CONCISE REVISION COURSE
CSEC
Human and
®
Social Biology
Anne Tindale &
Shaun deSouza
CONCISE REVISION COURSE
CSEC
Human and
®
Social Biology
Anne Tindale &
Shaun deSouza
William Collins’ dream of knowledge for all began with the publication of his first book in 1819.
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eBook Edition © September 2018
Print book Edition ISBN 9780008273408
eBook Edition ISBN 9780008326296
Version: 2018-08-29
Contents
1
2
3
4
5
The pathway to success
v
Section A – Living organisms and the
environment
1
Living organisms and cells 1
The characteristics of living
organisms
1
Cells
1
Movement of substances into and
out of cells
6
6
Photosynthesis, food chains 7
and cycles
10
Photosynthesis
10
Food chains
11
Recycling of carbon and nitrogen in
nature
13
Section B – Life processes
19
Nutrition
19
The human diet
19
A balanced diet
25
Digestion
27
Teeth and mechanical digestion 28
The chemical digestion of food 30
Absorption
34
Egestion
35
Assimilation
35
The respiratory system 37
Breathing and gaseous exchange 37
Structure of the human respiratory
system
37
The mechanism of breathing and
gaseous exchange
39
Mouth-to-mouth resuscitation
(rescue breathing)
41
The effects of smoking cigarettes 41
Respiration
43
The circulatory system
46
The need for a transport system in
the human body
46
The cardiovascular system
46
8
9
Blood
Blood vessels
The heart
Circulation
Causes and effects of
heart attacks
The lymphatic system
46
49
51
52
53
54
The skeletal system
56
The human skeleton
56
Movement
58
Excretion and homeostasis 63
Excretion
63
The kidneys and excretion
63
The skin
65
Homeostasis
67
Coordination and control 71
Some important definitions
71
Coordination by the nervous and
endocrine systems
71
The nervous system
71
Voluntary actions
74
Involuntary actions
74
Sense organs
77
The eye
77
Sight defects and their corrections 79
The endocrine system
81
The reproductive system 83
Asexual and sexual reproduction
compared
83
The female and male reproductive
systems
83
The menstrual cycle
86
Bringing sperm and ova together 87
From fertilisation to birth
87
Prenatal and postnatal care
88
Birth control and family planning 89
Issues related to abortion
92
Contents
iii
10
Section C – Heredity and variation 102
Cell division and variation 102
An introduction to chromosomes
and genes
102
Cell division
102
Variation
105
14 Drug use and misuse
108
Monohybrid inheritance
108
The inheritance of sex in humans 111
Sex-linked characteristics
112
Some important genetic terms 113
Genetic engineering
113
Section D – Disease and its impact
on humans
119
Health and disease
119
Types of disease
119
Signs and symptoms of disease 119
Asthma
119
Lifestyle-related diseases
121
Infectious diseases (communicable
diseases)
124
Vectors and vector-borne infectious
diseases
128
The impact of diseases on the human
population
132
15
11 Inheritance and genetic
engineering
12
13 Hygiene and defences
against disease
Personal hygiene
Controlling the growth of
microorganisms
Defence against disease
iv
Contents
133
133
134
135
138
Drug dependence
138
Prescription drugs
138
Non-prescription drugs
138
The social effects of drug misuse 141
Section E – The impact of health
practices on the environment
144
Pollution and its effects 144
Air pollution
144
Water pollution
145
Methods of controlling pollution 147
16 The cycling and treatment
of water
148
The water cycle
148
Water purification
149
The impact of human activities on
water supplies
150
17 The treatment and disposal
of human waste
152
Sewage disposal
Sewage treatment
Domestic refuse disposal
Index
152
154
155
161
The pathway to success
About this book
This book has been written primarily as a revision course for students studying for
the CSEC® Human and Social Biology examination. The facts are presented concisely
using a variety of formats which makes them easy to understand and learn. Key
words are highlighted in bold type and important definitions which must be learned
are written in italics and highlighted in colour. Annotated diagrams and tables have
been used wherever possible and the relationship between structure and function is
continually emphasised. Questions to help test knowledge and understanding, and to
provide practice for the actual examination, are included throughout the book.
The following sections provide valuable information on the format of the CSEC®
examination, how to revise successfully, successful examination technique and key
terms used on examination papers.
The CSEC® Human and Social Biology syllabus and this book
The CSEC® Human and Social Biology syllabus is available online at http://cxc-store.com.
You are strongly advised to read through the syllabus carefully since it provides
detailed information on the specific objectives of each topic of the course and the
format of the CSEC® examination. Each chapter in this book covers a particular topic in
the syllabus.
• Chapters 1 and 2 cover topics in Section A, Living organisms and the environment
• Chapters 3 to 9 cover topics in Section B, Life processes
• Chapters 10 and 11 cover topics in Section C, Heredity and variation
• Chapters 12 to 14 cover topics in Section D, Disease and its impact on humans
• Chapters 15 to 17 cover topics in Section E, The impact of health practices on the
environment
At the end of each chapter, or section within a chapter, you will find a selection of
revision questions. These questions test your knowledge and understanding of the topic
covered in the chapter or section. At the end Chapters 2, 9, 11, 14 and 17 you will find
a selection of exam-style questions, which also test how you apply the knowledge you
have gained and help prepare you to answer the different styles of questions that
you will encounter in your CSEC® examination. You will find the answers to all these
questions online at www.collins.co.uk/caribbeanschools.
The format of the CSEC® Human and Social Biology examination
The examination consists of two papers and your performance is evaluated using the
following two profiles:
• Knowledge and comprehension
• Use of knowledge
The pathway to success
v
Paper 01 (1 ¼ hours)
Paper 01 consists of 60 multiple choice questions. Each question is worth 1 mark. Four
choices of answer are provided for each question of which one is correct.
• Make sure you read each question thoroughly; some questions may ask which
answer is incorrect.
• Some questions may give two or more correct answers and ask which answer is the
best; you must consider each answer very carefully before making your choice.
• If you do not know the answer, try to work it out by eliminating the incorrect
answers. Never leave a question unanswered.
Paper 02 (2 hours)
Paper 02 is divided into Sections A and B, and consists of six compulsory questions.
Each question is divided into several parts and is worth 15 marks. The answers are
to be written in spaces provided on the paper. These spaces indicate the length of
answer required and answers should be restricted to them. Take time to read the
entire paper before beginning to answer any of the questions.
• Section A consists of four compulsory structured questions whose parts require
short answers, usually a word, a sentence or a short paragraph. The questions
usually begin with some kind of stimulus material, very often a diagram, which you
will be asked questions about.
One question will be an investigative/practical-related question, which will provide
you with some form of data that you will be expected to answer questions about.
The data might be in the form of a table or a graph. If you are given a table, you
may be asked to draw a graph using the data and may then be asked questions
about the graph. Make sure you know how to draw graphs (see page ix).
• Section B consists of two compulsory structured essay questions, each worth 15
marks. These questions require a greater element of essay writing in their answers
than those in section A.
The marks allocated for the different parts of each question are clearly given. A total
of 90 marks is available for Paper 02 and the time allowed is 120 minutes. You should
allow between 15 and 20 minutes for each question. This will allow you time to read
the paper fully before you begin and time to check over your answers when you
have finished.
Successful revision
The following should provide a guide for successful revision.
• Begin you revision early. You should start your revision at least two months before
the examination and should plan a revision timetable to cover this period. Plan
to revise in the evenings when you do not have much homework, at weekends,
during the Easter vacation and during study leave.
• When you have a full day available for revision, consider the day as three sessions of
about three to four hours each, morning, afternoon and evening. Study during two of
these sessions only, do something non-academic and relaxing during the third.
vi
The pathway to success
• Read through the topic you plan to learn to make sure you understand it before
starting to learn it; understanding is a lot safer than thoughtless learning.
• Try to understand and learn one topic in each revision session, more if topics are
short and fewer if topics are long.
• Revise every topic in the syllabus. Do not pick and choose topics since all questions
on your exam paper are compulsory.
• Learn the topics in order. When you have learned all topics once, go back to the first
topic and begin again. Try to cover each topic several times.
• Revise in a quiet location without any form of distraction.
• Sit up to revise, preferably at a table. Do not sit in a comfy chair or lie on a bed
where you can easily fall asleep.
• Obtain copies of past CSEC® Human and Social Biology examination papers and use
them to practise answering exam-style questions, starting with the most recent
papers. These can be purchased online from the CXC® Store.
• You can use a variety of different methods to learn your work. Chose which ones
work best for you.
Read the topic several times, then close the book and try to write down the main points.
Do not try to memorise your work word for word since work learned by heart is not
usually understood, and questions test understanding as well as the ability to repeat facts.
Summarise the main points of each topic on flash cards and use these to help you study.
Draw simple diagrams with annotations, spider diagrams and flow charts to
summarise topics in visual ways which are easy to learn.
Practise labelling diagrams that you have been given. You may be asked to do this
in your exam.
Use memory aids such as:
– acronyms, e.g. GRIMNER for the seven life processes; growth, reproduction,
irritability, movement, nutrition, excretion, reproduction.
– mnemonics, e.g. ‘many people support basketball players’ for the five functions of
the skeleton; movement, protection, support, breathing, production of blood cells.
– associations between words, e.g. tricuspid – right (therefore the bicuspid valve
must be on the left side of the heart), arteries – away (therefore veins must
take blood towards the heart).
Test yourself using the questions throughout this book and others from past
CSEC® examination papers.
Successful examination technique
• Read the instructions at the start of each paper very carefully and do precisely what
they require.
• Read through the entire paper before you begin to answer any of the questions.
• Read each question at least twice before beginning your answer to ensure you
understand what it asks.
• Underline the important words in each question to help you answer precisely what
the question is asking.
The pathway to success
vii
• Reread the question when you are part way through your answer to check that you
are answering what it asks
• Give precise and factual answers. You will not get marks for information which
is ‘padded out’ or irrelevant. The number of marks awarded for each answer
indicates how long and detailed it should be.
• Use correct terminology throughout your answers.
• Give any numerical answer the appropriate unit using the proper abbreviation/
symbol e.g. cm3, g, °C.
• If a question asks you to give a specific number of points, use bullet points to make
each separate point clear.
• If you are asked to give similarities and differences, you must make it clear which
points you are proposing as similarities and which points as differences. The same
applies if you are asked to give advantages and disadvantages.
• Watch the time as you work. Know the time available for each question and stick to it.
• Check over your answers when you have completed all the questions.
• Remain in the examination room until the end of the examination and recheck your
answers again if you have time to ensure you have done your very best. Never
leave the examination room early.
Some key terms used on examination papers
Account for: provide reasons for the information given.
Annotate: add brief notes to the labels of drawings to describe the structure and/or
the function of the structures labelled.
Compare: give similarities and differences.
Contrast: give differences.
Construct: draw a graph, histogram, bar chart, pie chart or table using data provided
or obtained.
Deduce: use data provided or obtained to arrive at a conclusion.
Define: state concisely the meaning of a word or term.
Describe: provide a detailed account which includes all relevant information.
Discuss: provide a balanced argument which considers points both for and against.
Distinguish between or among: give differences.
Evaluate: determine the significance or worth of the point in question.
Explain: give a clear, detailed account which makes given information easy to
understand and provides reasons for the information.
Give an account of: give a written description which includes all the relevant details.
viii
The pathway to success
Give an illustrated account of: give a written description which includes diagrams
referred to in the description.
Illustrate: make the answer clearer by including examples or diagrams.
Justify: provide adequate grounds for your reasoning.
Outline: write an account which includes the main points only.
Predict: use information provided to arrive at a likely conclusion or suggest a
possible outcome.
Relate: show connections between different sets of information or data.
State or list: give brief, precise facts without detail.
Suggest: put forward an idea.
Tabulate: construct a table to show information or data which has been given or obtained.
Drawing graphs
Graphs are used to display numerical data. When drawing a graph:
• Plot the manipulated variable on the x-axis (horizontal axis) and the responding
variable on the y-axis (vertical axis):
The manipulated variable is the factor that is changed by the person carrying out
the investigation. It will be given in the left column of the table of data.
The responding variable is the factor that is measured by the person carrying out
the investigation. It will be given in the right column of the table of data.
• Choose appropriate scales which are easy to work with and which use as much of
the graph grid as possible and enter the variables along the axes.
• Label each axis to indicate the variable that it is showing. To do this, use the column
headings in the table of data.
• When drawing a line graph, use a small dot surrounded by a small circle to plot each
point, plot each point accurately, and join the points with a sharp continuous line.
• When drawing a histogram or bar chart, the height of each bar indicates the
value of the responding variable. Draw vertical bars of equal width and draw an
accurately positioned horizontal line to show the top of each bar.
When drawing a histogram ensure that the bars touch each other.
When drawing a bar chart ensure that spaces of equal width are left between the
y-axis and the first bar, and between each of the other bars.
• Give the graph an appropriate title which must include reference to the
responding variable and the manipulated variable.
The pathway to success
ix
Section A – Living organisms and
the environment
1 Living organisms and cells
All living organisms are made of cells. Cells are so small that they can only be seen with a microscope
and not with the naked eye. From the simplest unicellular organisms to the most complex
multicellular organisms, living organisms all share certain characteristics.
The characteristics of living organisms
All living organisms share the following seven characteristics:
• Nutrition (feeding): the process by which living organisms obtain or make food.
Animals take in ready-made food and are called heterotrophs. Plants make their own food by the
process of photosynthesis and are called autotrophs.
• Respiration: the process by which energy is released from food by all living cells.
Aerobic respiration requires oxygen and takes place in most cells. Anaerobic respiration takes place
without oxygen in certain cells.
• Excretion: the process by which waste and harmful substances, produced by the body’s metabolism,
are removed from the body.
• Growth: a permanent increase in the size and complexity of an organism.
• Irritability (sensitivity): the ability of organisms to detect and respond to changes in their
environment or within themselves.
• Movement: a change in the position of a whole organism or of parts of an organism.
Most animals can move their whole bodies from place to place, known as locomotion. Plants and
some animals can only move parts of their bodies.
• Reproduction is the process by which living organisms generate new individuals of the same kind as
themselves.
Sexual reproduction involves the fusion of gametes (sex cells) produced by two parents. Asexual
reproduction does not involve the fusion of gametes and requires only one parent.
Cells
The cell is the basic structural and functional unit of all living organisms. A single cell possesses all of
the seven characteristics of living organisms. Some organisms are unicellular, being composed of a
single cell; others are multicellular, being composed of many cells.
Plant and animal cells
All plant and animal cells contain structures called organelles that are specialised to carry out one
or more vital functions, for example the nucleus, mitochondria, endoplasmic reticulum, ribosomes,
chloroplasts and vacuoles. Organelles are found within the cytoplasm of the cells and most are
surrounded by one or two membranes.
The following structures are found in all plant and animal cells:
• a cell membrane or plasma membrane
• mitochondria (singular mitochondrion)
• cytoplasm
• endoplasmic reticulum
• a nucleus
• ribosomes
1 Living organisms and cells
1
In addition to the above, plant cells also possess:
• a cell wall
• chloroplasts
• a large vacuole
ribosomes – small circular organelles
cell membrane – a partially (differentially) permeable layer
composed of protein and lipid around the outside
of the cell
cytoplasm – a jelly-like substance composed of about
80% water and 20% dissolved substances,
especially protein
nuclear envelope
nucleoplasm
chromatin thread
nucleolus
nucleus – surrounded by a double
membrane. Chromatin threads
contain genetic information in
the form of DNA
rough endoplasmic reticulum – a network of tubules
throughout the cytoplasm. Has ribosomes attached
smooth endoplasmic reticulum – no ribosomes attached
mitochondrion – a rod-shaped organelle with a smooth
outer membrane and folded inner membrane. Contains
respiratory enzymes
vacuoles – small, membrane-bound compartments which may
contain water, food, cell secretions or waste products
Figure 1.1 Structure of a generalised animal cell
cell wall – a freely permeable wall made
of cellulose
cell membrane
chloroplast – a disc-shaped organelle surrounded by a double
membrane. Contains many internal membranes, the green
pigment called chlorophyll and photosynthetic enzymes
ribosomes
mitochondrion
vacuole – a large membrane-bound compartment containing
cell sap, a solution of sugars, mineral salts, amino acids
and waste products
rough endoplasmic reticulum
nucleus
cytoplasm
smooth endoplasmic reticulum
Figure 1.2 Structure of a generalised plant cell
2
1 Concise Revision Course: Human and Social Biology
Table 1.1 A summary of the functions of the different cell structures
Cell structure
Function
Cell membrane Controls what substances enter and leave the cell.
