the air
entering the nose. Messages are sent to the brain to determine the smell.
(continued)
225
Life Processes and Disease
Sense organ
Stimulus to which it responds
skin
There are many different nerve endings in the skin. It is thus very sensitive to
many different stimuli - pain, touch, temperature change and pressure. The skin
'touches' the environment. The receptors in the skin send messages to the brain
to determine what we have touched. The skin is also a protective barrier against
the environment. The internal organs are protected from the dangers of the t
physical environment, such as UV rays and microorganisms (pathogens).
ear
The ear collects and directs sound waves (pressure changes) to the eardrum.
Vibrations of the eardrum eventually cause movement of the sensory hairs in the
cochlea. This causes nerve impulses in the auditory nerve which are interpreted
by the brain as sounds.
eye
Sensitive cells on the retina of the eye detect light reflected from objects. An
image is formed in the brain when we see.
Table 19. 1 The main sense organs in humans and the stimuli to which they respond.
The eye
Structure of the human eye
The eye is a ligh t-sen sitive orga n that enab les us to see small va riations
of colo ur, sh ape, size, brightness and dista nce. Light rays from objects are
co nve ned to nerve impulses w hich are sent Lo the brain. Th e braio, not the
eye, is w here the actual process of seeing is p er formed.
The eyebas a num ber o r re lated strucwres (figure 19 .l}:
• eyebro w directs sweat mov ing down the [orehead away fro m the eye;
• eyelids close to protect the eye against dust and bright Light;
• tear gland prod uces tears wh ich wash away d ust particles and conta in the
enzyme lysozyme which ki ll s bacteria;
•
•
eyelas hes keep the front. o f the eye free from dust a nd dirt;
pupil is the bo le w hich a llows light to em er the eyeba ll;
• iris gives colo ur t0 the eye and con trols the size of the pu pil .
• scle ra is the white fibrous coa t w hicb protects the eyeba ll.
.~
V'--J
Where are the eyes positioned in
the human body and how is this
different from a herbivore such as
a zebra?
(ii) Give an explanation for the
difference in the position of the
eyes between a carnivore and a
herbivore.
(i)
~;;::.:___
upper eyelid
and lashes
!--..IJ~-- lower
eyelid
.;_...__
protect
the eye
_ duct draining
tears to nose
~
Figure 19. 1 The eye and associated structures.
V'--J
The eyeballs are ba ll- li ke structure situated in cavities in the sku ll ca lled orbits.
Figure L9.2 shows a sectio n th ro ugh the human eye and figure 19.3 describes
the functions of vario us parts of the eye.
IT:Q2
List three reasons why eyes are
important to a human.
226
19 ·The Eye, the Ear and the Skin
,,
eye lid "
,f./
/.<
'iY.:V,All'~-Y:~
eyelash ~~
ciliary body ---h~•
iris - -----,7'7"--.• I
aqueous humour - --r-.-+cornea --~
lens - -+---+--- -;
su spenso ry --~
ligament
Figure 19.2 A section through the human eye.
conjunctiva - thin transparent skin
continuous with lining of
eyelids: pro tects cornea
iris - coloured disc composed
o f muscle; controls amount
of light entering eye ~
aqueous humour - colourless fluid .
sclera - tough, white fibrous
coat; protects eyeball
ciliary body
c horoid - contains blood vessels to
supply retina with food and oxygen;
black pigment to prevent reflection
of light insid e the eye
1'
/
/
1 .:- / ...411
~
~'/
/,/.
'""~--- re tina - contains light-
cornea - transparent front part
of sclera; refracts (bends) light -~~•
rays to a focus on the retina
pupil - hole In centre of iris;
allows light to enter eyeball
sensitive cells: rods
and cones
fo vea - contains cones only;
most sensitive part of retina;
most light rays are focused here
blind sp ot - point where
op tic nerve leaves eye;
no light-sensitive cells
lens - transparent, elastic, biconvex /
structure; makes fine adjustments
to focus light on retina
optic nerve - carries
impulses from retina to b rain
susp ensory ligament - attaches
lens to ciliary body
ciliary muscle - circular ring
of muscle fibres; alters lens
shape during accommodation
Figure 19.3 Functions of the various parts of the human eye.
How we see
rnhieijH
Light rays from the o bject travel in a straigh t lin e to th e eyeba lls. They pass
thro ugh th e stru ctures a t the fro nt o f the e ye ba ll , th ro ugh the p upil and
a re focu se d on the retina (fig ure l 9.4, overlea f). Th e ligh t stimula tes ligb.rse nsitive cell s of. the retin a w hich send impu lses a long t he op tic nerve to the
bra in. The brai n the n fo rms a n image o f size, shape. colo u r and di stan ce away
fro m the o bject.
227
Life Processes and Disease
l'Alt:fffll
The cornea ben ds (o r refracts) the light LOwards the retina. The lens,
however, can vary tJ1e amo unt of bending or refraction and thus ensures the
accurate focusin g of th e image on the retina (figure 19.5). The iris is composed
of circular a nd radial muscles and con trols the size of the p upil which then
va ri es the amo un t of light that enters the eye. The iris closes down in brigh t
light to protect the cells in the retina.
Th e len s is transparent an d bi convex in shape. The amo unt o ( refraction~
of the ligh t passing thro ugh it depends o n its shape. It can be flattened (less
convex) or made m ore ro unded (more convex). Th is adjustmem is needed fo.r
focusing on objects that are different distances away (figure 19.6).
lens - varies the amount of refraction
so as to focus the light rays into a
sharp image on the retina
light rays
light rays
;~\
lens
to brain
Figure 19.4 Light rays pass through the cornea. pupil, lens and
humours and are focused on the retina.
(a) Flattened lens, less refraction of light
light rays from a
distant object
(b) Rounded lens, more refraction of light
cornea - refracts \
the light
\
to brain
"
Figure 19.5 Light refracts as it passes through the cornea and lens.
Detail of ciliary muscle,
ligaments and lens
less refraction
'/ /
light rays
light rays from a
near object
bulged lens shape
more refraction
The ciliary muscle Is ring-shaped ; on contraction
the ring gets smaller. This causes the suspensory
ligaments to slacken and the lens becomes a more b ulged shape.
Figure 19.6 The lens in the eye changes its shape to ensure that the rays focus on the retina.
228
19 ·The Eye, the Ear and the Skin
Accommodation
accommodation >
~
IT:Q3
V'-'
Name in order the parts of the eye
through which a light ray passes on its
way from the conjunctiva to the retina.
The adj ustm ent of the lens fo r focusing on near and distant objects is called
accommodation. The len s is connected by ligam ents to the ring-shaped
ciliary muscle. Contraction and relaxation of the ci liary muscle affects the
tension in the ligam ents which cbanges the shape o f the lens.
Wh en focusing on a distant object, the ciliary muscles relax. This pulls the
suspensory liga ments tight which m akes the lens flatten ed (less con vex). Thi~
shape refracts the light less a nd the image is focused sh a rpl y on the retina
(figure 19.7).
When focusing on a nea r object, 1..he ciliary muscles contract. This reduces the
tension on the suspensory ligam ents an d they slacken. The ligaments pull less
on the lens and it becomes more rounded (more convex). A very curved shape
refracts the light m ore. Th e image is again sha rp on the retin a (figure 19.8).
/
lens flattened
less refraction
light rays from
distant object
light rays from
near object
to brain
Figure 19.8 Focusing on a near object.
Figure 19.7 Focusing on a distant object.
The effect of pupil size
QSb
IT:Q'I
V'-'
What is meant by the term
'accommodation'?
If you wear glasses, try making an artificially
small pupil with the tips of three fingers and look
through it (without your glasses on) at something
which looks blurred (figure 19.10). Because of
the increased depth of focus, you should see
it more clearly.
When the p upil is wide open, more light enters the eye than w hen the pupil
is sm all. In bright light the pupil contracts to protect th e eye from excess ligh t.
ln dim light th e p up il expands to tak e advan tage of as much ligh t as possible
(fig ure 19.9).
To expa nd the pupil the circu lar muscles in the iris re lax and the radia l
muscles contract, pulling th e iris back an d so op ening the pupil .
To m ake th e pupil smaller th e radial muscles re lax and the circular mu scles
contract.
Figure 19.9 Changing pupil size in different light conditions.
Figure 19. 1O An artificial pupil.
depth of focus >
Depth of focus
Wh en th e pupil is sm all (in bright Ligh t) the eye has a grea te r depth of focus .
The sh a pe of the lens does not n eed to chan ge quite so much to sw itch from
viewing a distant obj ect to viewing a n ea re r o ne. In dim light w hen the pupil is
wide, the depth of focus is less and the lens m ust change m ore.
229
Life Processes and Disease
This is sometimes noticed if a person is slightly Jong-sighted or slightl y
short-sighted. ln bright Light the y will see objects clearly which in dim ligh t
appear a little blurred.
Also, as a person ages, their power of accommodation gets less and the
range of distances over wbich they can see sharp images is reduced. This is
much more noticeable in dim light than in bright light.
The retina
The retina is a photosensitive layer at the back of the eye. It is made up or two
mm H·leI:tJI types of phororeceptor ca lled rods and cones (figure 19.11) . The rods are
l(.l@fil
sensitive to light and dark onJy; the y do not react to colour. They function best
in low light intensities such as when it is getting dark. This is why we see on ly
in black and whjte at night. The rods are located around the sides or the retina
away from the fovea .
Rods are desensitised by bright light, whid1 explains why yo u cannot see
clearJ y if yo u move from a bright area to a dim or dark o ne. After a few minutes
though , the rods recover th eiT sensitivity and yo u can see more dearly aga in.
retina
B
-
-+--
ID-CC~
-
-fovea
(cones only)
retina
magnified
A
blind spot -~~~
optic nerve - messages from
all the photoreceptors go to the brain
Figure 19.11 The retina is made up of rods and cones (light-sensitive cells). Light falling on the
cells causes nerve impulses which travel to the brain via the optic nerve.
~
IT:QS
V'-1
Describe how we see.
liJnml#l•i•iH
The cones are sensitive to colour and function best in high light intensities.
They are located mostly around the centre of the retina. Tbe fovea is composed
entirely of cones and is at the centre of the retina. Light focused on the fovea
produce a clear well -defined image in tbe brightest colour.
Th e point of exit o[ the optic nerve from th e eye is called the blind spot
because it lacks photoreceptors and is in sensitive to light. Light fa lling on thls
spot does not ca use a response in the nerve, so you are 'bli nd' at th.is point.
Sight defects and their corrections
A sight defect is caused by any condition that prevents proper focu sing of Light
on the retina . A faulty focusing mechanism may be ca used by a number of
fa ctors, such as th e shape of the eyeba ll or hard ening of the lens. Some common
sight defects a re lo ng-sightedness, near-sightedness, cata ract and glaucoma.
230
19 · The Eye , the Ear and the Skin
Long-sightedness
hypermetro ia >
Long-sightedness, o r hypermetropia , is ca used by the eyeba ll being too
short from rront to back, or the lens being too fla t. As a resu lt, li gh t from
distant objects can focus on the retina, but light from nea r objects is focused
behind the retina. So disra11 t objecrs are seen m ore clearl y than near ones.
The condition can be corrected by wear ing con vex o r con ve rging lens
(fi gure l 9. 12).
light rays from
near object
- - - -tt:JCTb~::::=:::'.~
focus of light rays
from near object before
correction - behind retina
converging lens bends
light rays inwards before
entering the eye
Figure 19.12 Long-sightedness and its correction.
Near-sightedness
~
Nea r-sighted ness (or sl1o n -sigbted11ess), or myopia , is ca used by the eyeball
being too long from front to back, or the le ns being too cu rved. As a res ult,
lig ht rays fro m a distant o bj ect a re bent m ore tha n necessary a nd focus in frolll
o f th e retina. However, light rays from near o bjects focus 0~1 the re tina . So near
objects are seen more cl ea rl y than d istant o nes. Wea ring concave o r diverging ·
len s h e lps the person to see far objects clearly (figure L9.l3).
IT:Q6
V'-'
What kind of lens is needed to
correct (i) long-sightedness (ii) nearsightedness?
focus of light rays
from distant object after
correction - on retina
light rays from
distant object
diverging lens bends
light rays outwards before
entering the eye
'-1
focus of light rays
fro m distant object before
correction - in front of retina
~
"\.. ' \
Figure 19.13 Near-sightedness and its correction.
Astigmatism
This is ca used by the surface o f Lhe lens or corn ea being curved irreg ula rly.
Specia ll y shaped lenses, whid1 balance o ut these irreg ula rid es, need to be worn
to provide a clear image o n tbe re tina .
Cataract
Figure 19. 74 A cataract reduces the light
entering the eye.
This occu rs when the Lens becomes opaqu e a nd light cannot pass th ro ug h, so
the person is una bl e to see (figure 19.14) . The le ns ca n be removed during
surgery. Adjustments t:O vision ca n be made with approp ri ate specrad es or
conta ct lenses, so that the person ca n see clearly again. Alternatively, tbe lens
ca n be replaced w ith an intra ocu lar le n s.
231
Life Processes and Disease
Glaucoma
W-,
IT:Q7
V'-'
(i) What are defects of the eye?
(ii) Name two defects of the eye and
explain what causes them.
This occu rs w he n there is a build-u p o f pressure in Lhe aqueous h umou r. This
increased pressure inside Lhe eyebaU ca n da mage the optic ne rve. The sufferer
expe ri e nces pa in ful and infla m ed e yes, and a ha lo is seen a ro und objects.
Visio n is p oor, and the su ffe re r may experie nce sightless a reas io the fiel d of
visio n. It is associa ted w itb an increase in age bu t may develop a t a n y time
fro m in [an cy on .
t
The ris k factors for gla ucoma a re age, h ered ity, myopia, and general diseas.e
such as a su o ke . In its earl y stages, glau coma can be effecti vely treated with
m edicatio n, li ke e ye drops a nd o ral m edi catio n . Tf left un treated, it ca n cause
vision loss o r blindness. ln its late r stages, su rge ry ma y be necessary to ease the
pressure in the eyeba lls.
Gla uco ma is the most common ca use o f bli ndness. Damage to th e optic
ne rve is irreve rsible .
The ear
Structure of the human ear
The ma mma lian ear per[orms two fu nctions:
•
hea ring;
•
ba la nce.
It is d ivided into three regio ns: the o u te r ear, the m iddle ear a nd the in ne r ear.
Figure 19. l 5 sho ws tbe str uctu re o f the hum a n ear.
pinna
bones of skull
semicircular canals
vestibular
apparatus
stapes
ossicles
[
incus
--~
malleus
tympanum
(eardrum)
outer ear
middle ear
Figure 19. 15 Structure of the human ear.
232
inner ear
19 ·The Eye, the Ear and the Skin
How we hear
A n o ise is se t o f vibrari ons o r so und waves in th e a ir. Th e so und wa ves reach
l•liehfiH th e ea r a nd rh e pinna (tbe o u te r ear ) directs the m into the a ud itory ca na l. Th e
l•1'i'·U'9!4'1J
13-13E@IJ
la@l+@QIJ
so un d waves travel down th e ear ca nal to the ea rdrum. The ea rdrum vib ra tes
w h e n hi t by the so und waves. This ca uses rhe ea r ossicles, o r ear bo n es, in the
middle ea r w vibra te. Th e inne r ea r is filled w ith flu id . The vibra tio ns a t th e ,
ova l w indow start up press ure waves i11 the flui d o r th e coch lea (fi gures 19. 16
a nd 19 .17 ).
The iJ1ne r ear is made up o f two pa ns, th e cochlea a nd th e vestibu la r
a ppa ra tus. Th e cochlea is a lo ng, coiled, three-cha mbe red tu be w hi ch is
res pon sible [o r o ur sen se oJ h earing. The i11ne r ea r is fill ed w ith fluid. Th e
vibra tion s at rh e ova l window start up press u re waves in th e fluid o f th e cochlea.
Th e cochlea conrains receptor s ca lled hair cells which vibra te in respo nse
to the press ure waves in the cochl ea r fl u id. Nerve impul ses a re gen e ra red
which pass a lon g th e aucfaor y n erve to
th e brain and we h ea r. Th e vib ra tio ns
th e n pa ss a way lO the roun d wi ndow
and we are read y to h ea r aga in.
middle ear
outer ear
vibration is amplified - -
inner ear (fluid-filled)
membrane covering
oval window
sensory cell stimulated impulse sent to the brain
-------~~---- impulse taken
to the brain
-+
- j~
sound wave
membrane covering round window
(absorbs the waves and prepares the
fluid to detect new waves)
cochlea
Figure 19. 16 Sound waves are vibrations that travel through air to the outer ear. They are
amplified as they pass through ossicles of the middle ear and then converted to pressure waves
in the cochlea.
Figure 19. 17 The three bones (ossicles) of
the middle ear.
m anic membrane >
The eardrum
tympanic membrane or eardrum
kept taut by equal pressure on both sides
inner ear
outer ear
pressure
fluid
air
\
ressure
~
\
\
Eustachian tube from the
throat controls the pressure
of the air in the middle ear
1
The ea rdrum is a thin membran e which is puU ed
ta ut a nd separa tes th e o u te r a nd middle pa rt o[ the
ear (fi gure 19. 18). lt is a lso called th e tympanic
membrane. Th e vi bra ti o ns in the sound waves a re
con ve rted to m ovem ent w h e n th ey ' hit' th e eardrum
a nd are amplifi e d as they pass thro ugh the tb ree
ea r bo n es. Pressure o n both sides o f th e ty rnpan ic
me mbra n e must be eq ua l so tha t it stays stra ight and
ra ut, and sound m essages ca n be passed o n effi cie n tly.
We som etimes feel o ur ea rs 'pop', such as w he n
fl yin g in an ae ropla n e. This ha ppens as rhe rympa ni c
m e m bra n e m oves back ifl to positio n w hen th e press ure
o n both sides equa li ses (Figure 19.1 9, overl ea f).
~
IT:Q8
V'--J
When we hear, what is the role of (i) the pinna (ii) the ear
bones (iii) the cochlea?
Rgure 19. 18 The eardrum separates two air-filled regions of the ear.
233
Life Processes and Disease
m iddle ear
Equal pressure on the eardrum
whilst airplane on the ground.
sound waves
As the airplane g oes up, the
atmospheric pressure is lower.
The pressure in the middle ear
is now greater and the eardrum
'bends'. Hearing is distorted.
The p ressure may equalise
(naturally, or by chewing gum)
and the eardrum returns to the
normal position. It 'pops' as it does so.
Agure 19. 19 The eardrum can 'bend' if the pressures on either side are unequal.
Balance
vest ibular apparatu s >
sem icirc ular canals )
The vestibu lar apparatus is responsible for o ur sense of ba lance and
in formation about the position and movement o f our body. Th e vestibu lar
apparatu s is made up of:
• th e semicircu lar canals w hich detect movement o f th e head;
mmam ..1uaa11m • the utricle and saccu le (ea r sac) wh ich detect the position of th e head .
Elule!iilrn
Receptors inside these stru ctu res are the ha ir cells tha r deflect o n mo vement.
This causes a n impu lse co be sent to the brain.
The semicircuJar ca na ls are at right-an gles co each other, in th e three pla nes,
so that any movement of the head, and th erefore the body, is detecteo. At the
base of each sem ici rcular cana l is a sweUing ca lled a n ampu lla . Figure 19.20
sh o ws how the am.p ulla works.
movement of the body
/
cupula displaced by _ __
movement of endolymph
Figure 19.20 Movement of the body moves
fluid in the ampullae in the opposite direction.
The brain gets impulses from all three ampullae
and interprets the messages as movement.
234
vestibular nerve to the brain, which interprets the message
-
--
relative movement of endolymph
because of movement of the body
19 ·The Eye, the Ear and the Skin
~
l'.'f:Q9
\.../"-'
Even with the eyes closed, the brain can
detect movement of the body, that is,
the direction and the relative speed of
the movement. How is this possible?
Tbe ea r sac is posirio n ed below the sem i-circu la r ca na ls. lnfo rmation a bo m
tbe position of rh e h ead and therefo re the body is de tected by receptor cells
a nd impulses are sent to th e bra in. Th e utricle responds Lo verrica l movemems
o f the bead and th e saccul e responds LO la tera l o r sid eways m ovem e m of rhe
head. Fig ures 19.2 1 a nd 19.22 illustrate h ow they wo rk.
lean forward
ball pulls on sensory hairs
Figure 19.21 Movement of the head vertically, pulls on
sensory hairs in the utricle. Impulses are sent to the brain
which are interpreted as movement of the head.
Rgure 19.22 The saccule
responds to lateral or sideways
movement of the head.
The skin
World te mpera LU re varies
fro m -58 °c in th e col d polar
regio ns LO around 30 °C in
tropica l ra info rest a nd over
60 °C in h o t deserts. Some
a nim als are adapted to live in
extrem ely cold enviro n m e nts
w hile others ex ist whe re
e n vironme nta l te mpe ra tu res
can exceed 60 °C. Despite
the te m perature o f th e
e n vironme nt, th e bod y
te mpera ture o f a huma n
is a lways abo ut 37 °C
(fig ure 19.23).
Figure 19.23 The body temperature of both boys is
about 37 °C, even though one lives in an extremely
hot environment and the other in an extremely cold
environment
Temperature control
homeotherm >
oikilotherm >
In the an imal kingdo m , birds and mamma ls a re a ble to mai nta in a fa irly
constam body te m perarnre. They are described as being homeotherm ic (or,
less co rrectl y, as warm -b looded). Th is fa irly constan t body temperature is
ma i;1rained using ph ysiologica l m echanisms o r processes w hich occur wit hin
th e body, fo r exa mple respiratio n w hi ch gen e rates heat, a nd consrrictio n o f
blood vessels which reduces b lood flow to the skin a nd the re fore h ea t loss.
All invertebra tes, fish, amp h ibia ns a nd repti les are unable to regula te
the ir body Le mperarure by ph ysio logica l means. They are described as
poi kilothermic (or, less correctl y, as cold-blooded) . They re ly o n heat derived
from th e e nvi ro nm e nt ro kee p the body warm. Conrrol o[ bod y te mpera ture
235
Life Processes and Disease
is ach ie ved by beha vio ura l mecharusms, fo r example moving ro a cool place
under a rock a nd basking in sunsh ioe. The body tempera ture or poiki lo t11erms
usuall y depe nds on their e nvironment (figure 19.24).
~
l:tQil 0
Noon - lizard hides from the Sun
Morning - lizard warms up
l/'-)
Define (i) homeothermy (ii)
poikilothermy, giving examples of each.
Its body temperature was low
from the night. so It basks
in the Sun to increase
its body temperature.
Its body temperature could
rise too high if exposed to the
Sun so it hides under a rock.
Rgure 19.24 The body temperature of a lizard (poikilotherm) varies with the environment.
~
l:tQ·
11
l/'-)
Why are humans able to live in
extremely hot and extremely cold
environmental conditions, unlike some
animals?
Th e gra ph Lo figure I 9.25 compares the body te mpera tures of a hu man and a
lizard for 24 hours of a day. The change in body tempe rature of the liza rd may
be m o re than 10 °C, while th e change in body tempe rature o r a human is less
than 2 °C. The bo dy temperature o r the lizard may drop Lo abo ut 5 °C a t n igh t
when the re is no solar heat, and be raised to a bout 20 °C in the hea t of the day.
liemperat ure 1
50
air temperature varies from
morning to noon to evening
-·· ·-- -·i----······ ····· -· · ·--:r-·
'°C)
40 ····- -· - --~-··-·-·--·-·
~--------
-------
· - -· - ·
1
- -- - - - · -
----·--1
so ----~
i
I
20
----1--7''-----=4--=:--- t - -Y-"'
-
12
noon
human temperature
-------1- - stays about the same
18
I
lizard comes out of hiding
to bask or move around
looking for food
lizard in a cool place - its
body temperature is lower
than air temperature
24
midnight
Rgure 19.25 How the body temperature of a lizard and a human. and the air temperature
may vary in one day.
CHAPTER 16
236
~
A body te mpe rature o f about 37 °C is idea l fo r chemi ca l reactions to ra ke
place as maoy en zymatic reactions have an optim um temperature o f aro und
37 °C. These reactions are impo rtant Lo sustain life; they occu r continuo usly
in eve ry cell. The regu la tio n a nd maioteoan ce o f cons taot condition s wi th in
an o rganism is called ho meostasis (chapter 16). Therefore, keeping the
te mperatu re of tlle tissue fluid surround ing cells fairl y constant is an example
of ho meostasis.
The temperat ure r ange o n Earth is ve ry w ide and va ries with lalitude
(from the poles ro the equator) : con ditions range from extrem e cold in the
po lar regio ns to extreme beat in the tropics (figure 19.26). Mosq u itoes and
fli es {invertebrates) are poikilo the rmic and infest the tropics w he re the
e n vironmental temperature (28-3 1 °C) is idea l fo r them to live a nd nourish.
M a n y are vectors o f disease, and so tb e tropics team w ith disease-ca rrying
and disease-ca using organ.ism s. Diseases li ke ch o le ra, malaria, de ngue fever
a nd yello w fe ver are m onitored con sta ntly in order to try to keep them unde r
19 ·The Eye, the Ear and the Skin
~
ll!Q-1 2
V'-1
Why are people who live on and around
the equator more likely to suffer from
certain diseases, such as malaria and
dengue fever?
control. Poikilo therms a re restricted
polar
N
to ce rtain a reas in th e wo rld because
th ey beco me sluggish a nd e ven rorally
inactive in low temperatures. Low
te mpera tures slow down e n zymatic
reactions.
Mamma ls a re able to ma intain th eir
bod y tempe rature close to o p tim um
despite changes in th e environm e nt.
They ca n re main acti ve da y a n d night,
summ e r a nd winter, a nd can inhabit or
li ve in a ny part of the wo rld . Howeve r,
the y req uire more food . Mainta ining
s
region
a bod y te mperature diffe rent from the
environme n t requires a lot oJ e ne rgy. A Figure 19.26 The surface temperature of
m o use, ror example, eats about its own the Earth varies with latitude.
bod y mass of food per day w h ereas a
cockroach can go for days without a
mea l. All a nimals wi ll die in te mpe rature extrem es.
Temperature regulation in humans
Practical activity
SBA 19.1: Heat flow from a warm object,
page 361
Meta bo lic reactions (especia lly in 1he Uver ) ge ne rate h eat and this h eat is
transported by b lood thro u gh o ut the body to keep it warm at 37 °C. Som e heat
is lost to the environmenr through the skin . The loss o f this gene ra ted hea t is
regu lated a nd controll ed; for example, in a cold e n vironme nt, less is lost and
mo re is conserved.
Regu la tion of body temperature is contro lled by the h ypotha lam us of th e
brain. The organ wh ich brings abo u t the changes if n ecessa ry, to conserve or
lose h eat, is the skin (fi gure 19.27). Temperature receptors in th e skin receive
the stim u lus o f ch a nging external te mpe rature (fig ure 19.28, overlea f) . T hey
send impulses to the hypotha lam us, which mon ito rs these stim uli as well as
interna l body temperature. If body temperature is chan ging, the hypotha la mus
responds by sending impul ses to effectors in the skin to bring a bo ut the
responses sh own in table 19.2 (overleaf) .
sweat pore
epidermis[
cornified layer
(old skin cells)
~I ·
I-
~
Malp ighian layer
(pigmented}
- j p igment protects tower
layers from damage by
ultraviolet rays in sunlight
- - .F------19-
~~-
dermis
hair erector
muscle
sebaceous gland
produces oil that coats
and protects hair
capillary network
-+--
hair follicle
·'----"-...n..:'"'._..__...,,,.
_ fatty layer
below skin
i.,;.---1--
.__-...~_.__.,.,
sweat g land
Figure 19.27 A section of human skin.
237
Life Processes and Disease
Heat gain
Sun
Heat toss
convection of heat
by wind
- - • • • atmosphere warmed
evaporation of water
from body surface
,__,_____ __
reflected
sunlight
/
~
~"'of""
to cooler parts
of the environment
radiation of heat from
warmer parts of the environment
heat lost in urine
and faeces
soil
conduction lo the
cooler ground
close to water
conduction from the warmer
ground heated by the Sun
Figure 19.28 The skin of a mammal is important tor temperature regulation.
To conserve heat
To lose heat
• Sweating increases evaporation of the sweat
removes heat from the body
• Vasodilation occurs - capillaries
in the dermis dilate so blood
flow through skin increases, heat
is lost from the blood
• Hair erector muscles relax hairs lie flat so moving air can
get closer to skin and remove
heat
sweat
heat is carried away
./" as sweat evaporates
•
Sweating decreases
less blood now
close to the skin
sweat gland
\ t I
a lot of b lood flow
close to the skin heat is lost from
the blood
• Vasoconstriction occurs capillaries of the dermis
constrict so blood flow to skin
decreases, heat is retained in
blood vessels deeper in the body
• Hair erector muscle contract hairs stand up trapping a layer
of warm air next to the skin
(insulation)
layer o f warm air trapped which
keeps body warm
hair erector muscles contract
--.~_..,___ arterioles
dilate
heat can be easily
lost from the skin
hair erector muscles relax
Table 19.2 Responses in the skin of a mammal that help it to conserve or lose heat.
238
19 ·The Eye, the Ear and the Skin
Name the main organ of temperature
regulation in humans. Describe two
ways it is adapted to perform this
function.
Humans can gene rate an excessive amo unt o r hea t du ri ng exercise o r increased
activi ty. To maimain a consrant temperature we have 10 lose th is excess heat.
Temperawre reg ul ation is physio logica l in huma ns si nce we are a mamma l.
However, we may cha nge our behaviour to h elp the process. If yo u are is hot
because o f stre nuo us exerci se, yo u co u ld:
• re move some clothing;
~
IT:Q-1 4
•
•
bave a co ld dr ink;
move to a coo le r place;
•
stop activity.
~
IT:Q-1 3
\J'-1
\J'-1
What changes occur to control body
temperature in the body of a human
who is running a race?
Humans do n ot have a Ll1ick laye r o[ hair an d, if the e nvirornn ent is very cold,
th ey d o not ha ve effective insu latio n . Heat is genera ted by th e live r, bur this
may not be e no ugh to kee p body temperatu re at the ri ght level. M uscles sta rt
LO shiver involu ntarily, to genera te more heat. Huma ns get 'goose b u mps' as
the ha ir erector muscles contract. However, we are conside red Lo be 'na ked '
o r hai rless and can on ly tra p a thin laye r of warm air arou nd the skin . We can
b e lp by:
• putting on thick cl o thing;
• having hot d rinks;
• moving to a warmer place;
•
m oving a ro und ro generate more heat.
Temperature regulation in birds
The e ffect o[ e rector muscles is m ost marked in birds. In cold weather, the
mu scles contact, as in hum ans, and th e birds' feathe rs sta nd o ut fro m U1e skin .
(fig u re 19.29). This tra ps a great deal of air next to th e skin. wh ich acts as a
good ins ula ro r. Tt a lso srops air fl ow over th e skin, vvhi ch redu ces loss o [ beat
by convecti on .
Skin care
O ne o f tb e most imponam way tO take ca re o f the skin is to protect it from the
Sun. Ultravio let rays o f the Sun ca n ca use w rin kles, age spots and increase rbe
risk o [ cance r. To protect skin fro m th e Su n :
• use sunscree n;
• seek sh ade;
• wear protective cloth ing.
Figure 19.29 A bird can insulate itself
from the worst of the cold by fluffing up its
feathers.
Smokin g m ay damage co llage n and e lasrin, the fi bres tha t give skin it"s e lasticit:y
and stren gth. So, a good skin ca re regim e incl udes no t smoking. Daily cl eansing
a nd shaving can ta ke a tall on th e skin so strong soaps shou ld be avoided and a
moi sturiser used. A healthy diet and ma naged stress p ro m ote yo unger loo king
and hea lthy skin .
239
Life Processes and D isease
r Chapter summary
•
•
•
•
•
•
•
•
•
•
•
•
•
The main sense organs in humans are the tongue, nose, skin, ear and eye.
The eye enables us to see variations in colour, shape, size, brightness and distance.
We see when light enters the eye.
Light is refracted as it passes through the cornea and lens.
The iris controls the amount of light entering the eye.
The lens controls refraction of light for near and far objects - this is called
accommodation.
Anything that prevents proper focusing of light on the retina is a sight defect.
Astigmatism occurs when the surface of the lens or cornea is irregular.
A cataract occurs when the lens become opaque and light cannot pass through.
A build-up of pressure in the aqueous humour results in glaucoma.
The ear is a sense organ that enables us to hear sounds from the environment.
The ear detects sound waves from the environment.
The ear is made up of three parts: the outer ear, middle ear and inner ear.
•
•
•
•
•
•
Sound waves reach the cochlea from which impulses are sent to the brain.
The ear is also involved with balance.
The semicircular canals detect movement.
The utricle and saccule in the ear sac detect the position of the head.
Surface temperatures on the Earth vary greatly.
Animals can be grouped as poikilotherms and homeotherms depending on their
ability to control body temperature.
• In humans, the skin is an organ of temperature regulation, meaning that skin care is
important.
ITQ1 (i) Ln humans, the eyes are posirioned o n the uppe r front side of the
face. The human skull bas a pair of bo les ca lled eye sockets wh ich 'cradl e' th e
eyes. In this position, th e eyes obta in som e protection and the optic n e rve can
easily connect w ith the b rain . Human eyes a re used mainJ y fo r mo vem e nt and
to focus o n the task at ha nd . A zeb ra's eyes are positioned on eithe r side of its
head wh ich greatly increases the a nimal's field o( visio n so it ca n spot predators
easi ly. H uman s do no t need to be on th e con stant lookout for predato rs.
(ii) A zebra is a la rge h erbi vo re and is prey to many la rge cats sucb as lio ns
and cheeta hs. Having eyes o n the sides o f its head allow it to h ave an a lmost
comple te view of its surro u ndings at any time, even while it is grazing and
feeding. The e nables the anima l to be on th e lookou t for preda tors and aware
of any m ovem e nt in its surroundings. Carn ivores, on the o the r hand , need to
focus o n their p rey. Th e ir eyes are p ositio ned in front o [ their faces. This makes
it possible for them to judge the distance between the m selves and their prey.
ITQ2 To aid in movement (avoid obstacles, note di stances. etc.); to aid
eatiJ1 g (finding food, ingestion, etc.); to focus o n an y task (reading. cookin g).
Other a nswe rs are possible.
ITQ3 Conj un cti va -+cornea -+ [pupil] -+aqueous hum o u r-+ lens-+
vi treous hu mo ur -+ retina
ITQ4 Accommodation descri bes the adjustm em or th e pupil a nd the le ns to
allow a person to see objects at diffe rent distances.
ITQ5
Light rays from an object ente r the eye. a nd a message is sent to the
brain, which interprets tl1 e message. The light rays pass th rough maJl y structures
240
f ·
19 ·The Eye, the Ear and the Skin
in the eye, each performing an importanr function. The lighL rays from an object
mu st focus or meet at a point on tbe retina, from w here the opti c nerve sends
a message to the brain. The cornea, aqueous humour and lens are important
because they bend the ligh Lrays to focus on the retina. The cornea and aqueous
hu mour bend ligh t automatica ll y, but the Lens can control the degree of ben ding.
The pupils a re ' holes' in the eyes, the size of which ca n be adjusted to aJJow
controlled amo u nts o f ligh t to e nter the eye. The deg ree of refraction is adjusted
by the lens and th e rays focus on the retina . At the retina, ligh t-sensi ti ve cells {
send messages to the brain, which interprets rhe message as sigh t.
ITQ6 (i) Converging or convex len s.
(ii) Diverging or concave lens.
ITQ7 (i) A de fect oJ the eye is th e malfunction ing of a n y o n e part of the eye
so thaL good vision is preve nted.
(ii) A cataract occurs when the lens becom e L1a rd e ned a nd ca nnot adjust
to focus light ra ys from o bjects ar varying distances. Astigmatism is a defect
which occurs when tb.e cornea does not have a smooth curve; the rays are not
refracted evenly as they enter the e ye. There are othe r de fects.
ITQ8 (i) The pitrna traps the so und waves and directs them into the
auditory ca n.al.
(ii) The ear bones ampli fy the sou n d waves afrer they have passed th rough
the ou te r ea r on their way LO the inner ear.
(ii i) The sound waves ca use pressure waves in the .flu id of Lhe coch lea.
Depend ing o n the pressu re of the wave, specific hair cells in the cochlea are
stim ulated a nd specific messages are sent to th e brain. The brain interprets
these m essages as sounds th at we hear. Th e coch lea is responsi ble for o ur sense
of hearing.
ITQ9 The ears are a lso concerned w ith ba lance, so any m ovement of the
body can be de tected by the ears. The sem i-circular ca nals in the ear are filled ·
w ith fluid . Any m ovement is detected b y this Ouid. At the base o f tbe semicircular ca nal are s tructures called ampullae. The fluid in the ampu llae moves
in the opposite direction to the bod y's movement, pulling on sensory ha ir cells
as it does so. Messages are sent to the brain from the sensory cells and are
iJJterpreted as movement.
ITQ10 (i) Hom eotherm y is the abili ty of an orga n ism LO comrol its body
te m pera tu re and keep it at a ce rtain val ue; for example, h um ans ma intain
their body tempera ture at aro und 37 °C (birds ha ve a slightly higher body
tempe ra ture around 39 °C).
(ii) Poikilotbermy describes the inability of an organism to co ntrol its bod y
temperature. Th e o rga nism 's body temperature varies w ith the e n vironmenra l
te mperature; for exa mple, the body tempera tures o f repLiles and fish vary with
the ir e nvironmenta l temperature.