Cytoplasm
Supports the organelles. The site of many chemical reactions.
Nucleus
Controls the characteristics and functioning of the cell. Essential for cell
division.
Mitochondrion Where respiration occurs to release energy for the cell.
Endoplasmic
Transports substances throughout the cell.
reticulum
Ribosome
Where proteins are synthesised (produced).
Vacuole
Stores food, cell secretions or cell waste. Supports plant cells when turgid.
Cell wall
Supports and protects the plant cell and gives it shape.
Chloroplast
Where photosynthesis occurs to produce food for the plant.
Table 1.2 Plant and animal cells compared
Animal cells
Do not have a cell wall.
Do not have chloroplasts or chlorophyll.
When present, the vacuoles are small and
scattered throughout the cytoplasm and their
contents vary.
May contain glycogen granules as a food store.
Can have a great variety of shapes.
Plant cells
Have a cell wall which is made of cellulose.
Usually have chloroplasts which contain
chlorophyll.
Usually have one large, central vacuole which
contains cell sap.
May contain starch grains as a food store.
Have a regular shape, usually round, square or
rectangular.
Microbes
Microbes or microorganisms are extremely small organisms which include viruses, bacteria, protozoa
and some fungi. Many microbes are pathogens, i.e. they cause disease (see Chapter 12, page 124).
• Viruses lack a cellular structure and they can only reproduce inside other living cells.
proteins
viral envelope – contains proteins
capsid – protein shell enclosing
the nucleic acid strands
nucleic acid strand
Figure 1.3 Structure of a typical virus particle
1 Living organisms and cells
3
• The cells of bacteria
lack a true nucleus
and other membranebound organelles.
Their DNA exists
in a region called
the nucleoid, which
lacks a nuclear
membrane, and also
in smaller regions
called plasmids.
capsule – slimy outer covering found in
some bacteria. Protects the cell
cell wall
cell membrane
nucleoid – a single, long, coiled loop
of DNA. Controls all cellular activities
cytoplasm
plasmid – small, circular piece of DNA
flagellum – long, whip-like projection.
Aids in movement
Figure 1.4 Structure of a generalised bacterial cell
• Most fungi are multicellular, though
yeasts are unicellular. Their cells
contain true nuclei and other
membrane-bound organelles except
chloroplasts, and are surrounded by
a cell wall made of chitin.
spores – used for reproduction
spore case
hypha – thread-like branching
structure composed of many
cells, or a single cell with many
nuclei and a central vacuole.
Surrounded by a cell wall
mycelium – body of the fungus
made up of a network of hyphae
Figure 1.5 Structure of a typical fungus
Cell specialisation and organisation in humans
The human body is composed of trillions of cells. These cells are of different types due to them
becoming specialised or differentiated to carry out specific functions. This enables humans to carry
out all essential life processes as efficiently as possible.
Table 1.3 Specialised cells and their functions
Cell type
Function
Epithelial
Covers and protects body surfaces.
Sperm (spermatozoon)
Male gamete; fuses with the female gamete during fertilisation to
form a zygote.
Egg (ovum)
Female gamete; fuses with the male gamete during fertilisation to
form a zygote.
Nerve (neurone)
Transmits impulses throughout the body to control and coordinate
the functioning of the body.
Muscle
Contracts to cause movement of parts of the body.
4
1 Concise Revision Course: Human and Social Biology
cell membrane
cytoplasm
tail – for
swimming
middle head
piece
nucleus
basement membrane
acrosome – contains
enzymes to dissolve a
passage into the ovum
nucleus
mitochondria – supply energy for swimming
Figure 1.6 Epithelial cells
Figure 1.7 A sperm cell or spermatozoon
follicle cells – act as protection
layer of jelly
membrane
cytoplasm – contains yolk which
supplies nutrients to the newly
formed embryo
nucleus
dendrites
cell body
Figure 1.8 An egg cell or ovum
motor end plates – pass
nerve impulses to a muscle
nucleus
axon – nerve fibre.
Carries impulses
myelin sheath – fatty layer.
Insulates the axon
Figure 1.9 A motor neurone (nerve cell)
cell membrane
light band
nuclei – many in each cell
dark band
nucleus
a smooth muscle cells
b skeletal muscle cells (muscle fibres)
Figure 1.10 Muscle cells
Cells of the same type that are specialised to carry out a particular function then work together in
groups called tissues. Tissues may contain one or, in some cases, more than one type of cell, e.g.
epithelial tissue, nerve tissue and muscle tissue. Different tissues are then grouped together to form
specialised organs which may perform one or more specific functions, e.g. the stomach is composed
of epithelial, connective, muscle and nerve tissues. Organs work together in organ systems to carry
out a major function. All organ systems then work together in an organised way to form an organism.
i.e. cells
ssues
organs
Table 1.4 Examples of organ systems
Organ system Organs
Digestive
Stomach, liver, pancreas, intestines
Reproductive Ovaries, uterus, testes, penis
Respiratory
Nose, larynx, trachea, bronchi, lungs
Nervous
Brain, spinal cord, nerves
Circulatory
Heart, blood vessels
organ systems
organism
Function
Digests and absorbs food.
Produces offspring.
Exchanges oxygen and carbon dioxide.
Detects and responds to stimuli.
Transports substances around the body.
1 Living organisms and cells
5
Revision questions
1 Explain THREE ways in which a car can be considered similar to a living organism and
2
3
4
5
6
7
8
THREE ways in which it is different from a living organism.
What is a cell?
Outline the function of EACH of the following cell structures:
a a mitochondrion
b the endoplasmic reticulum
c a chloroplast
d ribosomes
e the cell membrane
What would happen to a cell if its nucleus is removed?
Give FOUR differences and THREE similarities between the structure of a typical plant
cell and a typical animal cell.
What features would enable a scientist to distinguish a bacterial cell from other cells
when viewed under the microscope?
a Explain the need for cell specialisation in multicellular organisms.
b Name THREE different types of cells found in the human body and give the
function of EACH.
Suggest a definition for EACH of the following:
a a tissue
b an organ
c an organ system
Movement of substances into and out of cells
Substances can move into and out of cells, and from cell to cell by three different processes:
• diffusion
• osmosis
• active transport
Diffusion
Diffusion is the net movement of particles from an area of higher concentration to an area of lower
concentration until the particles are evenly distributed.
The particles (molecules or ions) are said to move down a concentration gradient. Particles in
gases, liquids and solutions are capable of diffusing. Diffusion is the way cells obtain many of their
requirements and get rid of their waste products which, if not removed, would poison them.
The importance of diffusion in living organisms
• Oxygen for use in aerobic respiration moves into cells by diffusion, and carbon dioxide produced in
aerobic respiration moves out of cells by diffusion.
• Some of the glucose and amino acids produced in digestion are absorbed through the cells in the
ileum and capillary walls and into the blood by diffusion.
• Carbon dioxide for use in photosynthesis moves into leaves and plant cells by diffusion, and oxygen
produced in photosynthesis moves out of plant cells and leaves by diffusion.
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1 Concise Revision Course: Human and Social Biology
Osmosis
Osmosis is a special form of diffusion.
Osmosis is the movement of water molecules through a partially (differentially) permeable membrane
from a solution containing a lot of water molecules, e.g. a dilute solution (or water), to a solution
containing fewer water molecules, e.g. a concentrated solution.
partially (differentially) permeable
membrane – has tiny pores which allow only
water molecules through
sucrose molecule – tries to diffuse through the
membrane into the dilute solution but is unable
to pass through
water molecule – is able to diffuse through the
membrane into the concentrated solution
dilute solution, e.g.
10% sucrose solution
concentrated solution, e.g.
50% sucrose solution
net movement of
water molecules
Figure 1.11 Explanation of osmosis
Visking tubing bag – partially
(differentially) permeable
40% sucrose solution
10% sucrose solution
a Water molecules enter the solution in the
bag. The volume of this solution increases
and the bag becomes turgid (firm).
Visking tubing bag
10% sucrose solution
40% sucrose solution
b Water molecules leave the solution in the
bag. The volume of this solution decreases
and the bag becomes flaccid (limp).
Figure 1.12 Demonstrating osmosis
In any cell, the cell
cytoplasm – a solution
membrane is partially
of about 80% water,
20% dissolved substances
water leaves the cytoplasm
(differentially)
through the cell membrane
cell membrane – differentially
permeable. There is
by osmosis
permeable
always cytoplasm, a
solution of protein and
water enters the cytoplasm
other substances in
through the cell membrane
by osmosis
water, on the inside
of the membrane, and
a An animal cell in water or a solution
b An animal cell in a solution that is
usually a solution on the
that is more dilute than its cytoplasm.
more concentrated than its cytoplasm.
The
cell
swells
and
eventually
bursts.
The cell shrinks.
outside. Water molecules,
therefore, move into and
Figure 1.13 The effect of different solutions on a single animal cell
out of cells by osmosis.
1 Living organisms and cells
7
Plant cells are surrounded by a strong, freely permeable cell wall. Because of this they behave
differently from animal cells when placed in different solutions.
1 Water enters the cytoplasm
and cell sap by osmosis
cell
membrane –
differentially
permeable
vacuole
membrane –
differentially
permeable
1 Water leaves the cytoplasm and
cell sap by osmosis
2 The vacuole and
cytoplasm swell
and press outwards
against the cell wall
a A plant cell in water or a solution
that is more dilute than its cytoplasm
and cell sap. The cell swells and
becomes turgid.
2 The vacuole and
cytoplasm shrink
and pull the cell
membrane away
from the cell wall
cell wall –
freely permeable
3 Concentrated solution
passes through
the permeable cell wall
b A plant cell in a solution that is more
concentrated than its cytoplasm
and cell sap. The cell shrinks and
becomes flaccid. When the membrane
has pulled away from the wall, the cell is
said to be plasmolysed.
Figure 1.14 The effect of different solutions on a single plant cell
The importance of osmosis in living organisms
• Water moves into animal cells from blood plasma and body fluids by osmosis. This keeps them
hydrated.
• Water is absorbed from the intestines into the blood by osmosis. This ensures that the body
obtains the water it needs from food and drink consumed.
• Water is reabsorbed from the filtrate in the kidney tubules into the blood by osmosis. This prevents
the body from losing too much water.
• Water moves into plant cells by osmosis. This keeps them turgid, which causes non-woody stems to
stand upright and keeps leaves firm.
• Water is absorbed from the soil by the root hairs of plants and moves through the cells of roots and
leaves by osmosis. This ensures that leaves get a constant supply of water for photosynthesis.
Active transport
Active transport is the movement of particles through cell membranes against a concentration
gradient using energy released in respiration.
During active transport, energy released in respiration in the form of ATP (see page 43) is used to
move the particles (molecules or ions) through cell membranes from areas of lower concentration
to areas of higher concentration. Active transport allows cells to accumulate high concentrations of
important substances, e.g. glucose, amino acids and ions.
The importance of active transport in living organisms
• Some of the glucose and amino acids produced in digestion are absorbed from the ileum into the
blood by active transport.
• Useful substances are reabsorbed from the filtrate in the kidney tubules into the blood by active
transport.
• Mineral ions move from the soil into plant roots by active transport.
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1 Concise Revision Course: Human and Social Biology
Revision questions
9 Distinguish between diffusion and osmosis.
100 Give THREE reasons to support the fact that diffusion is important to living organisms.
11 Explain what happens to an animal cell if it is placed in a solution more dilute than its
cytoplasm.
122 You place a plant cell in a solution that is more concentrated than its cell sap and
cytoplasm. Draw a labelled diagram to show how the cell would appear when
viewed under the microscope after being left for 15 minutes in the solution.
133 Give THREE reasons why osmosis is important to living organisms.
144 Why is the root of a plant unable to absorb mineral ions from the soil if it is given a
poison that prevents respiration?
1 Living organisms and cells
9
2 Photosynthesis, food chains
and cycles
Green plants produce their own food by photosynthesis. All other living organisms depend either
directly or indirectly on green plants for their food. This food is passed on from one living organism
to the next through food chains.
Photosynthesis
Photosynthesis is the process by which green plants convert carbon dioxide and water into glucose by
using energy from sunlight absorbed by chlorophyll in chloroplasts.
Oxygen is produced as a by-product. The process can be summarised by the following word equation:
carbon dioxide + water
energy from sunlight absorbed
by chlorophyll
glucose + oxygen
Photosynthesis occurs in any plant structure that contains chlorophyll, i.e. which is green; however, it
mainly occurs in the leaves. Chlorophyll molecules in the chloroplasts of leaf cells absorb the energy
from sunlight and use it to convert carbon dioxide, absorbed from the air, and water, absorbed from
the soil, into glucose and oxygen.
Fate of the products of photosynthesis
The plant uses the oxygen and glucose produced during photosynthesis for various different functions.
Oxygen
The oxygen is used by the leaf cells in respiration. Excess oxygen diffuses out of the leaves into the air.
Glucose
The glucose can be used in a variety of ways:
• It can be used by the leaf cells in respiration to release energy.
• It can be converted to starch by the leaf cells and stored. The starch can then be converted back to
glucose and used, e.g. during the night.
• It can be converted to other useful organic substances by leaf cells, e.g. amino acids and protein,
vitamins or chlorophyll.
• It can be converted to sucrose and transported to other parts of the plant such as growing parts and
storage organs, where it can be converted to:
Glucose, and used in respiration to release energy.
Starch, and stored in seeds, e.g. wheat and rice; in fruits, e.g. breadfruit; and in tubers, e.g. English
(Irish) potato and sweet potato.
Amino acids and protein, by the addition of nitrogen from nitrates and sulfur from sulfates
obtained from the soil. Protein is then used for growth.
Lipids, and stored, mainly in seeds, e.g. peanuts and soya beans.
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2 Concise Revision Course: Human and Social Biology
Food chains
Energy from sunlight enters living organisms through photosynthesis occurring in green plants, which
are also known as producers. This energy is incorporated into the organic food molecules produced by
the plants and is passed on to consumers through food chains.
A food chain is a diagram showing the flow of food and energy from one organism to the next.
A food chain includes:
• A producer, i.e. a green plant.
• A primary consumer that eats the primary producer.
• A secondary consumer that eats the primary consumer.
• A tertiary consumer that eats the secondary consumer.
• Some food chains may also include a quaternary consumer that eats the tertiary consumer.
Consumers can also be classified according to what they consume:
• Herbivores consume plants or plant material only, e.g. cows, grasshoppers, snails, slugs, parrot fish,
sea urchins.
• Carnivores consume animals or animal material only, e.g. lizards, toads, spiders, centipedes, eagles,
octopuses, sharks.
• Omnivores consume both plants and animals, or plant and animal material, e.g. hummingbirds,
crickets, humans and crayfish.
Trophic level refers to the position or level that an organism occupies in a food chain.
Trophic level
Organism’s status
A terrestrial food chain
A marine food chain
5
quaternary consumer
(carnivore)
hawk
tiger shark
4
tertiary consumer
(carnivore)
snake
barracuda
3
secondary consumer
(carnivore)
lizard
flying fish
2
primary consumer
(herbivore)
grasshopper
zooplankton
1
producer
(green plant)
grass
phytoplankton
Figure 2.1 Examples of food chains
2 Photosynthesis, food chains and cycles
11
Food webs
Any environment usually has
more than one producer and most
consumers have more than one source
of food. Consequently, food chains are
interrelated to form food webs.
Dependence of other living
organisms on plants
tertiary consumers
heron
secondary consumers
primary consumers
carp
pond snail
producers
tilapia
water flea
pond weed
mosquito larvae
phytoplankton
All other living organisms, including
humans, depend both directly and
Figure 2.2 An example of a food web from a freshwater lake
indirectly on plants for food since
plants are the only living organisms capable of producing organic food molecules from simple
inorganic molecules, i.e. carbon dioxide and water. When a human eats any food of plant origin, e.g.
fruits, vegetables, cereals and nuts, he or she is depending directly on plants. When a human eats any
food of animal origin, e.g. meat or fish, he or she is depending indirectly on plants.
Energy transfer in food chains
Not all the energy incorporated into organic food molecules made by green plants during
photosynthesis is passed along a food chain, some is used and some is lost at each trophic level.
Some of the food produced by plants is used by the plants in respiration. This releases energy that the
plants use in life processes. The rest of the food is used by the plants for growth or is stored.
When plants are eaten by herbivores, some of the organic matter that contains energy is lost in faeces
and some is lost in organic excretory products, e.g. urea. Some is used in respiration during which
the stored energy is released and used in life processes, or is lost as heat. The remaining food that
contains energy is used to build body tissues or is stored, and is then passed on to the next trophic
level when herbivores are consumed. This then continues at each trophic level in a food chain.
Organisms that are not consumed eventually die. These dead organisms and the organic matter in
faeces and excretory products are decomposed by decomposers, which release the energy during
respiration. Energy, therefore, flows from producers to consumers and decomposers in one direction
and is not recycled. In general, only about 10% of the energy from one trophic level is transferred to
the next level.
energy from
energy lost
the Sun during respiration
energy lost
during respiration
energy lost
during respiration
energy lost
energy lost
during respiration during respiration
primary consumption primary consumption secondary consumption tertiary
producer
consumer
consumer
consumer
10%
10%
10%
death
faeces
and excretory
products
death
faeces
and excretory
products
death
faeces
and excretory
products
death
decomposers
Figure 2.3 Energy flow through a food chain
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2 Concise Revision Course: Human and Social Biology
Ecological pyramids
Because there is less energy and biomass
(mass of biological matter) at each trophic
level in a food chain, fewer organisms can be
supported at each level. Energy, biomass and the
number of organisms at successive levels can be
represented by ecological pyramids. Due to the
loss of energy and biomass at each level, food
chains rarely exceed four or five trophic levels.
trophic level
5
4
3
2
1
quaternary consumer
tertiary consumer
secondary consumer
primary consumer
primary producer
Figure 2.4 Pyramid of energy, biomass or numbers
Recycling of carbon and nitrogen in nature
The different chemical elements which make up the bodies of all living organisms, e.g. carbon and
nitrogen, are continually cycled through these living organisms and their physical environment.
Unlike the energy from the Sun, these elements are present in nature in finite amounts; therefore,
recycling is essential to prevent them from gradually running out.
Decomposers are essential for recycling. These are microorganisms, i.e. bacteria and fungi, which
feed on dead and waste organic matter causing it to decompose. Decomposers are also known
as saprophytes.
The carbon cycle
The cycling of carbon (C) atoms occurs by them being converted into different carbon-containing
compounds, including carbon dioxide (CO2) present in the air, and various organic compounds,
mainly carbohydrates, proteins and lipids, present in living organisms.
• Carbon dioxide is removed from the air and converted to organic compounds by green plants
during photosynthesis.
• Carbon dioxide is returned to the air by:
Respiration occurring in all living organisms including plants, animals and decomposers.
Combustion, mainly of fossil fuels such as coal, oil and natural gas, though all materials containing
organic compounds release carbon dioxide when burned, e.g. wood and paper.
carbon dioxide
(CO2) in the air –
0.038%
photosynthesis
organic compounds
in green plants
respiration
eaten by
animals
respiration
combustion
respiration
organic compounds
in fossil fuels
organic compounds
in animals
death and
decomposition
death and
decomposition
organic compounds
in decomposers
fossilisation
fossilisation
Figure 2.5 A simplified carbon cycle
2 Photosynthesis, food chains and cycles
13
The nitrogen cycle
Most living organisms are unable to use nitrogen (N2) gas directly. The cycling of nitrogen (N) atoms
occurs mainly by them being converted into different nitrogen-containing compounds including
proteins present in living organisms, and ammonium (NH4+) compounds, nitrites (NO2−) and nitrates
(NO3−) present in the soil.
• Nitrogen is removed from the air and converted into ammonium compounds by nitrogen-fixing
bacteria in the soil and in the root nodules of legumes, e.g. peas and beans. The legumes use these
compounds to make proteins.
• Nitrogen is returned to the air by denitrifying bacteria which convert nitrates in the soil to nitrogen.
• Nitrate ions in the soil are removed from the soil by plants and used to make protein. This protein is
passed on to animals when the plants are eaten.
• Nitrate ions are returned to the soil by the decomposition of dead plants and animals by
decomposers (saprophytic bacteria and fungi). This decomposition forms ammonium compounds
which are then converted into nitrites and nitrates by nitrifying bacteria.
nitrogen (N2)
in the air – 78%
denitrifying
bacteria
in the soil
excretion
of urea
fixation by
nitrogen fixing
bacteria
in root
nodules of
legumes
animal protein
eaten by
animals
plant protein
in the
soil
death and
decomposition by
decomposers
ammonium (NH4+)
compounds in the soil
death and
decomposition by
decomposers
absorbed
by plants
nitrates (N03–)
in the soil
nitrifying
bacteria
in the soil
nitrites (N02–)
in the soil
nitrifying
bacteria
in the soil
Figure 2.6 A simplified nitrogen cycle
14
2 Concise Revision Course: Human and Social Biology
Revision questions
1 Define the term ‘photosynthesis’ and give a word equation to summarise the process.
2 Suggest FOUR ways that the plant can make use of the glucose produced
3
4
5
6
7
8
9
in photosynthesis.
a What is a food chain?
b Some aphids were observed on the tomato plants in a garden and ladybird beetles
were seen feeding on the aphids. The ladybirds were, in turn, being eaten by
dragonflies which were, themselves, being fed on by toads. Use this information to
draw a food chain for the organisms in the garden.
From the organisms in item 3 b above, identify:
a a carnivore
b a herbivore
c a producer
d a primary consumer e a secondary consumer
When Jared eats a barracuda he only gets about 10% of the energy that the barracuda
obtained from the flying fish it ate. Explain THREE reasons why so little energy is
passed on to Jared.
Why is it important that elements such as carbon and nitrogen are recycled in nature?
Outline how carbon is recycled in nature.
Identify FOUR different types of bacteria responsible for recycling nitrogen in nature.
Explain each of the following:
a How nitrates in the soil can be returned to the soil after being absorbed by grass
growing in a field.
b How bacteria can remove nitrogen from the air and return it to the air.
2 Photosynthesis, food chains and cycles
15
Exam-style questions –
Chapters 1 to 2
Structured questions
1 a) Figure 1 shows a generalised animal cell.
W
X
Y
Z
Figure 1 A generalised animal cell
i) Name the structures labelled W and X.
ii) State ONE function of EACH organelle labelled Y and Z.
iii) In what way does the property of structure W differ from the cell wall
in a plant cell?
b) Figure 2 shows two different specialised cells found in the human body.
Cell A
(2 marks)
(2 marks)
(2 marks)
Cell B
Figure 2 Specialised cells found in the human body
i) Identify cell A.
ii) Explain TWO ways in which the structure of cell B makes it suitable for
its function.
iii) Why is it important that the human body is made of specialised cells?
c) i) Anya thinks that a virus is a living organism. Do you agree with her?
Give ONE reason for your opinion.
ii) Anton and Elijah are playing a game of tennis. Identify and explain
TWO characteristics of living organisms that they are displaying.
16
Exam-style questions – Chapters 1 to 2
(1 mark)
(2 marks)
(1 mark)
(1 mark)
(4 marks)
Total 15 marks
2 a) Figure 3 summarises the process of photosynthesis.
sunlight energy
absorbed by
substance C
used to convert
substance D and water
into
substance E and oxygen
Figure 3 The process of photosynthesis
i) Identify substances C, D and E.
(3 marks)
ii) Explain TWO ways in which the leaves of plants use substance E.
(2 marks)
iii) Tasha tells Mia that they both depend directly and indirectly on plants
(2 marks)
to survive. Provide a suitable explanation to support what Tasha said.
b) Table 1 below shows the food sources of several organisms found in the ocean.
Table 1 Food sources of some organisms found in the ocean
Organism
Food source
zooplankton
phytoplankton
shrimp
phytoplankton
jellyfish
zooplankton and shrimp
crab
shrimp
sea turtle
crab and jellyfish
i) Using only the information contained in Table 1, construct a food web for the
(2 marks)
organisms.
ii) Which organism in the food web would you expect to be present in the
(1 mark)
LOWEST numbers?
iii) Outline the reason for your answer to b) ii) above.
(3 marks)
c) Ramon and Sean both cut their lawns each week. Ramon leaves his grass
cuttings on his lawn, whereas Sean rakes up his cuttings, puts them in bags
and throws them out with the rest of his garbage. After many months of doing
this, Ramon finds his grass grows faster and looks healthier than Sean’s.
(2 marks)
Use your knowledge of natural cycles to explain Ramon’s observations.
Total 15 marks
Exam-style questions – Chapters 1 to 2
17
Structured essay question
3 a) Jacinta set up the apparatus in Figure 4 below and observed that the level of the meniscus in
the capillary tube gradually rose up the tube.
capillary tube
meniscus of the
sucrose solution
beaker
25% sucrose solution
Visking tubing –
partially permeable
water
Figure 4 Apparatus used to study the movement of particles
i) Give an account of why the meniscus gradually rose up the capillary tube.
(4 marks)
ii) Explain TWO differences between the process occurring in Jacinta’s apparatus
and the process of diffusion. At the beginning of your answer, name the process
(5 marks)
occurring in the apparatus.
b) i) Define the term ‘active transport’.
(2 marks)
ii) By referring to TWO different places in your body where active transport
(4 marks)
occurs, explain its importance to you.
Total 15 marks
18
Exam-style questions – Chapters 1 to 2
Section B – Life processes
3 Nutrition
Humans need a variety of nutrients to provide them with energy, to enable them to grow and develop,
and to keep them healthy. These nutrients include carbohydrates, proteins, lipids, vitamins and
minerals, and they are contained in the food we eat.
Nutrition is the process by which living organisms obtain or make food.
The human diet
The food an animal eats is called its diet. The human diet must contain the following:
• Carbohydrates, proteins and lipids, also known as macronutrients. These are required in relatively
large quantities.
• Vitamins and minerals, also known as micronutrients. These are required in relatively small
quantities.
• Water and dietary fibre (roughage).
Carbohydrates, proteins and lipids
Carbohydrates
Carbohydrates include reducing sugars, non-reducing sugars and starch. They are molecules composed
of carbon, hydrogen and oxygen atoms. The ratio of hydrogen atoms to oxygen atoms is always 2:1.
Based on their chemical structure, carbohydrates can be classified into three groups: monosaccharides,
disaccharides and polysaccharides.
• Monosaccharides are the simplest carbohydrate molecules, they have the formula C6H12O6. All
monosaccharides are reducing sugars (see page 25).
• Disaccharides are formed by chemically joining two monosaccharide molecules together; they
have the formula C12H22O11. All disaccharides are reducing sugars except sucrose, which is a nonreducing sugar.
• Polysaccharides are formed by joining many monosaccharide molecules into straight or branched
chains. Polysaccharides include starch, cellulose and glycogen (animal starch).
single monosaccharide
molecule
monosaccharide
molecules
two monosaccharide
molecules joined
many monosaccharide
molecules joined
disaccharide
part of a polysaccharide
molecules
molecule
condensation – joining molecules with the loss of water
hydrolysis – splitting molecules by adding water
Figure 3.1 The three types of carbohydrates
3 Nutrition
19
Table 3.1 Properties of different carbohydrates
Carbohydrate
Physical and chemical properties
Reducing sugars
Have a sweet taste.
Soluble in water.
React with Benedict’s solution.
Non-reducing sugars
Starch
Have a sweet taste.
Soluble in water.
Do not react with Benedict’s
solution.
Does not have a sweet taste.
Insoluble in water.
Reacts with iodine solution.
Examples
Glucose (a monosaccharide)
Fructose (a monosaccharide)
Galactose (a monosaccharide)
Maltose (a disaccharide)
Lactose (a disaccharide)
Sucrose (a disaccharide)
Proteins
Proteins are molecules composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur and
phosphorus atoms. These atoms form small molecules known as amino acids. There are 20 different
common amino acids. Protein molecules are formed by joining hundreds or thousands of amino acid
molecules together in long chains.
different amino acids
peptide links
part of a
protein molecule
Figure 3.2 Part of a protein molecule
Proteins have the following properties:
• Their chemical structure can be changed by heat or certain other chemicals, i.e. they can be
denatured.
• Some are globular in structure and are soluble in water, e.g. haemoglobin and albumen, others are
fibrous and are insoluble, e.g. collagen and keratin.
• They react with biuret reagent.
Lipids
Lipids are fats and oils. They are molecules
composed of carbon, hydrogen and oxygen
3 fatty acid
atoms. Their molecules have fewer oxygen
molecules
atoms than carbohydrate molecules, e.g.
a lipid molecule
beef fat has the formula C57H110O6. Each lipid
molecule is made up of four smaller molecules
joined together; three fatty acid molecules and Figure 3.3 A lipid molecule
one glycerol molecule.
Lipids feel greasy, are insoluble in water and they leave a grease spot on paper.
20
3 Concise Revision Course: Human and Social Biology
1 glycerol
molecule
Recognising carbohydrates, proteins and lipids
Tests can be performed in the laboratory to identify carbohydrates, proteins and lipids. Apart from the
tests for lipids, the tests are usually carried out on about 2 cm3 of a solution of the test substance in a
test tube.
Table 3.2 Laboratory tests to identify carbohydrates, proteins and lipids
Food substance
Test
Positive result
Reducing sugars
Add an equal volume of Benedict’s solution An orange-red precipitate
and shake. Heat the mixture.
forms.
Non-reducing sugars Add a few drops of dilute hydrochloric
An orange-red precipitate
acid and heat for 1 minute. Add sodium
forms.
hydrogencarbonate until effervescence
stops. Add an equal volume of Benedict’s
solution and shake. Heat the mixture.
Starch
Add a few drops of iodine solution and
Solution turns blue-black.
shake.
Protein – the biuret Add an equal volume of sodium hydroxide Solution turns purple.
solution and shake. Add drops of dilute
test
copper sulfate solution and shake.
Or add an equal volume of biuret reagent
and shake.
Lipid – the emulsion Place 4 cm3 of ethanol in a dry test tube. A milky-white emulsion forms.
test
Add 1 drop of test substance and shake.
Add an equal volume of water and shake.
Lipid – the grease
Rub a drop of test substance onto
A translucent mark (grease spot)
absorbent paper. Leave for 10 minutes.
spot test
remains.
Reducing sugars form an orange-red
precipitate with Benedict's solution
Starch turns iodine solution
blue-black
Figure 3.4 Laboratory tests to identify reducing sugars and starch
3 Nutrition
21
Sources and functions of carbohydrates, proteins and lipids
Carbohydrates, proteins and lipids are organic compounds which supply the body with energy and the
materials for growth and repair.
Table 3.3 Sources and functions of carbohydrates, proteins and lipids
Class
Sources
Functions
Carbohydrates Sugars: fruits, cakes, • To provide energy (16 kJ g−1): energy is easily released
when respired.
sweets, jams
• For storage: glycogen granules are stored in many cells.
Starch: yams,
potatoes, rice, pasta,
bread
Fish, lean meat,
• To make new cells for growth and to repair damaged
Proteins
tissues.
milk, cheese, eggs,
peas, beans, nuts • To make enzymes that catalyse (speed up) reactions
in the body.
• To make hormones that control various processes in
the body.
• To make antibodies to fight disease.
• To provide energy (17 kJ g−1): used only when stored
carbohydrates and lipids have been used up.
Butter, vegetable
• To make cell membranes of newly formed cells.
Lipids
oils, margarine,
• To provide energy (39 kJ g−1): used after carbohydrates
nuts, fatty meats
because their metabolism is more complex and takes
longer.
• For storage: fat is stored under the skin and around
organs.
• For insulation: fat under the skin acts as an insulator.
Vitamins and minerals
Vitamins are organic compounds and minerals are inorganic substances. They are only required in small
amounts by the human body, but they are essential for healthy growth and development.
• Vitamins required include:
Vitamins A, D, E and K, which are fat soluble.
Group B vitamins and vitamin C, which are water soluble.
• Minerals required include calcium, iron, phosphorus, iodine, sodium, potassium and fluorine.
Table 3.4 Some important vitamins and minerals required by the human body
Vitamin/mineral Sources
Functions
Vitamin A
Liver, cod liver oil, yellow and
• Helps to keep the skin, cornea and
mucous membranes healthy.
orange vegetables and fruits, e.g.
carrots and pumpkin, green leafy • Helps vision in dim light (night vision).
vegetables, e.g. spinach
• Strengthens the immune system.