ITQ11 Humans can live in extremely hot a nd extremely cold e n viro nments
because th ey be lp mainta in their bod y tempera ture ar a constanL va lue by
some beh.avio LLral processes. For examp le, they can wear clothes to su it the ir
needs, live in buildings which protect them and whi ch may be cooled or
heated . Al so, huma ns do not ha ve to go in sea rch of food every day in extreme
te rn pera w res.
ITQ12 Organisms lik e bacteria and viruses that cause disease can su rvive in
any tempe ra ture, but the vectors that carry the pa thogen from host ro host
are usua ll y insects (like mosq uiros and flies) wh ich a re poikilotherm ic. These
no u rish in the stea dy wa rm temperawres around the equator.
ITQ13 The skin is th e major o rgan of tempe ra ture regula tion . l Lis adapted to
sui t thi s fu n ction in several ways:
• it co nta ins a layer o f [at, which acts as ins ulalio n;
• it can co ntrol the fl ow o f blood into the many capillary networks close to the
skin;
241
Life Processes and Disease
• it has hai rs wh ich can be ra ised o r lowered to increase o r reduce air now
next to the skin;
• it conta ins sweat glands which produce swea t tha t evaporates to cool the
sur[ace o( the body. (Any two o[ tha above)
ITQ14•
Sweat is produced by the sweat glands.
• Erector muscles rela x, causing the hai rs to li e fl at againsLthe ski n .
• Hea r is lost from the body as the water prod uced in sweat uses the h eat from
the body to evapo ra te.
• B lood vessels n ea r the skin open wider, allowing blood LO fl ow through
the many capillaries close to Lhe skin. As a result, hea t is brough t close to th e
surface o f the body, and ca n be lost by radiation, conductio n, or eva poration of
swear.
Examination-style questions
(i)
Make a diagram of the eye as seen in a vertical section. Label these parts in each
case stating its function:
(e) retina
(a) iris
cornea
(n sclera
(g) choroid
pupil
lens
What is the shape of the lens when the eye is focused on a near object?
Describe fully the mechanism that changes the shape of the lens when focusing
on a near object.
(iii) (a) Which structure controls the size of the pupil?
(b) Using annotated diagrams only, explain how the size of the pupil is controlled.
(iv) Suggest why, on first entering a dimly lit room , it is difficult to see objects clearly, but
that they gradually become more clearly visible.
(b)
(c)
(d)
(ii) (a)
(b)
242
- - - ---- ·
2
(i)
A sight defect is caused by any condition that prevents proper focusing of light on the
retina. Describe fully these common sight defects:
(a) long-sightedness;
(b) short-sightedness;
(c) glaucoma.
(ii) Using annotated diagrams only, describe how these eye defects are corrected:
(a) short-sightedness;
(b) long-sightedness.
3
(i) The diagram below shows the structure of the human ear. Copy the diagram and label
the parts listed below and in each case state its function.
19 ·The Eye, the Ear and the Skin
(a) pinna
(b) tympani um
(c) ear ossicles
(d) vestibular apparatus
(e) cochlea
(n auditory nerve
(ii) Describe how the ear functions as an organ of balance when
(a) the position of the head changes;
(b) the body moves.
4
(i)
Explain the meaning of the following terms:
(a) homeotherm ;
(b) poikilotherm.
(ii) The graph below shows the variations in temperature during the course of one day for
a human, a lizard and the air. Copy the graph and label, appropriately, the three lines
in the graph.
·
50
40 - -- --------- - -..:::::::.::.: :.:~~·:,._____ __ _
··..
. :·
30
.
.....
Temperature (OC)
..
..
.
20
10
.· .·
6
12
noon
18
24
midnight
(iii) Explain fully, the changes seen in the body temperature of the human.
(iv) Explain the changes seen in the air temperature.
(v) Suggest what the lizard might be doing and where it might be found during these
times:
(a) 6.00 a.m.
(b) 12.00 noon
(c) 6.00 p.m.
(d) 12.00 midnight
5
(i)
Draw a diagram of a section of human skin and include the following labels:
(a) epidermis
(b) dermis
(c) receptor
(d) capillary network
(e) sweat gland
(n sweat pore
(g) hair follicle
(h) hair erector muscle
(ii) Describe fully the possible behavioural activities and physiological mechanisms
that enable the human body to lose excess heat and maintain a fairly constant
temperature.
243
--
--- -
- --
-
- ---
-
-
-
-
-
-
•
0
0
0
0
0
0
0
0
0
0
distinguish between sexual and asexual reproduction
describe the structure and function of the human male reproductive system
describe the structure and function of the human female reproductive system
describe the structure and function of the ovum and spermatozoon
understand the menstrual cycle
understand fertilisation
understand the development of the embryo in humans
understand the role and methods of contraception
discuss the advangates and disadvantages of contraception
discuss the transmission and control of AIDS and gonorrhoea
reproduction
I
t
""sexual
asexual
advantages and
disadvantages
reproduction in humans
contraception
Reproduction
I
Reprod uctio n is a characteris tic o f We. Every living thing mu st di e and,
a ltho ugh ind ividua ls die, a s pecies w ill continu e as lo n g as its me mbe rs a re able
to live lo ng eno ugh l"O reprodu ce. n the m embers o f a species die be l'ore the y
ca n reprod u ce the n tha t species is in danger o f becoming extinct. Reprodu ctio n
is th e re fo re im porta nt fo r a species to conrinu e ro exist, to be ab le to colon ise
new ha bi ta ts and r.o s m vive ch a nging e n viro nrne llla l conditio ns.
Th er-e a re two ma in types o [ reprod u ction :
• asexual;
•
sexual.
Asexual reproduction (one parent)
Asex ua l rep rodu cti o n hap pe n s w he n o n e indi vidua l p rodu ces o Hspri ng
w itho u t ferti lisatio n . Th.is invo lves cell division by m itos is o nl y (cha pter 23).
Th ese o ffs p rin g a re geneticall y ide mica l to each oth e r a nd tO th e ir parent. ft is
described as bei ng con se rvative a nd, in esse nce, clon es a re p roduced.
Advantages of asexual reproduction
•
No time o r e n e rgy is wasted seeking a mare.
•
Large numbers o f o ffspring ca n be prod u ced .
20 · Reproduction in Animals
•
Offspring ca n be prod u ced continu ously and therefore q u ickly.
•
O([spring can make good use of fa vo urab le e n vironrnem al co nd irions.
• lf the pare nt is of 's uperior' quality, all th e offspring wi ll also be of ' superior'
q ua lity.
Disadvantages of asexual reproduction
Figure 20. 1 An aphid producing live
young
•
Uthe e nvironme nt is cha ng ing, the offspring may fi nd it d ifficu lt LO surviv e.
•
If th e parenr is o f ' poor' q ua li ty, th e offspring w il l also be o nl y o f that ' poo r.'
quality.
•
Over-crowding a n d competition rnay occu r as o ffs pri ng colo nise th e same
a rea as tbe pare nt.
CHAPTER 23
There a re severa l rypes of asex u a l reproduction :
• vegetative propaga ti on (ch apte r 2 3);
CHAPTER 23
•
cl on ing (chapte r 2 3) (figure 20. l );
•
binary fissio n see n in unice llular orga nisms like bacteria and protozoans
such as Amoeba (Figure 20.2) .
C!J- 0 one parent
identical offspring
Figure 20.2 Asexual reproduction in Amoeba.
Sexual reproduction (two parents)
CHAPTER 24
Sexua l reproductio n involves two pare nrs prod ucing specia l re prod ucti ve
cells o r ga metes. This happens as a result o f meiosis (chapte r 24). fusion of
rh e gametes produ ces o ffspri ng tha t are di[(e renL fro m ea ch o ther and from
both parents.
Advantages of sexual reproduction
•
Generic va riabi lity o f the species is increased .
• The species is thus m o re li kely to be able ro adapt to a ch ang iJ1g
e ovironme nc.
• The species ma y be a ble to colo n ise new a reas successfull y.
• lI the pa rents are bo th of poor qu a lity, the o [fsp ring may be o f be tter quali ty.
~
IT:Q-1
\../'-'
Draw up a table to show the differences
between asexual and sexual
reproduction.
Disadvantages of sexual reproduction
•
A lo t o ( lime a nd e n ergy is spent se eki ng a mate.
•
O ffspring a re no t produ ced continuously a n d therefore not very q uickly.
~
•
Few o ffs pri ng may be p roduced (as in hu m a n s).
\..)'V
•
Even if th e pare nts a re o f good qua lit y, rhe o[(sp ring can be o f poo r q ua liry.
IT:Q2
What is the importance of
reproduction?
245
- - --- - - -
Life Processes and Disease ,
-- • •
CHAPTER 24
Practical activity
SBA 20.1 : Observing the reproductive
cells of a mammal, page 362
..,,.,...,
spermatozoon >
_
-·
Reproduction in humans
ln humans there are two sexes: ma le (ma n) and female (woma n ). Each sex
produces gametes o r reprodu ctive cells, by meiosis (chapter 24) . In ma les the
gam etes are ca lled spermatozoa, and in females, ova.
The sing ular or spermatozoa is spermatozoon , and the singular of ova is
ov u m (figu re 20.3).
~
Testes make spermatozoa
Ovaries make eggs
~
IT:Q3
/I
ovary
\/"-/
What type of reproduction do
humans show?
(ii) Describe two advantages of this
type of reproduction.
(i)
primary follicle, secretes
/~-- -:~r~:~s~:elops
( ~-@;, . ',
.
~
- + ' . ----@ \
\f ]J
"'"
.,_
- -
-· - -
~ ~~orpus
V '-
...... ~
v-v-
~:::::-
luteum
-
k
,.:::;--seminiferous tubule
p rogesterone
mature ovar~:~! "\.
Graafian follicle
~
·
• •
• • • •
-
- tail for swimming
•
spermatozoon
• one produced per month
• millions produced continuously
• live for about 3 - 4 days after
release from the ovary (ovulation)
• live for about 2 to 3 days in the
body of the female after release (ejaculation)
• moved along the oviduct by
the beating of cilia;
cannot move on its own
• can swim actively using its tail, secretions
from the seminal vesicles and prostate gland
help its movement
Figure 20.3 Details of the ovum and spermatozoon.
The male reproductive system
ltffiHFll
The plural of testis is testes.
l@11M•*I
246
The visible parts of the ma le reproductive syste m are the penis and scrotum
(figure 20.4) . The scrorw11 con tains a pa ir o f testes. Each testis is composed
or coiled tubes ca ll ed semini(erous tubules, inside of which spe rmatozoa (or
sperms) are fo rmed. After fo rm atio n, th e sperms are stored in the epidid ymis.
During sex ual inte rco urse, the sperms are moved o ut o f the epididym is and
pass thro ugh th e vas deferens on the wa y to the penis. Fluid is made in the
prostate gland a nd semina l vesicles which mixes with the sperms to make
semen . This se me n, conta ining 200-500 mi llio n sperms, is ejaculated o r
released from the erect penis during mati11g or cop ula tion.
·
20 · Reproduction in Animals
(a)
ureter
sperm
duct
spermatic cord _
(sperm duct and
blood vessels)
_
seminal
vesicle
_,______._
·~
prostate
gland
(b)
erectile tissue: blood sinuses that can fill
with blood from the
artery at the base
or the penis
urethra
~-- testis
foreskin
glans----"'--""~
~---:;;£..--- scrotum
Figure 20.4 The human male reproductive system (a) in section, (b) seen from the front (front
section).
~
IT:Q'4
V'-1
Describe the route taken by a
spermatozoon from its site of
production to ejaculation.
me ns truation >
~
The female reproductive system
The fema le reprodu cti ve system is positioned in the pelvic region (figure 20.5).
The re are two ovaries, each usua ll y releasing a single ov um (or egg) every
otber monch into the fuDJlel o f the oviduct. Th e ovu m is moved along rhe
oviduct, or Fa llopia n tube, by the beating o f ci lia w hich line the rube. ff sperms
a re not p resent, tbe o the ov u m moves down the u terus and out of the body
during menstruation . Each month the wa ll o r lining o f the ute ru s is b uilt up
in prepa ration for a fertilised ovum. The lining is shed if fe rti lisatio n does no t
take place.
IT:QS
V'-1
How does an ovum travel along the
oviduct?
(a)
Figure 20.5 The human female reproductive system (a) in
section, (b) seen from the front (front section)
247
Life Processes and Disease·;; : - .
_ -
_·
Hormones of the gonads
l'itl'!il'ftim
seconda
sexual c ha racteristics )
Th e gonads, testes in males and ovaries in fema les, also secrete hormones that
influence growth a nd deve lopme nt. Even before birth, while still in the ute rus,
rhe testes of a boy produce the hormooe testosterone w hid1 in fluen ces sex ua l
development and causes th e ma le sex organs to deve lop.
At puberty, the ovaries in girls secrete the hormone oestrogen. Boys, ·~
at this time, make larger amounts of testosterone from the testes. These
ho rmones are secreted in respon se to signa ls from the pituita ry which is able.
to determin e that further develo pment into a man or a woman must begin.
Th is sta rts between the ages of 10 and 14, as boys and gi rls begin to develop
the ph ysica l features that distinguish male from fema le. These district physica l
and emotiona l features, or chara cteristics, are called secon da r y sexu a l
c h a r acteristics (table 20. l ).
Males
Females
• enlargement of reproductive orgars. e.g.
penis, testes, etc.
• enlargement of reproductive organs and
breasts
• ejaculation is possible
• menstruation starts
• increased muscle development
• broadening of the hips for child-bearing
• growth of pubic and underarm hair
• growth of pubic and underarm hair
• extra growth of hair on face and chest
• deepening of the voice
Table 20.1
~
IT:Q6
V"-J
What are the secondary sex
characteristics?
(ii) When do they arise?
(iii) Why are they important?
~
IT:Q7
V"-J
How many ova are produced by a
normal adult female in a year?
(ii) How many spermatozoa are
produced by a normal adult male
in a year?
(i)
~
IT:Q8
V"-J
When in the menstrual cycle is the
likelihood of fertilisation of an ovum at
its lowest?
~
IT:Q9
V"-J
Why is the uterine lining built up every
month, only to be shed during each
monthly period?
Secondary sexual characteristics of males and females.
These be havio ura l and physica l changes are associa ted with co urtship, mating
a nd parenta l concerns.
More importantly, these
ho rmones also resu lt in the
release of the gam e tes. At
puberty, gi rls begin ro menstruate,
a sign that th e menstrual cycle
has begun . Female ga metes or ova
are released and can be ferti lised
by spermatozoa as boys also
begi n to ejacu late o r release ma le
ga metes in lO the environment.
A d1 il d grows and develops
into a sexua l indi vidu al with
easi ly recognisa bl e (ea tures
tha t are a ttractive lO a potentia l
partner, th us ensu ring
reproduction a nd co ntinuatio n
o r the species (figure 20.6) .
Prod uction o f yo ung is a natura l
d1a racte ri stic of li fe a nd th ese
ho rmo nes produced by the
gonads a re impo rtant, no t o nl y
for growth and development of
an organism into a sexual being,
but a lso fo r th ose attractive forces
n ecessary fo r the contin uation of
Rgure 20.6 Typical physical characteristics of adult
the species.
human female and male.
248
- - - - - - - - - - - -- -- - - - -- - -- - -- - - - - - -- -
- -
- -
-
-
20 · Reproduction in Animals
The menstrual cycle
On reaching puberty (around L2 years o ld ), a human fema le w ill Sta n to
re lease ova from he r ovaries: this is known as ovulation. Ovulation is one
part o[ her monrhly menstrual cycle, which sLarts at p ube rt y and continues
un Lil menopause (around the age o [ 45- 50 yea rs). Each cycle laSLS for
approx ima tely 28 days. The events o f the cycle a re controll ed by ho rmo n es
which e n sure that, if the ovum is fe rtilised, the ute ru s is rea dy LO receive it. ~
Th e cycl e starts w ith m e nstrua tion (Lhe sh edding of t he uterus lin in g) whid~
lasts for abo ut 5 da ys (fig ure 20.7). After a few days th e uterus lining starts
LO build back up agam - by day 14 o f r..he cycle it has th ickened considera bl y
and has a n increa sed blood suppl y. This is ca ll ed the follic ul a r pha se and is
control led by the h ormone oestrogen . The events a re syn chronised so that on e
ov um is n ow fu ll y developed in a Graafi a n fo llicle in the ova ry and o vulation
takes place (the ovu lato ry phase) . The peak lr1 oestrogen le ve l ca uses ovu lation.
After ovu lation, th e Graa£i an follicle develops into th e corpus lute um . The
hormone progestero ne is secreted by the corpu s lute um and is responsible for
ma intaining th e built-up u teru s lining. This is the lucea l phase of the cycle.
U rhe o vum is no t fe rti lised by a sperm, it passes th roug h the uterus and
vagina during menstruatio n . The co rpus lute um degenerates and th e le vel
of progesterone dec reases. This ca uses the built-up uterus lining to start to
disintegrate and peel away fro m the ute rus wal l. It passes ou t o f the vagina in
menstruation or the m o nthl y period. And Lhe cycle stares aga in .
me ns trua l c c le >
me no pa use >
l~O
V'-1
When does ovulation occur in the
menstrual cycle, and which hormone is
responsible for ovulation?
~
IT:Q-1 1
V'-1
What is the importance of the
corpus luteum?
(ii) Why is progesterone called the
pregnancy hormone?
(i)
Figure 20.7 The human menstrual cycle
Events in the ovary during a cycle
ovulation
ovarian follicle
growing
@
'~JJ·
~ ~,--
®
no fertilisation
corpus lu teum
secretes oeslrogen
~
degenerates
produces progesterone
•
release of ovum (ovulalion)
Hormone levels during a cycle
a peak in oestrogen - results in ovulation
progesterone level rises.
stays high if fertilisation occurs
J• • • • • •• • • •
....
..
,.··
.·..
........ .. ....···•··•••••••·•·••·••·····•···· ....... ' ... ··
Events in the uterus during a c ycle
menstruation
shedding
of lhe uterine walls
walls built up as
oestrogen level rises
-+
start or
another cycle
I
no fertilisation w alls shed
fertilisation - walls
stay built up
2
3
4
5
6
7
8
g
10
11
12
13
14
15
16
17
18
1g
20
21
22
23
24
25
26
27
28
Days
249
Life Processes and Disease
Ferti Iisation
pregnancy >
gestation period >
co ulation >
fertilisation >
~
l:tQ12
vv
What do you understand by the terms
(i) courtship behaviour (ii) copulation?
~
l:tQ-1 3
vv
(i) What is fertilisation and where
does it occur?
(ii) Describe the route taken by a
sperm after ejaculation in the
vagina until it fertilises an ovum.
implantation >
Tf fe rrilisa tio n takes place and the zygoce successfull y implants itse lf inLO
th e bu ilt -up uterus li ning the fe male is sa id to be pregnant. The ute ru s
lining musr now sta y bui lt-up LO nouris h th e embryo, so the re is no mo re
m e nstrua tion (' pe riods'). This lasts for rhe e n tire pregnancy (o r gestation
period ) w hich is usually 9 months in humans. Th is m ea ns that the wo mar 's
p roges tero ne level must remain high w ma inta in the bu il t- up ute ru s lining.
Also oesrroge n leve ls must remain low so that no more ovulat ion can
ta ke place.
Tb.e pregnan t woman may experience ' morn ing sic kn ess' (nausea) for the
first rbree months o r so as she gets used to th e high le vel o f progesterone and
its effects on he r body.
Mating, for huma ns (and other mamma ls) , is us ua lly preceded by
courtship behaviour. Co urtship establishes a bond betwee n rhe pa rt:ners tha t
may keep the m LOgethe r while the young are bro ught up . A m ale and fema le
are attracted LO each ocher a nd a s uccessfu l courtship leads to copulation
a nd fertilisation .
The act o [ copu latio n , o r mating, b ri ngs the gam e tes close LOgether. The
penis becomes erect during sex ual aro usa l as the erecti le tissu e fill s w ith b lood.
In the fe male, sexua l aro usal res ul ts in the lubrication o f the vagina . The pen is
is then inserted into the vagina, bringing the ga m etes close r togethe r. The
spe rms a re usua ll y eja cu lated just below the ce rvix, a nd the n 'swim ' across the
u te r us and up the ovidu ct. Close LO 500 million spe rms are re leased, bu t only
o n e w ill fuse with the ovum. This is fertili sation.
Development of the embryo, fetus and
placenta
Tbe nucle i o f the spe rm a nd fe rti li sed egg fu se ro form 1be zygote (figure 20 .8).
Th e zygo te di vides as it m oves slowly to th e ute rus. After seve ral h ours, it is
a ba ll of cells ca lle d a n embryo, a11d on reaching the uterus, it sinks into the
th ick spon gy lin ing (fig ure 20.9). This is ca lled implantation . He re it obta ins
protectio n and nutri ern s unri l th e pla cen ta develo ps.
more
mi tosis -"--------'~
oviduct
occurs
stage
stage
fertilisation (fusion of
the nuclei of ovum
and spermatozoon)
uterus
implantation - ball of cells
becomes attached to
the uterine wall
Figure 20.8 A human sperm fertilising an
ovum.
(
~--ovary
Rgure 20.9 Events that occur in the oviduct leading to implantation.
250
20 · Reproduction in Animals
•m••~'*'
F1€iB§eiFH
~
The e mbryo deve lo ps tissues and organs and by 8 weeks it is clearly human. It
is now a fet u s (figure 20 .10).
As the embryo grows, it develops a p lacenta whid1 con nects i1 very closely
w ith the wall o ( cbe uterus (figu re 20.1 1).
IT:Q·1 4
vv
Describe implantation and explain
its importance.
Figure 20. 1O The embryo
develops into a fetus and lives for
nine months in the uterus.
motlier's blood] diffusion occurs sending
nutrients to fetus' blood
and waste products to
lhe mother's blood
fetus' blood
! l
to
fetus
mother's blood
from
fetus
uterus wall
space filled with
mother's blood
vessels
umbilical cord
! l
Figure 20. 11
Structure of the placenta.
251
Life Processes and Disease
The structure of the placenta is shown in figure 20. l I . Th e placenta ha s various
[un ctio ns w hi ch include the fo ll owing.
• Il al lows exchange of materials between the mother and the fetu s, by
bringin g tbeir blood sys te ms very close togetJ1er w ithout the two bloods
mixing. Oxygen , water, amino acids, glu cose and essential minera ls diffu se
thro ugh the placenta to the blood of the fetus. Carbon diox id e, urea and
other wastes diffu se from the fetus into the mo ther's blood.
~
• It protects the embryo by pre venting many pathogens and chemicals from
crossing the placenta. Howeve r, there are some exceptio ns, lik e the German
measles virus, the HIV virus, nicotine, alcohol and heroin , wh ich are all able
to cross the placenta.
• It protects th e fems and the mother since it a llows their two blood systems
to ope rate at different pressures (the m othe r's body needs a highe r pressure
to get blood round a larger syste m) .
•
lt produces the hormones iJnportant for a successful pregnancy.
Effects of drug abuse in pregnancy
Nutrients diffuse from the m o ther's blood to the placenta, and the n trave l to
tbe fetu s during gestation . Harmful substances ma y also diHu se across to th e
fetus if they are present in th e m othe r's bloodstream .
• Carbon monoxide and nicotine from cigarette smoke - Problems
associated w ith ciga rette smoking incl ude prematu re birtl1, red uced birth
weight and the risk of mi scarriage .
• AJcohol - There a re seri o us conseq ue nces of alcohol abuse during
pregnancy. Alcoho l crosses tl1e placenta easil y and ca uses symptoms in
the baby includi ng poor m enta l dvelopm ent, small h ead and brain size,
h yperactivity, poor concentra tion and reduced growth ra te.
1~5
\....)'-./
The placenta is described as the lungs,
kidneys and alimentary canal of the
embryo. Why is it so described?
• Drugs like heroin and cocaine - Babies may become addi cted to these
drugs whi le inside the m other's wom b.
• Pharmaceutical products -These a re carefu ll y tested for harmful e ffects,
but it is a wise preca uti on not to use any drugs (even for headach es or
nausea) d uring pregn an cy unless prescribed by a doctor.
Birth
amnioti c fluid >
l•J#limiOt•hi 1m;1m1
lftl•I•liill
£6b
IT:Q·1 6
\....)'-./
Give a brief explanation of (i) gestation
(ii) parturition (iii) prenatal care (iv)
postnatal care.
252
The fetus is surro unded by a stron g m embrane called the a mnio n . Insid e is
a liquid called amniotic fluid wrucb helps to keep a consrant environment
aro und the [ems. The amniotic fluid a lso helps to sup port and protect the fetus
from ba rm.
A[ter 40 weeks in the m other's ute rus (a lso ca ll ed th e womb), the baby is
sent o ur .into tbe world . Parturition is the act o f giving birth and is controlled
by hormones. The hormone oxytocin ca uses contractio ns of th e ute rus w hich
ca n be very pa inful. This is known as 'labour' o r ' labo ur pa ins'.
During th ese powerful contractio ns, tb e amn iotic sac bu rsts. The amn io tic
fluid po urs o ur o f the uterus and the baby is the n pushed o ur. The umbi lica l
cord is cut, sepa ra ting the baby from its mother. After a few minutes, the
placenta sepa rates fro m the uterus wall a nd passes out of the body. Th is is
sometim es ca lle d th e a fte r-birth.
Prenatal (a ntenata l) ca re ensures good .hea lth of the baby a nd m m her
during the pregnancy. The m other should, for example, eat a balanced d iet,
should not smoke o r drink a lco hol a nd should avo id dru gs.
Postna ta l ca re describes care of tbe child Cro m birth to teens. fr in volves
the physica l, e motio na l and me ntal ca re essential for hea lthy growth
and deve lopme nt.
20 · Reproduction in Animals
Breast-feeding
l•li•IF:tiJIGI limGmiiiluU
Mamma ls suckle their yo ung. After birth of a baby, milk is produced by th e
breasts o r mam mary glands as a result of th e effects of m a n y horm o nes, in
particu lar, prolactin. The firs t secretio n of th e breast is called colostrum. It
is rich in antibod ies and protects th e n ew-born from som e pathogens it may
e11counte r on th e first days of its life o ut of the ute rus.
Hum an breast milk conta ins the appropriate prop ortio ns of sugar, fat and {
protein sui table for a yo ung human ba by. If she is breastfeedjn g, the mother's .
ilie t sho uld be rich in foods that w ill provide th e e nergy, p ro te ins, vitarruns and
min erals n ecessa ry for hea lth y growth and develop me nt of t he infa nt.
'Formula' milk, w hich is ofte n bottle-fed co infams, at.tem pts to recreate Lhis
balan ce. It consists o f dri ed m ilk made to a special fo rmula and is mixed w ith
water and fed to the baby in a bo ttle.
The role of contraception
The wo rl d's popula tion is do ubli ng every 44 yea rs or so. It may soon be di tficult
to su ppl y all the needs of a ll of its people. A solution to t he ove r-popula tion
pro blem lies in contracep tio n (a lso known as birth control). Table 20.2
summa rises some commo n methods o f contraception and figure 20.12
(overlea f) shows the si.tes of action of some contracep tive methods.
Method
How it works
Effectiveness
Advantages
Disadvantages
sterilisation
male (vasectomy) - the vas
deferens are cut and tied off
100%
no drugs or artificial device used, irreversible
no further costs
100%
very reliable if taken as
prescribed
possible nausea, breast
tenderness, and water retention
leading to an increase in weight;
may increase risk of cervical
cancer, but decreases risk of
breast cancer
female (tubal ligation) - the
oviducts are cut and tied off
contraceptive pill contains progesterone which
prevents fertilisation, some also
contain oestrogen which prevents
ovulation
intra-uterine
device (IUD)
(loop, coil)
device inserted into the womb by a 99-100%
doctor - prevents implantation
reliable
possible menstrual discomfort
spermicide
cream, jelly or foam inserted in
vagina before copulation
not reliable alone
simple to use
may reduce the sensitivity of the
penis
mechanical
barriers
male (condom) - sheath of latex
unrolled onto the erect penis
reliable especially available for use by all men and may reduce the sensitivity of the
when used with
women, and the condom gives
penis
spermicide
some protection against sexually
transmitted diseases
female (diaphragm, cap) - domeshaped sheet of thin rubber inserted
over the cervix before copulation
rhythm method
refraining from sexual intercourse
during those times in menstrual
cycle when fertilisation is likely
not very reliable
no devices or drugs used
not really reliable because
women can have irregular
menstrual cycles
(continued)
253
Life Processes and Disease
Method
How it works
Effectiveness
Advantages
Disadvantages
injectable
hormone
prevents release of ova and
thickens the mucus in a woman's
cervix
very reliable
no need to remember
medication, no device used
injection must be repeated by a
doctor every 13 weeks
abstinence
no traditional sexual intercourse (i.e. almost 100%
penis I sperm entering vagina)
protects against sexually transmitted diseases if there is no transfer
of fluids
Table 20.2 Some methods of contraception, their effectiveness, advantages and disadvantaqes.
1?at.7
In the female
\...)'..J
Match these forms of contraceptive
with mode of action A or B:
• contraceptive pill
• IUD
• spermicide
• condom
• rhythm method
• tubal ligation
• vasectomy
Mode of action:
A prevents implantation
B prevents fertilisation.
Intra-uterine
device (IUD)
injection/implant (contraceptive pill)
barrier techniques -
--\--1
In the male
• diaphragm (cap)
• contraceptive sponge
• spermicides
• female condom
Agure 20. 12 The sites of action of different contraception methods.
HIV/AIDS and other STDs
liJlB
opportunistic infections >
254
STDs are sexua lly rransmitted diseases; th is mea ns they a re diseases th at
are transferred fro m o ne person to a nother during sex ua l inte rcourse. AIDS
(acqu ired immune defi cie ncy syndrome) is tho ught to have origi nated in
Central Africa and bas a lrea dy killed over 3 mi lli on people worldwide. AIDS is
ca used by the human immunodeficiency virus (HIV ), wh ich can onJ y survive
in body flu ids. HIV can be transferred in other ways as well as by sexual
intercou rse beca use is transmi tted wben t be blood or semen of a n infected
person m ixes with th e body fluids of another person . This can ha ppen during
sexua l interco urse, blood transfusion or when sha ring a hypodermic needle.
An infected pregnant woman can also pass HJV to h er ba by through the
p lacenta or by la ter breast-feeding. Close contact between people with ope n
wounds has also been known to pass on the viru s.
Infection w ith HIV weakens the body's natura l defence syste m (th e
immune system) because the virus attacks particular white blood cells, ca lled
T-Lymphocytes (figure 20 .13). This means t he body is vulnerable to other
infection s (known as opp o r tunistic infectio n s) like common viral, bacterial
and [un gal infections.
Table 20.3 compa res two STDs: HIV/AID S a nd gono rrhoea .
20 · Reproduction in Animals
Figure 20. 13 False-colour scanning
electron micrograph of a T lymphocyte white
blood cell infected with HIV
Disease
Causative
agent
Symptoms
Control
AIDS
(acquired
immune
deficiency
syndrome)
Virus (HIV)
• Persistent cough, fever. Skin
rashes, swollen lymph glands,
diarrhoea, wasting away of
body, weakness.
• Secondary (opportunistic)
infections - pneumonia,
tuberculosis (TB), candidiasis
(fungal), cancers.
• Keep to one sexual partner
(or to partners who have been
safely screened for STDs)
• Do not inject drugs
• Use condom during sex
• Education about the spread I
prevention of disease
• A vaccine is being sought
Gonorrhoea Bacterium
• Yellowish discharge from urethra, • Keep to one sexual partner
pain when urinating. Often
(or to partners who have been
not noticed in females. If left
safely screened for STDs)
untreated, causes inflammation • Treatment by anti-biotics, e.g.
of Fallopian tubes and sperm
penicillin, streptomycin
ducts leading to sterility.
• No known vaccine
• Arthritis, weakened heart,
blindness.
Table 20.3 Information on AIDS and gonorrhoea.
~
IT:Q-1 8
V"-J
What kind of disease is an STD and why
is it so called?
Prevalence (%) by WHO region
0 Western pacilic: 0.1 (0.1-0.11
0 Eastern Meditteranean: [0.1-0.31
0 South-East Asia: 0.3 (0.2-0.41
Europe: 0.4 (0.4-0.51
• Americas: 0.5 (0.4-0.61
• Africa: 4.6 [4.4-4.81
'
0
)
Global prevalence: 0.8% [0.7-0.8]
Figure 20. 14 Estimate of the numbers of people (15-49 years) living with HIV (2011) .
Social and economic implications of STDs especially HIV/AIDS
• Th e cosLo f rrea ri n g and carin g for chose a fl'ecLed is h igh , especia ll y in
co un tries whe re a high perce nrage o ( Lhe pop u la tion is infected .
• Th ere is a reduCLio n in the wor kfo rce a n d loss o f va lua ble working h ours.
• The family o f a n in fected person suffers e m otio n a lly a nd fin an cia lly.
• M illi on s o f do llars a re s pe n t w o rldwide o n resea rch for a possible cure fo r
HJ V infection .
• People w ith AIDS .(in cl udi ng childre n ) ma y be scorned and a lie nated fro m
so cie ty.
• STDs a re easily s pread by sexu a l inte rco u rse.
• M illio n s o f child re n worldw id e are living w ith the e ffecLs o f HIV /AID S;
man y a re orph a n s.
255
Life Processes and D isease
r Chapter summary
• Reproduction is necessary for the propagation of life on Earth.
• Asexual reproduction involves only one parent and no fertilisation. The offspring are
genetically identical to the parent and each other.
• Sexual reproduction involves two parents and fertilisation. The offspring are differen\
from each other and their parents.
• Variation in offspring resulting from sexual reproduction is important when there are
changes in the environment.
• In humans there are two sexes: female and male.
• The female gamete is the ovum and the male gamete is the spermatozoon.
• The menstrual cycle starts at puberty and is usually a 28-day cycle in human females.
• Ovulation, the build-up of the uterine walls and menstruation are processes which
are part of the menstrual cycle. They are controlled by the hormones oestrogen and
progesterone.
• If fertilisation of the female gamete by the male gamete occurs in the oviduct, a
zygote is formed.
• The zygote implants itself in the wall of the uterus.
• The developing embryo is protected by the amniotic fluid and is nourished by the
developing placenta.
• Drug and alcohol abuse are very harmful to a developing fetus.
• Contraception methods prevent pregnancy from occurring.
ITQ1
Asexual reproduction
Sexual reproduction
single parent involved
two parents involved
offspring identical to parent
offspring different from parents
offspring identical to each other O.e. no variation offspring different from each other (i.e. variation
between individuals)
is seen)
less likely to survive a changing environment
(none may be able to survive because no
variation in offspring)
more likely to survive a changing environment
(some offspring may be able to survive as a
result of variation in offspring)
evolution of the species less likely (only through evolution of the species can occur more readily
mutation
because of variation
type of cell division is only mitosis
type of cell division involves meiosis
ITQ2 Reproduction is the prod uction of offspring and it ensures the
continu atio n of the species. lf m ost individuals in a po pula tio n die be fore th ey
reprodu ce, the n that popu la tion cou ld beco me extin ct.
ITQ3 (i) Sexua l reproduction.
(ii) Any of th e adva ntages mentioned on page 000 could be me ntion ed.
ITQ4 testes - epididymis - sperm du ct - ureth ra
ITQS An o vum is pushed a long the oviduct o n release fro m the ovary. Tt
is 's ucked ' in ro the oviduct and is pushed along by a curre nt produced by the
256
20 · Reproduction in Animals
beating o f the cilia that Line the ovid uct. Also, contractions of the oviduct walls
he lp to move the ov um aJong.
ITQ6 (i) Secondary sexual characteristics are those special [eatures that
make a male orga n ism look different Erom a fema le organism (e.g. broad hips,
deep voice).
(ii) Th ey start a t pu be rty.
(iii) Th ey are im porta nt for a ttraction to the opposite sex and courtship.
ITQ7 (i) A femaJe usuaJ ly produ ces o ne ovum a month, that is a to ta l of ~
twelve ova in a year.
.
(ii} A male ca n produce over 1 mrnio n spermatozoa in one ejaculation. There
is no set rate at w hich he ejacu la tes, as it depends on how often he h as sex ual
intercourse or e ngages in some so rt of sexua l activity. A m a le can produce
bi1lions o f spermatozoa in a yea r.
ITQ8 An average menstr ual cycle is take n to be abou t 28 days. During
the first 10 days, no ovum is presen t to be fertilised. Spermarozoa can live
inside the fema le for 2- 3 days after ejacu lation, so inte rcourse 2- 3 days before
ovulation may res ul t in fertilisation. The ovum may live for 3-4 days, so sexual
intercou rse up to 5 days a fter ovulation may result in fertil isation. Ovulation
usua lly occurs around day 14. So, in an average cycle, intercourse is least likely
to resu lt in fertilisation during days 1-10, and 20- 28.
ITQ9 Every m onth , ovulation occurs, so that fertilisation can occur. Thus,
every mon th, the ute ru s has to be prepa red for implantation. If implantatio n
does n ot occu r, that m onth's lining is shed .
ITQ10 Ovu lation occurs in the m id dJe of the cycle, around day 14 in a 28 -day
cycle. Oestrogen is the hormone responsible for ovulation. 1t is secreted by the
Graa fi an fo ll icle as it develops in th e ovary. When the oestrogen concentration
in rhe blood reach es a certain level, ovula tion occurs.
ITQ11 (i) The co rp us lu te u m produces the hormone progesterone, whid1
ma in ta ins the lini ng of the uterus fo r a few days a fter ovu latio n . This prepares
the body for imp lanta tion, if fertilisation occurs.