Vitamin B1
Whole-grain cereals and bread, • Aids in respiration to produce energy.
brown rice, peas, beans, nuts,
• Important for the proper functioning of
yeast extract, lean pork
the nervous system.
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3 Concise Revision Course: Human and Social Biology
Vitamin/mineral Sources
Functions
Vitamin C
West Indian cherries, citrus fruits, • Keeps tissues healthy, especially the skin
and connective tissue.
raw green vegetables
• Strengthens the immune system.
• Helps the body absorb iron in the ileum.
Vitamin D
Oily fish, eggs, cod liver oil.
• Promotes the absorption of calcium and
Made in the body by the action of phosphorus in the ileum.
sunlight on the skin
• Helps build and maintain strong bones
and teeth.
• Strengthens the immune system.
Calcium
Dairy products, e.g. milk, cheese • To build and maintain healthy bones and
teeth.
(Ca)
and yoghurt, green vegetables,
e.g. broccoli
• Helps blood to clot at cuts.
Iron
Red meat, liver, eggs, beans, nuts, • To make haemoglobin, the red pigment in
red blood cells which transports oxygen
(Fe)
dark green leafy vegetables
around the body for use in respiration.
Vitamin and mineral deficiency diseases
A shortage or lack of any of the essential vitamins or minerals in the diet can lead to health problems
and certain deficiency diseases.
Table 3.5 Some vitamin and mineral deficiency diseases
Disease
Cause
Symptoms
Treatment
Night
Deficiency of • Poor vision in dim light.
• Increase the intake of foods
rich in vitamin A.
blindness
vitamin A
• Vision adapts slowly between
bright and dim conditions.
• Take vitamin A supplements.
Rickets
Deficiency • Soft, weak, painful, deformed • Increase the intake of foods
bones, especially limb bones.
rich in vitamin D and calcium.
(in children) of vitamin
D and/or
• Bow legs.
• Take vitamin D and calcium
calcium
supplements.
• Increase exposure to sunlight.
Anaemia
Deficiency of • A reduced number of red
• Increase the intake of foods
blood cells in the blood.
rich in iron.
iron
• Pale complexion.
• Take iron supplements.
• Tiredness.
• Increase the intake of foods
rich in vitamin C.
• Lack of energy.
Water
Water is essential in the diet since the human body is about 65% water.
• Water acts as a solvent to dissolve chemicals in cells so that they can react.
• Water acts as a solvent to dissolve substances so that they can be transported around the body,
e.g. products of digestion are dissolved in blood plasma.
• Water acts as a solvent to dissolve waste substances so that they can be excreted from the body,
e.g. urine contains dissolved urea.
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23
• Water acts as a reactant, e.g. in hydrolysis which occurs during digestion of food.
• Water acts as a coolant, removing heat from the body when it evaporates from sweat.
Dietary fibre (roughage)
Dietary fibre is food that cannot be digested. It
consists mainly of the cellulose of plant cell
walls, lignin of plant xylem vessels, husks of
brown rice and bran of wholegrain cereals.
Fruits, vegetables and grains are excellent
sources of dietary fibre.
Dietary fibre adds bulk to the food which
stimulates peristalsis (see page 34) so that food
is kept moving through the digestive system.
This helps prevent constipation and reduces the
risk of colorectal (bowel) cancer.
Constipation and diarrhoea
Figure 3.5 Fruit and cereals are rich in dietary fibre
Constipation is a condition of the bowels (colon and rectum) in which the faeces are dry and hard,
difficult and often painful to pass, and passed infrequently. Diarrhoea is a condition in which faeces
are passed frequently and in a liquid form. It is usually a symptom of gastroenteritis (see page 126).
Table 3.6 Common causes and effects of constipation and diarrhoea
Condition
Causes
Effects
Constipation • Not eating enough dietary fibre.
• Bloating.
• Not drinking enough water or other fluids.
• Abdominal pain.
• Not exercising or being inactive.
• Haemorrhoids (piles).
• A change in diet or daily routine.
• Faecal impaction.
• Ignoring the urge to defaecate.
• Colorectal (bowel) cancer.
• Stress, anxiety or depression, and certain
medications.
Diarrhoea
• Being infected with certain viruses, e.g. norovirus. • Dehydration.
• Being infected with certain bacteria,
• Electrolyte imbalance.
e.g. Salmonella, E. coli, Shigella.
• Impaired kidney function
• Being infected with an intestinal parasite,
(kidney failure).
e.g. Giardia.
• Malnutrition in severe
• Conditions such as irritable bowel syndrome,
cases.
colorectal cancer, coeliac or Crohn’s disease.
Food poisoning, i.e. eating contaminated food, is a common way of becoming infected with pathogens
that cause diarrhoea. Chances of getting food poisoning can be reduced by practising good food
hygiene when preparing food:
• Wash hands, utensils and food preparation surfaces regularly.
• Wash fruits and vegetables thoroughly before cooking or eating.
• Keep uncooked foods, especially meat, poultry and fish, separate from ready-to-eat foods.
• Cook food thoroughly, especially meat, poultry and fish.
• Defrost frozen food thoroughly and safely, i.e. in a refrigerator, before cooking.
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3 Concise Revision Course: Human and Social Biology
A balanced diet
ug
sem
slam
morf doinoA
F
r
F
s ti u
Energy requirements
Le
selpa
tS
Humans must consume a
balanced diet each day. This
must contain carbohydrates,
proteins, lipids, vitamins,
minerals, water and dietary
fibre in the correct proportions
to supply the body with
enough energy for daily
activities and the correct
materials for growth and
development, and to keep the
body in a healthy state.
A balanced diet should contain
a variety of foods selected
from each of the six different
Caribbean food groups shown
in Figure 3.6. Each group
contains foods that supply
similar nutrients in similar
proportions. The size of each
sector indicates the relative
amount of each group that
should be eaten daily.
Fats &
O il s
Vegetables
The amount of energy required Figure 3.6 The six Caribbean food groups
daily from the diet depends on
a person’s age, occupation and gender (sex). In general, daily energy requirements:
• Increase as age increases up to adulthood. They then remain fairly constant up to old age when less
energy is required daily.
• Increase as activity increases, e.g. a manual labourer requires more energy than a person working in
an office.
• Are higher in males than in females of the same age and occupation.
• Increase in a female when she is pregnant or breastfeeding.
Malnutrition
Malnutrition occurs when a person’s diet does not contain the right amount of nutrients.
Malnutrition can be caused by eating a diet in which certain nutrients are lacking, known
as undernutrition, or are in excess, known as overnutrition. Malnutrition can lead to several
serious conditions.
Obesity
Obesity is characterised by an excessive accumulation and storage of fat in the body. It is generally
caused by the excessive consumption of energy rich foods high in sugar and/or fat, especially animal
fat, and a lack of physical activity. Obesity increases a person’s risk of hypertension (high blood
pressure), heart disease, stroke, diabetes, osteoarthritis and some cancers (see page 121).
3 Nutrition
25
Anorexia
Anorexia is a serious mental health condition where a person keeps his or her body weight as low as
possible by eating very little, vomiting, using laxatives and exercising excessively. It mainly affects girls
and young women, and can eventually lead to death.
Bulimia
Bulimia is an eating disorder and mental health condition where a person tries to control his or her
weight by repeating a cycle of binge eating followed by purging. The person eats large quantities of
food very quickly and then induces vomiting or takes laxatives to get rid of the food.
Protein-energy malnutrition (PEM)
Protein-energy malnutrition (PEM) refers to a group of related disorders, including kwashiorkor and
marasmus, which are caused by an inadequate protein or energy intake. Both disorders mainly affect
young children in developing countries.
• Kwashiorkor is caused by a severe shortage of protein in the diet. Its symptoms include loss of
muscle mass, failure to grow, oedema (swelling) of the abdomen and legs, changes in skin and hair
pigmentation, and fat accumulation in the liver.
• Marasmus is caused by a severe shortage of protein and energy rich foods such as carbohydrates in the
diet. Its symptoms include low body weight, thin face with sunken eyes, ribs and shoulders clearly
visible through the skin, thin arms and legs with very little muscle and fat, dry skin and brittle hair.
Figure 3.7 A child with kwashiorkor
Figure 3.8 A child with marasmus
Body mass index (BMI)
Body mass index can be used as an indicator of body fat. It compares the mass of a person, determined
by weighing the person, to his or her height using the following formula:
body mass (in kilograms)
body mass index (kg per m2) =
height (in metres) × height (in metres)
Table 3.7 Body mass index for adults
Body mass index in kg per m2
18.4 and below
18.5 to 24.9
25.0 to 29.9
30.0 to 39.9
40.0 and above
26
Condition
Underweight
Healthy weight
Overweight
Obese
Severely obese
3 Concise Revision Course: Human and Social Biology
Revision questions
1 Construct a table to give TWO physical properties, TWO sources and TWO functions
of EACH of the following macronutrients in the human diet: starch, proteins, lipids.
2 Distinguish between a reducing sugar and a non-reducing sugar and give a named
example of EACH.
3 You are given three solutions labelled X, Y and Z and told that they contain starch,
glucose and gelatin (a protein), respectively. Describe THREE laboratory tests you
could perform to confirm what you are told about X, Y and Z
4 Classify vitamins based on their solubility in water or fat.
5 Construct a table to give ONE source and the major functions of the following
micronutrients: vitamin B1, vitamin C and iron.
6 Identify the cause, symptoms and treatment of EACH of the following:
a night blindness
b rickets
c anaemia
7 Identify THREE reasons why water is important in the diet.
8 Outline the consequences of Annette not consuming enough dietary fibre daily.
9 Food poisoning can result in a person suffering from diarrhoea. Suggest THREE
consequences of diarrhoea and THREE ways a person can reduce their chances of
food poisoning.
100 What is a balanced diet?
11 a What is malnutrition?
b Name THREE serious conditions that can result from malnutrition.
122 a Keenan is 1.5 m tall and weighs 75 kg. Determine his body mass index (BMI).
b What can you deduce about Keenan?
Digestion
Digestion is the process by which food is broken down into a form that is useful for body activities,
i.e. simple, soluble food molecules. It occurs in the alimentary canal which is a tube, 8 to 9 metres
long with muscular walls, running from the mouth to the anus. The alimentary canal and its various
associated organs including the liver, gall bladder and pancreas make up the digestive system
(see Figure 3.14, page 32).
The digestive process involves:
• Mechanical digestion during which large pieces of food are broken down into smaller pieces.
Mechanical digestion begins in the mouth where food is chewed by the teeth, and it continues in
the stomach where contractions of the stomach walls churn the food.
• Chemical digestion during which large, usually insoluble food molecules are broken down into small,
soluble food molecules by enzymes (see pages 30–32). Chemical digestion begins in the mouth and
is completed in the ileum.
3 Nutrition
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Teeth and mechanical digestion
The importance of teeth in digestion
When food is chewed or masticated, the teeth break up large pieces of food into smaller pieces. This is
important because:
• It gives the pieces of food a larger surface area for digestive enzymes to act on, making chemical
digestion quicker and easier.
• It makes food easier to swallow.
Types of teeth
incisors
Humans have four different types of teeth,
incisors, canines, premolars and molars,
canine or eyetooth
and they have two sets of these teeth in
their lifetime:
premolars or bicuspid
• Milk teeth start to appear from about
molars
6 months and start falling out from about
6 years old. They consist of 8 incisors, 4
canines and 8 molars.
• Permanent teeth replace the 20 lost milk
teeth and an additional 12 develop. They Figure 3.9 Teeth of the upper jaw of an adult human
consist of 8 incisors, 4 canines, 8 premolars and 12 molars.
Table 3.8 The different types of teeth in humans
Type
Position
Shape
Functions
Incisor
At the front of the jaw.
Chisel-shaped
crown To cut food.
with sharp,
To bite off pieces of food.
root
thin edges.
Canine
Next to the incisors.
(eye tooth)
Premolar
Cone-shaped
and pointed.
To grip food.
To tear off pieces of food.
At the side of the jaw next
to the canines.
cuspp To crush and grind food.
Have a fairly
broad surface
root
with two
pointed cusps.
Molar
At the back of the jaw next Have a broad
To crush and grind food.
to the premolars.
surface with
4 or 5 pointed
cusps.
A tooth is divided into two parts; the crown which is the part above the jaw and the root which is the
part embedded in the jawbone. The internal structure of all teeth is similar.
Tooth structure
A tooth is divided into two parts; the crown, which is the part above the jaw, and the root, which is
the part embedded in the jawbone. The internal structure of all teeth is similar. The crown is covered
with enamel and the root with a thin layer of cement and the periodontal membrane. The bulk of the
tooth is composed of dentine and the pulp cavity occupies the centre. Nerves and blood vessels run
throughout the pulp cavity.
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3 Concise Revision Course: Human and Social Biology
enamel – non-living. Covers the crown of the tooth.
The hardest substance in the body. Resistant to
chipping and relatively resistant to decay; however,
it can be dissolved by acid produced by bacteria in
the mouth
dentine – bone-like. Contains channels of living
cytoplasm from cells in the pulp cavity
crown
pulp cavity – composed of living cells
blood vessels
gum
jawbone
nerves
cement – bone-like. Covers the root
of the tooth
periodontal membrane – contains fibres which are
embedded in the cement at one end and the jawbone
at the other end
root
Figure 3.10 Internal structure of a canine tooth
Table 3.9 Functions of the main parts of a tooth
Structure
Functions
Enamel
Protects the tooth against decay. Insulates the tooth against hot and cold foods.
Provides a hard surface for chewing.
Dentine
Forms the bulk of the tooth. Supports the enamel. Protects the pulp.
Pulp cavity Blood vessels supply living cells of the tooth with food and oxygen, and remove
carbon dioxide and other waste.
Nerves are sensitive to pain, hot and cold.
Cement
Covers the dentine in the root of the tooth.
Periodontal Anchors the root of the tooth in the jawbone. Allows slight movement for shock
membrane absorption.
Tooth decay
(dental caries)
Tooth decay occurs
when bacteria, saliva
and food particles
in the mouth form a
sticky layer on teeth
and gums called
plaque. Bacteria in
the plaque feed on
sugars in food and
make acid, which eats
away at teeth.
1 Acid in plaque
slowly eats away
the hard enamel.
2 Acid eats away
3 The decay continues 4 The infection spreads
the softer dentine
and the cavity
and reaches a root
more quickly forming reaches the pulp.
causing an abscess
a hole or cavity.
Bacteria enter the
to form.
pulp causing infection.
enamel
dentine
pulp
No toothache
abscess
Some toothache
Severe toothache
Agony
Figure 3.11 The process of tooth decay
3 Nutrition
29
Causes of tooth decay
Tooth decay is made more likely by:
• Eating foods with a high sugar or starch content, and drinking drinks with a high sugar or acid
content, e.g. fruit juices.
• Poor oral hygiene practices, e.g. not brushing properly, not brushing and flossing regularly, and not
visiting the dentist regularly.
• Not getting enough fluoride.
• Grinding the teeth.
• Smoking.
Guidelines for the care of teeth
• Brush teeth and gums in the proper way, twice a day.
• Use a fluoride toothpaste and good quality toothbrush when brushing.
• Use dental floss and an interdental brush once a day.
• Use an antibacterial mouthwash after brushing and flossing.
• Avoid eating sugary and starchy foods and drinking sugary drinks, especially between meals and
before going to bed.
• Visit a dentist regularly for a checkup and cleaning.
The chemical digestion of food
During chemical digestion the large food molecules are broken down into small molecules by
hydrolysis. During hydrolysis, the bonds within the large food molecules are broken down by the
addition of water molecules. Chemical digestion is catalysed (speeded up) by digestive enzymes
(see Table 3.10, page 32).
Enzymes
Enzymes are biological catalysts produced by all living cells. They speed up chemical reactions
occurring in living organisms without being changed themselves.
Enzymes are proteins that living cells produce from amino acids obtained from the diet. Without
enzymes, chemical reactions would occur too slowly to maintain life.
Examples
• Amylase catalyses the breakdown of starch into sugars, mainly maltose. It is present in saliva and
pancreatic juice.
starch amylase maltose
• Catalase catalyses the breakdown of hydrogen peroxide into water and oxygen:
hydrogen peroxide catalase
water + oxygen
Catalase is found in most cells. It prevents the build-up of harmful hydrogen peroxide, which is
produced as a by-product of many chemical reactions occurring in cells.