(ii) Progesterone is ca lled the pregnancy hormone because its level stays h igh
during pregnancy. This h ormone causes the uterine lining co stay thick and rich
w ith blood vessels, so that the developing offspring can obtain the nutrients it
needs.
ITQ12 (i) Courtship behavio u r is used to attract a mate and, hopefu ll y,
results in m a ting and p roduction of offspring. Tc includes special body
movemem s, ca lls a nd da n ces.
(ii) Copulation is th e sex act, th e insertio n o f the pen is into the vagi na. O n
ejacula tion, sperma tozoa are r eleased at the base o f the cervix . Copu lation
res ults in th e transfe r o f m ale gametes to the female w here fertilisation with
the fem ale gam ete is possible.
ITQ13 (i) Fertilisatio n is th e fu sion of the ma le nucle us, carried by the
sp e rmatozoo n, w ith the female n ucleus that is in the ovum. l r occurs in tbe
ovid u ct or Fallopian tube.
(ii) vagina-+ cervix ...... u teru s ...... ovid uct ...... ovum
ITQ14 The zygote or fertilised egg travels down the oviduct to the uterus. Ir
implants itself in the wa ll of the tJ1ickened uterus. A placenta then develops
from the emb ryo a nd bei ngs to obtain nutrients and oxygen from the mother's
blood.
ITQ15 The placenta is th e site o f exchan ge of materials berween mother and
fe tus. By diffusion across the p lacenta, the fetus obta ins oxygen and nutrients
an d gets rid of its waste products. These are the fu nctions that the lungs,
kidneys and a lin1entary canal w ill ca rry ou t after birth.
ITQ16 (i) Gestation is the pe riod o f develop ment from impla nta tion to binh.
In hu mans it is a bo ut nin e m o nths.
(ii) Partu ritio n is birth . I t is the expulsion of the baby from the uterus.
257
Life Processes and Disease
(iii) Prenata l care describes rhe care of pregnant woman takes during
pregnancy to ensure the birth of a h ea lr11y baby. It includes a proper diet and
abstinence from drugs and alcohol.
(i v) The newly born baby is tora ll y helpless and dependent on irs mother to
sa tisfy all its needs. Postnatal care is care of the baby after it is born.
ITQ17 An l.UD has mode of acrion A; al l the other forms of contraception
have mode of action B.
ITQ 18 An STD is a sexuall y rransmined disease.
Tb is means it can be passed on by sexual Lnrercourse.
Examination-style questions
(i) Make a labelled drawing of the human female reproductive system.
(ii) Indicate on your drawing with:
(a) an X, where fertilisation normally occurs;
(b) a Y, where spermatozoa are deposited during copulation;
(c) a Z, where implantation can occur.
(iii) List three advantages of sexual reproduction.
(iv) Is it possible for a woman to have 30 children? Explain fully.
(v) Suggest reasons why you think it is disadvantageous to have many children.
(vi) List four methods of contraception.
2
(i)
Define the following terms:
(a) implantation;
(b) fertilisation;
(c) gestation period;
(d) contraception;
(e) asexual reproduction.
(ii) Illustrate, using large, clearly labelled diagrams, to show the differences in size, shape
and activity of male and female gametes.
(iii) Give full and accurate accounts of how:
(a) the zygote develops and moves to be implanted, from the time right after
fertilisation to implantation;
(b) the embryo is nourished and protected as it develops in the uterus:
(c) the baby is nourished and protected right after birth.
3
The events of the menstrual cycle are divided into three phases: the follicular, ovulatory
and the luteal.
(i)
Copy and complete the table below to show the activities in the uterus and ovary
during these phases.
Events that occur in the ovary
Events that occur in the uterus
Follicular phase
Ovulatory phase
Luteal phase
(ii) In human females, the menstrual cycle lasts approximately 28 days. What significant
events happen during these parts of the cycle?
(a) days 0- 5
(b) days 5-1 O
(c) days 13- 15
(d) days 15-25
(iii) Describe and explain the changes that take place in the menstrual cycle after
fertilisation.
258
Reproduction
Plants
0
0
0
•
understand the life cycle of a plant
describe the structure of a flower and relate the structures to their functions
understand the differences between wind-pollinatd and insect-pollinated
flowers
0
understand fertilisation in a flowering plant and the development of fruit and
seed
0
0
describe the structure of a fr.uit and adaptations for dispersal
understand why dispersal is necessary and how it can be brought about
plant
I
flower
pollen grain male gamete
ovule - female
gamete
~,~~~~~~~~~--...--------------------'
cross
self
}- pollination
fertilisation
development
of seed/fruit
wind
water
dispersal
animal
germination
exploding
new plant
Life cycle of a plant
Reprod uction is important for the conlinuatio n o f life. Tr is the process by
wh id1 new orga nism s are produced. Flowering plants reproduce sexua ll y
(fusion of m a le and fema le ga m etes). Sexual reproduction in hu mans in volves
two sexes: the mal e produces the ma le ga mete, a nd rbe fema le prod uces
259
Life Processes and Disease
the female gamete. However, in plants, the reproductive organ, which is the
flower, usuall y produces both male and female gametes (figure 21.1).
Sexual reproduction in animals
involves two sexes:
male
female
reproductive organ
produces the
male gamete
reproductive organ
produces the
female gamete
Sexual reproduction in flowering plants
usually involves one flower that produces
both male and female gametes.
Figure 21.1 Parents in sexual reproduction of animals and plants.
The life cycle of a typical flowering plant is seen in figure 21.2.
~
IT:Q-1
v'-'
Why is the flower described as a
reproductive organ?
pollination followed
by fertilisation
occurs
~
fruit containing seed
...............
seeds are
~ • dispersed
IT:Q2
V'-'
.\
•••
Put these in the correct sequence of the
plant life cycle, starting with (a):
(a) development of flowers
(b) germination
(c) fertilisation
(d) dispersal of seeds
(e) pollination
(f) formation of seeds
(g) growth of plant
,,
Figure 21.2 Life cycle of a typical flowering plant.
The plant grows until it is mature and produces flowers. These flowers are
I elelllijfilitelelJ the organs of reproduction. After pollination (bringing the gametes closer
together) and fertilisation (fusion of the gametes), fruits are formed which
contain seeds. The seed conta ins the embryos or developing plants which
are usua lly dispersed. Dispersal ta.ke them to new places where the seeds
germinate, if possible, into seed li ngs or young plants . The seedling then grows
and mature into ao adult plant and the cyde repeats itself.
260
21 · Reproduction in Plants
Structure of a flower
pollen grain >
Flowers are the reproductive organs of a plant. This m eans tha t the fl owers,
regardless of the colour, size or sbape, produce and contain the ga me tes or
sex cells. The fema le game te is the ovule and the ma le gamete is the pollen
grain. A flowe r is structured to protect, house and bring togethe r the ma le and
female gametes.
,
A typica l flower has fi ve main parts. Th e n umbers in the paragraphs below
refer to figure 21. 3
stigma
I'
1
Gynaecium -+ carpels (pistils) -+ style
\,
ovary -+ ovu le (female gamete);
./'
2
3
4
5
filamen t
Androecium -+ stamens ..,.. a nther -+ pollen grains (male gametes);
Corolla --+ petals;
Calyx -+ sepals;
Receptacle .
e
-
petals form the corolla - -- - - - - often brightly coloured
and scented
gynaec ium is composed of:
ca~el
androecium is
composed of:
anther
l sti: : : _ __
L
- - - filament
ovary - --
J
stamen
the anther c ontains
pollen grains (male gametes)
(several carpels fused
together are called a pistil)
sepal - part of the calyx
which protects the flower
in the bud stage
nectary contains nectar
rec eptacle
flower stalk
Rgure 21 .3 Parts of a flower.
~
IT:Q3
Ta ble 2 1. 1 sh ows th e importance of th efive ma in fl ower pa rts.
Label the parts of the flower below.
Part of flower Importance of function
V'-1
A
B
c
gynaecium
produces and contains the female gamete
androecium
produces and contains the male gamete
corolla
attracts pollinators, such as insects, to the flower
calyx
protects the flower in the bud stage
receptacle
holdings the flower and then the fruit/seed
Table 21.1 The roles of different parts of a flower.
261
Life Processes and Disease
Pollination
self-pollination >
cross-pollination >
Pol lination is tbe transfer of the pollen gra in from the amher to the stig ma or
othe r flowe rs o f the sa me species (figure 21.4). Self-pollination is th e trans fe r
of po llen to the sa me flower o r flowers on the sa me plant. Cross-pollination
is the transfer of poll en to flowers on another plant of tbe sa m e species. Most
plants undergo cross- polli nati o n, w h ich increases the va riety in the o ffspring
\
p rodu ced. Seli-po!Jination gene ra ll y happe ns w he n cross-polli natio n cam1ot be
ach ieved .
flower
cross-pollination
----- - plants of the same species - -
Agure 21.4 Self-pollination and cross-pollination.
Figure 21.5 Flowers are pollinated by
different agents, such as insects and birds.
~
IT:.Q~
\./'-'
(i) What is pollination?
(ii) Why are agents of pollination
necessary?
(iii) Name three agents of pollination.
~
IT:.QS
In plants, tb e mal e and fema le ga me tes (po llen gra ins a nd ovules) are bro ught
cl oser togethe r usuall y by w ind o r by a nima ls, most co mmonl y insecrs and
birds. Tbe planr is dependent on these agents to help bring their ga m etes
toge ther. Plowers o f these plants ha ve evolved over mill io ns o r years into
orga n s that are high ly specialised to tl1e type of po llin atin g agenr (figure 21.5).
For example, if insects are to transfer pollen, then they musr be suffici e n tly
attracted tO the flowe rs to approach them . This is achieved by insect-po lJ inared
flowers h aving nectar, a sugary liquid which is a food so urce fo r insects. Tl1e
insects mu st go tbe flowe rs fo r food. Flowers a lso attract insects with brig l1L
colo u rs and strong scents. And so, a n in sect visiting fl ower afte r flo we r as it
feeds, picks up the pollen gra ins (male gam etes) from o ne fl ower and tra nsfers
them to the fem a le gam et e of other flowers .
A wind -pollinated fl ower h as a diffe re nt type o f fl ower. These fl owers ca n
be inconspicuous and sm alJ beca use they do n o t need w a m act insecrs o r birds.
They a re specia Lised i_n a way that allows rh eir pollen to be p icked up by wind
curre nrs. Insect-po linated fl owers an d wind-pollinared fl owe rs are compared in
fi g ure 21.6 and ta ble 2 1.2.
colourful
petal
\./'-'
Define (i) cross-pollination (ii) selfpollination.
r-~~1--- stamen inside
flower
stamen hangs
out of flower
Figure 21.6 Flowers are adapted for either insect-pollination or wind-pollination.
262
Reproduction in Plants
Q6t.,
Insect-pollinated flower
Wind-pollinated flower
Examples
Pride of Barbados, pea (Crotalaria)
corn (Zea mays), grass, sugar cane
Flower
large and brightly coloured
small and inconspicuous
Petal
large, brightly coloured scented nectaries small, green or brown in colour, no scent
at the base of petal
and no nectaries
Stamen
short, with anthers firmly attached inside long filaments, with anthers that hang
the flower
outside the flower
Stigma
sticky and situated inside the flower
large, branched and feathery
Pollen grain
large, sticky or spiky- small quantities
produced
small, smooth and light - large
quantities are produced
ITQ6
\..?V
How is the flower below pollinated?
Give reasons to support your answer.
'
~
ITQ7
v'-.J
Describe what happens in the flower
after pollination, leading to successful
fertilisation.
Table 21.2 Comparison of insect-pollinated and wind-pollinated flowers.
fiower
Fertilisation and development of seed
After fertilisation, the ovules
develop into seeds and the
ovary into a fruit.
-+--~--
style -
2 pollen tube grows down
t11e style to the ovary
!
The fruit grows more as
the petals begin to drop off.
pollen tube enters micropyle
to reach female nucleus
Figure 21.7 The male nucleus is brought close to the female nucleus for their fusion (fertilisation).
The fruit containing the seeds
~
continues to mature.
Figure 21 .8 Development of a fruit.
Afrer fertilisa tion, the ovu le d evelops into a seed contain in g th e em bryo. The
ova ry grows into th e frui t as the pe ta ls shrivel a nd drop o ff. Th e stigma, style
and stame rts a lso d rop off. Th e sepa ls may rema in (figure 21.8).
263
- - - - - -- -
-
Life Processes and Disease
The structure of the fru it and seed of a dicory ledonous plant are related to
rbe structure of the fl ower. A fruit, whici1. contains one or mo re seeds, deve lops
from the ovary. Its shape and the position of the seeds in it relate directly to the
shape of the ovary and the posi tion of the ovu les imide (table 21.3 ).
Ovary with ovule(s)
Fruit with seed(s)
long ovary containing four ovules
in a row
long pod-like fruit containing four
seeds in a row
ovary containing one ovule
oval-shaped fruit containing one
seed
round ovary with rows of ovules
a
'i'
round-shaped fruit containing
rows of seeds.
Table 21.3 After fertilisation, a fruit develops which relates to the shape of the ovary and the
number and position of the ovules.
Dispersal
Practical activity
SBA 21.1: Dispersal of fruits, page 363
Practical activity
SBA 21.2: Seeds and food storage,
page 364
The fruits conta ining the seeds a re 6rmly attached to Lhe pla nt as the y develop,
grow and mature. When mature, o r ripe, they a re dispersed o r sent away from
the parent plant. Most plants depend on the he lp of agents Uke w ind, water
and anima ls to di sperse their seeds. Each fruit is th us highly specia lised in
structure, size, shape and compositio n fo r its type of dispersa l.
Spreading th e seeds away from the parent p lant is im porranr ro:
• pre ve nt overcrowding and th e refore competition for light, space, water and
mine rals;
• a ll ow colonisa tio n of new areas o r habitats.
Dispersal by animals
~
IT:Q8
V"-'
Why does a fruit have two scars?
The wa ll o.f the fruit is ca ll ed the perica rp and may be composed of three layers
- the epica rp, mesocarp and endocarp. In some fruits, these layers are fl esh y
and succulent and a nimals are attracted to th em for food (fig ure 2 J .9).
-
colourful scented fruit
7---
endocarp
sweet, soft
(succulent)
succulent/fleshy inside
Rgure 21.9 A succulent fruit, like a passion fruit or orange, is colourful and scented.
264
~ production in Plants
hooksonthefruit
Fruits li ke .mangoes, romaroes, oranges, and wate rm e lons conta in srored food,
a nd a re colo urful and seemed to attract animals. The fruir. may be green,
unscen ted and in conspicuous w hen young but, as it ripens and is read y for
dispersa l, it develops bright colo urs li ke red and orange, and becomes scented,
so that animals a re attracted LO the plant for food. As they eat the fru its, they
may move away and so disperse the seeds. If the seeds are large, they a re spa t
out or discarded in a new place away f rom the parent plant. 1f the seeds are ,
small, th ey may be swa llowed and then egested (figure 21.10). Some, like
to mato seeds, ca n pass tbrougb the dlgestive system u n harmed.
b ird then flies away
seeds in the faeces
of the bird fall far away
from the parent plant
fruit hooks onto animal's fur
or clothing as they pass through
bird eats fruit
swallowing the seed
Figure 21.10 Berries are succulent fruits. They can be taken far away from the parent plant by
birds.
Figure 21.11 Some fruits have hook-like
structures.
Fru its ca n also be dispersed by animals in a different way. These ki11ds of fruit
do nor. anract a n ima ls for food because they a re dry. They have hooks or hairs
or spikes, and become attached to the an ima l instead (figu re 2 1. 11 ). When the
an imal is wa lking tl1ro ugh the env ironment, these fruits, li ke sweetheart and
burr grass, stick or book on to the anima l's legs or body and ge l dispe rsed as
the animal moves away from the parent plant.
Dispersal by water
Fruits d ispersed by water rnusr be buoyant so that they can fl oa t away, for
examp le, coconu t trees a re usua ll y found on coastlines. Cocon u ts can be
taken by ocean currents to otl1er coasts, islands or countries. The ep icarp is
waterproof and the mesocarp fibrous and ligh t - adaptations fo r dispersa l by
water (figure 2 1.1 2).
the mesocarp is fibrous and traps air
which makes the large fruit buoyant
coconut oats on water and is
taken away from the parent plant
coconut sprouting on a new beach
Figure 21.12 Some fruits such as coconuts are dispersed by water.
Dispersal by wind
Some fruits a re ca rried by the gentlest of w ind currents a nd so mu st be li ght
and particu lar adaptations (fig u re 2 1.1 3, overleaf). Dan delion and silk corron
265
Life Processes and Disease
~
seeds ha ve radiaring rhrea ds that form a parac.hure; mahogany seeds h ave
w ing- li ke stru clllres w hich a llo w them to be carried away fro m the ir pa re nt.
IT:Q9
V'-1
wing-like structure
What is dispersal?
The fruit spins in the wind
and can be taken far away
1--- - parachute shape can
take fruit far away
Figure 21. 13 Some fruits are adapted to 'fly' in wind currents.
Dispersal by explosive devices
W h en expl osive fr uits dry, th ey split and curl su ddenly to nick o ul Lhe seeds
(fi gure 2 l.1.4). These are fr u its with pods like ga rden pea (Crotalaria), thorn
apple and Pride o f Barbados. This is al so ca lled se lf-di spersa l o r m ech an ical
dispe rsa l. ln th is case, the h e lp o f som e oth e r agen t is n ot needed - th e drying
out o f the pod ca uses it to spl it a lo n g its line o r wea kness a lo ng th e side.
~
IT:Q·10
V'-1
Draw a table with named examples
of plants which show each of the
following methods of dispersal:
animals, water, wind, self-explosive.
Describe how their seeds are adapted
for dispersal in this way and make a
simple sketch in each case.
266
Figure 27.14 Some fruits such as thorn apple (Datura stramonium) 'explode' and release their
seeds The pod splits when the walls curl back as they dry out. The seeds are flicked out.
21 · Reproduction in Plants
lf the seeds eventuall y I.and o n fertile soil, away from the parent, the y have
a good chance o f germina ting into a seed ling wh ich can then grow into new
plant. Life continues and the cycle continues.
'
ITQ1
Tbe fl ower produces the rep rod u ctive cells or ga meces which, on
fu sion, prod uce oCfspring.
ITQ2 a, e, c, f, d, b, g
ITQ3
A petal
Banther
~~~.........,..~~- C ovule
ITQ4 (i) Po lli nation is the transfer of polle n grains from th e a nthe r to a
stigma o f a flower o f the same s pecies.
(ii) Po lle n gra ins cannot move by themselves. They requ ire agents to move
them from th e anther to th e stigma.
(iii) Insects (e.g. bee); birds (e.g. hummingbird) ; wind.
ITQS (i) Cross-pollination is the transfer o[ pollen grains from the anther o f
o ne pla nt to the stigma o f another plant o r the sa m e speci es.
(ii ) SeH-pollinatio n is the tra nsfe r o f pollen g rains from the anther o [ one
fl ower to the stigm a o f the sa m e flo wer, or to OLher flowers on the same p lan t.
267
Life Processes and Disease
ITQ6 Th is flower is insect-po ll inated because:
• it is brightly colo ured;
• th e stig ma is inside the fl ower;
• it has large peta ls;
• the anthe rs a re [ound inside the fl ower.
ITQ7 During pollina tion, th e pollen gra ins land on tJ1e stigm a or a fl owe r.
U th e polle n a nd th e stigma a re o f th e same species, th e pollen grain th en ,
germin ates and develops a lo ng polle n tube w hich grows down in side the
style. The pollen tube conta ins two m ale nuclei an d it contin ues to grow un til
it reach es the ova ry and th en the ovules. It grows th roug h the micropyle an d
e nters the ov ule. A male n ucle us in rh e pollen tu be the n fuses w ith the [ema le
n ucl eu s in tJ1e ovul e. This is fe rtilisation
ITQS Whe n a frui t develo ps from an ova ry, it has a sca r wher e it was
atta d 1ed to the rece ptacle or stem a nd a scar wh ich used to be the style.
ITQ9 Dispersal is the p rocess which describes how the offspring of a pla n t
m ove away from the parent plant. Neither the fru its containing the o ffspri ng
n or the seed (offspring) ca n m ove from place to place, so they depend o n
age nts of dispersa l li ke water, w ind and animals.
ITQ10
Fruit
Agent of
dispersal
Adaptations for dispersal in this way
Cherry
Animals
The fruit is brightly coloured and juicy. Animals are
attracted to it for food, and they disperse the seeds
when they move away from the parent plant with
the fruit.
Coconut
Water
The fruit is dull and very large; it is also buoyant and
light. It can stay afloat for long periods of time.
Purple petria
Wind
Wing-like structures are present. Seeds are light
and small and can be picked up and carried by wind
currents for miles.
Thorn apple
Self-explosive
It is dull-coloured and has four parts. They lose
water and become harder and harder, placing strain
where they join together. Eventually the parts 'burst'
and scatter the seeds which were Inside the fruit.
268
-- --~--
- - - - -- -
21 · Reproduction in Plants
Examination-style questions
(i)
Define:
(c) germination
(a) pollination
(d) dispersal
(b) fertilisation
(ii) Examine the diagrams of the two fruits I and II below and describe fully how dispersal
occurs in each.
(iii) List two advantages of dispersal.
(iv) List three conditions necessary for germination.
2
(i) Name the parts of the flower in the diagrams I and II below.
H
269
Life Processes and Disease
(ii) State some differences between the stamens of the wind-pollinated flower and
insect-pollinated flower.
(iii) List two characteristics of the pollen grains of insect-pollinated plants.
(iv) What is the main advantage of cross-pollination?
(v) Pollination can be described as an example of symbiosis. Describe fully the
relationship between bees and flowers.
3
(i)
Copy and complete the diagram below which shows the reproductive cycle of a
flowering plant.
adult plant
with
flowers
(
I
I
..•.
·-
fertilisation
dispersal
(fusion of gametes)
t.____ _ __
-!
(ii) Name A, B, C, D, E, F and G in the diagram below.
:L=--
GI
-
- A
l-+--8
c
F
E
(iii) Distinguish between pollination and fertilisation.
(iv) Pollen grains from many different species may land on a stigma. However, the seeds
produced belong only to the same species as the flower. Explain why this happens.
270
~D) isease and Humans
0
underst and what is meant by pathogenic, deficiency, hereditary and
physiological diseases
0
distinguish among the methods used to treat and control the four main groups
of diseases
0
0
understand the role of vectors in the transmission of disease
0
understand the importance of knowing the life history of a vector in relstion to
control
understand the social and economic implications of disease in plants and
animals
disease
r
deficiency
pathogenic
r
I
vector
I
} MOS
control of
disease
hereditary
'
role of blood
immunity
physiological
'
social and economic
implications
drugs
• alcohol
• caffeine
• cocaine
• heroin
life cycle
'
(
natural
artificial
vaccination
Health and disease
Hea lth h as been de fined a s 'co mplete ph ysica l, m e nta l a nd social we ll -being'.
l t is m ore t han just rhe absence of disea se; it incl udes th e me nra l a nd socia l
d imension s o [ li fe. A disease is a condiri.0n in w hic h th e h ea lth o f an o rgan ism
is impaired.
Note that a proper diet a nd adequate exercise a re im po rta nt to good hea lth.
Th ey h elp to preve m the onse t of, a nd even he lp to treat, diseases. Eati ng foods
Lh.a t make up a ba lanced diet increases the body's resista n ce to in fection. A
p rog ramme o f exercise stre n gthens a ll the o rga n systems and leads to overa ll
good hea lth - physical, me nta l and socia l.
Types and control of disease
Diseases can be divided imo fo ur main types - pathogenic, deficiency,
h e redhary and physio logica l.
271
Life Processes and Disease
Table 22. L distingu ish es between th ese types of disease, describes one
exa mple of each type and discusses the m ethods used to treat and control these
Lypes of diseases.
Type of disease
Named
example
cause
Symptoms
Pathogenic Caused
by parasitic organisms
(pathogens) like viruses,
bacteria, fungi, protozoa
and worms.
Examples: malaria, TB,
cholera, influenza
Influenza
Virus (pathogen) invades Headache, sore throat,
the body by contact
muscular pains, fever
with infected person. It
is airborne or dropletborne.
Deficiency Caused by a
shortage of a nutrient (e.g.
vitamin, mineral) in diet.
Examples: kwashiorkor,
night-blindness, irondeficiency anaemia
Iron-deficiency Deficiency of iron
Weakness, fatigue,
anaemia
causes a reduction in
shortness of breath,
the number of red blood increased heartbeat,
cells which reduces
pale appearance
the oxygen-carrying
capacity of the blood.
This is because iron is
an integral part of the
structure of haemoglobin
in red blood cells.
Hereditary Caused by
genes passed on from one
generation to the next.
Examples: haemophilia,
cystic fibrosis, sickle cell
anaemia
Sickle cell
anaemia
Gene for the disease
is passed to the
offspring. The gene
causes the red blood
cells to be sickle shaped
which reduces oxygencarrying ability.
Physiological Caused by
a malfunction of body's
organ.
Examples: asthma,
hypertension, diabetes,
glaucoma, stroke
Diabetes
Inability of the islet of Tiredness, continual
Langerhans to produce thirst, weight loss,
insulin. Body cells are increased urination,
unable to absorb glucose coma
which stays in the blood.
Weakness, tiredness,
weight loss, May lead
to kidney failure, heart
failure
Treatment
Control
Rest and treatment for Prevent overthe symptoms. Vaccine crowding and
for specific strains of
exposure to the
the virus.
virus. Prevent droplet
infection through
coughs, sneezes, etc.
Eat iron-rich foods
(e.g. red meat, green
leafy vegetables). Take
iron tablets.
Education about a
balanced diet, food
groups, etc.
Avoid situations where Genetic counselling
oxygen supply is
reduced. No treatment
or cure available.
Insulin injection/tablet
Low carbohydrate
diet, exercise.
Education on the
importance of diet and
exercise.
Table 22.1 Some diseases in humans.
CHAPTER 13
~
IT:Q·1
V'-.1
What do you understand by the terms:
(i) pathogenic disease
(ii) hereditary disease
(iii) physiological disease
(iv) deficiency disease?
272
Som e djseases are more common ly found in certain pa n s of the wo rld than
in oth e rs. For example, in developing countries a grea ter proportion of
dea Lbs occur as a result of infectio us diseases, like den gue fever, ch ole ra a nd
tube rculosis. In developed co um ries, a smaller proportion of people die from
infect ious ruseases. and more death s are d ue to p hysiologica l diseases like
ca nce r and hea n disease. These kjnds o f disease are infl uenced by facto rs such
as diet, life style, genetic prerusposition and exposure to ha rmful cond itions.
For example, hypertension (chapter L3) results from a stressful li fe, filled wi th
worry, a nger, nervo us fatigue, n o rest or relaxation, and u nh ea lth y ea ti ng
habits (e.g. too mu ch fatty, sa lty fast-food) . Hyperte n sion can to some extent
be controlle d by good diet and exercise.
This difference in distributio n is refe rred to as th e globa l distributi on of
disease. It often reflects th e wea lth and sta ndards ol medica l care in the
diffe rent coun tries. Th us, the occu rren ce o f disease in deve loping countries is
often iofl uenced by facto rs such as overcrowrung, lack of clea n water, lack of
preventative medkin es and lack of proper nutrition.
22 · Disease and Humans
Pathogenic diseases and vectors
l•fi\hr•lo!4•*J
A pathogen , or disease -causing organism, Lives on or inside an organism, the
host, causing it to be diseased o r sick. Pathogens ca n move from one host to
a nother, or inrect another organ ism in a number of wa ys including by:
• water;
• food ;
• airbo rne droplets;
• direct contact;
• du st pa rticles;
• contact w ith fa eces;
• anima ls (ma inly insects), ca lJ ed vectors.
Vectors
l@AMIJ
Vectors spread disease- by carryi ng the pathogen from host to host. Examples
o f vectors in cl ude fl ies, mosqu itoes a nd rats (figu res 22. 1,22. 2 and 22.3).
Table 22 .2 gives sosme examples ..
Vector
Examples of disease(s) spread
mosquitoes
yellow fever, malaria, dengue fever,
flies
gastroenteritis
rat flea
plague
rat
leptospirosis
Table 22.2 Some vectors and the disease they spread.
vector 'bites' infected host
and picks up the pathogen
vector with
the pathogen
l
-- -
~~ ~ "
/
--
vector 'bites'
new host,
transferring
the pathogen
infected host
Figure 22.1
new host. infected
by a vector
Mosquitoes are vectors for malaria and many other diseases in humans.
~
l:F:Q2
V'-1
Figure 22.2 Flies feed on the food we then
eat and so spread disease.
(i) What is a vector?
(ii) Discuss why a fly can be considered to be a vector.
273
Life Processes and Disease
Controlling mosquitoes
If the vector can be controlled, Lheo th e spread o f tile d isease will also be
comrolled, since Lhe chance o[ being in contact wiLh Lhe vector and so getting Lhe
infeaio n w ill be red uced. Th us, it is important to study th e venor's life cycle ro
find ou t how to prevent them laying eggs, or how to prevent their development
into adulrs, or how to destroy the adults. A good example of this is the atLempt to
control the mosq uitoes rhar act as vectors (o r malaria (figure 22.3).
t
spiracles for breathing
/
larva lives in water
~
egg laid on water
pupa lives in water
/
Agure 22.3 The life cycle of a mosquito.
Tbe erad ica tion o ( a d isease sprea d by m osquitoes wo u ld be poss ible if a
concened effort were made by the genera l public in the following areas.
• Drai n stagnan t w ater around t h e ho m e a nd workplaces - Th is wou ld
drastica ll y reduce th e number o( places for female mosqu itoes to la y eggs as
well as reduce the numbe r o( eggs and pupae s urviving to deveJop into adu lts .
• Spread a thi n layer of oil ove r w ater which must be ke pt - This
would preveoc larvae a nd pupae in th e water from breathing and so kill
th em .
•
Kill t he adu lts with insecticide.
• Use mosqui t o nets - TIJ.js would reduce the possibility of being bine n
when mosquitoes are a round .
• Keep the area a round the l1o use clear of bush where adu lt mosquitoes rest.
In tile sa me way, knowing where flies lay their eggs, how they develop a nd
whar Lhey feed o n, can help to reduce the number of flies and thus reduce the
incidence of diseases spread by flies .
Pathogens
~111fll
274
Pathogens are usua ll y m icroscopic organisms (li ke viruses, bacteria and
protozoans) that Live in Lhe blood and tissues of their host. Some are larger, li ke
fungi and worms, which are easie r to get rid of and control.
Some pathogens spread by direct comact o r dose in teraction between
Lhe infected host and a new hosr. These include the sex ually trans mitted
diseases (STDs) like herpes, AIDS, gonorrhoea and syphilis. AJDS is of most
impo rtance beca use it has reached epidemic statu s in the world and can lead co
22 · Disease and Humans
dea th because it compromises the body's immune system leaving the pa tient
defenceless against secondary opportunistic infections. Expensive drug regimes
can prolo ng rhe life of someone li ving w ith HIV, but there is no means of
elimating the virus from th e body and no cu re for AIDS. Herpes is also incurable
but not fa tal. The other STDs can be trea ted and conrrolled if diagnosed ea rly.
Social and economic implications of
disease
The loss of life and loss of wo rking hours to disease a re important socia l
and eco nomic fa ctors. Trearmems for pathogenic diseases sud1 a s AlDS a nd
degenerative disea ses su ch as cancer place increasin g demand s on health
services. Lifestyl e diseases related to smoking, lack of exercise and over-eating
are increasingly important economica lly in develo ped countries, again beca use
of the cost of treatment and their effects o n social and econo mic life.
Implications for humans of disease in plants and
animals
Human s a re also a ffected eco no mically by the hea lth o f the crops and animal
stocks grown for food. Loss of li vestock (cows, pigs, chi cke ns, e tc. ) and
agricultural crops (rice, wheat, porntoes, etc.) due to disease can have se rio u s
economic impli cation s. A disease can grea tly reduce o r w ipe o ut the livestock
o r food crop oJ any area in a short space o f time; [or exa mple, m ea ly bu g
in festation in the Caribbean, and foot-and-mo uth disease in Europe. This
results in loss of income for the farmers and reduction in food ava ilability.
Food, in the form of livestock and ag ricultural prod uce, moves a ll over the
world io ships a nd a irpla nes o n a daily basis. Disease control is therdore ve ry
difficult. Quarantine procedures at porrs and ai rports help but do n ot prevent
the sp read of diseases. Many pathogen s a re microorga ni sms so are not seen;
man y can ex ist as spores for long periods of time.
Chapter summary
• A healthy person is physically, socially and mentally well.
• A disease impairs good health.
• There are four main classes of disease: pathogenic, deficiency, hereditary and
physiological diseases.
• A pathogenic disease is caused by parasitic (and often microscopic) organisms like
viruses, bacteria, fungi , protozoans and worms.
• A deficiency disease results when there is a deficiency of a nutrient in the diet.
• A hereditary disease is passed on by genes from a person to their offspring .
• A physiological disease is caused by a malfunction of an organ in the body.
,
II
• A vector transports pathogens from one host to another.
• Vectors are usually insects, such as mosquitoes and flies.
• Understanding the life cycle of a vector can help to control or eradicate a disease
spread by that vector.
• The social , environmental and economic implications of disease include loss of life,
loss of working hours, loss of money. Disease in crops and livestock can lead to
famine. Research into cures for disease is expensive.
_,....
275
Life Processes and Disease
ITQ1 (i) Pathogen ic disease - symptoms of disease a re seen because of the
presen ce of another organ ism (a pathogen ) in th e body.
(i i) Hereditar y disease - sym ptoms of di sease seen beca use of the presence of
a 'disease-carrying' gene which was passed to an o rga nism from its pare nts.
(iii) Physiologica l di sease - symptom s o f disease seen because an orga n o r part
of the body is not working.
(iv) Deficiency disease - sympto ms of disease seen w he n a nutrient o r
nutrients are la cking in the dlet of the orga nism.
ITQ2 (i) A vector ca rries a pa thogen from host to bost. It is able to pi ck l:IP
the pathogen in or on its body w hen it feeds and then transfe rs the pathogen
when it m oves to another host.
(ii) Flies pick up microorganisms wben they feed. They feed o n any
orga nic matter, especially dead a nd rotting o rganic ma trer. The ir bod ies
are hairy a nd can easil y ca rry pa thoge ns. They a lso regurgitate or vomit
previous food whe n they eat. If they land to Jeed o n any substance
th at is go ing to be food or drink to another anima l, they can pass
th e pathogen to a new host. Flies are thus con sidered to be vectors.
Examination-style questions
(i)
Explain what is meant by the following types of disease and give one example of each:
(a) hereditary;
(c) deficiency;
(b) physiological;
(d) infectious.
(ii) Describe the causes and symptoms of:
(a) gonorrhoea
(b) diabetes.
(iii) Explain how diseases like malaria and sickle-cell anaemia are spread and describe
the importance of these diseases worldwide.
(iv) Describe the social and economic implications of AIDS. List some ways the spread of
AIDS can be prevented and controlled.
(v) Describe and compare the global pattern of distribution of yellow fever and coronary
heart disease.
2
(i) Describe how phagocytes protect the body against infection.
{ii) List four ways the skin and openings on the skin are adapted to control the entry of
pathogens into the bo"dy.
(iii) (a) Distinguish between active natural immunity and active artificial immunity.
(b) Give one example of artificial passive immunity and one example of natural
passive immunity.
(iv) It is estimated that a human can synthesise 1Omillion different types of antibodies.
Describe three ways antibodies defend the body against disease.
(v) Copy and complete the table.
Drug
Two effects on the body
Social or economic implications
Alcohol
Cocaine
Caffeine
3
276
(i)
Explain the meaning of the term 'drug'. Using named examples discuss the use and
abuse of drugs.
(ii) Describe the immediate and long-term consequences of alcohol consumption.
(iii) Discuss the social consequences of excessive alcohol use with particular reference to
drink driving, aggressive behaviour, family breakdown and petty crime.
Section C:
Continuity and
Variation
0
0
0
0
0
understand the importance of maintaining species chromosome number
describe the process of mitosis
understand the role of mitosis in growth
explain the role of mitosis in asexual reproduction
explain why asexual reproduction gives rise to genetically identical offspring
cell
cell division
(
meiosis
'\
mitosis
(
prophase
metaphase
anaphase
telophase
'\
cloning of
animals
tissue culture
in plants
asexual
reproduction
growth
Dolly
Chromosome number
,.
chromosome number >
Ch ro mosomes a re presen t in th e nudei of ce lls. They com a in geneti c
info rmacion in the form o f genes. Each species bas a speci fi c nu mber of
chro m osomes in its body cell - this is call ed th e chromosome number for
th a t species (fi gure 23 .J a n d table 23. J ).
~
ll:Qjl
~
(i) What is meant by the 'chromosome
_number' of an organism?
What is the chromosome number
for (a) humans and (b) an onion?
Figure 23. 1 Each species has its own chromosome number.
23 ·Mitosis
Species
Chromosome number
onion
16
tomato
24
locust
24
corn
40
mouse
40
human
46
potato
48
Th e ch ro m osom e n umbe r for hu mans is 4 6. This mea ns rha t in every bod y
cell o [ every hu man rh e re a re 46 ch rom o somes. A chromosom e is m ade up
o f gen es. Wh ile th e ch rom osom e o u m be r is th e same fo r all h uma ns, the
combina tion of genes is diffe re nt (figure 2 3.2 ). The 46 ch ro m osomes a re
diffe re nL fo r e ver y hu m a n except id e n tical twin s.
Table 23. 1 Chromosome numbers for
seven different species
~
IT:Q2
\./'-I
(i)
List three differences between the
people in figure 23.2.
(ii) List three similarities.
(iii) Why can these differences be
seen?
There are 46 chromosomes in each of his
She also has 46 chromosomes in each of her
body cells, but the combination of genes 1s
cells but with her own combination of genes on
special to this individual. This produces outward the 46 chromosomes. Each individual is unique
characteristics that are special to this individual. and special.
Figure 23.2 Members of the same species have the same chromosome number, but the
combination of genes is different for each.
The eel I cycle
RRl!ii1fft:IJ
[jjlU.~·U•'IJ
IGl@•hfiM:tJ
The cell cycle is the sequ e n ce o f e ve nts rha r occurs be tween the s1a n of o ne
cell d ivisio n (mitosis) a nd th e Starr o r th e n ext (fi gure 23. 3) . Th e lo ngesr e ve nt
in rh e cell cycle is ca ll ed interphase du ring which the cell grovvs a nd carries
o u t its fu n ctions. A L the e nd of inte rphase ce ll division begins.
M itosis is di vided into fo u r stages: prophase, m e rap hase, a naph ase and
relo phase. At th e end o f telo phase, l\<\' O nuclei ha ve been fo rmed but th e
cytop las m is n ot fu lly d ivided be twee n two cell s. Th is happe ns n ext a nd th e
process is called cyto ke n isis (figu re 23 .4) .
interphase
Figure 23.3 The cell cycle.
Figure 23.4 Mitosis has four stages and is a part of the cell cycle.
279
Continuity and Variation
- - 1----- nuclear envelope
centrioles
The processes of mitosis and cytokinesis
are shown in figure 23.5 . The numbers in
the text on page 281 relate to figure23.5.
i;•~-f-- nucleolus
chromosome
Y.
r:-1
chromatids
~ centromere
prophas
,,
0
metaphase
E
anaphase
4 telophase
10
OI
IO
10
cleavage
Figure 23.5 Mitosis and cytokinesis.
280
01
identical cells
23 · Mitosis
lnterphase before mitosis
• The cell is prepared for ctivision.
• The chromosomes become shorter and fatter (and are easily seen).
• Each chromosome makes an exact copy of itself, forming two chromatids
joined at a centromere.
Prophase (1)
•
•
•
•
•
Chromosomes (made of two chromatids) are visible.
The nucleolus shrinks and disappears.
The centrioles move to opposite sides of the cell.
The spindle fibres form.
The nuclear envelope breaks down.
The centrioles play an important part in cell ctivision: the spindle fibres
originate from them. The spindle fibres attach to chromosomes and pull them
to either side of the cell.
Metaphase (2)
• The chromosomes line up along the 'equator' of the cell.
• NB Each chromosome is still made up of two chromatids joined at the
centromere.
Anaphase (3)
• The ch romatids separate and move to opposite sid es of the cell.
• The chromatids reach opposite sides of the cell.
• Exact copies of chromosomes a re at both sides of the cell.
Telophase (4)
• The ch romosomes lengthen as they umavel.
• Th e nuclear envelope forms around each group of chromosomes to make
two nuclei.
• New nucleoLi form in each nucleus.
• Two identica l nuclei a re formed.
Cytokinesis (5)
~
• The cell membrane develops down the middle of the cell to djvide it into
two (cleavage).
• Two identical cells are produced.
IT:.Q3
V"-J
(i) What is mitosis?
(ii) Why does mitosis occur?
~
IT:.Q~
V"-J
Why is it important to maintain the
species chromosome number?
Importance of maintaining species
chromosome number
As you know, each species has its chromosome number and its own set of
characteristics that make it unique a nd set it apart from other species.
Rapid and repeated cell division must occur after fertilisation so that an
organism can grow and develop from one cell (the zygote). It is important that
after cell ctivision, the chromosome number remains the same and all the cells
in a multicellular organism retain the correct number of chromosomes and the
chara cteristics of the species.
281
Continuity and Variation
The process of mitosis
CHAPTER20 ~
The only variation that can happen in cells produced by mitosis is mutation,
when a gene is copied incorrectly. Even minor faults in copying can result
in major changes. An example occurs in sickle cell anaemia where a major
change in the structure of haemoglobin arises from just a single fault in
copying of the gene at some time in the past (chapter 26).
Every cell of an organism has, locked within the nucleus, the 'blueprint' or
complete set of instructions needed for that organism to develop. Remember that
after the male gamete fuses with the female gamete at fertilisation, a single cell is
formed which contains the complete set of information needed for development
of the organism. Mitosis then occurs over and over, producing thousands of
identical cells that differentiate to perform different functions. This leads to the
formation of a multicellular organism in which every cell has maintained the
chromosome number of the species with its unique combination of genes.
CHAPTER 26
~
IT:QS
L/V
Put these in order as they would occur
during mitosis.
A
B
Mitosis is cell division that occurs in all body cells except in gamete formation.
It results in the formation of two genetically identical cells, each containing the
same number of chromosomes and the same combination of genes. A cell is
described as being diploid or 2n when it has the full chromosome number.
Mitosis is essential for cell repair and for growth from the zygote to the
multicellular organism as described in chapter 20. It is important that all
body cells have the full chromosome number and thus carry all the genetic
information to allow that cell to develop its role within the body.
Mitosis is also the method by which organisms reproduce asexually forming
offspring identical to the parent. It ensures that:
• the species chromosome number is maintained;
• each daughter cell receives an identical combination of genes.
c
Figure 23.6 Replication of
a DNA molecule results in two
identical copies.
Replication of chromosomes
Replication is the process during interphase by which a chromosome is able
to copy itself exactly. A chromosome carries genetic material in the form of
deoxyribonucleic acid (DNA). Watson and Crick published the first description
of DNA in 1953. The structure is a double helix, made of two chains. By the
process of replication, a cell is able to produce two identical cells when it
divides by mitosis (figure 23.6).
DNA made up of
two chains
The chains unwind from
one another (DNA 'unzips')
Each chain makes an
exact copy of itself
Two exact copies of DNA
at the end of the replication
Mitosis and asexual reproduction
Asexual reproduction requires only a single parent. In essence, the parent
divides into two, or a pan of the parent separates and then develops into a new
individual. It is important to note that the offspring are genetically identical
to the parent. This means that the physical and behavioural characteristics
are also identical to the parent except for variation due to the environment.
282
23 ·Mitosis
Binary fission, vegetative propagation and cloning in animals are examples of
asexual reproduction. Mitosis results in the formation of identica l cells. When
organisms divide asexually, they divide by mitosis.
Binary fission
binary fission >
~
This occurs in simple, unicellular (one-cell ed ) organisms, like bacteria and
protozoans such as Amoeba (figure 23.7). The organism divides into two part ,
each of which develops into a new organism. This is known as binary fission .
In Amoeba/ protozoa the chromosomes replicate first, then the nucleus divides ·
into two, followed by the cytoplasm . Two identical organisms are formed.
ll:Q6
\../'J
An Amoeba seen today is identical to
one that existed 100 years ago. How
can this be so?
Figure 23. 7 Binary
fission in Amoeba.
the cytoplasm begins
the nucleus begins
to divide into two
activities stop as
the Amoeba
prepares for division
two identical Amoeba move
(J tod©- ~ ·:c~JM'
nuclear division
is complete
cytokinesis
continues
~
Vegetative propagation
vegetative propagation >
CHAPTER 15
X
ljihUI§il
11mi.u11
Vegetative reproduction or vegetative propagation is a common form of
asexual reproduction in plants. In some plants, a bud grows and develops into
a new plant, and then becomes detached from th e parent plant. Bulbs, corms,
rhizomes, tubers, tap roots (chapter 15), runners, stolons and tillers can all give
rise to new plants by vegetative reproduction.
In a runner, such as those on a strawberry plant, a number of stem s grow
out from the parent plant. The runner touches the ground, adventitious roots
develop and a new plant forms. The runner connecting it to the parent plant
decays and the new plant becomes established (figure 23.8 (a)).
A stolon is simply a runner formed underground. This method of
reproduction can be very effective; nut grass, for example, is very difficult to
eradicate once it is established.
A B1yophyllum leaf ('leaf of life' ) will generate n ew plants around its
edges. After a while these plamlets become detached from th e parent leaf
(figure 23.8 (b)).
(b)
(a)
side branch/ 'runner'
adventitious roots
new plants
Figure 23.8 (a) New plants are established from a side branch or runner. (b) Many new plants can
be propagated from a single Bryophyflum leaf.
283
Continuity and Variation
Artificial propagation
Horticulturists and agriculturists have extended asexual propagation to
include cuttings, budding, layering and grafting. This is termed artificial
propagation . These techniques are commonly used in gardening and the
commercial growing of plants.
artificial propagation >
new plant
(fl
cut stem is
placed in a
suitable medium
for growth
lb)
Cuttings
A stem is cut near a node and pushed into the soil (figure 23.9 (a)). New roots
grow ou t from the submerging part of the stem, Particularly if treated with a
plant growth substa nce (e.g. rooting powder). Examp les includ e sugar cane,
geranium, African violet. chrysanthemum.
adventitious roots
new plant
•tockroot'~
~
Grafting
with a
system
A cutting, called the scion, which is co be propagated is inserted into a slit in
the stem of another plant (the stock), and the joint is bound up to seat it. The
stock a lready has a root system so the scion is able to grow into a new plant
(figure 23.9 (b)).
scion cutting
of plant to
be propagated
Figure 23.9 Art1fic1al propagation of plants
by (a) cutting, and (b) gnft11g
Tissue culture
tissue culture >
Tissue culture is a form of vegetative propagation used to make large
numbers of identical plants (figure 23.10). Like binary fi ssion, it also results
from mitosis. Using tissue culture propagation or cloning, whole plants can be
made from very sma ll pieces cut from the parent plant. This depends on the
fact that the majority of plant cells have the potential to form a whole plant.
A very small piece
of tissue is taken
from this plant.
The tissue is cultured on a sterile nutrient
medium. The piece of tissue is made
up of a number of identical cells.
nutrient medium
/
The cells
divide by mitosis to form
a callus - a ball of cells.
Rgure 23. 1O Tissue
culture in plants.
284
The callus is stimulated to
develop into a plantlet.
Plantlet transferred to soil. This
is genetically identical (clone) to
the original plant. Many clones
can be made from one plant.
23 ·Mitosis
Advantages of tissue culture
~
IT:Q7
V'-1
(i) Define the term 'tissue culture'?
(ii) Describe how tissue culture is
used to generate many identical
plants.
• Large numbers of identical plants can be produced relatively quickly from
'superior' individuals. This can make them much cheaper.
• Tissue culture can be used to propagate plant species which do not
develop naturally through sexual reproduction easily, such as orchids. The
propagation of orchids for sale on a massive scale is now possible.
Disadvantage of tissue culture
• Variety within a plant species is being replaced with similarity because it
is cheaper. This is risky because if that one kind becomes susceptible to a
particular disease or pest, the whole crop may be lost.
Cloning of animals
identical twins >
~
IT:Q8
V'-1
(i)
Explain what is meant by
'cloning'?
(ii) Describe a natural occurrence of
cloning?
A clone is an exact copy of an organism. Identical twins are, in essence,
clones, since after the first cell division of the zygote, two identica l cells are
formed. These two identical cells somehow separate from each other and
then grow and develop into separate beings that are identical to each other
(figure 23. 11 ). The environment confers subtle differences as they grow
and develop.
one organism
~ --+
w
zygote divides
into two
~ ---+
two-cell stage
w
separation of the two
cells occurs resulting in
two identical cells
each divides and
develops separately
•
another organism
~ ·twin')
they develop in their
mother's womb and
identical twins are born
Figure 23. 11 The development of identical twins.
CHAPTER 26
Scientists can now easily separate the first four cells of a zygote and use these
to create clones of the organism (figure 23.12, overleaf). This is practised
mainly in the livestock and dairy industries. It is financia ll y advantageous to
make clones of a 'superio r' animal, such as one which produces large amounts
of a high-quality milk or high -protein mea t. It is also used to 'copy' individuals
which have been genetically engineered (chapter 26). An example here would
be Hvestock with genes to produce human hormones in the animal's milk.
Cloning may be used to produce an animal with some specia l characteristic
(such as speed in a racehorse) as that could be financially beneficial.
Clones need a surrogate mother in which to develop. This is a female who is
not the genetic mother but in whose womb the fertilised ovum is implanted so
that it can develop as a fetus until birth.
285
Continuity and Variation
- - - - - - - - - - - - - - - - - - organism
growth and development in mother's womb
zygote
2-cell stage
4-cell stage
_ __. organism
•
2-cell stage
4-cell stage
each of the four ' cells are separated ~
clones
(exact copies)
..
~0
zygote of a
'superior' organism
Clones would all have
the same 'superior'
characteristics.
_ __,. organism
_ __,. organism
(!)
- - - organism
Each cell then continues to grow and develop into an organism. They are exact
copies of each other. Each can be implanted in a female's womb (surrogate mother).
Rgure 23. 12 Cloning of fertilised eggs.
~
ll'!Q9
\...l'-1
Describe one way that scientists can
make copies or clones of a 'superior'
animal?
A second way to create a clone is to ta ke the nucleus of a body cell from the
'superior' individual and use it to replace the nucleus of an unfertilised ovum.
The cell can be made to divide as it would have done if it was a fertilised ovum
and implanted in the womb of a surrogate mother, but all the cells it makes
now have the chromosomes from the 'superior' animal. The first example of
this kind of cloning was the sheep called Dolly(figure 23.13).
normal
development
how Dolly
was cloned
(9\
unfertilised
~
egg
unfertilised
egg
/
1 ~ 1 ~~om
00
.
(!)
egg fertilised byE f
sperm forms M
a zygote
II"
•
1
starts to
divide
II'
1
@
@
1
l
/
The nucleus is removed and replaces the
nucleus of the ovum. Development continues
in the surrogate mother. The dividing nucleus contains
Dolly's chromosomes. A surrogate mother is one
in which the embryo is implanted and she
•oam~· • b•by th•t ;, oot "'"
Surrogate mother
gives birth to Dolly who is genetically
identical (a clone) with the original sheep.
~
ll'!Q·1 0
\...l'-1
How was Dolly cloned?
Rgure 23. 13 How Dolly the sheep was cloned.
286
a sheep
23 ·Mitosis
Advantages of animal cloning
CHAPTER24 ~
• Superior traits can be passed on to offspring without the risk of losing them
through genetic exchange during meiosis (chapter 24).
• The use of surrogate m others means that more 'superior' offspring can be
created than could be carried by just the genetic mother.
Disadvantages of animal cloning
• The effects of using a body cell, as in crea ting Dolly, are still being studied: It
is possible that using what is in effect an 'old ' nucle us may cause problems .
in the cloned individual.
• The technique used to crea te Dolly could be used to clone humans. Many
countries now have legislation to prevent this because it is considered
unethical. For example, it might be done for purely selfish reasons.
Chapter summary
• Each species has its own chromosome number, that is the number of chromosomes
found in each nucleus in the cells of the individual.
• The chromosome number of humans is 46. This means that there are 46
chromosomes in every nucleus in every body cell of a human.
• Although each individual of a species has the same chromosome number, the
combination of genes in the chromosomes varies and so members of a species differ.
• Cells divide by mitosis to produce two genetically identical cells.
• Mitosis is important for growth, repair and asexual reproduction .
• Mitosis is divided into four stages: prophase, metaphase, anaphase and telophase.
• During replication each chromosome makes an exact copy of itself. This occurs in
interphase, just before prophase. ·
• These two copies of a chromosome are called chromatids - they lie side by side and
are joined at the centromere.
• During prophase, the chromosomes become shorter and fatter and are easily stained
and seen.
• During metaphase, the chromosomes line up along the middle of the cell.
• During anaphase, the chromatids are pulled apart to opposite sides of the cell.
• During telophase, two identical nuclei are formed.
• In cytokinesis, a new cell membrane develops to divide the cell in two identical cells.
• Binary fission in Amoeba is an example of cloning.
• Cloning is the production of identical copies of an individual.
• Animals and plants can be cloned using several techniques.
• Tissue culture is one way of cloning plants.
The chromosome number is the number of chromosomes found in
a typical cell of an individual of the species. It is a fixed and specific number to
each species.
ITQ1 (i)
(ii)
(a) 46 (b) 16
ITQ2 (i) The eyebrows are shaped differently and of different thickness.
The size and shape of their lips are different .
The shapes of their faces are dillerent.
(There are other differences that you may have seen.)
287
on 1nu1ty and Variation
(ii) Both individuals have two eyes.
In both individuals, the nose is in the middle of the face.
The position of both their lips is the sa me.
(There may be other similarities that yo u have mentioned, relating to
characteristics that are general to being of the same species.)
(iii) Differences can be seen because, altho ugh they both have 46
chromosomes in each cell, the composition of the chromosomes is different.
Their genes code for different characteristics.
•
ITQ3 (i) Mitosis is cell division that res ults in the formation of two identiq1J
daughter cells.
(ii) Mitosis is important for growth and repair.
ITQ4 A species has special characteristics that separate it from other species.
The number of chromosomes is very important. A change in chromosome
number may change the species-specific characteristics.
ITQS 1 C, 2 B, 3 A.
ITQ6 Amoeba divides by mitosis producing gen etically identical offspring.
Over the years, when it divided, identical offspring were produced, so that one
seen today wou ld be genetica lJy iden tica l to one which existed 100 years ago.
ITQ7 (i) Tissue culture uses a piece of tissue from a 'parent' plant to make
many plants that are identical to the parent plant.
(ii) A piece of tissue is taken from a parent plant. It is placed in a medium
conta ining nutrients and growth hormones . It is kept under sterile conditions
to prevent microorganisms from entering the medium. In the nutrient
medium, the piece of tissue divides rapidly by mitosis, forming a structure
called a callus, which is a ball of cells. The callus may be divided and placed in
many jars containing the nutrient medium. Each piece develops into a plantlet
which is cared for carefully. The many plantlets are all identical to the parent
plant.
ITQ8 (i) Cloning means making exact copie.s. An exact copy of an individual
is m ade when it is cloned.
(ii) Cloning may occur naturally in the formation of identical twins. After
the zygote is formed it divides into two cells. Usually the two cells stay stuck
together and continue to divide to make one individual. In identical twins,
these first two cells separate and develop into individual organisms. They are
genetically identical.
ITQ9 Scientists allow a zygote of a 'superior' animal to divide naturally
twice, producing four identical nuclei. These are then separated and implanted
in the uterus of other animals (surrogate mothers) and allowed to develop .
Four clones of the superior animal are thus made.
ITQ10 Dolly was cloned by extracting the nucleus from one of the cells of
a ewe. This nucleus contained all the information needed for the forma tion
of Dolly. The nucleus of an ovum was also removed and replaced with
Dolly's nucleus. The ovum containing Dolly's nucleus was made to implant
in a surrogate mother and it developed into an individual which was Dolly.
Examination-style questions
(i) List the stages of mitosis.
(ii) Explain fully the importance of interphase just before mitosis begins.
(iii) Explain the meaning of the term 'diploid'.
(iv) (a) Label the parts A to Gin the diagram on the next page.
(b) Identify each stage.
(c) Describe what happens in each stage of mitosis.
288
23 ·Mitosis
2
(i)
Explain the following terms:
(a) asexual reproduction ;
(b) binary fission.
(ii) List two advantages of asexual reproduction.
(iii) One major disadvantage of asexual reproduction is that the offspring vary only rarely.
Many species use only asexual reproduction but their offspring are not all clones.
Suggest how variation comes about in these asexually reproducing species.
(iv) What is a clone?
(v) Suggest an argument:
(a) for animal cloning;
(b) against human cloning.
(vi) Give a brief description of tissue culture. Discuss some advantages and disadvantages
of the use of tissue culture in agriculture.
289
/
understand the importance of halving of the chromosome number in the
formation of gametes
0
0
describe the process of meiosis
f7
understand the role of meiosis in the transmission of inheritable genetic
characteristics
distinguish between mitosis and meiosis
cell
I
division
(
mitosis
'
meiosis
r
meiosis
I and II
'
variation
evolution
The importance of meiosis
Body cells divide for growth and repair, and it is important that the new cells
are identical to the existing o nes. This is the significance of mitosis. However,
cells of th e reprod uctive o rgans must also divide, but in this case, to form the
gametes or reprod uctive cells.
Two gametes, one from the ma le and one from the female, fuse to form the
zygote which develops into the new organ ism. These gametes must therefore
concain half the chromosome number of d1romosomes. If they did not, the
new organism would have twice the species chromosome number.
Meiosis is the cell division which occurs only in the reproductive organs
during gamete formation, and results in the formation of cells containing
half the number of chromosomes as the parent cell. Half the number of
chromosomes is the haploid o r n n umber.
For example, a h uman body cell has 46 chromosomes. When body cells
divide by mitosis for growth and repair, cells containing 46 chromosomes
(d iplo id or 2n number) are always produced. However, cells of the reproductive
organs must divide by meiosis to make gametes. The gametes must contain 23
chromosomes (haploid or n number) so that, after fu sio n with another gamete,
the original number of 46 d1romosomes is restored (figure 24. l ).
24 · Meiosis
diploid (2n)
~
l:T:.Q·1
l../V
mitosis
diploid (2n) _ _.,. diploid (2n)
Where does meiosis occur (i) in females
(ii) in males?
~
l:T:.Q2
l../V
list the differences between a diploid
cell and a haploid cell. Give an example
of where each can be found in the
human body.
~ reproductive cell
diploid (2n) ( . : \ reproductive cell
~
of female
~
meiosy / \'
haploid (n) @
@
haploid (n)
~
GAMETES
meiosis
fertilisation
Figure 24.1 The importance of meiosis in
maintaining the chromosome number.
haplok:t
(n)
~
~ ~
0 0
diploid
(2n)
/I \"'eiosis
of male
GAMETES
fertilisation or fusion of
gametes to form a diploid zygote
diploid
v~
I
(2n)
+
The process of meiosis
develops into an organism with
46 chromosomes like its parents
Meiosis ensures that:
• each da ughter cell has the haploid number of chrom osomes so that the
diploid number can be restored after fertilisation;
• each daughter cell has a different combination of genes which leads to
variation among th e offspring.
homologous pair >
A human cell has 46 chromosomes: 23 came from the m other and 23 came
from th e father. Each chrom osome from the set from the mother pairs up with
a corresponding chromosome from the fa ther. These are called homologous
pairs. The ch romosome in hom ologous pairs in humans are the same size an d
shape apart from the sex chrom osome (figure 24.2).
nuclear membrane
a homologous pair
centrioles
Figure 24.2 The homologous pairs
of chromosomes in a cell with four
chromosomes
two chromosomes
of maternal origin
homologous chromosomes
(a homologous pair) similar chromosomes, one from
the mother, one from the father
291
Continuity and Variation
~
crossing over >
IT:Q3
V'-J
Why is meiosis important in
gamete cells?
~
IT:Q'I
V'-J
Explain the terms (i) homologous pairs
(ii) chromatid.
At the beginning of meiosis, each chromosome forms two chroma tids
joined by a centromere, as in mitosis. The homologous chromosomes then
come together, so there are now four chromatids dose together. Genetic
information is exchanged randomly between the chromatids. This is known as
crossing over.
In metaphase I, the homologous chromosomes align randomly across the
equator of the cell, and then the members of homologous pairs separate and
move to opposite sides of the cell. The cell then splits to form two cells. The ·
division repeats with the chromosomes again lining up randomly along the
equator of the cell, only the second time around the chromatids separate,
resulting in four daughter cells, each with different genetic information
(figure 24.3 and table 24.1).
Prophase II
• centrioles migrate to
opposite sides of the cells
lnterphase
• replication of all four
chromosomes occurs
• cell with diploid number
l
Prophase I
• homologous chromosomes
come together (bivalent)
• pieces of chromatlds are
exchanged (crossing over)
.~X~ .
~ :~
bivalent
Met aphase II
• chromosomes line up
along the equator
Met aphase I
• bivalents line up along
the equator
CHROMATIDS
SEPARATE!
Anaphase I
• bivalents separate
• chromosomes move to
opposite sides
CHROMOSOMES
SEPARATE!
Telophase II
• nuclear membranes form
around each set of
chromosomes
Telophase I
• two cells are formed each
with the haploid number
.
•
Figure 24.3 Meiosis of a cell with four chromosomes.
292
Anaphase II
• chromatids move away
from each other
Four cells formed, each with
the haploid number of
chromosomes, and are
different from each other.
24 · Meiosis
Mitosis
Meiosis
occurs in body cells or somatic cells
either occurs in reproductive cells only or occurs
in formation of gametes only
number of chromosomes remains the same in
the daughter cells
number of chromosomes is halved in the
daughter cells
daughter cells are identical to parent cells and
each other
daughter cells are genetically different to parent
cell and each other
two daughter cells are formed
four daughter cells are formed
homologous chromosomes do not come
together
homologous chromosomes come together
no exchange of genetic material between
chromosomes
exchange of genetic material between
chromosomes
Table 24. 1 The differences between m1tos1s and me1os1s
Variation of gametes
A single human male can prod uce over 100 million spermatozoa or male
gametes in one ejaculation. These gametes are all different. This variation of
the gametes comes about when the cell divides by meiosis. Variation results
from the following processes.
• Crossing over between homologous pairs of chromosomes in the early
stages of meiosis is random. There are no limits to how this happens. Every
homologous pair of ch romosomes exchanges genetic material differently.
Imagine the various ways a cell yvith 23 homologous pairs can exchange
genetic material.
• During metaphase I. the pairs of chromosomes align themselves long
the equator of the cell randomly. Imagine the various ways 23 pairs of
chromosomes can be aligned along the equator. The pattern of alignment
determines which chromosomes are grouped together.
• During metaph ase II, the chromosomes (now formed of two chromatids)
align randomly along the equator of the cell. This also determines how the
chromosomes are grouped in the gamete.
Significance of meiosis
Figure 24.4 These people all belong to the same family and so share
some of the same genes.
At the en d of meiosis, four genetica ll y different cells are
produced from each original cell. This means that the
gametes from each individual are all different. When
these fuse with gametes from another individual, there
will be even more variation in the genetic information
of the offspring (figure 24.4).
The gametes carry genetic information from
the parents . When they fuse to form an offspring,
genetic information is transmitted from the parents
to the offspring. The offspring are all differenr from
each o ther, since the gametes are all different. They
are also different from their parents, though some
characteristics will clearly come from the mother and
some from the father. Some features may appear that
are unlike either parent.
293
Continuity and Variation
~
IT:Q5
\.,..)'....J
The daughter cells of meiosis are all
different from each other. List three
ways in which this variation is brought
about.
Conditions in the environment are not constant. They may change,
sometimes abruptly. The survival of a species depends on the ability of the
individuals in that species to adapt to changes in the environment. When
there is variation among offspring, some will be able to withstand the changes
of the environment and survive to reproduce. The surviva l of the species is
thus ensured.
Darwin's theory of evolution
Darwin's theory of evolution >
~
IT:Q6
\.,..)'....J
Variation obtained from meiosis
ensures that the gametes are all
different. Give one advantage and one
disadvantage of this variation.
Darwin's theory of evolution through natural selection is based on the
fact that among the variety of offspring produced, some will be better able to
withstand changes in living conditions than others. That is, some are better
adapted or 'fitter' to survive in the struggle for existence. These offspring will
then produce offspring that are similar (not identical ) to themselves, passing on
the advantageou s characteristics. Through these gradual changes, over many
generations, the evolution of new species is possible.
• During meiosis, homologous chromosomes come together and crossing over occurs,
whereby genetic information is exchanged.
• Each gamete of the millions produced is unique and so each organism produced by
their fusion is unique.
• Inheritable genetic characteristics are transmitted from the parents to the offspring by
the gametes.
• The resulting offspring are all different to or vary from each other and to their parents.
• This variation can be important if the environment changed, as those organism better
adapted will survive.
• This variation can lead to evolution.
294
24 ·Meiosis
ITQ1 (i) In females, meiosis occurs in the ovaries.
(ii) In males, meiosis occurs in the testes.
ITQ2
Haploid cell
Diploid cell
half the number of chromosomes in the nucleus the full number of chromosomes in the nucleus
found only as gametes in the reproductive
organs - ovaries and testes
found all over the body
occur as individual cells as gametes, some are
able to move (e.g. sperm)
most are fixed and occur together, forming
tissues
ITQ3 Meiosis is important for the formation of haploid gametes so that,
when two gametes fu se during fertilisation, a diploid zygote with the original
number of chromosomes is obtained.
ITQ4 (i) The 46 chromosomes of a human cell are made up of 23
homologous, or corresponding, pairs. One chromosome of each homologous
pair came from the father and one from the mother.
(ii) In the early stages of cell division each chromosome replicates to form
two identical copies of itself that are joined by a centromere. Each copy is
called a chromatid.
ITQ5 •
Crossing over - the exchange of genetic information between
chromosomes.
• Random alignment of the homologous pairs of chromosomes along the
equator before separation of the chromosomes.
• Random alignment of the chromosomes along the equator before separation
of the chromatids.
ITQ6
One advantage is that all the offspring have different characteristics,
so some may be able to survive a change in an environmental condition. The
propagation of the species is more likely to be ensured.
One disadvantage is that all the organisms may be
different from the parents and not as adapted to the
environment as the parents. All the offspring may die easily.
Examination-style questions
2
(i) Explain these terms and state and importance of each:
(a) mitosis;
(b) meiosis.
(ii) List four differences between mitosis and meiosis.
(iii) Explain the following terms, giving an example of each:
(a) diploid number;
(b) chromosome number.
(iv) Explain the importance of crossing over which occurs during meiosis.
Explain the importance of meiosis in making evolution possible.
295
0
understand the terms gene, allele, dominant, recessive, genotype and
phenotype
0
0
0
explain the meaning of the terms codominance, homozygous and heterozygous
0
predict the results of crosses involving one pair of alleles
use a genetic diagram to explain the inheritance of a single pair of characters
explain the inheritance of traits using sickle cell anaemia and albinism
/) understand the inheritance of sex in humans
0
understand crosses involving sex-linked characters
variation
continuous
discontinuous
l
)
genes on
chromosomes/DNA
I
phenotype -
genotype -
alleles
~
dominant
recessive
back cross
incomplete
dominance
co-dominance
inheritance
of characters
blood groups
pedigree charts
sickle cell anaemia
sex determination -
sex-linked characters
The Earth is h om e to billions of organ ism s, eve ry on e of w hich is un iq ue.
Millio ns of species can be found on the land, and in the wa te r and air of the
Earth 's surface. Different species m ay differ greatly from each other and may
be easy to distinguish . For example, birds differ grea tly from fish . However, the
membe rs of rhe sa me species ma y differ in only sm all ways .
Th ese dilferen ces a re the result of the genotype a nd the enviro nment.
The gen otype of organism is its generic m ake-up. Th e envi ron m ent is the
25 · Heredity and Genetics
su rrounding of the organism. Identical twins have the same genetic make-up
but their environments are different (such as the food they eat, th eir activities,
relationships and experiences) and so subtle differences develop between them
(figure 25. 1).
Genes
Figure 25. 7 The differences between
identical twins are due to the environment.
as they have the same genes
homologous
Generic information is passed o n
chromosomes
from parents to offspring in the
/
chromosomes. Chromosomes occur in
pa irs in body cells. In a human body
cell, there are 23 pairs of chromosomes:
23 individual chromosomes are
paternal (from the father) and 23 are
maternal (from the mother). Pairs
are caUed homologous chromosomes
(figure 25.2 ).
Each chromosome is made up of
genes, or units of inherita nce. These
control specifi c characteristics in the
homologous
organism. Each chromosome of a
chromosomes
homologo us pair carries the same set of
genes, therefore each body cell has two Figure 25.2 A diploid cell h:t..
chromosomes has two pairs of homologous
copies o f each gene. However a gene
that are the same as each other, or two chromosomes.
alleles for a gene that are different. If
the alleles of a gene are the same, we say the organism is homozygous for
that gene o r character. If the alleles are different, the o rgan isms is sa id to be
heterozygous for that gene o r character (figure 25.3 ).
uu
homozygous >
heterozygous >
gene for eye colour
gene for hair colour
gene for hair texture
Chromosomes exist in homologous pairs the genes are the same but the
form the gene can take may be
different. These are called alleles.
gene for shape of nose
brown
gene for size of lip
gene for length of finger
gene for length of arm
gene for
eye colour
gene for
hair colour
gene for
hair texture
A chromosome is made up
of genes. This is a very simplified
diagram of a chromosome.
In the gene for hair colour, there are many alleles
for hair colour, producing many different hair colours.
In this case the two alleles are for red and brown.
The alleles present determine what the individual will
look like: the outward charactenstics. Alleles exist for
every feature of every organism and each organism has
its own combination of alleles which make it unique.
Figure 25.3 Homologous chromosomes.
297
Continuity and Variation
Dominance
dominant allele >
recessive allele >
If the alleles are different, one may mask the expression of the other. The
one that is expressed (visible in the organism) is called the dominant allele,
and the one that is masked is the recessive a llele . We use capital and lowercase letters to represent the different alleles. For example, in the gene for hair
colour, B represent the allele for black hair, and b represents the allele for red
hair. Black hair, B is dominant to red hair, b; and red hair, b, is recessive to
black hair, B. The dominant allele is expressed in the homozygous (BB ) or
heterozygous (Bb) genotype, whereas the recessive allele is expressed only in
the homozygous (bb) genotype (figure 25 .4).
homologous chromosomes
'"" foe Mic "'"""
l
allele for black hair
symbol B (dominant)
genotype is the genetic make-up, the alleles
allele for red hair
symbol b (recessive)
B and b
phenotype is the outward characteristic - - - black hair
homozygous genotype has same alleles, e.g. BB
bb
heterozygous g enotype has different alleles, e.g. Bb
Figure 25.4 The allele for black hair, B, will mask the expression of the allele for red hair, b. The
heterozygous individual will have black hair
phenotype )
£19..,
The composition of genes, or genetic make-up, within the cells of an organism
is its genotype. The phenotyp e is the observable characteristics of the
organism. These observable characteristics are the result of the genotype and
the environment interacting (table 25.1).
genotype
phenotype
BB (homozygous)
black hair
Bb (heterozygous)
black hair: B is dominant to b
bb (homozygous)
red hair
Table 25.1
Phenotype 1s determined by the genotype.
11'.Q-1
\../'-'
Define the following: (i) chromosome
(ii) gene (iii) allele.
~
l'.fQ2
\../'-'
Define the following: (i) genotype (ii)
phenotype.
298
Genetic diagrams
A genetic diagram shows the cross between two genotypes. It shows the
phenotypes and genotypes of the parents and the possible genotypes and
phenotypes of the offspring. For example, a cross between a homozygous
dominant genotype (BB) and homozygous recessive genotype (bb) is shown in
figure 22.5.
25 · Heredity and Genetics
phenotype of parents
black hair
x
red hair
genotype
BB
x
bb
I
I
0
gametes
offspring genotype
~ Bb /
offspring phenotype
black hair
segregation
8
All offspring heterozygous with black hair.
Probability of a red-haired offspring is 0%
Ratio 4 black hair : 0 red hair
Figure 25.5 A genetic cross of a homozygous black-haired parent and a red-haired parent.
Note in the diagrams that the offspring from a single cross are ca lled the F 1
(which means first filial) generation. We then use the term 'F2 generation' to
refer to offspring of a cross between individuals of the F 1 generation.
If both parents are heterozygous, the cross is as shown in figure 25.6.
phenotype of parents
black hair
genotype
Bb
x
black hair
Bb
gametes
segregation
offspring genotype
offspring phenotype
BB
Bb
Bb
bb
black
black
red
black
hair
hair
hair
hair
(homozygous) (heterozygous) (heterozygous) (homozygous)
Ratio of 1 red hair : 3 black hair
~
25% probability of an offspring having red hair
IT:Q3
lJ'-1
Albinism (absence of pigmentation)
in humans is caused by a recessive
gene which is transmitted in a normal
fashion. A phenotypically normal (nonalbino) couple have four children: the
first three are normal and the fourth is
albino.
(i) What can you say about the
genotype of the parents?
(ii) What is the possibility that their
next child will be albino?
(iii) One of the normal children
eventually marries a normal
woman. What predictions can be
made of their first child?
(iv) The albino child eventually marries
a normal woman. What predictions
can be made of their first child?
Where there are several possibilities,
state them all.
Figure 25.6 A genetic cross showing how two black-haired parents can have a red-haired child.
A cross can also be represented in another way. A cross between a
heterozygous parent and a homozygous recessive parent can be drawn as in
figure 25.7.
x
phenotype of parents
black hair
genotype
Bb
bb
~
~
gametes
0
8
red hair
8
8
gametes
Bb
Bb
®
B
black hair black hair
---- ----··- -------·- ·-- ---- bb
red hair
...
bb
red hair
Ratio 1 black hair : 1 red hair
1, 2 offspring are heterozygous with black hair
1t2 offsprlng are homozygous with red hair
Chances of an offspring having red hair is 50%
Figure 25.7 A genetic cross using a table.
299
Continuity and Variation
Test cross or back cross
Homozygous dominant and heterozygous individuals have the same phenotype
- you cannot teU which is which just by looking at them . A test cross (back
cross) is used to determine the genotype of individuals which have the same
phenotype. In a test cross, the individual is crossed with a homozygous
recessive and the offspring examined, as shown in figure 25 .8.
~
l:F:Q'I
\./'-I
A breed of dogs has long hair dominant
over short hair. A long-haired bitch
was first mated with a short-haired
dog and produced three long-haired
and three short-haired puppies. Her
second mating, with a long-haired dog,
produced a litter with all the puppies
long-haired. Use the symbol L to
represent the allele for long hair and I
to represent the allele for short hair.