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3 Concise Revision Course: Human and Social Biology
Properties of enzymes
All enzymes have similar properties:
• Enzymes are specific, i.e. each type of enzyme catalyses only one type of reaction.
• Enzymes work best at a particular temperature known as the optimum temperature. This is about
37 oC for human enzymes.
as temperature increases, the rate
of enzyme activity increases
optimum temperature
noitcaer fo etar
0
as temperature increases,
the rate of enzyme activity
rapidly decreases
10
20 30 40 50
temperature (°C)
60
Figure 3.12 The effect of temperature on the rate of a
reaction catalysed by enzymes
• High temperatures denature enzymes, i.e. the shape of the enzyme molecules changes so that they
are inactivated. Enzymes start to be denatured at about 40 oC to 45 oC.
• Enzymes work best at a particular pH known as the optimum pH. This is about pH 7 for
most enzymes.
as acidity increases,
the rate of enzyme
activity decreases
optimum pH
noitcaer fo etar
as alkalinity increases,
the rate of enzyme
activity decreases
0
increasing
acidity
7
pH
increasing
alkalinity
14
Figure 3.13 The effect of pH on the rate of a reaction
catalysed by enzymes
• Extremes of acidity or alkalinity denature most enzymes.
• The action of enzymes is helped by certain vitamins and minerals, e.g. vitamin B1 helps the action of
respiratory enzymes.
• The action of enzymes is inhibited by certain poisons, e.g. arsenic and cyanide.
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3 Nutrition
Digestive enzymes
There are three categories of digestive enzymes and several different enzymes may belong to each
category (see Tables 3.10 and 3.11).
Table 3.10 Categories of digestive enzymes
Category of digestive enzyme Food molecules hydrolysed
Products of hydrolysis
Carbohydrases
Polysaccharides and disaccharides Monosaccharides
Proteases
Proteins
Amino acids
Lipases
Lipids
Fatty acids and glycerol
The digestive system and chemical digestion
The process of chemical digestion is summarised in Table 3.11.
nasal cavity
mouth – digestion
of starch
begins
salivary gland –
produces saliva
pharynx (throat)
teeth – used in
mechanical
digestion
tongue
salivary glands
trachea
epiglottis – closes over the
trachea during swallowing
oesophagus – transports
food to the stomach
diaphragm
stomach – produces
gastric juice. Digestion
of proteins begins
liver –
produces bile
pyloric sphincter – a muscle which
relaxes periodically to release
food from the stomach
gall bladder –
stores bile
pancreas – produces
pancreatic juice
bile duct
pancreatic duct
no
function
in
humans
duodenum
ileum
caecum
appendix
anal sphincter – a
muscle which relaxes
during egestion
anus
small intestine – receives
bile and pancreatic juice.
Produces intestinal juice.
Digestion of starch,
maltose, sucrose, lactose,
lipids, proteins and
peptides is completed.
Products of digestion
are absorbed
colon – absorbs water and mineral salts
rectum – stores faeces
for egestion
Figure 3.14 The structures of the human digestive system and their functions
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3 Concise Revision Course: Human and Social Biology
Table 3.11 A summary of chemical digestion
Organ
Digestive juice Source
Main
components
Mouth
Saliva
Salivary
• Water and
mucus
(pH 7–8)
glands.
Functions of the components
• Moisten and lubricate the
food allowing tasting and easy
swallowing.
• Salivary
• Begins to digest:
amylase*
starch
maltose
(a disaccharide)
Stomach
Gastric juice Cells in the • Hydrochloric • Maintains an optimum pH of 1–2
acid
for pepsin and rennin, and kills
(pH 1–2)
stomach
bacteria.
wall.
• Rennin*
• Produced in infants to clot
soluble protein in milk so
the protein is retained in the
stomach.
• Pepsin*
• Begins to digest:
protein
peptides (shorter
chains of amino acids)
Small intestine Bile
Cells in
• Bile
• Excretory products from the
pigments,
breakdown of haemoglobin in
(duodenum (pH 7–8)
the liver. It
e.g. bilirubin the liver. Have no function in
and ileum)
is stored
digestion.
in the gall
bladder and • Organic bile • Emulsify lipids, i.e. break large
salts
lipid droplets into smaller
enters the
droplets increasing their surface
duodenum
area for digestion.
via the bile
duct.
Pancreatic
Cells in the • Pancreatic
• Continues to digest:
starch
maltose
juice
pancreas. It amylase*
(pH 7–8)
enters the • Trypsin*
• Continues to digest:
duodenum
protein
peptides
via the
• Pancreatic
• Digests:
pancreatic
lipase*
lipids
fatty acids and glycerol
duct.
Intestinal
Cells in the • Maltase*
• Digests:
maltose
glucose
juice
walls of
(pH 7–8)
the small • Sucrase*
• Digests:
intestine.
sucrose
glucose and fructose
• Lactase*
• Digests:
lactose
glucose and galactose
• Peptidase*
• Digests:
(erepsin)
peptides
amino acids
* digestive enzymes
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Movement of food through the alimentary canal
circular muscles – in the walls of the
oesophagus and intestines
Food is moved through the oesophagus and the rest
of the alimentary canal by a process known as peristalsis.
circular muscles contract behind the
bolus, squeezing it along
Absorption
Absorption is the process by which the soluble food
molecules, produced in digestion, move into the body
fluids and body cells. Absorption occurs in the small
intestine and colon.
Absorption in the small intestine
bolus of food
circular muscles relax around and
in front of the bolus
Figure 3.15 The mechanism of peristalsis
The products of digestion are absorbed through the lining of the small intestine, mainly the ileum,
and into the blood capillaries and lacteals (lymph capillaries) in its walls. Substances absorbed include
monosaccharides, amino acids, fatty acids, glycerol, vitamins, minerals and water. Water is absorbed
by osmosis; the other substances are absorbed by both diffusion and active transport (see pages 6
and 8).
The ileum is very long, about 5 m in an adult, and its inner surface has thousands of finger-like
projections called villi (singular villus); both features help to give it a very large surface area for
absorption. The wall of each villus, known as the epithelium, is only one cell thick and the epithelial
cells have tiny projections called microvilli. Each villus has a network of blood capillaries and a lacteal
(lymph capillary) inside.
microvilli – increase the
surface area of each
villus for rapid absorption
goblet cell –
secretes mucus
epithelial cell
arteriole from the
mesenteric artery
epithelium – one cell thick so food
molecules can pass rapidly through
into the capillaries and lacteal
blood capillaries – form an extensive network
to rapidly absorb the products of digestion
lacteal or lymph capillary – leads into a lymphatic
vessel and provides a means of absorbing fatty
substances
venule to the hepatic
portal vein – takes water-soluble
substances to the liver
lymphatic vessel – takes fatty
substances to the blood before
it enters the heart
Figure 3.16 Structure of a villus showing its adaptations for absorption
• Water-soluble substances, i.e. monosaccharides, amino acids, minerals, vitamins B and C, and some
water are absorbed into the blood in the capillaries.
• Fatty substances, i.e. fatty acids, glycerol, and vitamins A and D are absorbed into the lymph in the
lacteals.
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3 Concise Revision Course: Human and Social Biology
Absorption in the colon
Any food that is not digested in the small intestine passes into the colon where water and mineral
salts are absorbed from it. As this undigested waste moves along the colon to the rectum it becomes
progressively more solid as the water is absorbed.
Egestion
Egestion is the process by which undigested food material is removed from the body.
The almost solid material entering the rectum is called faeces and consists of undigested dietary
fibre, dead bacteria and intestinal cells, mucus and bile pigments. Faeces is stored in the rectum and
egested at intervals through the anus when the anal sphincter relaxes.
Egestion must not be confused with excretion which is the removal, from the body, of waste and
harmful substances produced by the body’s metabolism. Other than the bile pigments, the
components of faeces are not produced by the body’s metabolism, so their removal cannot be
classed as excretion.
Assimilation
Assimilation is the process by which the body uses the soluble food molecules absorbed
after digestion.
Monosaccharides
Monosaccharides are taken by the blood to the liver in the hepatic portal vein and the liver converts
any non-glucose monosaccharides to glucose. The glucose then enters the general circulation where:
• It is used by all body cells in respiration to release energy.
• Excess is condensed to glycogen by cells in the liver and muscles. These cells then store the
glycogen, or
• Excess is converted to fat by cells in the liver and adipose (fat) tissue found under the skin and
around organs. Fat made in adipose tissue is stored, and fat made in the liver is transported by the
blood to adipose tissue and stored.
Amino acids
Amino acids are taken by the blood to the liver in the hepatic portal vein. They then enter the general
circulation where:
• They are used by body cells to make proteins that are used for cell growth and repair.
• They are used by body cells to make enzymes.
• They are used by cells of endocrine glands to make hormones.
• They are used to make antibodies.
• Excess are deaminated by the liver because they cannot be stored. The nitrogen-containing amine
groups (NH2) are removed from the molecules and converted to urea (CO(NH2)2). The urea enters
the blood and is excreted by the kidneys. The remaining parts of the molecules are converted to
glucose which is used in respiration, or are converted to glycogen or fat and stored.
3 Nutrition
35
Fatty acids and glycerol
Fatty acids and glycerol are carried by the lymph to the general circulation where:
• They are used to make cell membranes of newly forming cells.
• They are used by body cells in respiration under some circumstances.
• Excess are converted to fat and stored in adipose tissue under the skin and around organs.
Revision questions
133 Describe what happens during:
a mechanical digestion b chemical digestion.
144 Why are teeth important in the digestive process?
155 Joyann has FOUR types of teeth in her mouth. Identify these and state the function
16
17
188
199
200
21
222
233
36
of EACH.
By means of a fully labelled and annotated diagram only, describe the internal
structure of a canine tooth.
Matthew develops a cavity in one of his teeth. Outline how this cavity formed and
suggest FOUR things he should do to prevent cavities forming in his other teeth.
What are enzymes?
a Outline the effect that temperature has on enzyme activity.
b Other than the effect of temperature on enzyme activity, give THREE other
properties of enzymes.
Sate the function of EACH of the following parts of the digestive system in the
digestive process.
a the oesophagus
b the liver
c the colon
d the rectum
For lunch, Beth consumes a ham sandwich made with two slices of buttered bread
and two slices of ham. Describe how this sandwich is digested as it passes through
Beth’s digestive system.
Explain how the structure of each villus in Beth’s ileum is adapted to absorb the
products of the digestion of her meal.
What use does the body make of any amino acids produced during digestion?
3 Concise Revision Course: Human and Social Biology
4 The respiratory system
All living organisms need energy to carry out life processes in order to survive. They obtain this
energy from food when the food is respired. Humans respire aerobically and their respiratory system is
responsible for taking in the oxygen they need to sustain this respiration and to constantly get rid of
the carbon dioxide they produce.
Breathing and gaseous exchange
Breathing refers to the movements that cause air to be moved into and out of the lungs. Breathing
must not be confused with respiration, which is the process by which energy is released from food by
all living cells (see page 43).
Gaseous exchange is the process by which oxygen diffuses into the blood and carbon dioxide diffuses
out of the blood through a gaseous exchange surface (see below).
Humans respire aerobically, meaning that they release energy from food using oxygen. Aerobic respiration
produces carbon dioxide as a waste product. Breathing and gaseous exchange are essential because:
• They ensure that humans have a continual supply of oxygen to meet the demands of aerobic respiration.
• They ensure that the carbon dioxide produced in aerobic respiration is continually removed so that it
does not build up and poison cells.
Gaseous exchange surfaces
In many animals, including humans, the surface through which gases are exchanged, known as the
gaseous exchange surface, forms part of the respiratory system. These surfaces have several adaptations
which make the exchange of gases through them as efficient as possible:
• They have a large surface area so that large quantities of gases can be exchanged.
• They are very thin so that gases can diffuse through them rapidly.
• They have a rich blood supply to quickly transport gases between the surface and the body cells.
• They are moist so that gases can dissolve before they diffuse through the surface.
Structure of the human respiratory system
In humans, the gaseous exchange surface is found in the lungs which make up part of the respiratory
system. Humans have two lungs composed of thousands of air passages called bronchioles and millions
of swollen air sacs called alveoli. Each lung is surrounded by two pleural membranes which have pleural
fluid between them. A single bronchus leads into each lung from the trachea. The larynx forms the top
part of the trachea and the nasal
cavities and the mouth lead into
nasal cavity – hollow space lined with
the pharynx or throat, which
cilia (microscopic hairs) and mucus
leads into the larynx.
pharynx or throat
Each lung receives blood from
the heart via a pulmonary artery nose
epiglottis – thin flap of cartilage behind
and blood is carried back to the upper lip
the tongue at the top of the larynx
heart via a pulmonary vein. The
two lungs are surrounded by
larynx or voice box – contains vocal cords
teeth
the ribs which form the chest
cavity or thorax. The ribs have
trachea
tongue
intercostal muscles between and
oesophagus
a dome-shaped sheet of muscle,
the diaphragm, stretches across
the floor of the thorax.
Figure 4.1 Structure of upper part of the human respiratory system
4 The respiratory system
37
larynx
trachea – hollow tube
with rings of cartilage
in its walls. Lined with
cilia and mucus
external inercostal
muscles
between the ribs
internal inercostal
muscles
left lung
left bronchus –
hollow tube with
rings of cartilage
in its walls. Lined with
cilia and mucus
heart
bronchioles – hollow
tubes branching
throughout the lung.
Lined with moisture
pleural cavity – airtight
cavity filled
with pleural fluid
pleural membranes –
one surrounds the
outside of the lung,
one lines the rib cage
and diaphragm
cut end of a rib
ribs
diaphragm –
a muscular sheet
magnified cluster
of alveoli at the
end of a bronchiole
Figure 4.2 Structure of the human thorax
capillary from the
pulmonary artery –
carries deoxygenated
blood
alveoli – thin-walled.
Provide a large surface
area for gaseous
exchange
capillary to the
pulmonary vein –
carries oxygenated
blood
bronchiole
network of capillaries –
surrounds the alveoli
Figure 4.3 Surface view of a cluster of alveoli showing the blood supply
Table 4.1 Summary of the functions of the main parts of the respiratory system
Structure
Functions
Nasal cavities
Warm the inhaled air. Mucus traps dust and pathogens in the inhaled air and
moistens the air. Cilia move the mucus to the throat to be swallowed.
Epiglottis
Prevents food from entering the trachea when swallowing.
Larynx
Vocal cords produce the sounds of speech.
Trachea and bronchi Carry air into and out of the lungs. Rings of cartilage in their walls keep
them open.
Bronchioles
Carry air to and from the alveoli.
Alveoli
Exchange oxygen and carbon dioxide between inhaled air and blood in the
capillaries.
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4 Concise Revision Course: Human and Social Biology
Structure
Pleural membranes
and pleural fluid
Intercostal muscles
and diaphragm
Functions
Form an airtight cavity between the lungs and the rib-cage and diaphragm so
that any changes in volume of the chest cavity causes the volume inside the
lungs to change. Pleural fluid also acts as a lubricant during breathing.
Contract and relax to change the volume inside the chest cavity and lungs,
which causes air to move into and out of the lungs.
The mechanism of breathing and gaseous exchange
Breathing is brought about two sets of muscles, the intercostal muscles and the diaphragm.
Table 4.2 The mechanism of breathing
Features
Inhalation (inspiration)
Exhalation (expiration)
4
4
1
3
1
3
2
2
External intercostal muscles
Contract
Relax
Internal intercostal muscles
Relax
Contract
Ribs and sternum
Move upwards and outwards Move downwards and inwards
2 Diaphragm muscles
Contract
Relax
Diaphragm
Moves downwards or flattens Domes upwards
3 Volume inside thorax and lungs Increases
Decreases
Pressure inside thorax and lungs Decreases
Increases
4 Movement of air
Air is drawn into the lungs due Air is pushed out of the lungs
to the decrease in pressure
due to the increase in pressure
1
As the air is drawn in during inhalation it is warmed in the nasal passages, and cleaned and moistened
by mucus lining the nasal passages and trachea. The air passes through the bronchi and bronchioles
and enters the alveoli where gaseous exchange occurs between the air and the blood in the capillaries.
The walls of the alveoli form the gaseous exchange surface. Each alveolus:
• Has a pocket shape. A human has two lungs, each containing over 350 million alveoli, giving a very
large total surface area of about 90 m2.