(i) What was the genotype of the
long-haired bitch?
(ii) How could it be determined which
of the long-haired puppies of the
second mating were homozygous?
phenotype of Individual
- - - - + black hair
possible genotypes - - - - - BB
and
Bb
Individual is crossed with bb and offspring examined.
gametes
0
0
®
Bb
Bb
·0 --
gametes
®
Bb
'0
Bb
-
0
I 0
Bb
Bb
bb
bb
1-
If there are red-haired individuals
in the offspring, then the genotype is Bb.
If all the offspring are black-haired,
then the genotype is BB.
Rgure 25.B A test cross.
Incomplete dominance
incomplete dominance >
QSb
l:F:QS
\./'-I
What offspring will you expect, and in
what proportions, if two pink-flowered
plants are crossed?
Flower colour in some plants, such as Impatiens, shows incomplete
dominance of the alleles. This means that there is a blending or combination
of expression of both alleles in the h eterozygous condition. If allele CR
produces red flowers {genotype CRR) and the allele cw produces white flowers
(genotype cww), then the genotype CRW produces pink flowers (figure 25.9). A
blending of red and white will produce pink.
99:,
l:F:Q6
\./'-I
The figure shows the result from a
cross between a red-flowered plant
and a white-flowered plant, and what
happens when the offspring produced
are crossed with red-flowered plants.
•
A
x
B
x
•
•
' D
300
white
red
c RR
x
cWW
I
offspring genotype
0
a11 c Rw
offspring phenotype
F
Using the alleles CR and CW,
give the genotypes of the plants
labelled A-F.
(ii) If plant D had been white, what
would the result of the cross
between C and D have been?
(i)
genotype
gametes
l
E
phenotype of parents
Figure 25.9 Incomplete dominance as seen in Impatiens.
all pink
25 · Heredity and Genetics
Co-dominance
co-dominance >
In co-dominance, there is expression of both alleles in the heterozygous
genotype. In this case, the gen otype cRw produces fl owers that have patches of
red and white colour. There is n o blending, each allele is expressed as shown in
figure 25. 10.
phenotype of parents
red
white
cRR
genotype
c ww
x
I
I
0
gametes
0
au c Rw
offspring genotype
offspring phenotype
all red and white
Figure 25.1O Co-dominance in Impatiens.
Genotype
Phenotype
IAA
blood group A
!AO
blood group A
!BB
blood group B
IBO
blood group B
IAB
blood group AB
Worked example
100
blood group 0
1
Table 25.2 Genotypes and phenotypes of
blood group in humans.
~
Another example of co -dominance is found in ABO blood groups in
humans. Your blood group is controlled by three different alleles: JA, 18 and
1°. IA and 18 are equally or co-dominant to each other and both are dominant
to 1°. Only two alleles can be present in any cell, one on each homologous
chromosom e that carries the gen e for blood group. This gives four possible
phenotypes for blood group (table 25.2).
What are the possible blood groups of children whose parents are blood
group A (h eterozygou s) and B (h omozygous)?
The h eterozygo us gen otype fo r blood group A is JA0 .
The h om ozygou s gen otype for blood group B is 18 8 •
l:tQ7
genotype
of parents
What offspring will you expect, and in
what proportion, if two Ft generation
plants from figure 25.10 were crossed?
gametes
V"-1
~
l:tQS
V"-1
A baby has blood type B, his mother
had blood type A. His paternal
grandfather has blood type A and his
paternal grandmother has blood type B.
Determine {i) the genotype of the baby,
and {ii) the possible genotypes of the
baby's father.
offspring
genotypes
! AO
~~
1AB
1BB
x
1AB
100
JBO
Possible blood groups of children are AB and B.
301
Continuity and Variation
Worked example
2
What if both parents had heterozygous genotypes?
The heterozygous genotype for blood group A is JA 0 .
The heterozygous genotype for blood group B is 18°.
X
genotype of parents
JAO
gametes
gametes
®
@
®
JAB
1BO
@
1AO
·--
100
Possible blood groups of children are A, B, AB and 0.
Examples of genetic effects
Sex determination
Practical activity
SBA 25.1: How the sex of an offspring is
determined, page 365
Of the 23 pairs of chromosomes in any human cell, one pair determines the
sex of the organism. There are two sex chromosomes, X and Y. The genotype
XX is female and the genotype XY is male in humans (figure 25.11).
®
®
human cell
I
All the cells of a female have
two X-shaped chromosomes
nucleus has 23 pairs of
homologous chromosomes
one pair determines the
sex of the individual
Figure 25. 11
All the cells of a male have one X-shaped
chromosome and one Y-shaped chromosome.
The Y chromosome is an X chromosome
with a missing piece.
How sex is determined in humans.
Figure 25.12 sh ows the inheritance of sex in humans. Each time a couple has a
child, there is a 50% possibility it could be a boy and a 50% possibility it could
be a girl.
x
male
phenotype of parents
female
genotype
gametes
offspring genotype
offspring phenotype
female
female
male
Ratio 1 male : 1 female
Figure 25. 12 How sex is inherited in humans.
302
male
25 · Heredity and Genetics
Sex-linked characteristics
The sex chromosomes also carry genes other than those which determine sex.
The characteristic of those genes are said to be sex-linked, and they are carried
on the X chromosome.
Haemophilia or bleeder's disease
sex-linked characteristics
haemophilia >
Sex-linked characteristics include haemophilia and colour-blindness.
Table 25.3 shows sex-linkage in haemophilia.
Genotype
Phenotype
XHXH
female, normal clotting of blood
female, normal clotting of blood; she is a carrier since she carries the recessive
allele but it is not expressed.
XhXh
female, a haemophiliac
XHY
male, normal clotting of blood
Table 25.3 The genotypes and phenotypes in haemophilia.
The dominant allele, H , causes blood to clot normally. The recessive allele, h ,
causes haemophilia, a condition in which blood does not clot and any small
cut will bleed for a long time. The inheritance of haemophilia is shown in
figure 25.13.
~
IT:Q9
V'-J
(i)
What is mean by the term 'sex
linkage'?
(ii) A normal man marred a normal
woman and all the female
offspring were normal, but half of
the male offspring were colourblind and the other half were
normal. How do you account for
this?
Worked example
3
A carrier female marred a normal male. What is the possibility of their
having a haemophiliac child?
carrier female
normal female
normal male
x
normal male
normal female
(carrier)
haemophiliac
male
Figure 25. 13 Haemophilia inheritance
The mother transfers the haemophiliac gene to her son. There is a 25 %
possibility of having a haemophiliac son .
Other genetic disorders
Sickle cell anaemia
sickle cell anaemia >
CHAPTER 26
In sickle cell anaemia (chapter 26), the red blood cell can take a sickle shape
instead of the normal biconcave shape. Allele HbNproduces normal red blood
cells and the allele Hb5 produces sickle-shaped red blood cells; the possible
genotypes and phenotypes are shown in table 25.4 (overleaf). The inheritance
of sickle cell anaemia is shown in figure 25 .14 (overleaf).
303
Continuity and Variation
Genotype
Phenotype
HbNN
all red blood cells are normal, the person is normal
Hb55
all red blood cells take the sickle shape, the person has sickle cell anaemia
HbNs
30-40% of the red blood cells are sickle shaped, the person has sickle cell trait
Table 25.4 Genotypes and phenotypes in sickle cell anaemia.
Worked example
4
If two people with the sickle cell trait were to marry, what are the
possible genotypes and phenotypes of their offspring?
parental phenotypes
x
trait
trait
parental genotypes
gametes
offspring genotype
offspring photype
normal
trait
trait
sickle cell
anaemia
Figure 25.14 Sickle cell anaemia inheritance.
The possibility of having a child who suffers sickle cell anaemia is 25%.
The possibility of having a normal child is 25%.
Ratio is 1 normal : 2 rraH : I anaemia .
Pedigree charts
A pedigree chart shows the occurrence of a particular characteristic in a family
tree (figure 2 5. l 5). The chart can be used to show the possible genotypes of
individuals in the chart, which can be important in genetic counselling.
304
25 · Heredity and Genetics
2
•
female with black hair
II
male with black hair
female with red hair
3
4
5
6
7
8
9
10
12
13
14
15
16
17
18
II
male with red hair
II
11
The allele for black hair B is dominant to the allele for red hair b.
What are the genotypes of all the individuals?
The males and females with red hair would have to be bb.
I
(
bb
3
B?
4
B?
6
bb
1
(
~b r ~?
bb
3
(
I
bb
l=
I
1
I
I
To have a bb offspring, individual 2 would have to be Bb.
All their black-haired children are Bb.
B?
9
bb
7
Bb
2
Bb
6
I I
µ-; :·r~
8
bb
bb Bb
To have a bb offspring, individual 5 would have to be Bb.
bb
Figure 25. 15 A pedigree chart showing the inheritance of hair colour in members of a family.
~
l~Q·10
L-"-1
The family tree below shows how coat colour in mice is passed on from generation
to generation.
both parents are homozygous for coat colour
p
F,
5
11 e
D Q
brown coat colour
white coat colour
305
Continuity and Variation
(i) Explain the term 'homozygous'.
(ii) What do the symbols P, F1 and F2 stand for?
(iii) Which generation of mice is heterozygous for coat colour?
(iv) What is the percentage of brown and white mice in the F2 generation?
(v) Which allele for coat colour is recessive?
(vi) What might be the percentage of white coat mice if breeding pairs were set up
between:
(a) 1 and 4
(b) 1 and 5?
, Chapter summary
•
•
•
•
•
II
•
•
•
•
•
•
•
•
•
•
~
Each chromosome is made up of genes, or units of inheritance.
An allele is the form of gene taken.
The genetic make-up of an organism is its genotype.
The observable characteristics of an organism make up its phenotype.
If the alleles of a gene are the same on the homologous chromosomes, the genotype
is described as being homozygous.
If the alleles of the gene are different, the genotype is described as being
heterozygous.
In a heterozygous individual, the allele which is expressed in the phenotype is
described as being dominant.
Recessive alleles are only expressed in the phenotype if present in the homozygous
form. Their effect is masked by the presence of a dominant allele.
A test cross is used to determine the genotype of an individual.
A genetic diagram shows the cross between two organisms for a characteristic.
Incomplete dominance occurs when no one allele is completely dominant over the
other. As a result, the expressions of the alleles blend.
Equally dominant alleles are described as being codominant. Both alleles are
expressed in the phenotype.
The sex of an organism is determined by the sex chromosomes. In humans XX codes
for female and XY codes for male.
Characteristics carried on the X chromosome are said to be sex-linked. Examples are
haemophilia and colour-blindness in humans.
A pedigree chart shows the occurrence of particular characteristics in a family tree. ~
~
ITQ1 (i) Ch romosome - In humans there are 46 chrom osomes in sid e the
nucleus of each cell . Each chromosom e is a separa te stru cture which came
from a parent and is made up of a stand of DNA or deoxyribonucleic acid. Each
chromosome has its homologous partne r which came from the other parent .
(ii) A gen e is a sm all pa rt of a chromosome . It has the code to make a specific
protein which may lead to a specific ph ysical characteristic.
(iii) An allele is the form a gene can tak e. It is the actual code of the gene.
ITQ2 (i) The genotype of an organism is th e total com bina tion of all th e
alleles that make up tha t organism .
(ii) Th e phenotype describes the specific physical characteristics that can be
seen and result from the genotype and the effect of the environment.
ITQ3 Using N for the dominant allele of normal skin colouring, and n for
the recessive allele of albino colouring. Parents a re n ormal; children are 3
normal : l albino.
306
25 · Heredity and Genetics
(i) The albino child's genotype is nn. The parents' genotypes can only be Nn
and Nn (heterozygous) since they are both normal and the albino child must
get a n allele from each parent.
N
n
N
NN
N
Nn
Nn
nn
(ii) The probability of the next child, or any child of these parents, being
albino is 1 in 4 or 25%. Whenever this couple have a child, the probability of
having an albino child will be 25 % . It would be quite possible for them to have
4 albino children and no normal children.
(iii) The no rmal child can have either of two genotypes, Nn or NN. The
normal woman that he marries could also have either of the same two
genotypes. There are therefore three possible crosses:
• NN x NN offspring all normal
• NN x Nn
offspring all normal
• Nn x Nn
offspring 3 norma l : 1 albino
First child has a 75% to 100% of being normal.
(iv) The albino child (nn) marries a normal woman (Nn or NN). Two possible
crosses are:
• nn x NN offspring are all normal
• nn x Nn
offspring 1 normal : 1 albino
Their first child has a 50% to 100% chance of being normal.
ITQ4 (i) To produce short-haired puppies, the long-haired bitch must have
the genotype LI. The short-haired puppies, being 11. got one of the I alleles from
their mother.
(ii) The long-haired puppies from the second mating can have two possible
genotypes, LI (heterozygous) or U (homozygous). To determine which is
homozygous, the breeder must do a test cross, that is cross each puppy (when
mature) with a short-haired dog and examine the offspring of each mating. If
there is at least one sh ort-haired puppy in the litter, then the genotype is LI. If
all the o ffspring are long-haired, then the genotype is LL.
ITQS Crossing two pink- fl owered plants (CRw) would give the following
result: offspring 1 CRR (red ) : 2 cRw (pink) : 1 cww (white)
CR
ITQ6 (i)
cw
A: CRR, B: cww, C: cRw, D: CRR, E: cRw, F: CRR
(ii) Genotypes of offspring: CRW and CWW. Phenotypes of offspring: pink
and white.
ITQ7 The F 1 generation have the genotype cRw. If two of these are crossed,
the offspring woul d be produced as follows:
CR
cw
This would give a proportion of phenotypes of I red (CRR) : 2 red and white
(CRw) : 1 white (cww).
307
Continuity and Variation
ITQ8
~
grandparents
~
\/
m":"
\/
/
~
parents
d"
A
B
rath"
babyB
Mother has blood group A, possible genotypes are JAA or JA 0 . The baby
has blood group B, possible genotypes are 18 8 or 180 . The baby must get one
allele from the mother, but has no JA allele. So the mother's genotype must be
JA0 and the baby's genotype must be 18°.
(ii) The father must have given the baby the other allele, 18. The father's
mother had blood group B and so had genotype 188 or 180, and the father's
father had blood group A and so had genotype JAA or JA0 . The father got the 18
allele from his mother and could have inherited either the JA or the 1° allele
from his father. The possible genotypes for the baby's father are JAB or 180 .
ITQ9 (i) Characteristics that are carried on the X sex chromosome are
described as being sex-linked.
(i)
normal man
x
normal female
xNy
parents
gametes
/
y
offspring
X"Y
normal
female
normal
female
female offspring
all normal
normal
male
colour-blind
. male
male offspring about half normal and the
other half colour-blind
The gene for colour-blindness is recessive and sex-linked. The normal
female parent is heterozygous XNX" and passes the recessive allele to some of
her sons.
ITQ10 (i) Homozygous describes the genotype with two similar alleles, such
as BB or bb.
(ii) P stands for parents (genotypes and phenotypes). F 1 is the first (filial)
generation, and F2 is the second (filial) generation.
(iii) The F 1 generation.
(iv) 75 % are brown and 25% are white.
(v) The allele for white coat colour is recessive.
(vi) (a) Probability of cross Bb x Bb producing white mice is 25%.
(b) Probability of cross Bb x bb producing white mice is 50%.
(ii)
308
25 · Heredity and Genetics
Examination-style questions
(i)
2
3
4
Define the following:
(a) homozygous;
(b) heterozygous;
(c) dominant;
(d) recessive;
(e) allele.
(ii) Distinguish between genotype and phenotype.
(iii) Explain how mutation contributes to variation.
(iv) Cystic fibrosis is an inherited condition caused by a single recessive allele. The normal
gene is dominant and masks the recessive allele. What is the probability of two
healthy people being parents to a child born with cystic fibrosis? Show all the working
and use a genetic diagram.
(v) (a) Explain what is meant when a person is said to be a 'carrier' for cystic fibrosis.
(b) What is the probability of two healthy people (where one is a 'carrier') being
parents to a child born with cystic fibrosis?
(vi) Why are most lethal genes (genes which cause mortality) recessive?
(i) Distinguish between continuous and discontinuous variation.
(ii) List all the possible genotypes of a person belonging to blood group B.
(iii) A woman with blood group A has a child who is also of blood group A. What are all the
possible genotypes of the father? Explain fully, using genetic diagrams.
(i) Explain, using genetic diagrams, how sex is determined in humans.
(ii) Relating to the probability of having a boy or girl in part (i), suggest why:
(a) at birth there are about 106 boy babies for every 100 girl babies;
(b) at puberty the proportions of males and females are about equal;
(c) In old age, females outnumber males.
(iv) Define sex linkage and describe how haemophilia is inherited.
(v) What is the probability of a haemophilic father and a mother carrying the allele for
haemophilia having a haemophilic daughter?
(i) In a test cross, the genotype of an organism showing the dominant characteristic
(which can be homozygous or heterozygous) is determined. Using the symbols T for
tall plant and t for short plant, show the results of a test cross on a tall plant which
turned out to be homozygous for height. Draw a genetic diagram to illustrate your
answer.
(ii) Construct a pedigree chart of the following information.
Female
Male
parents
brown hair
red hair
children
one - red hair
two - both brown hair
grandchildren (from (:laughter who
married brown-haired man)
one - red hair
one - brown hair
(iii) Explain the following using an example for each:
(a) co-dominance;
(b) incomplete dominance.
309
0
0
0
0
0
distinguish between genetic and environmental variation
understand why genetic variation is important
distinguish between continuous and discontinuous variation
define a species
describe how new spec ies are formed
0
understand the process of natural selection in evolution
0
0
0
0
distinguish between natural and artificial selection
understand the causes and effects of mutation
understand what is meant by genetic engineering and how it can be used
discuss the advantages and disadvantages of genetic engineeering
discontinuous variation }
genotype
environment
l.._____......_____J
continuous variation
(
phenotype
(
variation in phenotype
I
artificial
selection
(
selective
breeding
mutation
'
natural
selection
'
genetic
engineering
(
sickle cell
anaemia
'
Down's
syndrome
selection
pressure
evolution
species
Genetic variation
Ead1 organism is unique. This uniqueness is a result of genetic differences
and influences of the environment, and is expressed in the phen otype. Each
organism is born with its own genetic make-up inhe rited from its parents.
The genetic make-up of every organism is different except for clones. Genetic
variation is inherited and the differences may be small or large (fi gure 26. l).
~
IT:Q·1
l....l'V
What is genetic variation?
26 · Variation and Evolution
Figure 26 1 Variation is seen among and between species.
Variation due to the environment
environmental variation >
The environment also plays a very important role in determining the
phenotype of an organism. The variation seen because of the influence
of tbe enviromnent is not inherited but occurs because of differences in
the surroundings of the organism. For example, ten genetically identical
plants grown from cuttings taken from a single parent should be identical in
appearance since the genes for all the characteristics are identical. Suppose
these plants are divided into two groups of five, and each group is grown in
rwo very different environments:
• good soil, watered regularly;
• poor soil, not watered,
After a while, the phenotypes of the two groups will vary greatly. Variation in
appearance will be seen be tween plants th at have the same genetic make-up
and therefore should look the same (figure 26.2).
cutting grown in rich
soil, watered regularly
~
genetically identical plants in
different environments (soil and water)
~
IT:Q2
\.../'-'
.
cutting from the same plant
grown In poor soil, watered little
1
(i)
What is the phenotype of an
organism?
(ii) How is the phenotype determined?
~
IT:Q3
\.../'-'
List three differences which may be
seen in the phenotypes of identical
twins even though they have identical
genotypes.
Figure 26.2 The environment plays a very important role in determining the phenotype of an
organism Genetically identical plans are very different if grown in different environments.
Genetically identical twins, as they grow and develop, acqu ire subtle
differences. These differences occur becau se their e nvironments are different,
even if they live in the same house . They eat different foods at different times
and in different amounts. Their da ily activities and inte rests are different, and
their intera ctions with people, even their parents, are different. The d ifferences
in their 'en vironments' may be subtle, but enough to produce differences in
their physical appearance. Identical twins also have different fingerprints.
311
Continuity and Variation
Importance of genetic variation
Genetic variation among a species ensures survival of that species if the
environment changed drastically. This can be seen in the following example.
A population of wolves living the wild vary with respect to body hair
length. A few have very long hair (5-6 cm) and a few have very short body
hair (1-2 cm) . Most have medium hair length (3-4 cm), which is well suited to
the temperature of the environment (figure 26. 3).
Practical activity
SBA 26.1 : Continuous variation,
page 366
_ _____.,__ most individuals in the population of
wolves will have body hair length 3-4 cm
Number of individuals in
the population of wolves
I
I
2
3
4
5
6
7
8
Body hair length (cm)
Figure 26.3 Graph showing how boay hair length varies in a population of wolves.
~
IT:Q't
1.../'--1
What do you think would happen
to the population of wolves shown
in figure 26.3 if the environmental
temperature got warmer?
Suppose the temperature changed drastically, say it got much colder, then
the wolves with short hair would be more likely to die, but those with long
hair would be more likely to live. Because of the variation which existed
naturally, the wolves with very long body hair would be able to survive the
cold temperatures better than those with short body hair. Those with long
body hair, therefore, would be more likely to reproduce. Surviva l of the species
is thus ensured because of natural variation. Figure 26.4 shows what would
happen to wolf body hair length in such circumstances.
-+-- --
Number of individuals in
the population
of wolves
Figure 26.4 Graph showing a change in
the occurrence of body hair length as the
environment changed.
continuous variation >
discontinuous variation >
2
3
4
5
6
most individuals now have body
hair length 5-6 cm to survive
the colder environment
7
8
Body hair length (cm)
Variation is thus the result of the genetic make-up and the influence of the
environment. There are two types of variation:
• continuous variation;
• discontinuou s variation.
In continu ous variation, the differences are slight and merge or grade into each
other to produce a smooth bell-shaped curve (Figure 26.5): for example, height
in humans, human foot length, human skin colour, leaf size and pod size in
legumes, and body hair length in wolves.
Number of 15-yr
olds in class
Figure 26.5 The height of a class of
15 year-olds shows contiuous variation.
312
-
145
150
most individuals in the population
-\--- - are between 160 and 170 cm
155 160 165 170 175
Height of individuals In cm
180
185
26 · Variation and Evolution
In discontinuous variation, the differences are separate and clear cut; they do
not merge or grade into each other (figure 26.6). Examples are tongue-rolling
in humans, blood groups in humans and horns in cattle.
Number of
individuals
Figure 26.6 Graph showing discontinuous
variation in human blood groups.
t
A
B
AB
0
Blood groups
DNA testing and forensic science
Agure 26. 7 Every individual has a unique
DNA pattern.
DNA testing or 'genetic fingerprinting' is a technique pioneered by Dr. Alec
Jeffreys. He found short DNA sequences from the non -coding part of the
DNA that were repeated several times and were uruque to each individual.
Dr. Jeffreys developed a genetic probe to look for these sequences and was
able to use electrophoresis and autoradiography to produce a DNA image
(figure 26. 7).
Each dark band in the autoradiograph shows as area w here the DNA probe
attached to a similar sequence in the subject's genome. Each person's genetic
fingerprint is unique - this means that each individual can be identified by
their DNA, perhaps from a strand of hair or a scrape of skin. This application
can be used in pa ternity and maternity tests and in as forensic evidence in rape
and murder trials.
Natural selection
natural selection >
Practical activity
SBA 26.2: Natural selection. page 367
Charles Darwin, an English naturalist, first spoke about natural selection. He
observed organisms that lived on the Ga lapagos Islands in the Pacific Ocean.
From his observations, Darwin concluded that within a population, although
many offspring are produced, m any individuals do not survive becuase they:
• compete for limited food and resources;
• try to avoid predators;
• struggle to avoid disease;
• try to tolerate changes in the environment.
There is a constant struggle for existence, and those individuals that are best
adapted to their environment have an advantage. That is, th ey are more likely
to survive and produce offspring. Their offspring will inherit the advantageous
characteristics and the population will
remain well adapted to its habitat. Selection
by the environment is known as natural
selection. It favours those that have the best
adaptations for the.environment in w hich
they live (figure 26 .8). These organisms
Nature 'selected ' birds with strong beaks.
Birds with pointed beaks were able
are said to have a selective advantage.
They were able to crack the hard shell
to feed on flying insects. Nature also
Sometimes we describe these individuals
of nuts and feed on the nuts.
'selected' these birds because of
as being the fittest for the environment.
They thus obtained food and lived to
the shape of their beaks.
reproduce; produce offspring with strong b eaks.
Because of this, natural selection has
become known as 'survival of the fittest'.
Figure 26.B Some individuals are better adapted to the environment.
selective advantage >
313
Continuity and Variation
Natural selection and evolution
Natural section provides the mechanism for one species co change into
another. The change is very slow and is called evolution as one species evolves
into another.
Long necks of giraffes
Figure 26.9 Long necks are an advantage
when feeding from tall trees.
antibiotic resistance >
insecticide resistance >
~
IT:Q5
V'-J
How do bacteria evolve to acquire
resistance to antibiotics?
The long n eck of the giraffe is thoug ht to have evolved when food was in
short supply and only rhe tallest inc:Uviduals co uld reach en o ugh food to
survive. The 'tallness' genes were passed on ro the n ext generation so they
were, on average, tal ler than their parent genera tion . As selection for lon g
necks continued, the gira ffes which produced most offspring were the ta llest
inc:Uviduals. After many gen erations of selection, the long-necked species of
giraffe have evolved (figure 26.9).
Antibiotic resistance in bacteria
Antibiotic resistance of bacteria is a serious problem . When antibiotics are
used o n a p opulation of bacteria, any bacteria with genes to resist the drug
will s urvive and most of the rest will be killed. The resistant bacteria then
multiply, prod ucing populations of antibiotic-resistant bacte ria. Because of the
w idespread use of antibiotics like penicillin, many kinds of bacteria a re n ow
resistant to these drugs.
Insects that are resistant to insecticides have evolved in much the same
way as antibiotic-resista nt bacteria, due to the w idespread use of insecticides
(fig ure 26.10). For exa mple, many populations of mosq uitoes are now resistant
to DDT which was widely used last centu ry to attempt to co ntrol them and the
spread o f ma laria.
R
original
gene pool
A
selection
+-pressure
All the genes present in this population of mosquitoes
make up the gene pool. The resistance gene R is also
present. There are some individuals with resistance to
insecticide.
The application of insecticide to the population of mosquitoes
puts a pressure on the gene pool (selection pressure).
Those individuals with the resistance gene are seen to be
fitter, i.e. able to survive. Most of the others die. (Some may
survive because they avoided the insecticide.)
The mosquitoes with the resistance gene live to reproduce,
passing the resistance gene to their offspring.
gene pool
after
the use of
insecticide
Most individuals are now resistant to the insecticide. The
population is said to have developed resistance to the
insecticide. A stronger dose or a new insecticide must
now be used.
Figure 26. 10 New populations evolve under pressure
Dark form of the peppered moth
camouflage >
314
The peppered moth (Biston betularia) is found in many parts of England
(figure 26. 11). Ir was origina lly found as a pale fo rm, well con cea led by
camouflage on the lichen-covered trees on which they rested. Predators
fo und the moth difficult to spot. Then in the ea rl y 19th to mid -20th century,
pollution in indu strial a reas, blackened the trunks of the trees witb soot. The
26 · Variation and Evolution
pale m oths were n ow easily seen by predators, but the rare black form was
better camouflaged. So the frequency (numbers) of the dark form increased as
they were better suited to the environment. ln the unpolluted areas, the pale
form still predominated. Today, as pollution from industry gets less, the pale
form is again becoming more common than the dark form.
(a)
(b)
dark form
p redominates
light form
predominates
selection pressure
Ondustrialisation)
Rgure 26. 11
(a) Pale and dark forms of Biston betularia moth. (b) Populations change with a change in the environment.
Geographical isolation and speciation
~
IT:Q6
V'-J
Describe briefly the following terms:
(i) natural selection (ii) selective
advantage (iii) survival of the fittest
(iv) evolution.
A popu lation that is geographically isolated from another may experience
different environmental conditions and so evolve differently due Lo natural
selection. Over time, the isolated population would become more and
more different from the origina l popu lation to fill a new and different
ecological niche.
During his visit to the Galapagos Islands, Darwin observed several different
species of finch (now called Darwin's finch es). This group of islands is in the
Pacific Ocean, about 600 miles from the South American mainland. Darwin
concluded that the islands must have been colonised by a few individuals
from a species of finch found on the mainland. These individuals then evolved
independently to fill the different ecological niches on each island. Today 14
different species o f finch are found on the Galapagos Islands, differing greatly
in size and other features, including beak size and shape (figure 26. 12).
warbler finch
beak long and thin.
feeds on insects
vegetarian tree finch
feeds on buds,
leaves and fruit
Galapagos Islands
Rgure 26. 12 Four
of the 14 species of
finches that Darwin
observed on the
Galapagos Islands.
probable common
ancestor. likely to have
been a seed-and
insect-feeder
woodpecker finch
often holds a small
twig and uses it
asa tool
cactus finch
beak long and
slightly curved
Mainland
315
Continuity and Variation
The islan ds of the Caribbean are a group of volcanic islands in the Atlantic
Ocean. This arc of islands sweeps north and west from t he South American
mainland and is ca lled the West Indies. It h as been suggested that the Anolis
lizards of the West Indies have evolved in much the same way as Darwin's
find1es. A few individuals may have drifted (for example on a log) along a
water current from South America and reached the banks of Grenada (th e
most likely arrival point for a rafting colonist). The original species may still
exist in Guyana, Venezuela or north-western Brazil.
The colonisa tion of other close islands followed, such as the islands of the
southe rn Lesser Antilles, including St Vincent, St Lucia, Martiniqu e, Barbados,
and La Blanquilla and Bonaire far to the west of Lhe main chain. Each
population would have been subjected to dillerent environmental conditions.
The vegetation, in sect population, air te mperature and weather patterns all
diifer from island to island. By natural selection, each p opulation would have
evolved inde pendently adapting to each new ecological niche (figure 26.13).
Over time, the popu la tions would have become different from each other,
evolving into nine different species (table 26 .1 and figure 26.14).
Locality
Species
Martinique
A. roquet
Barbados
A. extremis
Grenada
A. aeneus A. richardii
St Vincent
A. trinitatus A. griseus
St Lucia
A. luciae
La Blanquilla
A. blanqillenus
Bonaire
A. bonairensis
Martinique
St Lucia
(,
St Vincent
Barbados
La Blanquilla
Bonaore
Naturally occurring
current which
brought the Anolos
lizard to Grenada
.
Table 26. 1 Species of Ano/is lizards in the
Lesser Antilles.
South
American
Ma i nland
G U YAN A
Rgure 26. 13 Possible colonisation sequence of the Ano/is lizards of the southern part of the
Lesser Antilles.
(a)
(b)
(C)
Figure 26 14 Ano/is lizards of the Lesser Antilles. (a) Ano/is roquet, (b) Ano/is trmitatis, (c) Ano/is mtens tandae- a rare species found in Peru.
It is also suggested that two independent landings on St. Vincent separated
by sufficient time could have resu lted in a second colonisation. Two
reproductively isolated species are found there, the giant Ano/is griseus and the
smaller A. trinitatus.
316
26 · Variation and Evolution
Ecological speciation and
behavioural speciation
predators
present
no predator
~on
I
''
'
'''
'
fish here do not
interbreed with fish
from region A
some interbreeding
may occur between
fish from region A and
fish from region B
Figure 26. 15 Ecological spec1at1on
backyard feeding in
the UK means food
Is readily available for
birds in winter
Ecological speciation is the evolution
of barriers to gene flow resu lting
from ecologically based rnvergent
selection. For example, there are
two populations of the Bahamas
mosquitofish (Gambusia hubbsi),
one has larger and more powerful
caudal (tail) region than the other.
The fish with the larger tail regions
are in environments where there are
predatory fish that will feed on the
mosquitofish. The mosquito fish with
the smaller tail regions live in areas
without predators. Modern research
suggests that the more powerful tail
regions are more powerful swinuners
than the mosquito fish with the
sma ller tail regions. The bigger fish can
therefore escape from their predators
more easily. Speciation is resulting
because each fish chooses the same
type to mate with (figure 26.15).
Behavioral speciation is seen when
species engage in distinct courtship
and mating rituals. For example, the
birds called blackcaps from Germany.
These birds generally fl y to Spain
or north Africa to overwinter but
some have adapted to 'backyard bird
feeding' areas in the UK where there
is a ready supply of food waiting
for them. The change in migration
behaviour has led to a shift in mate
availability and populations are
becoming increasingly reproductively
isolated as they choose birds from
the sa me population to mate with
(figure 26.16).
Artificial selection
Rgure 26.16 Behavioural spec1ation.
artificial selection >
Artificial selection is the process by
which plants and anima ls used by
humans in agriculture, horticulture,
transport, companionship and
leisure have been obtained from wild
organisms. In natural selection, nature
selects the fittest individuals but, in
artificial selection, humans select
individuals with characteristics they
see as useful. Only those individuals
selected by humans are allowed to
produce offspring.
317
Continuity and Variation
selective breeding >
Due to the constant removal of those with unwanted features and breeding
of only chosen individuals, the genetic composition of the population changes.
This is called selective breeding and continues today by a combination of
inbreeding (between closely related individuals) and outbreeding (between
geneticall y distinct individuals).
The aim of artificial selection is to produce animals and plants with
characteristics humans find desirable. These include:
• high yield;
• improved quality;
• reduced production costs;
• faster growth rates;
• greater resistance to disease .
Drugs like growth hormones and steroids are sometimes used LO enhance or
quicken growth and development in animals that are used for food, such as
poultry. These can have negative effects on humans and increase the risk of
populations of antibiotic-resistant bacteria evolving.
A comparison of natural and artificial selection is made in figure 26. 17.
NATURAL SELECTION
ARTIFICIAL SELECTION
gene pool of
a population
selection pressure
selection pressure
The environment may
change, e.g. get hotter, colder,
drier, etc. Those that can
survive in the 'new'
environment live to reproduce,
passing on those genes.
Humans allow some individuals
to live to reproduce, passing
on those genes advantageous.
e.g. greater yield, speed (horses),
size, etc.
New population
New population
• able to survive in the wild
• is a natural part of the environment
• may not be advantageous to humans
• retains most genes
• may not be able to survive in the wild
• Is advantageous to humans
• may have lost other advantageous
genes
Rgure 26. 17 Similarities and differences between natural and artificial selection.
Examples of artificial selection in the Caribbean
Very productive (meat and milk) breeds of cattle have been developed in
temperate countries, such as the UK and the US. Beef cattle, like Hereford and
Angus, and dairy cattle, like Friesian and Jersey, do not thrive well in tropical
conditions because:
• they suffer from heat stress;
• tropical grasses are generally less nutritious than temperate species;
• diseases like tick fever, foot rot and mastitis are serious problems that these
breeds suffer from.
318
26 · Variation and Evolution
Thus, cattle fa rmers in the Caribbean have developed new breeds.
• In Jamaica, cross-breeding Indian and European breeds with local Creole
cattle has led to beef and dairy herds such as the Jamaica Red Poll and
the Jamaica Hope. These can cope with heat stress and poor pasture, and
are disease- resistant, while producing much more milk and mea t than
traditional Caribbean breeds.
• In Trinidad, a new breed, the Buffalypso, has been selectively bred from the
water buffalo brought from India in 1903 to pull cars and help in ploughing.
The matu re animal produces high grade meat, which is marketed as beef.
The ca lves are sold for breeding to va rio us countries, including Guyana,
Cuba and other Latin American countries, and the US .
Captive breeding
Plants and anima ls are kept b y scientists in order to introduce particular genes
into the population. The genome is improved by manipulated crossing of
parent organisms or breeding. For example, corn origina.lly grown from wild
seeds would gradually change as breeding introduced into the population
genes for resistance to disease, large cobs and gra ins rich in nutrients. Similarly,
animals can be kept in breeding programmes to maintain and improve
the genome. Captive breeding programmes a re important for p reventing
extinction and for improving on the diversity of the population of the
organism concerned.
Mutation
lu!mmt.leU A mutation is a change in the amount or number of chromosomes, or a
change in the structure of the ch romosome or DNA of an organism . It results
in a change in the genotype of an organism. An example of a gene mutation is
sickle cell anaemia, and an example of a chromosome mutation which d1anges
the number of chromosomes is Down's syndrome.
Mutation occurs randomly - you ca nnot predict exactly where or w hen a
change will happen.
The ca uses of mutation are:
• exposu re to high-energy electromagnetic radiation like X-rays, ultraviolet
light and gamma (g) rays;
• exposure to certain chemicals like m ustard gas, caffeine, formaldeh yde,
colchicine, tar in tobacco, a n increasing number of drugs, food preserva tives
and pesticides.
mutagenic >
Any substance or process that increases the frequency of mu tation is described
as mutagenic.
If a mutation happens in a body cell, it w ill not be inherited or passed on to
offspring and is lost when the organism dies. However, if it occurs in a gam ete
cell, it can be inherited. This ca n add variation to the population. The offspring
of sexual reproduction show variation naturally, because of crossing over and
random alignm ent of the chromosomes on the equator of the cell, before
anaphase. A muta tion which can be inhe rited, can add new variation. The
change in the chromosome because of the mutation is n ew information. It may
resu lt in an advantageous or disadvantageous chara cteristic in th e organism.
Most major mutations a re disadvantageous.
319
Continuity and Variation
Sickle cell anaemia
Figure 26. 18 Sickle and normal red
blood cells.
sickle cell disease >
sickle cell trait >
Sickle cell anaemia is a good example of how a mutation of a part of a
chromosome can have drastic effects. It also shows the role o f natural selection
in control lin g the occurrence of mutated genes.
ln sickle cell anaemia, the gene or part of the chromosome that determines
the shape of the haemoglobin in red blood celJs has mutated or changed. This
new form of a llele of this gene causes the red blood cell to take a sickle shape
instead of the n orma l biconcave disc shape (figure 26. 18). The sickle-shaped red
blood cell cannot transport oxygen efficiently which makes it a disadvantageous
characteristic. However, the presence of sickle-shaped red blood cells in the
body makes the person far less susceptible to infection by the malarial parasite
than a person withou t sickle-sh aped red blood cells. Thi s is an advantageous
characteristic since malaria is a leading cause of death in areas where it occurs.
Since every person carries two alleles for th is gene, one on each
homologous chromosome, there a re three possible genotypes:
• homozygous for normal haemoglobin;
• heterozygo us with one allele for normal a nd one allele for sickle cell
haemoglobin;
• homozygous for sickle cell haemoglobin.
Those people who are homozygous for sickle cell have sickle cell disease.
They experience severe pain in the joints, anaemia, kidney failure, poor
growth and development, are prone to infections and a re likely to die young.
In those who are heterozygous, only about half the red blood cells change
to sickle shape. These people are unaffected by the condition except at low
oxygen concentrations, such as when flying in an ai rplane or goi ng to high
a ltitudes. This conditions is known as sick le cell trait.
The sickle cell gene was selected for in those regions of the world where
malaria is seen (parts of Africa, the Middle East, Tndia and sou thern Europe).
People h ere who are heterozygous for the gene are at a selective advantage, as
they are less likely to die from malaria tha n those who do not have the sickle
cell allele, and less likely to die than those who have two sickle cell alleles. By
natu ral selection, the gene continues to be passed on to offspring, since these
people survive malaria.
However, the sickle cell alle le is at a selective disadvantage in areas where
rhere is no malaria. People who originally came from malarial areas. such
as Africa, bur now live in areas where there is n o malaria , such as America,
still carry the allele. Abou t l in 400 black people in America have sickle cell
anaemia. and the disease causes about 100 000 deaths per year worldwide.
Down's syndrome
Down's syndrome is a change in the number of chromosomes in a cell.
It occurs in all races and a correlation wi th the age of the mother is seen.
Inciden ce of th e disease rises with the mother's age, especia lly after 40 yea rs.
Th.is may be due to the fact that a woman is born with all her eggs and they
age with he r. Men, on the other hand, constantly produce new sperms.
The cells of a person with Down 's syndrome a ll have 47 ch romosomes
instead of 46. People with the cond ition show typical facial features (fl at and
rounded). Other symptoms include:
• learning difficulties;
•
•
•
•
320
sh ort stature;
heart defects;
increased risk of infection;
intestinal problems.
26 · Variation and Evolution
People with Down's syndrome are generally very friendly and cheerful, and
greatly enjoy music.
Genetic engineering
genetic engineering >
~
rr.01
\J'V
Describe brieflythe following terms: (i)
genetic engineering (ii) a transgenic
organism.
Biotechnology is the science which involves the harnessing and exploitation of
biological processes, systems and organisms (particularly microorganisms) iJ;l
manufacturing industries. The most powerful tool available to biotechnologists
is genetic engineering. The benefits of genetic engineering include the
development of high-performance food crops that grow quickly with less use
of fertiliser. This could ease the pressure on food supplies from the growing
human population. Another important area of development is diseaseresistance in crop plants, which would reduce the need for use of pesticides.
An organism that has genes added to it from another species by genetic
engineering is known as a transgenic organism.
Some examples of genetic engineering in food production include:
• resistance to pathogenic fungi in maize and potato;
• resistance to insect pests in many crop plants;
• increased growth rates in salmon and chicken;
• production of meat with less fat in
pork and beef animals;
bact~mjO ~J
pl~d I"'°"'" y
DNA
found in bacteria)
plasmid cut
using enzymes
@~ @""~"""'
v."'P./ /@
human DNA
(insulin gene)
~
~ DNA extracted from
• production of higher quality dairy
products (e.g. milk with more
protein);
•
•
human pancreatic cells
human DNA inserted
into bacterial plasmid
and joined back up again
bacterial DNA
l
recombinant DNA - DNA from
two different species
•
plasmid (recombinant DNA)
introduced into a bacterium
As bacteria multiply, the genes
are expressed to make their
different parts. The insulin gene
which was inserted will also
be expressed.
•
The plasmids are mass produced
as the bacteria multiply. The insulin
gene is also being mass produced
and insulin is produced when the
gene is expressed.
human insulin is separated and purified
•
•
•
increase in the proportion of
protein in seeds such as soya;
long shelf-life of fruits such as
tomato and bananas;
tastier and more nutritious foods
like tomato;
increase in size, and therefore in
yield, of many crop plants and
cattle and dairy animals;
production and subtropical
crops so they are able to grow
in temperate climates (e.g. sugar
cane and millet);
production of cows and sheep
from temperate areas so that they
can grow well in tropica I regions;
grain crops that can fix
atmospheric nitrogen (e.g. wheat
and maize).
Human insulin is now manufactured
in bacteria as a result of genetic
engineering (figure 26.19). Insulin
was previously obtained from cows
or pigs and caused many side-effects
in people with diabetes who needed
it. It is now produced by inserting the
human gene that codes for insulin
into bacteria and allowing them to
Agure 26.19 Using genetic engineering to make insulin from bacteria.
321
Continuity and Variation
grow and multiply. As they do so, they produce insulin. The insulin is then
separated, purified and packaged. Production of human insulin rhis way is now
a large-scale enterprise and rhe product is used by thousands of people w ith
diabetes.
Genetic engineering is also being used to help treat some hereditary diseases
in humans. Cystic fibrosis is a disease which affects around one in every 2500
babies. It is caused by a recessive allele which makes the mucus in the lungs
thick and sticky. Bacteria get trapped in the mucus and cause infections whlch
can lead to early death. Traditionally, the on ly treatment fo r cystic fibrosis
is daily physiotherapy to clear the mucus in the lungs. Current research is
studying trearment using a viral vector to transmit the normal a llele inro the
lungs. ti the vector is taken up by the cells, they wou ld than be able to make
normal mucus. Treatment wo uld have to be continuous because the ce lls lining
the lungs a re shed frequenrly and replaced with new ones.
Implications of genetic engineering
Are there risks to human health?
Some people argue thar there may be long-term risks from genetic engineering.
There is much discussion on the effects of genetically modified organisms
(GMOs) used in food production. An example is bovine somarotrophln (BST).
This hormone is produced artificially by bacteria and injected into cows to
stimulate growth and increase milk production. The hea lth o f humans drinking
the milk or eating the meat appears to be unaffected by the hormone. But are
there long-term effects on human health? As yet, we do not know. Should
genetically mod ified food be labelled as such ? What would you p refer?
Feeding the world
Many crop plants are modified for disease resistance and increased yield.
Plants can be engin eered to incorporate the characters of a number of different
species (e.g. starchy potatoes with bera-caroteoe from green vegetables and
vitamins from citrus fruirs). Millions of people are starving in the world - why
not use such foods to ease the problem of starvation?
Scientists have a lso been able to insert two genes from daffodil and one
gene from a bacterium into rice so thar it can now contain vitamin A and its
precursor beta-carotene. This gives the rice a yellow colour - hence it is w idely
known as golden rice. It is hoped that it will help to combat malnutrition in
less developed nations, especially those where a lack of beta-carotene in the
diet leads to blindness.
Economic and diversity problems
Figure 26.20 Genetically modified soya
bean could replace conventional crops.
322
There is also fear that small farmers would no longer find it economical
to culti va te loca l varieties of crop plants when they have to compete w irh
imported, economicall y superior varieties (figure 26.20). Cou ld this lead co a
serious loss of genetic diversity among cultivated crop plants? This would make
the dwindling genetic diversity problem worse. Are there dangers in relying on
just a few varieties of crop plants? A new strain of disease could then wipe out
a major crop. Gene banks o f many varieties of seeds and plants have been set
up in many countries to conserve diversity, for example cocoa seeds and planes
are stored in Trinidad .
Some people fear that the genetically engineered trait cou ld get transferred
into wild relatives of A engineered crop plant (it has been shown that pollen
from crops such as o il-seed rape can spread for at least I 00 m from the GM
plants). Might this produce pest species w hich cou ld spread uncontrollably
26 · Variation and Evolution
and eliminate other plants, upsetting th e ecological balance? What are the
implications of genetically engineered tra its transferring into other species?
Treating disease
Advances in genetic engineering will undo ubtedly eventually lead to the
control of genetic diseases, su ch as cystic fibrosis, by replacing defective
gen es with healthy ones. This could be wonderful for those livin g with theg'e
conditions. There are many advantages of this kind of technology. Might this
be taken further? Wou ld genes for low intelligence by replaced by those for ·
high er intelligence? Would this be good or bad? Are some human characters
superior to others? Who would decide?
~
r:roa
l/'V
Describe two benefits and two hazards
of genetic engineering.
The future
Should humans be allowed to genetically manipulate animals and plants
to serve the needs of humans rath er than the environment as a whole? Is
exploitation of living organisms, whether for commercial gain or to reduce
suffering, the height of misuse of the environment, or is it another example of
human s's triumph over adversity?
• The theory of natural selection is based on genetic variation among a population. It is
selection of the fittest organisms by nature.
• In artificial selection, humans select individuals that are allowed to reproduce and
produce offspring. We select characteristics advantageous to us like high yield and
reduced production costs.
• Mutation can occur that change the genotype of an organism .
• A mutation may be a change in the structure of the chromosome, such as sickle cell
anaemia.
• A mutation may change the number of chromosomes in a cell, as in Down's syndrome.
• Genetic engineering is the deliberate changing of the genotype of an organism by
humans.
• The production of human insulin by bacteria is an example of genetic engineering;
• There is much discussion around the possible advantages and disadvantages of
genetic engineering.
323
Continuity and Variation
Each organism has its own genotype which is different from every
other genotype (except for identical twins and individuals produced by asexual
reproduction). Genetic variation is variation in the genotype that helps to
determine differences in the phenotype. Genetic variation explains wh y every
organism is unique.
ITQ2 (i) The phen otype is the physical appearance of an organism. It
describes all its physical characteristics.
(ii) An organism develops its physical characteristics from a combination of
its genotype and its e nvironment. The genotype confers on the organ ism the
possibility of developing certain characteristics. The environ ment guides the
development of these characteristics.
ITQ3 Height - one may be taller; complexion - one may be darker; body size
- one may be fa tter (there are many other examples).
ITQ4 If the en vi ronmental temperature got warmer, all might survive, but
the ones with the shorter hair length would be at an advantage. The wolves
with long hair stand a chance of over-heating because of the insulation
provided by the thick coat of hair. They are at a disadvantage. The wolves with
the advantage for that new environment would be selected by nature (i.e. they
would be more able to Live and reproduce). Eventually a population of shorthaired wolves would be seen .
ITQ5 The use of an antibiotic on a population of bacteria results in an
increase in occurrence or frequency of those with the gene that gives resistance
to that antibiotic. Over time, and with constant use of many different
antibiotics, a population of bacteria could evolve that is resistant to many
different antibiotics.
ITQ6 (i) Natural selection is a theory first put forward by Charles Darwin.
He explained how the environment could select for characteristics in a
population showing variation. He concluded that new species could come into
being by slow and gradual changes, called evolution, as a result of the process
of natural selection.
(ii) A characteristic that suits an organism to its environment has selective
advantage because organism with that characteristic stands a better drnnce of
surviving and reproducing than those which do not have it.
(iii) The process of natural selection is also known as 'survival of the fittest'
because nature selects those individuals best 'fitted ' (adapted) to the environment.
(iv) Evolution describes the change which takes place in a species over time
and which leads to the formation of a new species.
ITQ7 (i) Genetic engineering is the technology in which genes from o ne
organism are transferred to another organism, often a different species.
(ii) A transgenic organism is one which has had gene (s) transferred to it from
another species. The transgenic organism s can live and reproduce normally
although it has been changed.
ITQ8 Any of the benefits and hazards mentioned in the text could be
mentioned, or you might have researched some more. This new area of
knowledge is constantly changing and new developments are frequently
reported in the media.
·ITQ1
324
26 · Variation and Evolution
Examination-style questions
1
(i)
Explain these terms:
(a) evolution;
(b) mutation;
(c) artificial selection;
(d) selection pressure.
(ii) Explain what is meant by 'selective advantage; using antibiotic resistance as an
example.
(iii) Describe, using an example, how the environment may affect the phenotype.
(iv) Explain, using the sickle cell gene, how mutation may affect the phenotype.
2
(i)
Describe four examples of artificial selection and the characteristics that are being
selected for by humans. ·
(ii) Explain, using examples, how environmental factors like temperature, act as forces of
natural selection.
(iii) Using a table, list five differences between natural and artificial selection.
(iv) If two offspring (not identical) are brought up in different environments, suggest why
there may be difference in the development of the following characteristics:
(a) body weight;
(b) intelligence.
Compare this with two identical offspring, brought up in the same environment.
3
(i)
The aim of artificial selection is to produce animals and plants with characteristics
desirable to humans. Suggest four characteristics of animals and plants that may be
chosen.
(ii) The peppered moth exists as two main types, a pale form and a dark form.
(a) What is the importance of the colour of the moth?
(b) What effect did industrialisation and the production of pollution have on both
forms?
(c) Why do you think heavy-metal tolerant plants are rare in unpolluted areas?
4
(i)
Outline the general process of genetic engineering.
(ii) Give two uses of genetic engineering in (a) agriculture, and (b) medicine.
(iii) Discuss the possible risks of genetic engineering. How can these risks be reduced?
(iv) Many people are against the practice of genetic engineering. Suggest some reasons
for this.
325
Section D:
School-Based
Assessment
Practical work in Biology
The present CSEC Biology syllabu s (201 3) makes clear that assessed practical
work - the School-Based Assessment (SBA) - is an integral part of a student's
studies. This aspect of the course gives the chance to personalise the
curriculum to meet students' particular needs and assess the development of
h is or her skills.
Specified topics
In biology, assessment in at least 18 exercises (spread across 7 specified topics)
is needed to satisfy the CXC requirements. The specified topics are:
1. Ecological study
2. Movement at molecular level (diffusion, osmosis)
3. Photosynthesis/respira tion
4. Food tests
5. Germination
6. Nutrition and diseases
7. Genetics
This chapter indudes outlines of 31 activities (in addition to those mentioned in
the syllabus itself), which are suitable, after proper development, for use in SBA
practical investigations. There are both qualitative and quantitative investigations.
The chapter comains at least one practical exercise associated with each of the
specified content areas, as well as other topics encountered in this course.
Sufficient detail is given to make possible the practical conduct of each
experiment, and each one can be developed to illu strate material in the
text. Each gives students the opportunity to develop their experimental and
reasoning skills and also their ability to present results in the clear, appropriate
way detailed in the syllabus.
Assessment of skills
If you are doing an experiment in class as part of your week's work, your
teacher may have done som e or all of the planning for you, collected alJ the
ma terials that you need, and give you instructions how to do the work, or
even a written worksheet to fo llow. But you still have to show that you can
follow the instructions, do the experiment and present your resu lts well. The
skills which will be tested are:
Experimental skills (XIS)
•
•
•
•
Manipulation and measurement (M/M)
Observation, recording and reporting (O/R/R)
Planning and designing (P/D)
Drawing (D)
27 • School-Based Assessment
• Use of knowledge (UK)
• Analysis and interpretation (A/I)
A three-step approach in preparing for your SBA
When planning and presenting your project, your SBA has three parts:
l . Planning and designing the experiment
2. Doing the laboratory work
3. Presenting a lab report
1
Planning and designing the experiment
In any experiment, you are trying to find an answer: it might be a relationship
or a value. You will need to devise and follow a logical series of steps to find
out that information. Therefore, whatever your hypothesis, you must have
a plan.
In some cases, the proposed activities already in this section contain an
outline plan. However, you would still need to design your experiment bearing
in mind the equipment and facilities ava ilable in your lab. In other activities,
you are given a problem to solve, and here you would have to Plan and Design
your investigation from the beginning. In this latter case that your work would
most likely be assessed under Planning and Designing [PD] .
Part of your planning is specifying, in detail, how to carry out your
experiment. You need to plan the experiment in such specific detail that
someon e else reading your design would be able to do exactly the san1e as you
did and get the same results.
Think about:
• What apparatus will you need? (e.g. 'a 250 cm 3 beaker' - n ot just 'a
beaker')
• What ch emicals will you need? (e.g. '3 or 4 potassium manganate(VII)
crystals abou t 2 mm long' )
• What will you do? (e.g. 'stir the mixture gently with a sturdy plastic
drinking straw just before taking each temperature' - not just 'stir the
mixture and take the temperature')
• What could go wrong?
• What are some possible hazards? What safety precautions should be taken?
You will n eed to put your plan in writing. It is always a good thing to have
your teacher, as well as colleagues, check your plan before attempting to carry
ou t your investigation.
Often, no matter how carefully you have planned an experiment, it doesn't
go as you thought it would . However, it has still told you something - an
experiment never 'fails'. If it didn't produce the effect you n eeded, find out
why. If the experiment 'worked' but didn't give the result you expected, then
you've found ou t som ething new.
2
Doing the laboratory work
Here you carry out your plan. Always consult with your teacher if you are not
sure exactly how to use the equipment, and how to use it safely. CSEC expects
you to have practised using equipment before being formally assessed in its use.
3
Presenting a lab report
Labs should be written up using the following format. The questions included
in each activity are a guide to the content of the discussion .
329
School-Based Assessment
Writing in the correct tense
Remember that your research is already finished. Use the past tense when talking about
the experiment: 'The objective of the experiment was ...' or 'The mixture was added to
the beaker.'
Your report, the theory you are testing and your equipment still exist; therefore, these get
the present tense: 'The purpose of this report is .. .'
Date and title
The title should be brief and describe the main point of the experiment or investigation.
Aim
Keeping it simple and achievable, describe the purpose of the experiment.
Discussion
Background information to relate the experiment to something you have learnt or seen,
or to a problem you have faced.
Hypothesis
Should be clear and be in the form of a question that you want to find the answer to, for
example: 'Does vitamin C in orange juice oxidise over time when exposed to the air?'
(From the data you obtain from your experiment you should be able to say if the
hypothesis has been either supported or not in your conclusion.)
Procedure
Use the past tense (see box above). In a bulleted list or in separate paragraphs, state,
in order, what you did. Include clear, quantifiable detail (e.g. quantities stated and
apparatus specified). Your teacher will suggest that you use one of these two forms of
words:
'I washed a 250 cmJ beaker.' or 'A 250 cmJ beaker was washed.'
if you have written a good account then someone else, having read it, should be able to
repeat the experiment exactly as you did it without any other help.
Diagram
Draw the apparatus as neatly as you can.
Results
• Table - title stated, neatly drawn with accurate data (times, volumes, masses, colours
.. .) and proper units for quantities.
• Graph (if necessary) - title stated, axes labelled with proper units, points accurately
plotted. Use a line or a bar graph as required. Remember that you should choose the
correct type ofgraph for the data you are presenting.
• Include any calculations you used.
Explain the results in detail, using values found in your results.
Answer the questions given in paragraph style.
Limitations
Explain any condition or factor that is out ofyour control and affects the results obtained.
Conclusion
One short paragraph to summarise results. Make it related to the aim. Review your data
and state your opinions and arguments of what the results show, for example, 'as graph
3 shows, there is a marked difference between group A and group B which allows the
conclusion that .. . ' .
330
27 · School-Based Assessment
State ifyour hypothesis has been supported or not. If the data you have obtained is
not sufficient to support or reject the hypothesis, state why and say what further work
could be done that would allow you to draw a stronger conclusion.
If you are undertaking a complete project (which will be the case in the second
year when you carry out your investigation) then more will be expected of
you, and you can see from page 45 of the syllabus how marks for the project
will be awarded. Your report will need to be more comprehensive than for a
class experiment. It will be assessed for Planning and Design and for Analysis
and Interpretation. Planning and Design has twice the marks of Analysis and ·
Interpretation.
Safety first
There are several sources of danger that you need to address as you develop
your SBA activities. There are dangers to yourself, your colleagues, the
equipment and even the school building itself. Here are a few safety symbols
concerning situations you should bear in mind.
Electrical hazard
Hot surface
Laser light
No food and drink
allowed
Biohazard
Wear safety goggles
Radioactive
No pointed objects
allowed
Corrosive substance Flammable materials
Toxic materials
•
331
School-Based Assessment
School-Based Assessment contents
332
Photocopiable
1.1 To observe visible characteristics of plants and animals
333
2.1 A simple ecological study
334
2.2 To compare the water-holding capacity of three types of soil
338
2.3 To estimate the percentage of water in a soil sample
339
2.4 To estimate the percentage of air in a soil sample
340
8.1 To observe diffusion in a solution
34~
8.2 To observe some effects of osmosis
342
9.1 To investigate the presence of starch in a green leaf
9.2 To see if light is needed for photosynthesis
343
344
9.3 To see if chlorophyll is needed for photosynthesis
345
9.4 To see if carbon dioxide is needed for photosynthesis
346
9.5 To see whether oxygen is produced during photosynthesis
347
10.1 To investigate the action of an enzyme
348
10.2 To investigate which food groups are present in a food sample
349
11 .1 To discover whether carbon dioxide is produced during
respiration
350
11.2 To observe whether heat is produced during respiration
351
11.3 To discover whether oxygen is used up during respiration
352
14.1 To investigate the rate of transpiration using a photometer
353
17.1 To discover how gravity can affect plant growth
354
17.2 To investigate the growth of a radicle
355
17.3 To discover how light can affect plant growth
356
17.4 To compare the movement of four animals
357
18.1 To find whether the skin of the back of the hand, the palm or
the back of the neck contains the most touch receptors
359
18.2 To investigate two reflex reactions
360
19.1 To investigate heat flow from a warm object
361
20.1 Observing the reproductive cells of a mammal
362
21 .1 Dispersal of fruits
363
21 .2 Seeds and food storage
364
25.1 To investigate how the sex of an offspring is determined
365
26.1 To investigate continuous variation
366
26.2 To investigate natural selection
367
© Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014.
27 · School-Based Assessment
1.1 To observe visible characteristics of animals and plants
Chapter 1 The Variety of Living Organisms ' ) (
Syllabus skills: O/R/R
Procedure: animals
1. Visit a backyard garden, a nearby cocoa estate, a nature centre, foothills of forest (anywhere a range of
organisms can be seen).
2. Copy the table below into your lab book and observe five animals (include three insects). Describe what
each animal was seen doing e.g. sucking nectar from a flower, sitting on the bark of a plant. Make a
simple drawing of each animal.
Animal
3.
4.
5.
6.
What it was seen doing
Simple drawing
For the three insects, list visible characteristics that they share.
Name the phylum and class they belong to.
List two ways one insect is different to the other two.
Draw a simple classification table to include the five animals.
Procedure: plants
1. Visit a backyard garden, a nearby cocoa estate, a nature centre, foothills of forest (anywhere a range of
organisms can be seen).
2. Copy the table below into your lab book and observe five plants. Make a simple drawing of a leaf from
each plant.
Plant
Drawing of a leaf (show parallel or branched veins)
3. List all the dicotyledonous and monocotyledonous leaves.
4. Choose two leaves and list three differences you observe.
5. Choose three leaves and list similarities you observe.
© Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable
333
School-Based Assessment
2.1 A simple ecological study
Chapter 2 Ecology and the Impact of Abiotic Factors on Living Organisms
Syllabus skills: O/R/R; M/M
The area to be studied should be small, such as a tree, a small pond,
a small area in the foothills, a small area in a cocoa estate or a small
garden. The aim is to study the biotic and abiotic factors of the area.
The area being studied can be marked by funning string and the area
calculated.
The biotic factors
A list of all the animals and plants seen in the area should be made. This
can be done by walking quietly and slowly through the area {if it is on land)
A representative sample of any study area
and observing the organisms. Organisms may be found in and on the soil,
can be taken .
under leaf litter and stones, on the stems and leaves of small plants, flying
in the area, on and under the bark of a tree, on the branches of a tree or just visiting the area for a short time.
Food chains and a simple food web can then be constructed using the organisms (plants and animals)
on the list. Interrelationships between the organisms may be noted as examples of the parasitism ,
commensalism and mutualism. Other interrelationships like competition (for light, space, etc.), camouflage,
pollination and protection should also be noted. A reader of the study should have a good idea of the
organisms seen there and what they are doing.
An ecological study may also involve collecting data about the abundance and distribution of organisms.
The population size of an organism in the area may be difficult to obtain since it means counting every
individual in the area. However, the population density may be calculated from a smaller area, as the number
of organisms present per square meter (m 3) . Then the population size of the whole area can be calcu lated if
the area is known.
To do this, representative samples of the area must be taken. These are usually chosen at random to
avoid bias. Sampling methods include line transects, belt transects and the use of quadrats and sweeping
nets. The most appropriate sampling method for a particular study depends on the area being studied.
Sampling methods
Quad rats
These can be used if the area is fairly uniform and flat. A quad rat is a square frame (meal, plastic or wooden)
of a know n area, usually 0.25 m2 or 1 m 2 . It is placed randomly at several places within the study area
and the number of individuals counted. This method is suitable for plants and slow-moving animals like
millipedes and some insets. The results can be tabulated as shown .
Quad rat
Number of individuals*
7
2
14
3
3
4
23
5
5
*number of individuals of one population e.g. millipedes or nutgrass.
The mean number of individuals per quadrat is then calculated and used to find the population density or
population size of the species counted in the whole study area.
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For example:
7 + 14 + 3 + 23 + 5 - 52 = 10 4
5
-
5
.
There are on average 10.4 individuals in every quadrat.
If the 1 m 2 quadrat was used then: population density = 10.4 individuals/m2
If the size of the area being studied is known, for example 25.6 m 2 , then the popu lation size can be
calculated:
If in 1 m 2 there are 10.4 individuals, then in 25.6 m 2 there are:
10.4 x 25.6
=266.24 individuals
So the population size for the area studied is 266 individuals (m illipedes or nutgrass or whatever was being
estimated).
Line transects
A line transect is a better sampling method if one type of habitat changes into another or the area is sloping,
such as a rocky or swampy shore. A string is pulled in a straight line across the area being studied . All the
animals (slow-moving) and plants actually touching the line are considered to be a representative sample of
the animals and plants there. Measuring the height of the line at regular points can describe the slope of t he
area.
A
B
c
D
E
A transect line
Position along line
Distance between
soil and string
Description of soil
(water present)
Plant and animals
observed
A
B
c
D
E
Worksheet for the transect line
Transect line across the edge of a pond, and a recording sheet.
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335
School-Based Assessment
Sweep nets
These are used for sampling insects, especially flying insects. At
randomly set places within the area a net is swept through the plants
(like grass) a fixed number of times and the individuals caught are
counted. The mean represents a sample of the insects found t here.
Sweep nets can be used with quadrats or line transects.
The abiotic factors
The distribution and abundance of organisms relate to abiotic factors.
Commonly measured and described factors are temperature, pH, light
intensity and wind. The soil is a very important abiotic factor since it
directly influences the distribution of plants and therefore the animals
that feed on them.
Temperature
Temperature can be measured using a thermometer. The temperature
range over a period of time like a day may be more important than
a reading at any particular moment. Standard maxim um/ minimum
thermometers can be used.
pH
pH is a measure of the alkalinity or acidity. To determine the pH of the
soil, about 1 cm 3 of soil can be missed with 10 cm3 of distilled water.
After shaking, the mixture is allowed to settle and the pH determined
with the use of universal indicator or pH paper.
Using various sampling techniques in an
ecological study. (a) Pond dipping. (b) Collet1ng
insects in a net.
14
13
12
pH strip
11
10
This one is pH 6
9
8
7
A pH strip
placed into the solution being tested, then compared to these standards 1n order to determine the pH of the solution.
Light intensity
Light can be measured at any
time using light meters (like
those used by photographers).
However, it is the light received
over a long period of time that
affects plant growth.
(a)
card
,.......,1-- pin upon which
vane 1s pivoted
tunnel
336
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card vane
wooden
arm
Wind
Wind speed and direction
affect those animals and plants
exposed to the elements
of nature. Wind speed is
~-+-- scale
- supporting pole
upon which wooden
arm pivots
I \
~
wind
direction
Two simple wind gauges.
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27 · School-Based Assessment
measured by an instrument called an anemometer and a simple wind vane can measure the direction.
Simple, but effective gauges can be improvised which may not give the exact speed values but give
comparative readings .
Water flow
Water speed can be determined by measuring the time taken by a floating object to travel a measured
distance of the stream or river. The speed per hour can then be determined.
'-
Soil
Factors of the soil which affect plant growth include the pH, water content, air content, humus content,
water-holding capacity and soil type (composition and distribution of inorganic soil particles). Investigations
to measure the water content, air content and water-holding capacity follow.
Humus content
A sample of soil is heated at 100 °C (to remove all the water) and weighed to give weight X. The dry
sample is then heated again until red hot; this mean that the humus is burnt off. It is then reweighed to give
weight Y.
The percentage of humus in the soil =
xx =100%
Y
Soil type
The distribution and composition of the rock particles can be determined using the sedimentation test.
A sample of the soil is taken and mixed with excess water in a measuring cylinder. The mixture is shaken
vigorously and left to settle. The largest and heaviest particles will settle first, the smallest last, the particles
will settle in layers. The thickness of each layer can be recorded to indicate soil type.
:S:::~~~~--- bits of twigs, leaves, etc.
·: · ·· .: : : : ·: : ..·: / .: :-..·:-.+-- -- very small particles (clay)
.
·:.:· ~ :' ·~ ·:..::. ·: ·.:
.~.=:::-. ~·:.:·: ~: :':::. :.:
·..:...:-:·
.··....
....·::.·:...
. . . ·. ·.· ·.·. ·:
... .·... .:..·. .·.·..:...
•
· •
.+--
- - small particles (silt)
• • : ••• : •: •• : • •- 1 - -- - large particles (sand)
....... ·......·
=+---
-
-
stones and gravel
Results of a sedimentation test.
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School-Based Assessment
2.2 To compare the water-holding capacity of three types of
SOil
Chapter 2 Ecology and the Impact of Abiotic Factors on Living Organisms
X:
Syllabus skills: O/R/R; M/M
Procedure
You need samples of a sandy soi l, a clay soil and a loamy soil.
measuring
cylinder
1. Set up three sets of apparatus as shown in the diagram. Use 100 g samples of soils A, B and C.
2. Draw up a table like the one shown below.
3. Pour 100 cm3 of tap water through each sample.
4. Wait until no more water is passing through the samples. (This may take some time!) Record the volume
of water which has passed through each.
Soil sample A
Soil sample B
Soil sample C
Amount of water drained through (cm~
Amount of water retained in soil (cm~
Questions
1. Through w hich soil did the water flow (i) most quickly (ii) most slowly?
2. Which soil retained (i) least water (ii) most water?
3. From this data, which do you think is the sandy soi l? Explain your reasoning.
4. From this data, which do you think is the clay soil? Explain your reasoning.
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2.3 To estimate the percentage of water in a soil sample
Chapter 2 Ecology and the Impact of Abiotic Factors on Living Organisms } (
Syllabus skills: M/M
Share the samples A, Band C from investigation 2.2 among class members.
Procedure
1. Weigh a suitable sized sample of soil.
2. Heat the sample of soil in a dish until it seems dry. Do not heat the soil strongly enough to decompose
organic matter - a temperature of about 90 °C is ideal.
3. Let the soil cool and reweigh it.
4. Reheat the soil for several minutes.
5. Repeat steps 3 and 4 until there is no further loss of weight.
6. Calculate the percentage of water in the soil from the formula:
% = mass of wet soil - m ass _of dry soil x 100
mass of wet soil
Questions
1. Which type of soil contained the highest percentage of water? (Your answer may be different from
season to season!)
2. Explain the necessity for step 3 in the experiment.
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School-Based Assessment
2.4 To estimate the percentage of air in .a soil sample
Chapter 2 Ecology and the Impact of Abiotic Factors on Living Organisms
X
Syllabus skills: O/R/R; M/M
Procedure
1. Choose a small tin with a volume of about 200 cm 3 • Punch several holes in the base.
2. Press the tin down into the soil which you are going to test. (Take care! Some tins have very sharp edges.)
A
tin
,,---.,
tin of soil collected,
the holes at the bottom
are plugged with plasticine
tin pressed into
the soil
3.
4.
5.
6.
Plug the holes in the base of the tin with plasticine.
Pull out the tin without losing any of the soil inside it.
Add 300 cm 3 of water to a large (1000 cm3 or larger) measuring cylinder.
Pour the soil from the tin into the water in the cylinder, swirl or stir the mixture and allow it to settle. Note
the new volume. Call this X cm3 .
B
15001400
1300
1200
1100
1000
900
eoo
700
volume of soil
3
and 300 cm
y
of water and tin
full of water
{
:
400
:
J
J
100
volume of the tin
{ volume of soil
X and 300 cm3
of water
7. Fill the tin with water to the brim and pour the water into the cylinder. Again note the new volume. Call
this Y cm3 .
Calculation
Volume of tin = Y - X cm 3• This is the volume of (soil + air).
X = 300 +total volume of the tin - volume of air in the soil (the air is lost as bubbles)
X = 300 + (Y - X) - volume of air.
Therefore volume of air = 300 + Y - 2X.
% of air = 300 +CY - 2 Xl x 100
(Y - X)
Questions
What is the importance of air in the soil?
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8 . 1 To observe diffusion in a solution
Chapter 8 Cells
Syllabus skills: O/R/R ; M/M
Data
Potassium manganite(Vll) is soluble in water giving an intensely purple solution.
Procedure
1. On a sheet of white paper draw five circles all with the same centre. Make their radii 1, 2, 3, 4 and 5 cm.
2. Place a large beaker over the circles and fill it to three-quarters with water. Put the beaker aside, out of
direct sunlight, for five minutes so that the water can become quite still.
3. Choose a single crystal of potassium manganite(Vll) (potassium permanganate) and drop it through the
water so that it lands near the centre of the rings you have drawn.
crystals
placed
4 . Time how long it takes for the pool of dark purple solution to spread out through each of the rings. Put
your results in a table.
Questions
1. Why was it important to keep the beaker of water out of the sunlight?
2. Why did the colour move through the water?
3. What is t he mean speed of diffusion of the purple coloration through the water?
4. In a vacuum the coloured particles would move very quickly. Why did they move so much more slowly in
your solution?
Extension
It is not easy to get the potassium manganite(Vll) crystal to fall where you want it. Can you devise a better
way of placing it in the water in the beaker? Remember that the water must remain still.
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School-Based Assessment
8.2 To observe some effects of osmosis
Chapter 8 Cells
X
Syllabus skills: A/I; O/R/R; M/M
Procedure
1. Cut two potato strips roughly 1 cm square and 3 cm long.
2. Measure the length of each as accurately as you can.
3. Rub the potato strips between your fingers to assess their texture.
4. Put each potato strip into a petri dish. Cover one with clean water and the other with a strong solution of
sodium chloride (common salt).
t
t
_........__ ___,,....___ _ _.....__,
wat~r
petn
dish
potato strip
5.
6.
7.
8.
Leave the potato strips in their dishes for 15 minutes.
Remove the potato strips, dry them, and measure the length of each as accurately as you can.
Note the texture of the potato strips.
Record your observations in a table like the one below.
First texture
Final texture
First length
Final length
Change in length %±
water
salt solution
Questions
1. In terms of the cells forming the potato strips, why have the lengths of the strips changed in the way
they have?
2. Do the changes in texture of the strips fit in with your explanation? Explain.
3. The cells of the potato contained water to start with . Why did more water move one way than the other
across each cell wall?
Extension
Design an experiment to investigate the effect of using different concentrations of sodium chloride to
surround the potato strips. What result would you expect to find in your experiment?
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9.1 To investigate the presence of starch in a green leaf
Chapter 9 Photosynthesis
Syllabus skills: M/M
Caution: ethanol is flammable.
Do not heat the tube directly
with a Bunsen flame
Data
Starch reacts with iodine to give a blue-black coloration.
Procedure
1. Take a small fresh green leaf from a suitable
dicotyledonous plant.
2. Dip the leaf into boiling water for about 10 seconds.
3. Put the leaf into a test-tube no more than one-third full
of ethanol (alcohol).
4. Place the test-tube into the beaker of boiling water.
5 . When the leaf appears colourless, remove the leaf and
rinse it in water.
6. Lay the leaf in a petri dish and pour a little iodine
solution over it. Leave the leaf for several minutes.
7 . Pour the iodine solution back into the beaker provided.
8. Rinse t he leaf in water. Observe t he colour of t he leaf.
Questions
1. What effect did the boiling water have on the leaf?
2. What happened when the leaf was boiled in alcohol?
What did the alcohol remove from the leaf?
3. Why was the leaf then rinsed in water?
4. What was the colour of the leaf at the end of the
experiment?
5. What do you conclude about the original green leaf?
The leaf is dipped in
bolling water
for about 10 seconds
l
beaker
The leaf is placed in a
test tube of alcohol that
is in boiling water.
NB alcohol is very inflammable
and must not be heated
directly over a bunsen flame.
test
tube
alcohol
leaf
boiling
water
l
The leaf is
dipped in water
The leaf is placed in a petri
dish and covered with iodine
solution. Iodine turns blueblack in the presence of starch.