• Has a very thin wall that is only one cell thick.
• Is surrounded by a network of capillaries giving it a rich blood supply.
• Is lined with moisture.
4 The respiratory system
39
exhaled air −
16% O2, 4.0% CO2
deoxygenated blood −
low oxygen content,
high carbon dioxide
content. Plasma and
red blood cells transport
carbon dioxide from
body cells
inhaled air −
21% O2, 0.04% CO2
oxygenated blood −
high oxygen content,
low carbon dioxide
content. Red blood cells
transport oxygen to body cells
carbon dioxide
diffuses out of
the plasma and
red blood cells
oxygen
dissolves
in moisture
lining the alveolus
and diffuses into
red blood cells
layer of moisture
lining the alveolus
red blood cell
wall of the capillary −
one cell thick
wall of the alveolus −
one cell thick
Figure 4.4 Gaseous exchange in an alveolus
Factors affecting the breathing rate
The normal breathing rate for a healthy adult at rest ranges from 12 to 16 breaths per minute. The
medulla of the brain (see page 69) controls the breathing rate by detecting the level of carbon dioxide
in the blood and sending impulses to the intercostal muscles and diaphragm.
• Any factor that increases the rate of respiration in body cells will cause the level of carbon dioxide
in the blood to increase. If carbon dioxide levels increase, breathing rate increases to remove the
excess carbon dioxide. Factors that increase breathing rate include:
Carrying out exercise.
Taking drugs that are stimulants, e.g. caffeine, amphetamines, cocaine.
Smoking cigarettes.
Suffering from anxiety or fear.
Being exposed to certain environmental factors, e.g. being in a confined space or in polluted air.
Being at high altitude.
Being overweight.
• Any factor that decreases the rate of respiration in body cells will cause the level of carbon dioxide
in the blood to decrease. If carbon dioxide levels decrease, breathing rate decreases. Factors that
decrease breathing rate include:
When resting or asleep.
Taking drugs that are depressants, e.g. sedatives, sleeping pills, alcohol.
Being exposed to certain environmental factors, e.g. being in fresh, unpolluted air.
Vital capacity
Vital capacity is the maximum volume of air that can be exhaled from the lungs after inhaling as
deeply as possible.
Measuring vital capacity can be used to indicate lung function and if a person is suffering from lung
disease. Vital capacity depends on age, gender, body size and fitness. It can be increased by regular
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4 Concise Revision Course: Human and Social Biology
exercise and is decreased by smoking, obesity or respiratory disease. Other volumes and capacities
associated with the lungs are shown in Figure 4.5.
6
5
)3md( emulov
4
3
vital capacity
tidal volume –
volume of air
inhaled and exhaled
in a single
normal breath
total lung
capacity –
volume of air
in the lungs
after maximum
inhalation
2
residual volume –
volume of air
remaining in the
lungs after
forceful exhalation
1
NB 1 dm3 = 1 litre
Figure 4.5 Lung capacities and volumes
Mouth-to-mouth resuscitation (rescue breathing)
Mouth-to-mouth resuscitation is a technique used to supply oxygen to a person who has stopped
breathing. The rescuer forces his or her exhaled air, which contains about 16% oxygen, into the
victim’s lungs every few seconds, allowing for passive exhalation between. To perform mouth-tomouth resuscitation:
• Lie the victim on his or her back.
• Gently tilt the victim’s head backwards to open the airways by lifting the chin.
• Open the victim’s mouth and remove any debris.
• Pinch the victim’s nostrils to close them and
breathe in.
• Seal your lips over the victim’s open mouth and
breathe out into the mouth for 1 second.
• If the victim’s chest rises, breathe into the
mouth a second time.
• Continue rescue breathing by giving one breath
every 5 seconds until normal breathing resumes
or medical help arrives.
The
effects
of
smoking
cigarettes
When smoking cigarettes made from tobacco,
smoke containing over 4000 thousand different
chemicals including nicotine, tar and carbon
monoxide is inhaled into the respiratory system.
Cigarette smoking poses serious health risks
including the following.
Figure 4.6 Some components of cigarette smoke
41
4 The respiratory system
Nicotine addiction
Nicotine is an addictive substance that causes smokers to continue to smoke and makes it extremely
difficult for them to stop. Addicted smokers need enough nicotine during each day to ‘feel normal’.
Reduced oxygen carrying capacity of the blood
Carbon monoxide combines more readily with haemoglobin than oxygen does, which reduces the
amount of oxygen carried to body cells. This reduces respiration and the smoker’s ability to exercise.
In a pregnant woman it deprives the foetus of oxygen, reducing its growth and development.
Lung damage
Cigarette smoke damages lungs:
• It causes mucus production to increase and it paralyses the cilia, which stops them from beating
so the mucus is not removed. The person then develops a persistent cough to try and remove
the mucus.
• It irritates and inflames the walls of the bronchi and bronchioles. This, together with the increased
mucus production and paralysis of the cilia, causes the airways to become obstructed, making
breathing difficult, and leads to chronic bronchitis.
• It causes the walls of the alveoli to become less elastic and the walls between the alveoli to break
down, which decreases their surface area. This reduces gaseous exchange, makes exhaling difficult
and causes air to remain trapped in the lungs, a condition known as emphysema. The bronchioles
often collapse when exhaling, obstructing the airways, making exhaling even harder.
Chronic bronchitis
healthy
healthy
inflammation and
excess mucus
Emphysema
alveolar
membranes
break down
Figure 4.7 Chronic obstructive pulmonary disease (COPD)
Cancer of the mouth, throat, oesophagus or lungs
Some components of tar and many other chemicals in cigarette smoke are carcinogenic. These cause
mutations in cells in different regions of the respiratory system. This leads to the development of
cancerous tumours which replace normal, healthy tissue in these regions.
Note that chronic bronchitis and emphysema are two types of chronic obstructive pulmonary disease
or COPD.
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4 Concise Revision Course: Human and Social Biology
Respiration
Respiration is the process by which energy is released from food by all living cells.
Respiration is catalysed by enzymes and occurs slowly in a large number of stages:
• Most of the energy released at each stage is used to build energy carrying molecules called
adenosine triphosphate or ATP. An ATP molecule is formed by combining some of the energy
released with an adenosine diphosphate or ADP molecule and a phosphate group present in the cell.
The energy can then be re-released where ever it is needed in the cell by the reverse reaction:
ADP + phosphate + energy
ATP
ATP is known as the ‘energy currency’ of cells. Cells earn ATP as a result of energy-producing
reacons, and spend it on reacons requiring energy. Energy released by ATP is used by cells:
To manufacture complex, biologically important molecules, e.g. proteins, DNA.
For cell growth and repair.
For cell division.
In active transport to move molecules and ions in and out of the cells through their membranes.
For special functions in specialised cells, e.g. contraction of muscle cells, transmission of
impulses in nerve cells.
• Some of the energy is released as heat and this helps to maintain the body temperature at 37 °C.
There are two types of respiration:
• aerobic respiration
• anaerobic respiration.
Aerobic respiration
Aerobic respiration is the process by which energy is released from food by living cells using oxygen.
Aerobic respiration occurs in most cells. It uses oxygen and takes place in the mitochondria. It always
produces carbon dioxide, water and about 38 ATP molecules per molecule of glucose.
enzymes in carbon dioxide + water + energy
glucose + oxygen mitochondria
Anaerobic respiration
Anaerobic respiration is the process by which energy is released from food by living cells without the
use of oxygen.
Anaerobic respiration occurs in some cells. It takes place without oxygen in the cytoplasm of the cells.
The products of anaerobic respiration vary and it produces considerably less energy per molecule of
glucose than aerobic respiration. Yeast cells, certain bacteria and muscle cells are capable of carrying
out anaerobic respiration.
4 The respiratory system
43
Industrial and domestic uses of anaerobic respiration
Making bread and alcoholic beverages
Yeast cells carry out anaerobic respiration known as fermentation. It produces ethanol, carbon dioxide
and 2 ATP molecules per molecule of glucose.
in ethanol + carbon dioxide + energy
glucose enzymes
cytoplasm
When making bread, the yeast ferments sugars present in dough. The carbon dioxide produced forms
bubbles in the dough which cause it to rise. When baked, heat from the oven causes the bubbles to
expand, kills the yeast and evaporates the ethanol.
When making alcoholic beverages such as beer, wine, rum and other spirits, the yeast ferments sugars
present in grains, fruits or molasses. Fermentation stops when the ethanol concentration reaches
about 14–16% because it kills yeast cells, so the ethanol content of beer and wine is always below
about 16%. Spirits are made by distillation of the fermentation mixture.
Making yoghurt
Certain bacteria, e.g. Lactobacillus, ferment the lactose in milk forming lactic acid. The lactic acid
makes the milk proteins curdle, which forms thick yoghurt and gives the yoghurt its sour taste.
Producing biogas
Certain bacteria are used to break down organic matter, e.g. manure and garden waste, anaerobically
in an anaerobic digester. This produces biogas which is a mixture of approximately 60% methane (CH4),
40% carbon dioxide and traces of other gases, e.g. hydrogen sulfide (H2S). Biogas can be used as a fuel
for cooking, heating and to generate electricity.
Oxygen debt
Muscle cells can carry out anaerobic respiration during strenuous exercise. During strenuous exercise,
if oxygen cannot be delivered to the muscle cells quickly enough for the demands of aerobic
respiration, the cells begin to respire anaerobically. This produces lactic acid and 2 ATP molecules per
molecule of glucose.
in lactic acid + energy
glucose enzymes
cytoplasm
Lactic acid builds up in the muscle cells and begins to harm them, causing fatigue and eventually
collapse as they stop contracting. The muscle cells are said to have built up an oxygen debt. This debt
must be repaid directly after exercise by resting and breathing deeply so that the lactic acid can be
removed by respiring it aerobically.
Revision questions
1 What is meant by the term ‘breathing’ and why is breathing important to humans?
2 State the function of EACH of the following structures found in the
3
44
respiratory system:
a the nasal cavities
b the bronchi
c the bronchioles
Identify the gaseous exchange surface in a human and explain FOUR ways in which
the surface is adapted to perform its function efficiently.
4 Concise Revision Course: Human and Social Biology
4 Explain the mechanism by which air is drawn into the lungs.
5 Give FOUR factors that can increase the breathing rate and TWO factors that can
decrease it.
6 a What is meant by the term ‘vital capacity’?
b Why is it important to measure a person’s vital capacity?
7 Your friend, Kendra, suddenly collapses and stops breathing. Outline the steps you
would take to perform mouth-to-mouth resuscitation on Kendra.
8 a Name the THREE main components of cigarette smoke.
b Outline how smoking cigarettes damages the lungs.
9 Distinguish between aerobic and anaerobic respiration and write ONE word equation
to summarise EACH process.
100 What is ATP and what is its role in body cells?
111 Ché carried out strenuous exercise for an extended period of time and eventually
collapsed and found he had to rest before resuming any exercise. Explain why he
collapsed and why he had to rest before he could exercise again.
4 The respiratory system
45
5 The circulatory system
Humans need to constantly exchange substances with their environment. They need to take in
useful substances and get rid of waste. The circulatory system provides a means of transporting these
substances between the surfaces where they are exchanged and the body cells. The circulatory
system is composed of the cardiovascular system and the lymphatic system.
The need for a transport system in the human body
The absorption and transport of substances in humans is affected by two factors:
• Their surface area to volume ratio.
• The limitations of simple diffusion.
Humans have a small surface area to volume ratio. Diffusion through their body surface is not
adequate to supply all their body cells with their requirements and remove their waste. In addition,
most of their body is too far from its surface for substances to move through it by simple diffusion.
Humans have, therefore, developed a transport system to carry useful substances from specialised
organs that absorb them, e.g. the lungs and ileum, to body cells, and to carry waste substances from
body cells to specialised organs that excrete them, e.g. the kidneys and lungs.
Materials transported around the human body
The following materials are transported around the human body:
• Useful substances: oxygen, water, digested food (mainly glucose and amino acids), vitamins,
minerals, hormones, antibodies and plasma proteins. Heat is also carried.
• Waste substances: carbon dioxide and nitrogenous waste, e.g. urea.
The cardiovascular system
The cardiovascular system consists of:
• Blood, which serves as the medium to transport substances around the body.
• Blood vessels, which are tubes through which the blood flows to and from all parts of the body.
• The heart, which pumps the blood through the blood vessels.
Blood
Blood is composed of three types of cells:
• red blood cells
• white blood cells
• platelets
These cells are suspended in a fluid called plasma. The
cells make up about 45% by volume of the blood and the
plasma makes up about 55%.
Figure 5.1 Red blood cells
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5 Concise Revision Course: Human and Social Biology
Composition of plasma
Plasma is a yellowish fluid composed of about 90% water and 10% dissolved substances. The dissolved
substances consist of:
• Products of digestion, e.g. glucose, amino acids, vitamins and minerals.
• Waste products, e.g. dissolved carbon dioxide and urea.
• Hormones, e.g. insulin and thyroxine.
• Plasma proteins, e.g. fibrinogen, prothrombin, albumen and antibodies.
Functions of plasma
The main function of plasma is transporting the following:
• Products of digestion, from the ileum to the liver and the body cells.
• Carbon dioxide, from body cells to the lungs.
• Urea, from the liver to the kidneys.
• Hormones, from the glands that produce them (endocrine glands) to target organs.
• Heat, from the liver and muscles to all parts of the body.
Serum
Serum is plasma without fibrinogen and other factors needed for the blood to clot (see page 48).
Serum is the part of the blood that is left over after red and white blood cells, platelets and clotting
factors have been removed.
serum = plasma – clotting factors
Blood cells
Table 5.1 Structure and functions of blood cells
Cell type and structure
Formation of cells
Functions
Red blood cells (erythrocytes)
• Formed in the red
• Transport oxygen as
oxyhaemoglobin from
bone marrow found
in flat bones, e.g. the the lungs to body cells.
cell
membrane
pelvis, scapula, ribs, • Transport small
sternum, cranium and amounts of carbon
vertebrae; and in the
dioxide from body cells
ends of long bones,
e.g. the humerus and to the lungs.
femur.
cytoplasm
cy
rich in hhaemoglobin,
• Broken down mainly
an iron-containing
iron-co
protein
in the liver and
spleen.
• Biconcave discs with a thin centre and
relatively large surface area to volume
ratio so gases easily diffuse in and out.
• Have no nucleus, therefore they only live
for about 3 to 4 months.
• Contain the red pigment haemoglobin.
• Slightly elastic allowing them to squeeze
through the narrowest capillaries.
5 The circulatory system
47
Cell type and structure
Formation of cells
Functions
White blood cells (leucocytes)
Slightly larger than red blood cells and less
numerous; approximately 1 white blood cell
to 600 red blood cells. There are two main
types; 25% are lymphocytes and 75% are
phagocytes.
• Develop from cells • Produce antibodies to
Lymphocytes
in the red bone
destroy disease-causing
marrow and mature
bacteria and viruses
cell membrane
in other organs, e.g.
(pathogens).
lymph nodes, spleen, • Produce antitoxins
large, round nucleus
thymus gland.
to neutralise toxins
non-granular cytoplasm
produced by pathogens.
• Have a rounded shape.
• Have a large, round nucleus that controls
the production of antibodies.
• Have only a small amount of cytoplasm.
• Formed in the red
Phagocytes
• Engulf and destroy
bone marrow.
pathogens.
cell membrane
• Engulf pathogens
destroyed by
lobed nucleus
antibodies.
granular cytoplasm
• Have a variable shape.
• Move by pseudopodia; can move out of
capillaries through their walls and engulf
pathogens using pseudopodia.
• Have a lobed nucleus.
Platelets (thrombocytes)
cell membrane
• Formed from cells in • Help the blood to clot
the red bone marrow. at a cut or wound (see
Blood clotting, below).
cytoplasm
• Cell fragments.
• Have no nucleus and only live for about
10 days.
Blood clotting
When the skin is cut and bleeds, the blood quickly clots. The following events occur to form the clot:
• Platelets in the blood at the cut become spiky in shape, stick to each other and begin to plug the
cut. They also release an enzyme called thrombokinase or thromboplastin.
• Thrombokinase, with the help of calcium ions (Ca2+) and vitamin K in the blood, converts the
inactive plasma protein, prothrombin, into active thrombin.