@
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School-Based Assessment
9.2 To see if light is needed for photosynthesis
Chapter 9 Photosynthesis
Syllabus skills: A/I; O/R/R; M/M
Procedure
1. Choose a small potted plant (such as Impatiens or a geranium). De-starch the whole plant by putting it
in darkness for at least 24 hours.
2. Cover a part of one leaf on the plant with foi l or black polythene held in place with paper-clips. (Leave
the leaf on the plant.)
3. Put the plant in the sunshine for at least 3 hours.
4. Remove the test leaf, remove the covering and at once test the leaf for starch.
5. Make a drawing to show your results.
Questions
1. Why was the plant de-starched?
2. What was used as a control in the experiment?
3. Which part of the leaf contained starch before the foil cover was added?
4. Which part of the leaf contained starch at the end of the experiment?
5. What do you conclude from your results? Explain fully why you reach this conclusion .
344
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27 · School-Based Assessment
9.3 To see if chlorophyll is needed for photosynthesis
Chapter 9 Photosynthesis
Syllabus skills: A/I; O/R/R; M/M
Procedure
1. Choose a small potted plant with strongly variegated leaves. Some portions of the leaves should be as
nearly white as possible.
2. De-starch the whole plant but putting it in darkness for at least 24 hours.
variegated leaf
chlorophyll - - + -absent
chlorophyll
present
3.
4.
5.
6.
Choose a boldly marked leaf and make a careful drawing of it to show the green and white areas.
Place the plant in the sunshine for at least three hours.
Carry out a starch test on the leaf that you sketched.
Make a drawing of the leaf showing the brown and the blue-black areas.
Questions
1. Why is a variegated leaf used for this experiment?
2. Why was a drawing of the leaf made before the experiment began?
3. What do the results of the starch test show?
4. Is there anything in common between the blue-black areas of the starch test and the green areas of t he
original leaf?
5 . What conclusions can you draw from your experiment?
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School-Based Assessment
9.4 To see if carbon dioxide is needed for photosynthesis
Chapter 9 Photosynthesis
X
Syllabus skills: A/I ; O/R/R ; M/M
1 - --
-
bell jar -
-----<
KOH
- distilled water
potassium
r:-;::::-!?.9-----+-- hydroxide
..__....:a__ solution
glass sheets smeared /
with Vaseline
Data
Potassium hydroxide, sodium hydroxide and soda-lime all combine with carbon dioxide.
Procedure
1. Set up the apparatus shown in the diagram. If potassium hydroxide is not available, sodium hydroxide
or soda-lime can be used. Leave the apparatus for some hours.
2. Place a thoroughly de-starched plant under each bell jar. Do this quickly so that the bell jar is not
removed from the glass sheet for any length of time.
3. Leave the plants for two days.
4. Test one leaf from each plant for starch.
Questions
1.
2.
3.
4.
5.
6.
7.
346
What does t he potassi um hydroxide do in this experiment?
What is another name for potassium hydroxide?
Which bell jar contains the control plant?
Why were the glass sheets smeared with Vaseline?
Which plant contained starch at t he end of the experiment?
How could you test the air in the bell jars for carbon dioxide?
Why would it be better to test more than one leaf from each plant?
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9.5 To discover whether oxygen is produced during
photosynthesis
Chapter 9 Photosynthesis
Syllabus skills: A/I; O/R/R; M/M
Procedure
1. Obtain a fresh sample of a water plant such as Elodea or Ceratorphyllum.
2. Set up the apparatus shown in t he diagram, making sure that the test-tube is full of water to begin with.
3. Leave the apparatus in sunlight until the tube is nearly full of gas. This may take hours or several days
depending on the conditions.
4. Light a wooden splint then blow out the flame. The tip should continue to glow.
5. Remove the test-tube from the apparatus and put the glowing splint half-way into the tube.
6. Record what happens.
gas
0
0
0
beaker filled
with water
glowing
splint
,,__--+- inverted funnel
llll'iii~l,---1- water plant
photosynthesising
test tube
Questions
1. What happened to the glowing splint?
2. What gas was present in the test-tube?
3. How do you know that the gas in the test-tube was not just ordinary air?
4. Where did the plant obtain the carbon dioxide needed for photosynthesis?
5. What can you deduce from this experiment?
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School-Based Assessment
10.1 To investigate which food groups are present in a food
Sample
Chapter 10 Feeding and Digestion
Syllabus skills: M/M
Procedure
1. A potato is peeled and a small piece (about 1 cm 3) is crushed and placed in a test-tube.
2. The test-tube is half-filled with water.
3. 2 cm 3 samples are removed from the test-tube and tested for the presence of reducing sugar, nonreducing sugar, starch, protein and fat.
4. Use a table like the one below to show the tests, the results of the tests and deductions.
5. The albumen (white) of an egg is collected in a test-tube.
6. Repeat steps 3 and 4.
Food tested
Details of test carried
out
Results or observations Deduction (presence or
absence of food group)
potato
Questions
1.
2.
3.
4.
5.
6.
348
Which food groups are present in the potato?
Which food groups are present in the egg albumen?
Why was the potato crushed before being tested?
Describe another method for testing for a reducing sugar.
What is the importance of protein in egg albumen?
Why is potato rich in starch?
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10.2 To investigate the action of an enzyme
Chapter 10 Feeding and Digestion
"1(
Syllabus skills: A/I
Data
Catalase is an enzyme which catalyses the breakdown of hydrogen peroxide (the substrate) into water and
oxygen gas (the products).
Hydrogen peroxide is available as a dilute solution in water.
Procedure
1. Cut four pieces of fresh liver, each roughly 1 cm2 square.
2. Draw up a table like the following and record your observations as you go along.
Effect of whole tissue Effect of boiled tissue Effect of crushed tissue Effect of whole tissue with acid
liver
potato
Set up four test-tubes each containing about 2 cm 3 of hydrogen peroxide solution.
Put one piece of liver into the first tube.
Boil one piece of liver in water for 2 minutes, cool the liver and add it to the second tube.
Crush one piece of liver and add it to the t hird tube.
Put a glowing splint into the mouth of this test-tube.
Put 2 cm3 of hydrogen peroxide solution and 1 cm3 of concentrated hydrochloric acid into a test-tube.
Add one piece of liver.
9. Repeat steps 3-8 using 1 cm3 pieces of potato.
3.
4.
5.
6.
7.
8.
Questions
1.
2.
3.
4.
5.
6.
Which gas was produced in the reaction? How do you know?
Which tissue, liver or potato, showed more reaction? Suggest why.
Why was the result using boiled tissue different from that using whole tissue?
Why was the result using crushed tissue different from that using whole tissue?
Why was the result of using whole tissue and acid different from that using whole tissue?
What general statement about the conditions necessary for enzyme-catalysed reactions could you write
as a result of these experiments?
Extension
The conditions used in some of these experiments were extreme (boiling; concentrated acid).
1. Devise experiments to investigate the activity of a state enzyme in conditions that vary less sharply.
2. Find out the optimum conditions for the action of a named enzyme.
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School-Based Assessment
11.1 To discover whether carbon dioxide is produced during
respiration
Chapter 11 Respiration X
Syllabus skills: All; O/R/R
filter pump
air drawn out
air in
t
1
0
0
0
0
0
0
A
potasium hydroxide
solution
(removes carbon
dioxide from the air
by absorbing it)
0
0
B
limewateror
hydrogencarbonate indicator
(tests for the presence
of carbon dioxide)
c
respiring mouse
(produces carbon dioxide)
limewater or
hydrogencarbonate indicator
(tests for the presence
of carbon dioxide)
Procedure
1. You need a healthy live mouse! (Do not try to use any wild rodent.)
2. Set up the apparatus as shown in the diagram. A, B and C can be flasks instead of jars. Put the mouse
gently into the other jar.
3. At once turn on the pump to draw air through the apparatus at a rate of about one or two bubbles per
second.
4. Wait until there is a definite change in the liquid in jar C.
5. Note the appearance of the liquid in jar C.
6. Release t he mouse gently back into its usual living space.
Questions
1. What is the function of flask A?
2. What did you observe happening in flask B? (For a good answer you must say what the liquid was like
at the start as well as what it was like at the end.)
3. What does this change tell you about the air going into the jar containing the mouse?
4. What can you deduce from the change you saw happening in jar C?
5. What can you deduce from this experiment?
6. Why might it have been better to have a second flask containing limewater between flask B and the jar
containing the mouse?
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11 .2 To observe whether heat is produced during respiration
Chapter 11 Respiration
Syllabus skills: A/I; M/M
vacuum flask
(e.g. a Thermos)
11---
dead peas
washed in
disinfectant
-1t-- - germinating
peas
washed in
disinfectant
cotton wool
1-1---
A
-
thermometer
B
Procedure
1. Soak some pea seeds for 24 hours. Divide the seeds into two sets of roughly equal number.
2. Kill one set by putting the seeds in boiling water for 5 minutes. Rinse the peas with a mild disinfectant
solution.
3. Rinse the live peas with the same disinfectant.
4. Put the two sets of peas into separate 'Thermos' (or simi lar) flasks. Wedge a thermometer into each
flask with cotton wool and then carefully invert the flasks, as in'the diagram.
5. Arrange the thermometers so that you can read the temperature on each.
6. Leave the flasks side-by-side for three days.
7. Read the two thermometers at the end of this time.
Questions
1. What was the purpose of the disinfectant solution?
2. Has the temperature indicated by the thermometer in the dead seeds changed? Account for this.
3. Has the temperature of the live seeds gone up or down? Account for this change.
4. Would you expect to find a difference between the reading shown by either thermometer in the morning
and in the evening? Why?
5. Suggest one way in which you could make the experiment more reliable.
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School-Based Assessment
11.3 To discover whether oxygen is used up during
respiration
Chapter 11 Respiration
Syllabus skills: A/I; O/R/R
Procedure
1. Set up the two sets of apparatus shown in the diagram. The capillary tubes must be gas-tight in the
bungs, which must be gas-tight in the flasks.
2. Once the apparatus is gas-tight you can adjust the position of the oil drop by very gently pressing the
bung into the flask or releasing it very slig htly.
3. Note the position of the right-hand edge of each oil drop. The drops should be near zero to start the
experiment. Put the flasks out of direct sunlight so that their temperatures do not change.
4. Draw a table recording the positions of the oil drops every 5 minutes.
5. Stop the experiment when you have enough readings to see the pattern of the results. A good method is
to draw a graph of position {y-axis) against time (x-axis) as you go along .
6. Release the animals gently back to where you found them.
capillary
tube
3 2 1
oil drop
O
wire gauze
soda lime (absorbs carbon dioxide)
A
bl111~1IIIii 1 1I1 1 I 11 'l' 11I11 I11 1~ 111
l
0
~=-+-- small animals, e.g.woodlice
or millipedes
soda lime (absorbs carbon dioxide)
B
Questions
1. Why was it important to keep the flasks at a constant temperature?
2. Why did the oil drop in A move in the way it did, quickly at first and then hardly at all? What was the
purpose of this part of the experiment?
3. What happened to the oil drop in B? How was it different from the behaviour of the oil drop in A?
4. Why did the oil drop in B behave in this different way? Explain what the experiment tells us about the
necessity for oxygen in respiration.
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27 · School-Based Assessment
14.1 To investigate the rate of transpiration using a
photometer
Chapter 14 Transport in Plants
Syllabus skills: All ; O/R/R; M/M
plant stem, e.g. geranium
Achillea or Impatiens
water containing
a few drops of ink
zero point
clip
10 9
8
7
6 5
4
3
2
1
I
0
meniscus
Procedure
1. Select a plant with stems which will fit into the rubber tubing on your potometer.
2. Put the stem under water (keep the leaves out if you can) and cut the stem with a sharp knife. Leave the
stem under water to stop air getting into the xylem vessels.
3. Still under water, attach the stem into the photometer which has been filled with coloured water.
(Coloured water is easier to see in the capillary tube.)
4. Take the apparatus to your bench. Open the clip slowly until the meniscus moves to a point near to zero.
Start timing form this point.
5. Record the position of the meniscus every two minutes until it reaches the end of the graduations.
6. Repeat steps 4 and 5 but:
7. (i) with a fan blowing air across the stem
8. (ii) with the lab closed up and lights out.
Questions
1. Draw three graphs (on the same set of axes) showing photometer reading (vertically) against time
(horizontally). Which conditions produced the highest transpiration rate? Which conditions produced the
lowest transpiration rate.
2. How do you deduce these answers from the graphs?
3. Why did the fan cause the transpiration rate to change as it did?
4. Why was the transpiration rate in the closed, darkened room different from that in the open, sunny lab?
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School-Based Assessment
17 .1 To discover how gravity can affect plant growth
Chapter 17 Movement
Syllabus skill s: A/I; O/R/R
(See also Investigation 17.2.)
Procedure
1. Place three kidney beans or red beans on some tissue paper soaked in water. Leave them for a day.
2. Place several layers of tissue paper along the inside of a glass and soak the tissue with water. The wet
tissue will stick to the glass.
3. Gently place the germinating beans between the glass and the tissue in the position shown in the
4.
5.
6.
7.
diagram. Leave the beans there for one day. Make sure t hat -the tissue is always moist.
At the end of one day make drawings of the seedlings.
Record your observations of the growth of the seedlings, particularly the growth of the radicle.
Turn the glass upside down and leave it for another day.
Make further drawings of the seedlings.
layers of moist
tissue paper
against the g lass
germinating seedling
placed between the
tisue paper and
the glass
glass turned
upside down
seedling, note in
particular the
growth of the radicle
Questions
1. Why is the tissue paper always kept moist?
2. Why did the radicle and the shoot now grow in the same direction?
3. From the point of view of the seedling, what effect does turning the glass upside down have?
4. What was the effect on the growth of the shoot and the growth of the radicle of turning the glass upside
down?
5. Why is this response important to a plant?
6. Suggest two ways in which the experiment might be improved.
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17 .2 To investigate the growth of a radicle
Chapter 17 Movement
Syllabus skills: D
Procedure
1. Soak three bean seeds in water for 24 hours.
2. Line the wall of a gas-jar or tall beaker with a piece of thick, wet blotting paper or several layers of wet
tissue paper.
3. Place the seeds between the blotting paper and the wall of the gas-jar.
~beaker
wet tissue
I,
-1--
---tt-
bean seed
I + - - - --++- marked
( \
I
,,
..-Y
-
~-
--
radicle
water
4. Put about 1 cm depth of water in the gas-jar to keep the paper moist.
5. When the radicles have reached a length of about 1 cm remove the seeds carefully and make marks
along each radicle at roughly 2 mm intervals using a fine cotton thread soaked in Indian or other
waterproof ink.
6. Return the seeds to the gas-jar making sure that the weight of the seedling is supported by the testa
and not the radicle.
7. For the next six days, make a sketch of each bean seedling showing how the ink marks have separated.
Make measurements of the gaps between the marked lines if you can do so. Arrange your sketches in a
table like the one below.
Questions
1. Why did you use more than one seed?
2. Did all three seeds behave in the same way?
3. Did the radicles grow uniformly, mostly at their base, or mostly at their tip?
4. What would be the effect on growth if the extreme tip of the radicle were cut off after three days?
5. What happens at the tip of the radicle to cause the effect you have observed?
6. Suggest why flowering plants continue to flower if dead flowers are removed.
0
2
3
4
5
6
seed 1
seed 2
seed 3
A possible way of arranging your sketches (after King, Soper and Tyrell Smith: Macmillan, 211d ed 1991 page 213).
© Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable
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School-Based Assessment
17 .3 To discover how light can affect plant growth
Chapter 17 Movement
Syllabus skills: All; O/R/R
Procedure
"1. Place three kidney beans or red beans in a small container lined with wet tissue paper. Leave them for
one day.
2. Cut a small hole in the short side of a box such as a shoe box.
3. Put the terminating beans, in their container, in the box as far away from the hole as possible. Keep the
tissue paper wet. Leave the experiment for two days in sunlight.
4. After this time make drawings of the seedlings and measure the length of each.
5. Replace the box lid and leave the seedlings for a further two days. Again , keep the tissue paper moist.
6. Draw up a table showing the lengths of the seedlings and their mean lengths after two days and after
four days.
7. Write a general statement describing the appearance of the seedlings at each stage.
seedlings
shoe box
length of seedling
-
hole
Questions
Why is it important that the tissue paper is kept moist?
Did the seedlings grow more in the first two days or the second two days? Why?
What external factor made the seedlings grow in the way they have?
What part does the plant hormone auxin play in this growth? Explain carefully how the effect is
important to the plant.
5. What is etiolation?
"1.
2.
3.
4.
Extension
Use six beans. Allow the shoots (coleoptiles) to reach a length of about 2 cm . Cover the tips of two shoots
with a small piece of aluminium foil. Cut off the top of two of the shoots. Do nothing to the remaining two
shoots.
Place all six beans in the growth box, making sure that the tissue is damp. After two days, examine the
shoots and explain why they are different from each other.
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27 · School-Based Assessment
17.4 To compare the movements of four animals
Chapter 17 Movement ~
Syllabus skills: O/R/R
In this investigation you will observe the movements of an earthworm, a fish , a frog and a human. Record
your observations in your notebook as you work. Where explanations are asked for, write them afterwards,
giving as much detail as you can. (You may have to look up material in your library.) Finally, answer the
questions set at the end of this set of experiments.
Procedure: earthworm
1. Place the earthworm (alive) on a sheet of white tile. Use your index finger to touch the outside of the
earthworm's body.
2. Is the skin hard or soft? The skin should feel moist. How does this moisture on the skin of the worm help
it to move?
3. Is the body of the worm segmented or unsegmented?
4. Does the external structure of the worm suit its ability to burrow in the soil? Explain your answer.
5. Allow the earthworm to crawl on the sheet of paper. Listen carefully as it moves. Do you hear a
scratching noise? What causes it?
6. Turn over the earthworm and, with the aid of a hand lens, observe each segment. What do you observe?
What are these stiff bristles used for?
7. Describe the movement of the earthworm over the paper. Explain how the earthworm bring about the
changes in its shape in order to move.
8. Place the earthworm on a white tile. Does the earthworm move as quickly on the tile as it did on the
paper? Explain your answer.
Procedure: fish
1.
2.
3.
4.
5.
Watch a fish swim in an aquarium .
Describe the motion of the body, fins and tail as the fish moves from one place to the next.
Which structure moves the fish in a forward motion? Explain how this occurs.
How does a fish turn around in the water to change direction of motion, whether to the left or right?
Did you notice the fish stopping in the water (not swimming around)? Explain how the fish is able to do
this.
6 . Use your hand to disturb the water by swaying it side to side. Did the fish sway with the water currents
created? If not, explain how it was able to remain steady in the water.
7. Observe the shape of the fish's body. Explain how the shape of the fish is suited for its movement in the
water.
Procedure: frog
1. Hold the frog firmly in your hand and observe the length of the front and back legs. Which set of legs are
longer and more muscular?
2. Place the frog in a cardboard box (keep the top open) and watch how it moves.
3. Describe the hopping or jumping motion of the frog .
4. Which set of legs (front or hind) played the more important role in its hopping movement? Explain your
answer.
5. Observe the structure of the feet of the frog .
6. Put the frog in a tank of water and observe it swimming. How did the frog move its legs in order to
obtain a forward motion?
7. Explain how the structure of the feet enables the frog to swim in water.
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357
School-Based Assessment
Procedure: human
For this experiment you will work with a partner. Your teacher will put on display in the front of the class a
human skeleton like the one shown here.
1. With you and your partner taking turns, walk up and down a short distance around your work area.
2. Describe the motion of your partner while walking.
3. Did your partner walk upright on two legs?
4. Look at the skeleton and identify the structure that is responsible for supporting the body in the upright
posture.
5. How did your partner move their legs while walking? Did they bend the legs or keep them straight?
6. Look at the skeleton and identify the structures used in the motion of the legs which you have
described. Make a list of the structures, stating the function of each.
7. Did your partner move their hands while walking? Can you give a reason why?
8. Are bones able to move on their own? If not, state the structures that are responsible for moving bones.
9. Explain how the muscles move the legs while walking.
Questions
1. How are the movements of the earthworm different from those of the frog and the fish?
2. How is this difference related to the fact that a frog has a bony skeleton while an earthworm does not?
3. Why can a human perform a wider range of movements than a frog , but cannot jump or swim so well?
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18.1 To find whether the skin of the back of the hand,
the palm or the back of the neck contains the most touch
receptors
Chapter 18 Irritability, Sensitivity and Coordination
Syllabus skills: A/I; O/R/R
Procedure
1. Attach two pins to a ruler, 2 cm apart, as shown I the diagram.
2. Draw up a table like that shown for your results.
3. Make sure that your partner understands what is going to happen in
the experiment. He or she then closes their eyes.
4. Touch your partner gently on the back of the hand with one or both
pins on the ru ler.
5. Ask how many pins they think are touching their hand. Record a tick if
they are right and a cross if they are wrong.
6. Repeat step 4 nine more times making ten in all.
7. Adjust the pins to be 1 cm apart and repeat steps 3, 4 and 5.
8. Adjust the pins to be 0.05 cm apart and repeat steps 3, 4 and 5.
9. Adjust the pins to be 0.2 cm apart and repeat steps 3, 4 and 5.
10. Present your results as a histogram like the one shown below.
Number correct
back
palm
neck
10
Number of correct responses
•
9
back of hand
D palm of hand
D back of neck
8
7
6
5
4
3
2
0
2cm
1 cm
0 .5cm
0. 1 cm
Distance apart of pins
Questions
1.
2.
3.
4.
Which of the three parts tested do you think has the most receptors? Give reasons.
Why do you think that this part of the body needs to be so sensitive?
Why is it important to have touch receptors in the skin all over the body?
What are some sources of error in the experiment? How can the experiment be improved?
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359
School-Based Assessment
18.2 To investigate two reflex actions
Chapter 18 Irritability, Sensitivity and Coordination
Syllabus skills: O/R/R
Procedure: effects of light on the pupil of the eye
Prop up a small mirror in front of your face. Look into the mirror and draw a diagram of one of your eyes.
Label the pupil and the iris.
2. Look again into the mirror. Close both your eyes and cover them with the palms of your hands. After
20 seconds remove one hand and at the same moment open that eye. What happens to the pupil
immediately after you uncover your eye? How long is it before there is no further change?
3. Look into the mirror once more. Shine a small torchlight into one eye and observe what happens.
4. Draw diagrams showing the appearance of your eye (a) in dim light, and (b) in bright light.
1.
Questions
1. Explain what caused the pupil of your eye to change size in 2 and 3. Draw a diagram to show the
changes.
2. Did your pupil change size quickly or very slowly? Suggest why this is important to your body.
Procedure: the knee-jerk reflex
1. Sit on the edge of a table with both feet hanging loosely.
2. Use your fingertips to locate the base of one knee-cap.
3. Tap the front of your leg firmly, just underneath your knee-cap, with the side of your hand or the edge of
a ruler.
4. Describe what happens when you do so.
Questions
1. How is this reflex different from the reflex change in pupil size which you studied?
2. Draw diagrams to illustrate this difference.
thigh
knee-cap
hand tapping leg
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19.1 To investigate heat flow from a warm object
Chapter 19The Eye, the Ear and the Skin ) (
Syllabus skills: A/I; O/R/R; M/M
Procedure
1. Set up three thin plastic cups as shown in the diagram.
• A is wrapped in several layers of tissue paper held in
place with elastic bands . The paper is soaked in cold
water.
• Bis not wrapped .
• C is wrapped with corrugated cardboard (from an old
box) held in place with elastic bands.
2. Draw up a table with four columns and 18 rows for the
measurements.
3. Heat a supply of water in a beaker or a kettle until it is hotter
than 70 °C.
4. Half-fill each cup with the hot water. (Take care!)
5. At once take the temperature of the water in each cup.
6. Take the temperature of the water in each cup every
30 seconds for the next 8 minutes. Record your results in
the table.
thermometer
Results
1. On the same axes, plot three graphs (one for each cup) of
temperature against time. Plot temperature vertically and
time horizontally.
2. Complete the graphs by drawing smooth curves through
the points.
3. Use the graphs to explain which cup lost heat most quickly
and which cooled most slowly.
elastic band
Questions
1. Why did wrapping the cups with the wet tissue and the
cardboard have these effects?
2. Why is it helpful to humans to sweat in hot weather and put
on more clothes when the weather turns colder?
c
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School-Based Assessment
20.1 Observing the reproductive cells of a mammal
Chapter 20 Reproduction in Animals
~
Syllabus skills: O/R/R; D
Procedure: observing the reproductive cells of a mammal
1. Your teacher will provide you with pre-prepared slides of mature ova and of the sperm of a mammal.
2. Observe the slide of the male gamete under the microscope, first under low power and then high power.
Make a note of the magnification at each power.
3. What structure is contained in the head of the sperm?
4. In your laboratory report book make an accurately labelled diagram of the sperm.
5. Write a description of the sperm.
6. Then remove the slide and replace it with the slide of the ova.
7. Which are the mature ova? How can you tell?
8. Locate the cell membrane with a jelly coat, nucleus containing chromosomes and cytoplasm.
9. Make an accurately labelled drawing of one mature ovum.
10. Write a description of the mature ovum in your laboratory report book.
Questions
1. Which are larger, sperm of ova? Make an estimate of their relative sizes.
2. Sate one advantage of sexual reproduction over asexual reproduction.
Procedure: observing the budding of yeast
1.
2.
3.
4.
5.
6.
7.
8.
Make a mixture of yeast, water and a little glucose.
Place a drop of the yeast mixture on a slide and stain it with methylene blue.
Cover with a cover slip.
Observe the slide under a microscope, first at low power then at high power.
Make a sketch in your notebook of a yeast cell.
How many budding cells can you see?
How long does it take for a bud to form and separate from its parent?
Make sketches to illustrate the stages in budding in yeast.
Questions
1. Each new cell must contain a nucleus. What must happen in the parent cell before the bud finally
detaches from it.
2. The family of yeasts are the saccharomycetes - meaning the 'sugar fungi '. How does this relate to one
important use of yeast?
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27 • School-Based Assessment
21 .1 Dispersal of fruits
Chapter 21 Reproduction in Plants ~
Syllabus skills: O/R/R; D
Procedure
1. Collect examples of fruit whose seeds are dispersed:
(i) by animals eating the fruit,
(ii) by animals passing by the plant,
(iii) by mechanical means,
(iv) by water,
(v) by the wind.
Example
2.
(i)
Tomato
(ii)
Sweetheart
(iii)
Pride of Barbados
~v)
Coconut
(v)
Dandelion
Make a sketch of each and, by each sketch, state wh ich features of the seed are important for that
method of dispersal.
Questions
1. Most plants, in the course of their evolution, have developed an efficient method of seed dispersal. What
would be the consequences for a plant which had no dispersal mechanism? Explain your reasoning
2. Oranges are brightly coloured and have an attractive scent. How do these factors help dispersal of the
seeds?
3. List four ways in which animals (including humans) help in the dispersal of fruits and seeds.
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School-Based Assessment
21.2 Seeds and food storage
Chapter 21 Reproduction in Plants
Syllabus skills: O/R/R; M/M ; D
Procedure
1.
2.
3.
4.
Remove the seeds from an orange.
Peel the seeds and crush them.
Collect some juice from the fleshy part of the orange.
Test the crushed seeds and the orange juice for sugars, starch, protein and lip (fat) using the tests given
in Chapter 10.
Questions
1. What food groups are stored in the fruit?
2. Why do fruits store these food groups?
3. What food groups are stored in the seeds?
4. Why do seeds store these food groups?
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25.1 To investigate how the sex of an offspring is
determined
Chapter 25 Heredity and Genetics
Syllabus skills: All ; O/R/R
Number of individuals
Procedure
1. Fifty black beads are placed in a container. In
another container, 25 black beads and 25 white
beads are mixed thoroughly together. The beakers
are placed side by side with two empty beakers
clearly labelled A and B.
2. Close your eyes. Pick one bead from each of the
first two beakers. If both beads are black , put them
into beaker A. If one is black and the other white,
put them into beaker B. Record the result in a table
like the one shown, but putting a tick to show the
combination of beads produced each time.
Selection number Both black
Height (cm)
(in 2 cm g roups)
Black and white
2
3
4
5
6
7
8
9
10
3. Do this nine more times, making ten in al l.
Questions
1.
2.
3.
4.
5.
What does each black bead represent?
What does each white bead represent?
What does the beaker represent?
Why did you have to close your eyes when taking beads?
Use a genetic diagram to predict the expected ratio of male to female offspring in humans. How does
this relate to the experiment you have just done?
6. How many pairs of black beads did you select?
7. How many pairs contai ning both black and white beads did you select?
8. What ratio of 'boys' to 'girls' did you find in the ten offspring of th is experiment?
9. Relate your obtained ratio to the prediction you made in 5.
10. In what ways does the experiment differ from what really happens?
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365
School-Based Assessment
26.1 To investigate continuous variation
Chapter 26 Variation and Evolution
Syllabus skills: A/I; O/R/R
Procedure
1. Measure the height of each member of your class.
2.
From the list, draw up a frequency table like that shown in the diagram. Make sure that you have enough
groups to take in all the measurements. (It is quite possible that there are may be a group with no
individual results in it.)
Height group (cm)
No. of individuals
150- 152
153-1 55
156- 158
159-161
etc.
3. Use the frequency table to draw a histogram showing how height varies among your classmates .
•
()
A
B
Questions
1. What is the height range (i.e. shortest to tallest) in your class?
2. Describe.the overall shape of your histogram?
3. Imagine that you had measured the height of a very large number of people, but grouped those heights
in 0.5 cm groups. Make a sketch of what you think that the histogram would look like.
4 . What kind of variation is.seen in the height of humans?
5. State three other examples of this type of variation in humans.
6. Name, and give one example of, a different type of variation .
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27 · School-Based Assessment
26.2 To investigate natural selection
Chapter 26 Variation and Evolution
Syllabus skills: A/I ; M/M
Procedure
1. You need 240 matchsticks (or- toothpicks) and some coloured marker pens.
2. Colour 60 matchsticks blue, 60 brown, 60 yellow and 60 green.
3. Scatter a mixture of 30 matchsticks of each colour onto a large surface such as the floor, a lab table or a
law n. These are the prey.
4. One student, the predator, has 10 seconds to 'catch ' as many prey as possible by picking up one
matchstick at a time and putting it into a beaker. The remaining matchsticks are the 'survivors' . The
number of survivors of each colour is counted.
5. Each survivor is given one offspring of the same colour.
6. Repeat steps 4 and 5.
7. Record the results in a table like the one below.
Prey population
Number of prey caught
Number of survivors
New prey population (after each
survivor is given one offspring)
30 blue
15
15
30
30 brown
5
25
50
30 yellow
20
10
20
29
58
30 green
30 blue
20
10
20
50 brown
7
43
86
20 yellow
15
5
10
58 green
0
58
116
Sample results from a background of lawn grass.
Questions
1.
2.
3.
4.
5.
6.
7.
8.
9.
What does each matchstick represent?
What does each colour represent?
How did the number of sticks of each colour change over time?
Which colour survived best? Why?
Which colour survived worst? Why?
How do these results relate to the process of natural selection?
Explain what is meant by camouflage.
.r
In this experiment, which characteristic is being pressured and selected?
Predict what would have happened in your experiment if the survivors had been given two offspring
instead of one.
10. Describe some s.ources of error in the experiment.
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Index
ca ffeine 220
calcium 104
calyx 261
camou fla ge 3 l4
canine tee th 109
Cannabis saliva 139, 22 1
capilla ri es 146, 147- 8
bursting of 152
gaseou s excha nge 132
ca pillariLy 165
car exhau st 68
carbohydra tes IO 1-2
metabo lism I 17
storage 80
see also glucose; sta rch
carbo n cycle 43-4
human effect on 44-5
ca rbon d ioxide
atmosph eric 4 3, 44, 45- 6. 133
in the body 191
diffusion 85
from fermentation 126
in phoiosymhesis 92- 3, 95,
343
concen tration 97
pollution from 68
from respira tion 123, 182. 347
tra n spon in the body l43.
150- 1
see a lso gaseous exchange
carbon monoxide 68, 138, 252
ca rdiac muscle 144
ca rd iovascular d isease I 08, 137
Ca ribbean
Anolis lizard s 315
a n ificia l selenio n in the
3 18- 19
endangered species 65
human activity effecLs on 71-2
carnivores 25, 26, 35
ca rrying capaci ty 53
cata lase 345
cata lysts I I O
cataracts 23 1
caule fa rming 3 18-19
cell cycle 279-80
cell membran e 79, 80
permeability 84. 86
cell wall 79
cel ls
capillaries su rround ing 147
gaseous exchange 133
homeosLasis I 90, 2 17
muvemem in and out of 83
respiration 123
size 78, 79
specia lisa ti on 8 1- 3
see a lso an ima l cells; human
cells; pla m cells
cellu lose I 02
cen tra l nervous sysLem (CNS) 211
response LO stimuli 2 14
centrioles 28 1
cemru m 202
cereb rospinal fluid 216
cerebrum 2 16
cervi ca l venebrae 200-2
ch emica l d igestion I I O
copper 20-1
chemical energy 34
c_o ppenulfate I 03
chlorophyll 92, I 00, 342
· ··•... ;_ - coral reefs destructio n 7 1, 72
.. wrms 175 ·
ch lo roplasts 5, 79, 80. 92 .
· co'rnea 227 ·
in the pa lisade layer 93
in photosyn thesis 95- 6
coro lla 26 1 . . ··. '. .
coro·naryaneries 148
ch o rdates 8- 9
choroid 227
corpus lu teum 249
cortex (kidney) 185
chroma tids 28 1. 292
chromosome nu m ber 278-9. 28 1, cortex ( root) 165-6
282
cotyledons 176, 177
and meiosis 290- 1
cou rtship 250
chromosomes 79
cows 29
Down's syndrome 320
cran ia l re fl exes 215
homologous pairs 29 1- 2, 293,
cretinism J 05
297
crop pla m s
in mitosis 281
diseases in 275
m uta tio n 3 19
genetica lly e ngin eered 32 1.
repl ication 282
322
see a lso game tes
green h ouse 97
ch yme 113, 114
cross-po llination 262
cilia 133
crossing o ver 292, 293
ci liary mu scle 227, 228. 229
crustaceans 8
circu lat0ry system, humans 143,
cu ticle 93, 94
149
cu n ings 284
ci r rhos is of the li ver 221
cystic fibros is 322, 323
class 11 , 12
cyto kinesis 279-8 1
classifica tion
cy1oplasm 79, 80
artificial and natural 9
binomial system I 0-12
Darwin, Charles 313, 315
dichotomous keys IO
Darwin's fin ches 3 l5
organisms 2
Darwin's theory of evo lution 294
cloning 245
daughter ce lls 29 1, 292
of ani mals 285- 7
DDT 38-9, 3 14
cnidaria 8
death rates 55
co-dominance 30 1- 2
decomposers 24-5, 28-9. 35
cocaine 22 1, 252
in Lhe ca rbon cycle 43-4
coccyx 200, 201
in the nitrogen cycle 4 8
cochlea 233
defecation 182
coconu ts 265
deficiency d iseases 272
cohesion 165
d efores tation 46, 65, 69- 70
collecting du ct 185. 187
and water shortage 66
colo n 11 5
degenerative diseases 55
colo n cancer 116
denitrifica tio n 47
colon isatio n 3 15- 16
deoxygen ated blood 132, 145, 149
colostrum 253
depth o f focus 229
commensalism 29- 30
desalination pla111s 66
commun icable diseases 155
detergents 67
com munity 16
detox ification I 17
com pan ion ce lls 162
detrilivores 28-9, 35
com petitive species 65
diabetes I08, 186, 272
compost 57, 59
dia lysis 188
concentra tion g radient 84, 85, 137 diaphragm (contraception ) 253,
condoms 253. 254
254
cones 230
diaphragm (t horax) 134
conjunctiva 227
diastole 145-6
conserva tion
dichotomous keys I 0
environmental 72
dicotyledons 7
reso u rces 72-3
diet 10 1- 6
soi l 73
ba lanced IOI . 106- 7, 27 1
wa ter in plants 167-8
sec also food ; nutrition
constipation 11 6
diet pills 220
consu mers 24-5. 26, 35. 92
diffusion 84-6
co min uous variation 312, 363
gaseous exchange 137
co mracept ion 253-4
oxygen 85, 142- 3
contraceptive pi ll 253, 254
in the placema 2 5 1- 2
converging le ns 231
in a solu tion 338
digestion
along the alimentary cana l
111-16
definition LOS
enzymes in 11 0-1 1
teeth and I 08- 1O
diploid numbe r 282. 291 , 297
disaccha rides 10 1- 2, 103, 110- 1 1
discontinuous variation 312·~
diseases
blood 's role defending against
153-5
communicable I 55
he red itary 272. 303-4
pathogenic 272, 273
in plams and an ima ls 27 5
and population g rowth 54, 55
from prot0zoa 81
social and economic
implications 275
types and control of 2 7 1- 2
vecto rs 236
from vi ruses and baderia 80, 272
dispersa l 260, 264
by animals 264-5
by explosive devices 266
by fru it 264-6, 360
by water 265
by wind 266
distal convoluted wbu le 185, 187
diverging lens 231
DNA
and evolution I 0
function of 46
replica tion 282
Dolly th e sh eep 286- 7
domestic sewage treatment 69
domesti c waste 57
cont rol o f 67
recycl ing 58
domina nt alle le 298
donors 151-2, 188
Down's synd rome 319, 320
drug abuse 220- 2
and HJ V/AJDS 254
in pregnancy 252
drugs
definition 2 19
p rescripti on 2 19-20. 252
DTP vaccine 155
duodenum I 14
dyes 84, l 05
ear sac 234-5
eardrum 233-4
ears 21 I
hearing 233
role in balance 234-5
a nd ~ Li mu l i response 226
structure 232
eanhworms 354
ecology 15- 16, 2 3
definition 15
speciation 3 17
study of 331-4
econom ic implica tions
diseases 275
369
Index
drug abu se 222
1-lfV/AfDS 255
ecosyste m s 16- 17
p roducti vit y 36
e cto pa rasites 30
eda phic factors 16
e ffe ct o rs 2 11 -1 3. 2 14
egesti o n I 08, 182
eggs 178
egre ts 29
e lect rica l im pu lses 2 13
e lectron m icroscopes 78
e mbryos 2 50- 1
emu lsification 1 14
e n dangered species 64, 65
protectio n 73
e n demic species 64 , 65
e n docrine gla nds 213. 2 17- 19
e nd ocrine syste m 2 17- 19
e nd opa rasi tes 30
e nd oske lc to n 199
e ndosperm 176. 177
e n e rgy
gain a n d loss in a·ni m a ls 34-5
ga in a n d loss in p lan ts 34, 35
n utritio na l re quire m e n ts 106
pyra mid s of 36- 7
reso urces 5 6
fro m resp irati o n 123-4
so la r 33-4
e n vironme n t
a da pta tion to 3 13
ca rryin g ca pacity 53
co nservation a n d reswra tion 7 2
a nd gene tic va ria tio n 3 1 L
a nd gen o type 296- 7
a nd hu m a n s 63-4
m a rin e a nd wetland 70, 7 1
a nd sh opp ing 59
was te prod u cts a nd 57- 9, 64, 67
environ m e nt a l !"acto rs 15-1 6, 17
e nzymes
act ion o r 34 5
in d igestio n I J O- I I
opti m u m te mpe rature 236
in p ho wsynth esis 96
in the sm a ll in testin e 1 14
e pigea l germi na tio n 177
e piglottis I 12
Eryngi11111 foe1idu111 I I
Esclteric/1ia coli 4
e than o l test I 04
e ti ola tion 97
e u kar yotes 3
e u trophicat io n 67, 69
e va pora tio n 164
evolutio n
Da rw in 's th eory of 294
a n d DNA LO
a n d n a tura l se lect.ion 313- 17
excretio n 3, 182
e xcretory prod ucts
in a nimals 182- 3
in plan ts 183-4
excretor y syste m , h u m a n 184-8
e xercise
a n d h ea lt h 27 1
370
and hea t ge n e ra tion 2 39
and respira t.ion 12 5-6. 183
exocrine glands 2 17- 18
exoske le to n 199
expira tion 133, 134
expo ne mia l growth ph ase 52
exte n sor mu scles 20 3
extinc tio n of species 64-6
a nd dt:foresta tio 11 70
eyes 2 1O
a nd stim u li response 22 6
Stru cture 226- 7
e yesig h t 227- 8
acco m m oda tio n 228- 9
defects and correctio ns 230- 2
a nd pupi l size 22 9- 30. 357
face t 202
faeces 11 5-16, 182
Fa llopia n tubes (ovid u cts) 2 47,
250
fa m ily (cl assifi ca tio n ) l 1, 12
fa mi ly tree.s 30 5
fa ts 10 6
as food sto re 178
see a lso lipids
fa u y acids I 0 2, I I 0- 1 I
assim ilat ion I 17
feed back m echan isms 190- 2
Fe h ling·s solut.ion 103
fema le
n ut ri tio n a l req u ire m e n ts 10 6-7
re p rod u ctive syste m 247
fe rme nta tion J 26, 127
fe rt ilisa tion
in hu mans 25 0
in pla n t.s 260 , 263-4
fe rtil isers 4 8, 67
fe tu s 25 1- 2
fib re 10 1. 1 16
fi brin 15 1
fi rmi ng agents I 0 6
fi sh 9
a daptat.ion to wate r 18
gaseou s excha nge in 136. L37
m ove men t 354
fi shi ng 65, 71
Oaccid cel ls 86, 87, 94-5
fl avo u rings 10 5
Oexor muscles 203
fli es 273
fl ooding 70
Oowe rs
colou r 300, 30 I
ga metes in 260 , 26 1, 263
pollina tion 262- 3
stru ct.u re 26 1
Ouo rides I I 0
focu sing 227- 9, 23 1
food
a bsorplion I 08, I I 1- 16
a dd itives 10 5- 6
from a ni ma ls I 06
di ffusion in the bod y 85
fruit as 264-5
gene tic engineering 32 1
pla nts as 9 1-2
in respi rin g cells 123
as stimu lu s 209
tests I 03-4, 346
t.ranspo n in th e bo d y 143, 148
transpo rt t.h roug h p la nts
168-70
see a lso d ie t; nutrit.io n
food cha ins 2 4. 25- 6
bioaccumu lati o n 38- 9
energ \' m ove m e nt th ro ug h
35- 6
p redator/ prey re la tio nshi ps 27
pyra mids o f e n e rgy 37
pyra m ids o f n um bers 37- 8
food storage
in an imals 178
carbo h yd ra tes 80
in fru its 176, 36 1
m ine ra ls a nd vit a m ins I 17, 178
in pla nts 173- 8
food webs 27. 3 1
form ula mi lk 253
fossi l fuels 56
a nd a cid ra i_n 4 9
combustio n 4 3, 44-5, 68
fovea 227, 230
fre sh wa te r 17- 18
fni its 106
developm e nt 263-4
d ispe rsa l 264-6. 36 0
rood storage 176, 36 1
forma tio n 2 60
fungi 3, 5- 6
in the ca r bo n cycle 43
in decompositio n 28
Ga la pa gos Isla nd s 3 I 3. 3 15
G11111b11sia hubbsi 3 17
ga m e tes 245, 246, 248. 302- 3
in fl owers 260, 26 1, 263
for111a 1io n 290- 1
va ria tio n of 293
see a lso ovum; spe rma tozoa
gaseous exchan ge
adapta tion s fo r 136- 7
in t.he hea rt 145
in h u ma n s 130-4
in pla n ts 135, 136, 137
su rraces 13 5-6
gast ric ju ice I 13
gene bank s 322
gene po ol 3 14
genes 2 79, 297
see a lso a lleles
genet ic d iagra ms 298- 9
genetic d isorders 303- 4
gen et ic e n gineering 28 5. 32 1- 2
implica tio n s o f 3 22- 3
genet ic varia tio n 3 10
a nd th e enviro n ment 31 1
importance of 3 1 1- 12
loss o f 322
a n d mu tation 3 19
in o ffspri n g 293-4
ge ne tically m o difi e d organ isms
(GMOs) 322
genotype. 296- 7, 298- 9
co-d o m inan ce 30 I
haem ophilia 303
in com ple te dom in a n ce 300
sickle cell an aemia 304
test cross 300
gen us I I , 12
geogra phi ca l isola tion 3 15
geotro pism 197-8. 35 1
germ ina t.io n 177
gesta tio n p e ri od 2 50
giraffes 3 13
gla u com a 232
glid ing jo int s 20 3
glo ba l
dis1ribu tio n o f d ise ase 272
distribu tion of HIV/ A I DS 255
tem pe ra w re ra nge 235. 236.
237
glo ba l wa rm ing 45-6
glo m e r ulu s 185- 6
glu cose 3 4, 46
in aerobic respira tion 123-4
in a naerobic respira tio n 125. 126
assimi lation 116
ba ll -a nd -stick m ode l IO I
blood glucose le ve ls 19 2
fro m h ydro lysis I 12
m a nu facture in plants 92- 3. 96
selective. re absorptio n 186
tests I 03
glycerol 10 2. 1 10-1 1
glyco gen I 02, 178
goit re 105
gold e n rice 322
go nads see ova ri es; testes
gonorrh oea 255
Graa fi a n fo ll icle 249
grafti ng 284
gravity see geotropism
gre ase spo t test. I 04
green house e ffect 4 5- 6
greenho u se gases 45, 72
see also carbon diox ide
greenho use pla m s 97
grey ma u e r 2 16
ground wa te r, de pletion o f 66
growth 3
horm o nes 219, 3 18
move m en ts L97- 8
see also populati o n growt h
g ua rd cells 94
Guya na, ba u xite in dustr\' 56
gynaeciu m 26 1
ha bita1 destru ct.ion 65
see a lso defo resta tion
habitats 16
ha e moglobi n I 50- 1, 183, 3 19- 20
ha e m o p h il ia 3 03
hae m o rrhage I 5 I
ha em o rrho ids I 16
ha ir cells 233, 234
ha ir co lo ur 297- 9. 305
ha ir e rector m uscles 238, 239
ha loph ytes 168
hap lo id n umbe r 290- 1
h ealt h 27 1
ris ks to 322
Index
healthy lifestyle 152, 271
hearing 2 33
heart
act ion o f the 144-6
blood supply 144
section th rough 144
stru cture o f 143-4
heart d isease J 08
and smoki n g 137
h ea rtbeat 14 5-6
h ea t
conservat ion a n d loss 238
fl ow from a warm object 358
p ro du ction 117, 183. 239, 348
see a lso tem pera ture
h eavy meta ls 20- 1, 68
Heimlich ma noeu vre 1 13
He/icobacler pylori I 14
herbicides 199
herbivores 2 5, 26, 35
h ered itary diseases 272, 30 3-4
h eroin 252
heterotrophs 9 l. 9 2
h eterozygou s 297-9
co-dom inance 301 - 2
inco mplete do mina n ee 300
for sickle cell a nae mia 320
h inge joi n ts 204
HI V/AIDS 254-5
pa thogens and 2 74-5
holozoic nu tri tion 108
homeostasis 189-90, 2 17, 236
h o111eot herm ic a ni ma ls 20, 235
Homo s pecies 12
ho m ologous pairs 29 1-2. 293, 297
ho m ozygo us 297-9
fo r sickle ce ll anaem ia 320
hormon es
amid iure tic 189, 219
gonads 24 8
growt h 2 19, 318
injecta ble 254
duri n g m e nstrual cycl e 249
pla n t 199
secretio n J 82. 2 18, 219
tra nspon 14 3, 148
hoSLS 30, 273. 274
human activiti es
and th e ca rbon cycle 44-5
effects in the Ca ribbean 7 1- 2
and marine/wet land
e nviron m e n ts 70, 7 1
a nd resou rce consumpti on
57- 9
and species ext inct ion 64-6, 70
a nd water sh o rt age 66
see also deforesta tio n :
in d u stria li sa tion ; pollutants;
po lluti o n
human cells 2 9 J, 297, 302
humans
al i111en tary cana l I I I , l 15
anaerobic respira tio n 125-6
body tem pe ra tu re 23 5, 2 36,
237-9
c hromosom e number 279
circ ulatory system 14 3. 14 9
class ifi catio n 11-1 2
diffusion in 84-6
ears 2 32- 5
efficienC)I Of J'o od Chai n s 36
e ndocrine syste m 2 17- 19
and th e enviro nme nt 63-4·
e xc re tory sysrem 184-8
eyes/eyesig ht 226-32
fe rt ilisa tion 250
gaseous exchange 130-4
gaseous excha nge in lungs
136- 7
min era ls needed by I 04-5
movement in 355
n ervous system 2 J 1- 17
nutritio na l require111e11ts I 06-7
a nd pla nt /anima l d iseases 275
pop ulat io n growth 54-5, 64
reprod uction in 246
respi ratory syste m 13 1
sense o rga ns 2 10- 1 I
skele ton 199-204
skin section 237
teet h 109
vitam in s needed by I 03
h umid ity, and tra nspira ti on rate
167
hum us 28, 337
hunting 65
h yd rochloric acid 113, I 14
h yd rogen pe ro xide 345
h ydrophyres J 67, 168
hyperm et ro pia 23 1
h ypertension I 08, I 52, 272
h yperto n ic sol ut io n 86, 87
h yphae 5
h ypogeal germ ina tion 177
hypotha la mus 189, 2 16, 219, 237
h ypoto ni c solu tio n 86, 87
ide ntica l twi ns 279, 285
differences be tween 297
variation 3 1 1
ileu m 1 14-15
im m o va ble joints 203
immune response 154
immune syste m 2 54
immu nisation 15 5
lmpnriens 300, 30 I
im pla ntatio n 250
inbreedin g 3 18
incisors I 09
incom plete domin a n ce 300
ind ividua ls
adaptation to the e nvironme nt
313
in a popu la tion 33 1- 2
Indust rial Revol u tio n 45
industria l sewage trea tment 69
indu strialisa tion 64. 70
an d pollu tio n 68
and wa te r s hortage 66
infectious diseases 55
infl uenza 272
ingestio n I 08
in ne r ear 232-3
inorganic n ut rients IOI , 104-5
in sect icides, resistance to 314
in sects 8
aph ids 170
pollinatio n 262-3
in spira tio n 133. 134
in suli n 2 18, 321
intercosta l muscl es I 34
Lnte rnationa l Un io n for the
Con serva tion of Nat u re (I UCN)
64
im e rphase 2 79- 81 , 2 92
intestine see la rge intestin e; small
int estin e
in t ra- ute rine device 253, 2 54
invasive s pecies 53
inve rt e bra tes
respo nse to sti m uli 210
see also insect s
iodine I 05
iris (eye ) 226. 227- 8
iron L04. 150, 183
de fi ciency 272
irr itability 3, 209
isoton ic solutio n 86
Jamaica, min e ral resources 56
Jamaica Hope 3 19
Jama ica Red Poll 319
joints 202
types of 203-4
kidneys 184-8
fa ilure 188
lon gi wdinal sectio n 185
osmoregu la t.ion 184, 189
press ure filtrat ion 186
se lective rcabso rp tio n 186
transplan rs 188
kingdoms 3-4, I L J 2
knee jerk reflex 215, 357
kwash iorkor 107
lab w rit e- up 328- 9
labo u r 252
lactati o n 106-7
lact ea l capil lary 1 15
lactic acid 126
lamellae 136, 137
land po ll ution 67
large intesti n e 11 5
lcacl1in g 4 8, 70
lead 20- 1
leaves
adaptations fo r photosynthesis
93-5
cells and tissu es 82
chloroplasts in p h otosyn thesis
95-6
evapora tion o f water from 164
food storage 174
gaseous exchange 135, 136.
137
m ovement of wa te r withi n 164
sect ion o f a 94
starch in 340
legumes I 06
legu m inous p la nts 29. 4 7
lens 227- 8
accommoda tion 22 8- 9
converging 23 1
diverging 231
Lesser Antilles 3 15- 16
life, characteristics o f 2. 3
lifestyle, a nd h ypert ension 152,
272
liga m e n ts 202-3
light
a biot ic facto r 333
in photosynthesis 92-3, 96.
97, 34 1
phototrupism 197- 8, 2 J 0, 353
and species d is t ribu Lion 20
and tra n spiratio n ra te 167
ligh t mic roscopes 78
light rays, focusing 227- 9, 231
lig htni ng 47
ligni n 16 1
limbs, 111ovem ent 202-3
limiting factors 96-7
li ne transects 332
Li nna eus, Carl I 0-1 I
lipase 11 4
lipids 101, 102
digestion I J 0- 1 1, 11 4, I 15
metabol ism I 17
tests I 04
see also fats
liver
cirrhosis 221
food storage 178
fu nctions of 1 17
living organ isms
binomia l system I 0- 12
ce ll special isation 81-3
classifica tio n of 2
d ecom position 28- 9
ecology and environment 1516, 23, 331 -4
major groups 3-9
o rga nic compo unds in 42- 3
respira tio n 122
transgenic 32 1
va rie ty of 2-14
visible characterist ics 9-1 0, 330
see also animals; pla nts
liza rds 236
lucom ot ion 196
lo ng bone 199, 20 I
long-sigh tedness 23 1
loop o f Henle 185, 186, 187
lumbar vertebrae 200- 2
lu ng ca nce r 137, 138
lu ngs
d iffu sio n in 85
gaseous exch a nge 13 1-3. L36
lymphocy tes 150. 154. 254, 255
m agnesi um 92, I 00, I 04
magn ification 78, 79
ma laria 5, 30, 273-4
su sceptibil ity to 320
m a le
nutritio nal requiremen ts 106- 7
re producti ve syste m 246-7
371
Index
ma lnutrition 107
ma lpighian layer 23 7
m a mmals
charac1eris1ics 9
reproductive cells 359
respi ri ng cells 123
tempera tu re reg ula ti on 238
ma ngroves 6
des1ructio n of7 1
zones of vegetation 19
marasmus l07
marijuana 139, 220
mecha nica l dispersa l 266
medulla 185
medulla oblongata 216
meiosis 245, 246
im porta nce of 290- 1
process of 291 -2
significance of 293-4
vs mi1osis 292
memory lym phocytes 154
meninges 2 16
menopause 249
menstrual cycle 249
menstrua tion 247, 248
mercu ry 20- 1
mesoph yll cells 94, 95
mesophytes l67
metabolism 117, 181 - 2
proteins 117, 183
metaphase 279- 8 1
metaphase I/II 292, 293
m ice, coat colo ur 305
microhabitat s 16
micronutrients 20
microorga nisms 80
see also bacteria; viruses
m icroscopes 7 8
microvilli 114
m iddle ea r 232-3
migra tio n 317
milk teeth J 09
mined areas 73
minerals (dieta ry) IO I, 104-5
requirements I 07
storage I 17, 178
minerals (resources) 56
minerals (soil) 168
miiochondria 7 9. 124
mi1osis 244, 27 9-8 1
and asex ua l reproductio n
282-8
process o f 282
vs meiosis 292
MMR vaccine 155
molars 109
mollu scs 8
monocotyledons 7
monosaccharides IO1-2. I 03,
110- 11
monosod ium glutama te I 05
mosqui1oes 273
cont rolling 274
DDT- resistant 3 14
mosquitofi sh 3 17 ·
m otor ne uro nes 211-1 3
response IO stimuli 214
372
mo uth I 11-12
movement 3
in a nimals 196, 354-5
and ba lance 234-5
by diffu sion 84-6
energy through rood chains
35-6
joints 204
limbs 202-3
mine ral sahs in plan1s 168
by osm osis 86- 7
in plants 163-6, 197-9
skel et0n a nd 199
substances in cells 8 3
wa ter 1hrough a pla nt J 63- 6
see a lso tra nspon system
muscle cells 82
m uscles
movement 202- 3
see a lso individual muscles
mushrooms 6
mutage ns 319
muta tion 282, 3 19- 20
muLUalism 29, 47
m yopia 231
naw ral cla ssifica1ion 9
natura l imm unity l 54
nawra l select.ion 294, 313
an d evolu1io n 3 13- 17
investigating 364
vs artificia l selec1io n 3 18
near-sightedness 231
nectar 262
nega tive feedba ck 19 1- 2
nematodes 8
nephrons 185- 6
nervou s pathway 2 12, 213
nervo us system 2 1 1-17
neural canal 202
neura l spine 202
neurones 82, 2 1 L- 13
niches 16
nicotine 137-8, 252
nit.ra tes 47, 48
ni trification 48
nitrogen 47. 92. 100-1 , 104
cycle 46-8
fixation 47-8
ni1rogen oxides 47, 49
nitrogeno us was1e 143, 183, 184
in Lhe kidneys 184
non-biodegradable ma te rials 57, 67
non- re newable resources 55
1iose 211 , 225
nucleus 79
in cloni ng 286
fo rma tion 281
numbe rs. pyramids o f 37- 8
nutritio n 3
holozoic I 08
human requ'iremen ts I 06-7
ma lnutrition l 07
see a lso diet; rood
obesi1y 55, 108, 178
ocelot 12
oesophagus 1 12-1 3
oestrogen 248, 249, 250. 253
offspring
genotype and phenotype 299,
300
sex determ inatio n 302, 362
varia tio n among 293-4
o il po ll ut ion 67
o m ni vores 25
o pportu nistic infections 254. 255
o ptic nerve 227
da mage IO 232
order I I, 12
orga nell es 79
organ ic nu1rients 10 1-4
orga ns 82- 3
protection or 199
se nse o rgans 210- 1 I. 225-6
osmorcgu la1 ion 184, 189
nega1 ive feedback 191
osmosis 86~7. 95-6. 164, 165-6
effects of 339
ossicles 23 3
osteoporosis 138
ou tbreed ing 3 18
ou te r ear 232-3
oval window 233
ovaries 246. 24 7
ho rmones 248
in plants 264
over-fish ing 65, 7 1
ovulat io n 249
o vu les 26 1, 262. 264
ovum 246, 247, 359
cloning of fertilised 286
feni lisa tion 250
release o[ 248, 249
oxygen
in air I 33
biochemica l demand 68
d iffusion 85, 142-3
from pho tosynthesis 92- 3. 96,
344
in respiration 123, 349
1ra nspo n in blood 150-1
1ranspo n in th e body L43, 148,
150
see also gaseous excha nge
oxygen de bt 126
oxygenated blood 132, 145 , 149
oxyhaemoglobin 151
oxytocin 252
'pacemaker' 146
pa inkillers 220
pa li sade layer 93, 94
pancreas 2 18
pa ncreaticju ice 114, 218
parasitism 30
pa nially movable joims 203
pa nu ri tio n 252
passively acqu ired immu nity 154,
155
pa1 hoge nic diseases 272, 273
pathogens 153-4, 272, 273, 274-5
pedigree charts 304-5
pelvis 185
pen ici ll in 6, 220, 313
pen is 246, 250
peppered moth 3 14
pepsin 113
peptic ulce rs 114
perennat ing o rga ns 176
pe ricarp 264
peripheral nervous system (PNS)
2 11
{
peristalsis I 13
permanent 1eeth I IO
permanent vacuole 79, 80
permeable membrane 84
pesticides 199
bioaccumu lation 38
DDT 38- 9, 3 14
effects a nd control o r 67
pe1als 26 1. 262, 263
pH 49. 333
o p1imum I l L
phagocytes 150, 153
phenotype 298-9
co-dominance 30 l
amt the environ mem 3 11
haemophilia 303
incom plete dom ina nce 300
sickle cell anaem ia 304
1es1 cross 300
ph loem 93, 94
and move me nt of food 169- 70
s1rucw re o f 162
in vascular bund les 163
phosph o rus 104, J 05
pho1o meter 350
pho1osy111hesis 24, 161
and carbon d ioxide 92- 3, 95,
97, 343
and chloroph yll 342
chloroplas1 in volvemen1 in 95-6
equa1ion 33, 92
lea f adaptations for 93-5
and light 92- 3, 96, 97, 34J
lim iLing factors in 96-7
oxygen from 92- 3, 96, 344
waste products 183
photo1 ropism 197-8, 2 10. 353
ph ylum 7-8. I I. 12
physica l d igestio n I 08
ph ysiological diseases 272
ph ytoplan kton 24
pinna 233
pilllil ary gla nd 189, 2 16, 2 19
pituita ry growth hormone 219
pivot joint.s 203
placenta 2 5 1-2
plan t cells 79-80
os mosis in 86- 7
in respiration 125
plan1 growth
and gra vit}' 351
and light 353
plant horm o nes 199
plants 3, 6-7
and acid rain 49
ada pta1ion LO ligh1 20
adap1atio11 10 water 18- 19,
167-8
Index
in the carbon cycle 43. 44
excretory produ cts 183-4
fertilisation in 260, 263-4
food ma nufacture 91 - 2, I 00
food sto rage in 173- 8
ga in and loss o f energy 34, 35
gaseous exchange 135, 136,
137
heavy metal tolerance 21
legu mino us 29, 47
life cycle 259- 60
minerals and 104, 168
movement .in 163-6, 197-9
in the nitrogen cycle 46- 7
photosy mhesis see
photosynt.hesis
as producers 24-5, 26
respo nse to stimul i 21 O
selective breeding 3 18
tissues, organs and systems 83
transpo rt system 161-3
t ra nspon th rough 160-1 ,
168- 70
variation 3 11
see also crop pla n ts; flowers;
leaves; living o rga nisms;
roots; stems
plasma proteins I 17
platelets 149, 150
plat yhelmimhes 8
plumules 177
poi kilothermic an imals 20, 235- 7
pollen gra ins 26 1. 262, 263
pollination 260, 262-3
pollu ta nt s
acid ra in 49
fl uorides as I 1 o
heavy metals 20
origin, effects and control 67- 8
pol lution 66- 9
fro m human activiti es 20, 64
mangrove swamps 7 1
red uction of 72
a nd water sho n age 66
polysaccha rides 102. 103, 11 0-11
pond ecosystem 16-17
population 16
geographica l isolation 3 15
in na t ural a nd artificia l
select ion 3 18
size 33 1- 2
po pulation growth 52-3
facto rs red ucing 53-4
human 54-5, 64
post na ta l care 252
potassium I 04
potassium manganite 338
predawrs 26-7
and populatio n growth 54
pregnancy 250
alcohol during 221, 252
drug a buse in 252
fetus 25 1-2
and HJ V/AIDS 254
m11ritional requiremen ts I 06-7
pn:mola rs I 09
prena tal ca re 252
prescription drugs 219-20, 252
preservatives I 05
pressure fi lt ra tion 186
pressure- flow hypothesis 169
prey 26- 7
primary consu me rs 26. 35
producers 24-5, 26, 35-6. 92
prod uct ivity 35-6
prod ucts (in digestion ) 111
progesterone 249. 250. 253
proka ryotes 3, 4-5
see a lso bacteria
prolact in 253
propagatio n see vegetative
propagat ion
propellants I 05
prophase 279-8 1
prophase I/I I 292
prote ins 101 . 102
a nima l and plam 46-7
digestion 11 0-11 . 113, 114
metabo lism I 17. 183
requ irement s I 07
tests I 04
see also enzymes
protoctists 3, 5
prowzoa 5. 81
see also a moeba
proxima l convolut ed tubule 185,
186
psychoactive drugs 220
pubert y 248
pulmonary circu lation 149
pupil (eye) 226, 227- 8
effect of size 229- 30, 357
refle x215
pyramids
biomass 38
energy 36-7
numbers 37-8
quadrat s 334-5
radicles 177, 352
ra dioisotopes 169
reabsorption 186, 187
receptacles 261
receptors 2 11- 13, 2 14
touch 356
recessive a llele 298
recipients 151-2, 188
rectum 1 15- 16
recycling 58, 59
red blood cells 149-50
amigens 15 1-2
breakdown I 17
manufa cture of 199
oxygen tra nsport 15 1
sickle shaped 3 19-20
waste prod ucts from 183
reduction of waste 57. 59
reflex act io ns 2 15, 357
re flex arc 2 15
refraction 227-8
relay neu rones 2 12
renal artery 184, 187-8
rena l ve in L84, 187-8
renewable resources 55, 56
ren nin 113
replica tion 282
reproduction 3. 244
in humans 246
see also asex ual reprod uction;
sexual reproductio n
reproduct.ive cells 290- 1, 359
reproductive system
female 247
ma le 246-7
reptiles 9
resources
conserva tion of 72-3
destru ction of 70
ene rgy 56
limi ts of 55
minera l 56
reducing consumption 56-9
respira tion 3. 34
aerobic 122-4, 12 5
ana ero bi c 125- 7
ca rbo n dioxide from 123, 182,
347
equa ti on 43
gases involved in 85
heat production from 348
oxygen in 123. 349
waste product.s 123, 182- 3
respiratory system, human 131
response to stimu li 209- 10, 2 14
in sense o rgan s 225- 6
retina 2 10. 227-8, 230
reuse of waste 57
Rhizobiu111 29, 47
rh izomes 175
rh ythm method 253
ribs 134
rickets L03
ringing 170
rods 230
root ha ir cells 166
root pressure 165
root lllbers 176
roots
development I 77
food storage 176
movement of wa ter across
165-6
tropism 198
vascular bu nd les 163
runners 283
sedime matio n test 334
seedlings 177
growth in 198
movemem in 197
seeds 176-7. 260
deve lopmen t 263-4
dispersal 264-5
see also frui ts
selection pressu re 31 4, 318
selective advantage 313
selecrive breeding 3 18
selecti ve reabsorption 186, 187
selecti vely permeable m embrane
86, 188
sel f-dispersa l 266
self-po llinatio n 262
semen 246
semi-l unar valves 145
semici rcular canals 234
seminife rous tubu les 246
sense o rgans 210-1 1
stimuli respondi ng LO 225- 6
sensory neu rones 2 I 1-1 3
response to SLimuli 214
sepa ls 261
sewage 67
treatment 68- 9
sex d1romosomes see gametes
sex determination 302, 362
sex -linked cha rac1eristics 303
sex ual intercou rse 246, 250
sex ua l reproduction 245
in plants 259-60
shoots see stems
shopping, environment and 59
sickle cell anaemia 272, 282.
303-4
and mu tation 3 19- 20
sickle cell disease 320
sickle cell tra it 320
side effects 2 19
sieve tubes 162, 169
sight see eyesigh t
sigmoid growth curve 53
skeleton I 99- 204
functions of 199
skin 21 1,235
ca re of 239
physica l barri er 153
section th rou gh 237
and stimuli response 226
temperatu re control in animals
235- 7
temperature control in birds 239
sa ccu le 234, 235
sacrum 200, 201
temperature control in humans
saliva 112
237-9
sa liva ry glands 217
touch receptors 356
sa lt wa te r 17- 18, 66
small int estine 114-1 5
sa mpling methods 33 1-3
cells and tiss ues 82
saprophytes 29, 9 1, 92
smoke 68
scle ra 226, 227
smoking 55. 137-8
scurvy 103
in pregnancy 252
sea levels 46
and skin damage 239
sebaceous glands 237
social implications
diseases 275
secondary consumers 26, 35
drug abuse 222
secondary sex ual d 1aracterisrics 248
secre tion 83, 182, 218, 2 19
HIV/AIDS 255
373
-
-
Index
soil
abiotic factor 334
conse rvatio n 73
degrada tio n 70
erosio n 69- 70
mo isture in 209
percentage o r a ir in 337
pe rccn Lage of wa ter in 336
a nd species d ist ribution 2 1
water- ho lding capacity 335
sola r e nergy 33--4
so und waves 23 3-4
species I I , 12
Ano lis lizards 3 16
chromosome n um be r 278, 279,
28 1
Darwin's fi nches 3 15
d istri butio n o r 17-2 1
a nd eco logy 3 17
e ndangered and vu lnerable 64.
65, 73
extincLion 64-6, 70
ge ne tic va riatio n 3 10, 3 11
geno type 296
invasive 53
surviva l o r 294, 3 11
spermatozoa 246, 248. 359
release of 250
spermi cide 253, 254
sphincter mu scles 184
spinal cu rd 2 16. 217
spinal reflexes 21 5
spo res 6
sta mens 26 1. 262, 263
staple foocls I 06
sta rch 96, I 02
hyd rolysis 11 2
in a leaf 340
sto rage in pla nts 174
tests I 03
sta rvat io n l07, 32 1
STDs (sexua lly transmi tted
diseases) 254-5
pa th ogens and 274-5
protection aga inst 253
stems
develop me m 177
food sto rage 174-5
photot.ro pism 197- 8
vascular bund les 163
ste rilisaLio n 253
steroids 220, 3 18
stigm a 26 1. 262, 263
stimulus 209- 10
in the ne rvo us pathwa y 2 12.
213
recep to rs, e ffecto rs a nd
respo nse 2 14
i reflex actio ns 2 15
respo nse to sense o rga ns 225-6
sto lo ns 283
stomach I I 3-14
stoma ta 93, 94-5, 135
in evapora tio n 164
374
SLro ke I 08, I 52
su b-phylu m I I , 12
su bstra te I 11
sucrose 96, I 0 2
Lests I 03
transport 169
sulfur I 04
su lfur diox ide 49, 68
surrogaLe mo th er 285-7
survival of a species 294. 3 11
s11spenso ry liga men ts 227. 228,
22 9
sustainabili ty 72
su Lures 203
swea ting 238
sweep nets 333
sweeteners I 0 5
symbiosis 29-30
synapse 2 13
synovia l jo ints 204
systemic ci rculation L49
system ic herbicides 199
sysLems 82-3
systo le 145-6
tra nq uillise rs 220
transgenic orga nisms 32 1
tra nslocatio n 168- 70. 199
t ranspira tion 164. 166-7, 350
pull 165
rate 167
transport syste m
in a nimals 142- 3
food t hrough pla nts 168- 70
in pla nts 161 - 3
sce also blood; hea rt ;
move me nt
tra nsvcrse process 202
trees, commensa lism 29
tri cuspid valve 1.45
Trin idad a nd Tobago, e nergy
resources 56
Lrophic levels 26
bioaccumu latio n 39
pyramids of e nergy 37
pyra mids o r numbers 37, 38
tropisms 197-8
trypsi n I 14
tuba l liga tion 253, 254
tu bers 175, 176
turgid cell s 86, 94-5
tympani c mem bra ne 233--4
T-lymphocytes 254, 255
tap roo ts 176
ta r 138
tanrazine I 05
unde r-ea ting 107
taste buds 2 1 I, 225
unde rground stems 174-5
tear glands 2 17. 226
unicellu lar o rganisms 80- 1
teeth I 08- 10
urea 183
te lophase 279- 8 1
u re ter 185
te lo phase I/II 292
ureth ra 1.84
te mpera wre
urine 184, 187
concent ra ti o n 189
a biotic factor 333
and enzyme cat alysis I I I
production 185
glo bal range 235. 236, 237
ute rus 247
globa l wa rming 45-6
fe ta l developm ent 251
and ph o tosynthesis 96
lining 249, 250
a nd species distributio n 20
uLricl e 234, 235
a nd tra nspiratio n rate 167
see also bod y tem pe ra ture; hea t vacci natio n 155
vagi na 250
te ndo ns 203
te rrestria l food diai ns 26
vascular bund les 163
Lerrcstria l rood webs 27, 3 1
vasecto my 253, 254
vasoconst riclio n 238
te rtia ry consumers 26, 35
test cross 30 0
vasud ila tio n 238
testa 177
vectors 236, 273--4, 322
testes 246
vege tables I 06
ho rm o nes 248
vegetative propagat io n 245, 283
testoster~.~Sf.4~· -·· ~·' · · '-'"'' _ ,, _.., . ·. :/r~'.fi~i~ l 284-5
thoracic vC!nc5fAe- WO~ .: · , •.. .ve111s .1'4'6'; -14'.7-,8
t ho rai 1 3~(<-:U ;4 ~ :\ • '1~ · _. 1 . ·.;::,'.~xi~~a -~iivC:l."4.8 ~
tissue cul tnf~ 'Z8~i ,.. • ;
~- ve.ilfril:lei t.f44f6
tissue fl u~ -~-90 [_ · 1 , , '. ' 1 ..."_~ -~.~· vcfitne!>i.146,).47
concehrrat10H·· U.91 , . . . ,,. . " ·. ' vette htai,:":2'0~2
tissues 82-3
· - ·" verlcbra·l- c~1w:ii111 200-2
tongue 21 1. 225
vert ebra tes 8-9
to uch rece pt ors 356
vesicles 83
•
vestibu lar appa ra tus 233, 234
toxic che mica ls 20. 67. 68
villi I 14- 15
waste produas 182
trace eleme nts I 04
viruses 4. 80, 272
trachea 11 2. 132, 133
vectors 322
.".i: ·;::.- '.
visibl e characteristi cs 9- 10, 330
vita mins IOI , 103
req uirem ent s I 07
slOrage I 17. 178
vuln erable species 64
waste products
build-up o r 190
cell ular 83. 148
e nvironmental 57-9, 64, 67
or pho tosyn thesis 183
respi ratio n 123, 182- 3
see also excretory products;
nit rogeno us waste
water
conserva tio n in pla nts 167- 8
in the d iet IO I
a nd disease 274
d ispe rsal by 265
flo w 334
movement th ro ugh a pla nt
163-6
in photosynt hesis 92-3. 95-6,
97
rea bsorptio n 187
shortage o r 66
in soil 335-6
and species distribu tion 17-1 9
wat er poll mio n 67- 8
mangrove swamps 7 1
white blood cells 143, 149-50
defence against d isease 153,
154
manu fa ct ure of 199
whi te ma iler 2 16
WH O Expa nclcd Program of
Immunisa tion 155
wind
d ispe rsa l 266
po ll ination 262- 3
speed 333--4
a nd transpi ratio n ra te J 67
w isdo m teeth I IO
withdrawal sympt oms 220, 221
wolves, body hair 3 I I
xeroph ytes 18. 167, 168
xylem 93. 94, 95
structure or 161 - 2
in vascula r bundles 163
in wa le r m oveme nt 164, 165
yeast 6
anaerobic respiratio n 126
budding 359
yoghurt manu fact.ure 127
zones or vegetatio n 19
zygote 250
d ivisio n 285, 286
Biology for CSEce Examinations is part of a well-established series
of books aimed at students preparing for their CSEC Science studies.
Rejuvenated In a third edition, Biology for CSEC- Examinations featul9
comprehensive, systematic coverage of the latest CSEC syllabus (2013).
Written by an expert team of science educators, this revised edition
benefits from a new, clear and accessible design and the most up
to date aclentiftc Information.
Key features of the CSEC Science series:
• Intuitive and easy-to-follow format makes It simple to study a whole
topic, or to find answers to specific problems
• Regular consolidation (In-text questions and exam preparation) checks
understanding and reinforces learning
• New group-work feature tests students' Investigative and problemsolvlng skllla and demor.sbates real-wor1d applications of key
syllabus points
• Practical activities aid experiments throughout the text encourage
hands-on learning
• Dedicated School-Based Assessment section gives step-by4pp tips
to maximise success in the CSEC coursework.
~
CSBC• is a registered trade mark of the
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BiOioqy for CSBC- Bzaminations is an
lnd.epCodcnt pubUcadon and bas not
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ISB N 9 78 ·0·230·43883·5
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