• Thrombin converts the soluble plasma protein, fibrinogen, into insoluble fibrin which forms fibres.
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5 Concise Revision Course: Human and Social Biology
• The fibrin fibres form a network across the cut, which
traps blood cells and forms a clot.
• The clot dries and develops into a scab. New skin forms
below the scab and the scab drops off.
Clotting is important because:
• The clot prevents further blood loss.
• The clot prevents pathogens from entering the body.
Blood groups
Blood can be classified into different blood groups based
on chemicals present on the surface of red blood cells
Figure 5.2 Red blood cells and platelets
known as antigens. There are two grouping systems:
• The ABO system, which divides blood into four groups; trapped in a network of fibrin fibres
group A, group B, group AB and group O.
• The rhesus system, which divides blood into two groups; rhesus positive and rhesus negative.
Blood vessels
There are three main types of blood vessels:
• arteries
• capillaries
• veins
artery
direction of
blood flow
organ
arteriole –
small artery
heart
capillary
venule –
small vein
oxygenated blood
deoxygenated blood
vein
Figure 5.3 The relationship between the different blood vessels
5 The circulatory system
49
Arteries carry blood away from the heart. On entering an organ, an artery branches into smaller
arteries called arterioles which then branch into a network of capillaries which run throughout the
organ. Capillaries then join into small veins called venules which join to form a single vein which leads
back from the organ towards the heart.
Table 5.2 Arteries, capillaries and veins compared
Arteries
Capillaries
Veins
Transport blood away from
Transport blood throughout
Transport blood back towards
the heart to body tissues and all body tissues and organs,
the heart from body tissues and
organs.
linking arteries to veins.
organs.
Blood flows through under high Blood flows through under low Blood flows through under low
pressure.
pressure.
pressure.
Blood moves in pulses created Blood flows smoothly.
Blood flows smoothly.
as the ventricles contract.
Blood flows rapidly.
Blood flows very slowly.
Blood flows slowly.
Blood is oxygenated, except in Blood becomes deoxygenated as Blood is deoxygenated, except
the pulmonary arteries.
it travels through capillaries.
in the pulmonary veins.
Most lie deep within the body Run throughout all tissues and Many lie close to the body
so they are protected.
organs.
surface.
Do not possess valves, except Do not possess valves.
Possess valves to prevent the
the aorta and pulmonary artery
low pressure, slow flowing
as they leave the ventricles of
blood from flowing backwards.
the heart.
free-flowing
blood – valve
open
Have walls composed of three
layers. The walls are thick and
elastic to withstand the high
pressure of the blood.
fibrous layer – fairly
thick and elastic
muscle and elastic
layer – thick
endothelium – one
cell thick
lumen – narrow
The walls are composed of
a single layer of endothelial
cells so substances pass easily
between the blood and body
cells. They are extremely
narrow and branch repeatedly
so that all body cells are close
to capillaries.
endothelial
cell
lumen –
extremely narrow
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5 Concise Revision Course: Human and Social Biology
back-flowing
blood – valve
closed
Have walls composed of
three layers. The walls are thin
because they do not have
to withstand high pressure.
The lumen is wide so it does
not resist the flow of low
pressure blood.
fibrous layer – thin
and elastic
muscle and elastic
layer – thin
endothelium – one
cell thick
lumen – wide
The heart
The pumping action of the heart maintains a constant circulation of blood around the body. The
walls of the heart are composed of cardiac muscle which contracts without nerve impulses, i.e. it is
myogenic, and it does not get tired.
The heart is divided into four chambers. The two on the right contain deoxygenated blood and are
completely separated from the two on the left, which contain oxygenated blood, by the septum.
• The top two chambers, called atria, have thin walls and they collect blood entering the heart from
the anterior and posterior vena cavae and the pulmonary veins. Their walls are thin because they only
have to pump blood a short distance into the ventricles.
• The bottom two chambers, called ventricles, have thick walls and they pump blood out of the heart
via the pulmonary artery and aorta. Their walls are thick because they have to pump blood longer
distances around the body and to the lungs. The wall of the left ventricle is thicker than the wall of
the right ventricle because it has to pump blood longer distances (see Figure 5.4).
Valves are present between each atrium and ventricle and in the pulmonary artery and aorta as they
leave the ventricles to ensure that blood flows through the heart in one direction.
pulmonary artery – carries deoxygenated
blood to the lungs
aorta – carries oxygenated
blood to the body
anterior vena cava –
carries deoxygenated
blood from the head
left atrium – collects oxygenated
blood from the lungs
pulmonary veins – carry oxygenated
blood from the lungs
right atrium – collects
deoxygenated blood from
the head and body
semi-lunar valves – prevent the backflow
of blood into the ventricles when they relax
posterior vena cava –
carries deoxygenated
blood from the body
bicuspid valve or mitral valve – same function
as the tricuspid valve
tricuspid valve –
prevents the blood flowing
back into the atrium when
the ventricle contracts
tendons – prevent the valve turning
inside out
right ventricle – pumps
deoxygenated blood to
the lungs
cardiac muscle
left ventricle – thicker walled than
the right ventricle to pump
oxygenated blood longer
distances around the body
septum
deoxygenated blood
oxygenated blood
Figure 5.4 Longitudinal section through the human heart showing the function of the parts
The heart’s pacemaker (sinoatrial node)
A group of specialised cells in the wall of the right atrium, called the pacemaker or sinoatrial node,
spontaneously produce electrical impulses which travel through the heart muscle causing it to
contract about 75 times per minute. This rate can be modified by nerve impulses or the hormone
adrenaline, e.g. the rate increases during exercise or when nervous.
An artificial pacemaker is a small, battery-operated device that generates electrical impulses to
regulate heartbeat. It is implanted under the skin and connected to the heart via tiny wires and may
be used if the heartbeat is too slow, too fast or irregular, or if a person has suffered a heart attack
(see pages 121–22).
5 The circulatory system
51
Cardiac cycle
The atria and ventricles at the two sides of the heart contract and relax together. The contraction of a
chamber is called systole and its relaxation is called diastole. One cardiac cycle or heartbeat involves
the following:
• Diastole – the atria and ventricles relax together, the semi-lunar valves close, the atria fill up with
blood from the anterior and posterior vena cavae and pulmonary veins, and the blood flows into
the ventricles. This takes 0.4 seconds.
• Atrial systole – the atria contract together forcing any remaining blood through the tricuspid and
bicuspid valves into the ventricles. This takes 0.1 second.
• Ventricular systole – the ventricles contract together, the tricuspid and bicuspid valves close and blood
is forced through the semi-lunar valves into the aorta and pulmonary arteries. This takes 0.3 seconds.
Blood pressure
Blood pressure is the pressure of circulating blood on the walls of blood vessels. It is usually measured
in the large arteries in millimetres of mercury or mm Hg. It is expressed as:
blood pressure (mm Hg) = systolic pressure (highest pressure when the heart contracts)
diastolic pressure (lowest pressure when the heart relaxes)
Ideal blood pressure is between 90/60 mm Hg and 120/80 mm Hg. High blood pressure or hypertension
results if a person’s pressure rises to 140/90 mm Hg or above. This can be caused by a variety of
factors (see page 122).
Circulation
During one complete circulation around the body, the blood flows through the heart twice,
therefore, humans have a double circulation:
• In the pulmonary circulation, blood travels from the right ventricle through the pulmonary arteries to
the lungs to pick up oxygen and lose carbon dioxide, i.e. it becomes oxygenated. It then travels back
via the pulmonary veins to the left atrium.
• In the systemic (body) circulation, blood
travels from the left ventricle through
lungs
the aorta to the body where it gives
up oxygen to the body cells and picks
up carbon dioxide, i.e. it becomes
pulmonary artery
pulmonary vein
deoxygenated. It then travels back via
the anterior or posterior vena cava to the
right atrium.
right atrium
left atrium
A double circulation is necessary because
blood loses pressure when it passes
left ventricle
right ventricle
through the lungs, so it goes back to
aorta
the heart to be given enough pressure
vena cava
to reach body organs to supply them
with oxygen. As it loses pressure passing
through organs, the blood goes back
body
to the heart again to be given enough
deoxygenated blood
oxygenated blood
pressure to reach the lungs to get rid
of waste carbon dioxide and pick up
Figure 5.5 Double circulation in the human body
more oxygen.
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jugular vein
head
carotid artery
arms
anterior vena cava
lungs
pulmonary vein
pulmonary artery
aorta
posterior vena cava
heart
hepatic vein
liver
hepatic artery
hepatic portal vein
intestines
renal vein
mesenteric artery
kidneys
renal artery
legs
deoxygenated blood
oxygenated blood
Figure 5.6 The major blood vessels in the human body
Causes and effects of heart attacks
The main cause of a heart attack or myocardial infarction is atherosclerosis. This occurs when fatty
deposits containing cholesterol, known as atheromas, build up on the inside of the walls of the coronary
arteries that supply oxygenated blood to the heart muscle. The atheromas cause the lumens of the
arteries to narrow, and their walls to harden and become less elastic. A blood clot, known as a coronary
thrombosis, may then form in one of the narrow arteries (see Figure 12.2, page 122). This clot can partially
or completely block the blood flow through the artery and the section of the heart muscle supplied by
the artery cannot get oxygen so starts to die, and a heart attack occurs.
The risk of a heart attack is increased if a person has hypertension (high blood pressure) or is exposed
to risk factors that can lead to hypertension, including:
• Being overweight or obese.
• Smoking.
• Too much salt or too much fat in the diet.
• Consumption of too much alcohol.
5 The circulatory system
53
• Lack of physical exercise.
• Stress.
Symptoms of a heart attack include:
• Chest pain or discomfort as the chest feels as if it is being pressed or squeezed.
• Upper body pain or discomfort, e.g. in the arms, shoulders, neck, jaw or back.
• Shortness of breath.
• Feeling weak, lightheaded or dizzy.
In some cases the heart stops beating, known as cardiac arrest, and it can result in death.
The lymphatic system
The lymphatic system consists of:
• Lymph, which serves as the transporting medium.
• Lymph vessels or lymphatic vessels, which are tubes through which lymph flows.
Lymph vessels begin inside tissues. They have thin muscular walls, valves to prevent the backflow of
low pressure lymph and oval-shaped swellings along their length called lymph nodes or lymph glands.
Lymph nodes form clusters in various parts of the body, especially in the neck, armpits and groin.
Lymphocytes and phagocytes are numerous in lymph nodes.
Lymph is a colourless watery fluid that contains lymphocytes. It is formed in body tissues from tissue fluid
which is constantly being formed from plasma. Lymph rejoins the plasma in the subclavian veins from the
arms just before they join the anterior vena cava. Lymph flows in one direction from tissues towards the
heart and its flow is helped by the contraction of surrounding muscles, especially during exercise.
lymph capillary – walls
are one cell thick
2
arteriole
3
1
2
lymph vessels
1
3
3
2
2
body cells surrounded
by tissue fluid
1
1
venule
blood capillary
1 Plasma containing oxygen and
nutrients is forced out of blood
capillaries where they branch from
arterioles. This forms tissue fluid.
Blood cells and plasma proteins remain
in the blood. Body cells absorb the
oxygen and nutrients from the tissue
fluid and give out carbon dioxide
and other cellular waste.
2 Some tissue fluid containing carbon
dioxide and other waste flows back into
the blood capillaries before they join into
venules. This reforms plasma.
3 The remaining tissue fluid containing
carbon dioxide and other waste flows
into lymph capillaries and forms lymph
which flows into larger lymphatic vessels.
Figure 5.7 The formation of tissue fluid and lymph
Functions of the lymphatic system
Functions of lymph
• Lymph removes cellular waste and cell debris from around body cells.
• Lymph drains excess tissue fluid from tissues, which helps to prevent fluid from building up in them.
• Lymph helps maintain normal blood volume and pressure.
• Lymphocytes in lymph defend the body against pathogens.
• Lymph in the lacteals (lymph capillaries) in the ileum absorbs fatty products of digestion.
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Functions of lymph nodes
• Lymphocytes and phagocytes in lymph nodes help destroy pathogens in lymph.
• Lymph nodes filter dead cells and cancerous cells out of lymph.
• Lymph nodes release lymphocytes into lymph during times of infection.
Revision questions
1 a Explain why the human body needs a transport system.
b Name FOUR materials transported around the human body.
2 Explain the relationship between plasma and serum.
3 a By means of TWO labelled and annotated diagrams, give THREE differences
between the structure of a red blood cell and a phagocyte.
b State the function of EACH of the cells you have drawn in a above.
4 Explain how the loss of blood at a cut is prevented.
5 State THREE differences between the structure of an artery and a vein and provide a
reason for EACH difference.
6 Explain:
a How blood flow through the heart is maintained in one direction.
b Why the wall of the left ventricle of the heart is thicker than the wall of the right
ventricle.
c How the beating of the heart is controlled.
7 Distinguish between systole and diastole.
8 Explain to Naomi why humans need a double circulation.
9 Draw a simple flow diagram to show the pathway that a red blood cell takes as it
journeys from the lungs around the body and back to the lungs.
100 What happens during a heart attack and how is it caused?
11 Explain the relationship between blood plasma, tissue fluid and lymph.
122 Give FOUR functions of the lymphatic system.
5 The circulatory system
55
6 The skeletal system
Humans need to be able to move their entire bodies from place to place as well as parts of their
bodies. They also need to have a means of supporting and protecting the soft tissues and organs of
their bodies. These functions are all carried out by the skeletal system.
The human skeleton
The human skeleton is made
of 206 bones, which are held
cranium
together at joints by ligaments.
The skeleton is made from two
skull upper jaw
clavicle
types of connective tissue, bone
lower jaw
(collar bone)
and cartilage.
pectoral girdle
scapula
(shoulder blade)
• Bone makes up the bulk of the
sternum
skeleton. It is composed of
rib
(breast bone)
living cells surrounded by the
non-living mineral, calcium
humerus
vertebral
phosphate, together with
column
forelimb (arm)
ulna
some collagen (protein) fibres.
radius
Bone is hard and has blood
vessels running throughout.
• Cartilage is composed of living
carpals
cells surrounded mainly by
metacarpals
collagen fibres. It is more
thumb
elastic and flexible than bone
and does not have blood
phalanges
vessels running through it.
pelvic girdle
Cartilage is important because:
femur
patella
It covers the ends of
hindlimb tibia
(knee cap)
(leg)
bones at joints where
fibula
its slipperiness helps to
reduce friction and it aids in
shock absorption.
It forms the skeleton of
tarsals
certain fleshy appendages,
metatarsals
e.g. the nose and outer
ear, which maintains
phalanges
their shape.
big toe
It makes up the
intervertebral discs between Figure 6.1 The human skeleton
the vertebrae enabling the
discs to act as shock absorbers.
The skeleton can be divided into the axial skeleton and the appendicular skeleton.
The axial skeleton
The axial skeleton consists of the skull, vertebral column, ribs and sternum:
• The skull is made up of the cranium and upper jaw which are fused, and the lower jaw which
articulates with the upper jaw. The skull encloses the brain and sense organs of the head.
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• The vertebral column is composed of 33 bones known as vertebrae. The spinal cord runs through
the vertebral column. The column supports the body, provides points of attachment for the
girdles and many muscles, and protects the spinal cord which runs through it. It also allows some
movement.
• The ribs are attached to the vertebral column dorsally and the sternum ventrally. They form the
rib cage around the heart and lungs, and movement of the ribs is essential for breathing.
The appendicular skeleton
forelimb
pectoral girdle
The appendicular skeleton is composed
of the pectoral girdle, the pelvic girdle,
the arms (forelimbs) and the legs
(hindlimbs).
• The girdles connect the limbs to the axial
skeleton and have broad flat surfaces
humerus
for the attachment of muscles that move
the limbs. The pelvic girdle is fused to
the bottom of the vertebral column to
provide support for the lower body and
to transmit the thrust from the legs to the
radius
vertebral column which moves the body
forwards.
ulna
• The limbs are composed of long bones
carpals –
which have joints between to allow for
wrist bones
metacarpals –
easy movement. Being long, the bones
hand bones
provide a large surface area for the
attachment of muscles and permit long
phalanges –
finger bones
strides to be taken.
thumb or
Both the arms and the legs are built on
big toe
the same basic pattern known as the
pentadactyl limb.
Figure 6.2 The pentadactyl limb
hindlimb
pelvic girdle
ball and
socket joint
femur
hinge joint
tibia
fibula
tarsals –
ankle bones
metatarsals –
foot bones
phalanges –
toe bones
articular cartilage – covers
the head of the humerus
head – ball shaped to
articulate with the socket
of the scapula at the
shoulder
shaft – long, hollow and
cylindrical. Reduces
chances of breakage
occurring across the bone
spongy bone – composed of
a structural network of bony
processes with red bone
marrow between. Light, strong
and withstands stress in all
directions. Red bone marrow
produces blood cells
compact bone – dense, hard,
strong bone. Main function is
support
articular cartilage
marrow cavity – contains fatty
yellow bone marrow which
serves as a fat store
points of articulation with the
radius and ulna at the elbow
lower end composed of
spongy bone
Figure 6.3 Structure and functions of parts of a typical long bone – the humerus
6 The skeletal system
57
Functions of the skeleton
The human skeleton has five main functions:
• Movement. The skeleton is jointed and muscles work across these joints to bring about movement.
Most movement is brought about by the legs and arms while the vertebral column allows some
movement.
• Protection for the internal organs. The skull protects the brain and sense organs of the head, i.e. the
eyes, ears, nasal cavities and tongue. The vertebral column protects the spinal cord. The rib cage and
sternum protect the lungs and heart.
• Support for the soft parts of the body. This is mainly carried out by the vertebral column, pelvic
girdle and legs.
• Breathing. Alternate contractions of the internal and external intercostal muscles between the ribs
bring about movements of the rib cage, which cause air to be drawn into the lungs and expelled
from the lungs (see page 37).
• Production of blood cells. Red blood cells, most white blood cells and platelets are produced in the
red bone marrow found in the spongy bone inside flat bones, e.g. the pelvis, scapula, ribs, sternum,
cranium and vertebrae, and in the ends of long bones, e.g. the humerus and femur.
Tendons and ligaments
Tendons and ligaments must not be confused:
• Tendons attach the ends of muscles to the bones of the skeleton. They are made of tough, fibrous
connective tissue. They are strong and non-elastic so that, when a muscle contracts, the force is
transmitted directly to the bone, causing the bone to move.
• Ligaments attach bones together at joints. They are made of tough, fibrous connective tissue with
some elastic tissue. They are strong but elastic so they hold the bones together firmly and prevent
dislocation, but can stretch slightly to allow movement at the joints.
Movement
Movement in humans is brought about by skeletal muscles working across joints.
Skeletal muscles
Skeletal muscles consist of bundles of multinucleate muscle fibres which are surrounded by
connective tissue. Tendons attach these muscles to the bones of the skeleton.
muscle
bundles of
muscle fibres
muscle fibre
nuclei
connective tissue
surrounds the bundles
of muscle fibres
tendon
Figure 6.4 A portion of a skeletal muscle
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Joints
A joint is formed where two bones meet.
Most joints allow the rigid skeleton to move. There are three types of joints:
• Fixed joints or fibrous joints. The bones are joined firmly together by fibrous connective tissue which
allows no movement, e.g. the cranium is made of several bones joined by fixed or immovable
joints.
• Partially movable joints or cartilaginous joints. The bones are separated by cartilage pads which allow
slight movement, e.g. the vertebrae are separated by intervertebral discs of cartilage.
• Moveable joints or synovial joints. The articulating surfaces of the bones are covered with articular
cartilage and synovial fluid fills the joint cavity between the bones. The bones are held together by
ligaments. There are two types of moveable joints:
Hinge joints are formed when the
articulating bone,
ends of the bones meet. They allow
e.g. humerus or femur
movement in one plane (direction)
capsule – composed of tough,
only. This limited movement provides
slightly elastic ligaments. Holds
the bones together. Can stretch
strength and the joints are capable of
to enable movement
bearing heavy loads, e.g. the elbow,
synovial membrane – lines the
knee, finger and toe joints.
capsule. Secretes synovial fluid
synovial fluid – lubrictes the joint
allowing friction-free movement,
and prevents damage to the cartilage
articular cartilage – reduces friction
between the bones, prevents damage
to the articulating surfaces and aids
in shock absorption
articulatory bone e.g. ulna or tibia
Figure 6.5 Structure and functions of the parts of
a generalised hinge joint
Ball and socket joints are formed
where a ball at the end of one
bone fits into a socket in the
other bone. They allow rotational
movement in all planes. The free
range of movement provides less
support and makes the joints
more susceptible to dislocation
than a hinge joint, e.g. the
shoulder and hip joints.
pelvic (or pectoral) girdle
articular cartilage
synovial membrane
rane
capsule
synovial fluid
femur (or humerus)
Figure 6.6 Structure of the parts of a ball and socket joint
Movement of a limb
When a muscle contracts it exerts a pull, but it cannot exert a push when it relaxes. Therefore, two
muscles, known as an antagonistic pair, are always needed to produce movement at a moveable joint:
• The flexor muscle is the muscle that bends the joint when it contracts.
• The extensor muscle is the muscle that straightens the joint when it contracts.
6 The skeletal system
59
Both muscles are attached by tendons at one of their ends to a bone that does not move and at the
other end to a bone that does move.
The origin of a muscle is the attachment point of the end of the muscle to a bone that does not move
during contraction.
The insertion of a muscle is the attachment point of the end of the muscle to the bone that moves
during contraction.
The origin is usually as far away as possible from the joint and the insertion is usually very close to
the joint.
Movement of the elbow joint
The biceps and triceps muscles move the radius and ulna causing the elbow joint to bend or
straighten:
• The biceps is the flexor muscle. Its origin is on the scapula which does not move, and its insertion
is on the radius close to the elbow joint.
• The triceps is the extensor muscle. Its origin is on the scapula and top of the humerus which do not
move, and its insertion is on the ulna close to the elbow joint.
To bend the elbow joint, the biceps contracts and the triceps relaxes. To straighten the elbow joint, the
triceps contracts and the biceps relaxes.
two origins
of the biceps
tendons
scapula
biceps (flexor) –
contracts pulling
the radius and
ulna upwards
humerus
triceps
(extensor) – relaxes
radius
ulna
a radius and ulna raised
three origins
of the triceps
triceps –
contracts pulling
the radius and
ulna downwards
biceps –
relaxes
insertion of the
biceps
insertion of the
triceps
b radius and ulna lowered
Figure 6.7 Movement of the elbow joint
The effect of exercise on the skeletal system
Exercise has many benefits:
• It improves muscle tone, which is the unconscious low-level contraction of muscles while they are
at rest. Good muscle tone is important because it maintains balance and a good, upright posture,
and it keeps muscles in an active state ready for coordinated action.
• It increases production of synovial fluid in joints which keeps joints healthy, reduces friction and
increases flexibility.
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6 Concise Revision Course: Human and Social Biology
• It improves the strength and elasticity of ligaments, which increases the range of movement at joints.
• It stimulates the growth of muscle tissue, which increases muscle size and strength.
• It encourages bone to lay down more mineral matter so bones become denser and stronger, which
reduces the risk of fractures and osteoporosis.
Factors which adversely affect the skeletal system
Poor posture
Posture refers to the relative position of the different parts of the body. A poor posture strains muscles
and causes them to need more energy to keep the body upright, which leads to fatigue and backache.
It also changes the curvature of the spine, which leads to back, neck and shoulder pain, puts stress on
certain joints and wears down the intervertebral discs in the spine causing a decrease in height.
Poor posture also causes major organs to become compressed and to function less efficiently.
Compression of the lungs and airways makes breathing less efficient, compression of the digestive
system makes it harder to digest food, and compression of blood vessels makes it harder for blood to
circulate properly.
Poor foot-wear
Wearing shoes with high heels causes the body weight to shift forwards to the ball of the foot, leading
to painful arches and a change in the curvature of the spine, which causes bad posture and can result
in lower back pain. High heels also cause calf muscles to shorten and bulge, and place excess pressure
on knee and hip joints. Wearing badly fitting shoes, narrow pointed shoes or high heels can lead to
corns, bunions, hammer toe or ingrown toenails.
Obesity
Extra weight puts strain on the skeleton, especially the joints. This causes cartilage to wear down and
leads to arthritis.
An unbalanced diet
A diet deficient in vitamin D leads to rickets in children (see page 23) and osteomalacia in adults. A diet
deficient in calcium leads to rickets in children and osteoporosis in adults. A diet deficient in protein
can cause a decrease in bone density and muscle mass.
The importance of locomotion to humans
Many human activities involve locomotion, i.e. movement from one place to another. Locomotion
is essential for work and recreation, to find food, to find a partner for reproduction, to escape from
danger, to avoid being overcrowded and for exercise to keep the body healthy. Walking on their two
hindlimbs means humans can use their forelimbs and hands for other activities, e.g. manipulating
tools and writing.
Revision questions
1 a Distinguish between bone and cartilage.
2
3
b State TWO reasons why cartilage is important in the skeleton.
By referring to the different parts of the human skeleton, discuss THREE of
its functions.
Distinguish between a tendon and a ligament.
6 The skeletal system
61
4 a What is a joint?
5
6
7
8
9
62
b How does movement at a hinge joint differ from movement at a ball and socket
joint?
c Identify TWO places in the human body where you would find EACH type of joint
named in b above.
a Why are two muscles needed to bring about movement of a hinge joint?
b Explain how muscles of the leg bring about bending and straightening of the knee
joint.
Name the muscle that bends Jaden’s elbow joint and the muscle that straightens it.
What is the difference between the insertion and the origin of a muscle?
What is meant by ‘muscle tone’ and why is good muscle tone important?
Outline the adverse effects that poor posture and poor foot-wear have on the
skeleton.
6 Concise Revision Course: Human and Social Biology
7 Excretion and homeostasis
Chemical reactions occurring in the human body constantly produce waste and harmful substances
which must be got rid of from the body. It is also essential that the body’s internal environment is
kept constant. The mechanisms of homeostasis are responsible for keeping conditions surrounding
cells constant.
Excretion
Excretion is the process by which waste and harmful substances, produced by chemical reactions
occurring inside body cells, i.e. the body’s metabolism, are removed from the body.
Excretion is important because:
• It prevents toxic metabolic waste substances from building up in the body and damaging or
killing cells.
• It helps to keep the environment within the body constant (see page 67).
Excretion must not be confused with egestion, which is the removal of undigested dietary fibre and
other materials from the body as faeces. This dietary fibre is not produced in the body’s metabolism,
so its removal cannot be classed as excretion.
Metabolic waste excreted by humans
Humans produce the following waste substances during metabolism:
• Carbon dioxide is produced in respiration.
• Water is produced in respiration.
• Urea (nitrogenous waste) is produced by the deamination of amino acids in the liver (see page 35).
• Bile pigments, e.g. bilirubin, are produced by the breakdown of haemoglobin from red blood cells
in the liver.
• Heat is produced in general metabolism.
Excretory organs
Humans have several organs that excrete waste products.
• The kidneys excrete water, urea and salts as urine.
• The lungs excrete carbon dioxide and water vapour during exhalation (see page 39).
• The skin excretes water, urea and salts as sweat. It also excretes heat (see page 68).
• The liver excretes bile pigments. It also makes urea.
The kidneys and excretion
Humans have two kidneys which form part of the urinary system. The kidneys have two functions:
• To excrete metabolic waste, mainly urea, from the body.
• To regulate the volume and concentration of blood plasma and body fluids by regulating the
amount of water they contain, a process known as osmoregulation (see page 67).
Each kidney is divided into three regions, an outer region called the cortex, an inner region called the
medulla, and a central hollow region called the pelvis. A renal artery carries blood to each kidney and
a renal vein carries blood away.
7 Excretion and homeostasis
63
posterior vena cava
aorta
renal artery
left kidney
renal vein
ureter – tube carrying
urine to the bladder
right kidney
bladder – bag with
muscular walls
which stores urine
sphincter muscle –
keeps the bladder
closed. Relaxes to
allow urine to leave
the bladder
urethra – tube which
carries urine out of the
bladder
Figure 7.1 Structure of the urinary system in a human
Each kidney is composed of thousands of kidney tubules or nephrons that produce urine. Each
nephron begins with a cup-shaped Bowman’s capsule in the cortex which surrounds an intertwined
cluster of capillaries called a glomerulus. After the Bowman’s capsule, each nephron is divided into
three sections:
• The first convoluted (coiled) tubule in the cortex.
• The loop of Henle in the medulla.
• The second convoluted (coiled) tubule in the cortex.
An arteriole, which
nephron
Bowman’s capsule –
branches from the renal
cup-shaped structure
artery, leads into each
around the glomerulus
collecting duct
glomerulus. A capillary
leads out of each
glomerulus –
glomerulus and branches
cluster of
to form a network of
renal artery
capillaries at
capillaries which wrap
the end of an
renal vein
arteriole
around each nephron and
then join into a venule,
pelvis –
hollow region
which leads into the renal
medulla –
vein. Nephrons join into
inner region
collecting ducts in the
cortex –
cortex and these ducts lead
outer region
pyramid –
inner part of
through the medulla and
the medulla
out into the pelvis.
ureter
Figure 7.2 A longitudinal section through a kidney showing the
position of a nephron
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Urine is produced in the nephrons by two processes:
• Ultra-filtration or pressure filtration
• Selective reabsorption
Bowman’s
capsule
first
convoluted
tubule
second
convoluted
tubule
A
glomerulus
C
arteriole from
the renal artery
B
venule to
the renal vein
B
cortex
medulla
capillaries
B
loop of
Henle
flow of filtrate
C
collecting duct
flow of urine
flow of blood
A Ultra-filtration occurs in the glomeruli.
The diameter of the capillary entering each
glomerulus from an arteriole decreases causing
the pressure of the blood to increase. Small
molecules are forced from the blood into
Bowman’s capsule forming filtrate. Filtrate
contains glucose, amino acids, hormones,
vitamins, water, salts and urea. Blood cells and
large molecules, e.g. plasma proteins, remain in
the blood.
B Selective reabsorption occurs in the nephrons.
Useful substances are reabsorbed from the
filtrate back into the blood travelling through the
capillaries wrapped around each nephron:
Glucose, amino acids, hormones,
vitamins, some water and some salts are
reabsorbed in the first convoluted tubule.
Some water is reabsorbed in the loop
of Henle.
Some salts and some water are
reabsorbed in the second convoluted tubule.
Water is reabsorbed by osmosis, the other
substances are reabsorbed by diffusion and
active transport.
C Filtrate containing urea, excess water and
excess salts enters the collecting ducts where
some water can be reabsorbed from it by
osmosis. The filtrate, now called urine, travels
down the collecting duct to the ureter and then
to the bladder where it is stored.
Figure 7.3 Detailed structure of a nephron showing how urine is formed
Renal dialysis
When nephrons stop functioning properly so that they are unable to remove waste from the blood
and regulate the volume and composition of blood plasma and body fluids, kidney failure occurs.
Harmful waste, especially urea, builds up in the blood and can reach toxic levels resulting in death.
Kidney failure can be treated by a kidney transplant or renal dialysis.
During dialysis blood from a vein, usually in the arm, flows through a dialysis machine and is then
returned to the body. In the machine, the blood is separated from dialysis fluid by a partially
permeable membrane. Waste products, mainly urea, pass from the blood into the dialysis fluid
together with excess water and excess salts. In this way, waste from the blood is removed and the
volume and composition of the blood plasma and body fluids are regulated. Dialysis must occur at
regular intervals; most people require three sessions a week, each lasting four hours.
The skin
The skin is the largest organ in the human body. It is made up of three layers:
• The epidermis, which is the outermost layer.
• The dermis, which is below the epidermis.
• The subcutaneous layer, which is the bottom layer made up mainly of fat cells.
7 Excretion and homeostasis
65
nerve endings
epidermis –
three layers
hair
hair follicle
sweat pore
sebaceous gland
malpighian layer –
actively dividing cells that form the
other layers of the epidermis and
contain melanin, a brown pigment
dermis –
connective
tissue
sweat duct
sweat gland
capillary – to the
sweat gland
arteriole
subcutaneous
layer
fat cells
cornified layer –
dead cells rich in
keratin. Layer is
waterproof
living layer –
living cells
venule
hair papilla – actively
dividing cells form the hair
hair erector
muscle
capillary network
Figure 7.4 A section through the human skin showing its structure
Table 7.1 Functions of the structures of the skin
Structure
Function
Epidermis
Protects the body against pathogens, water loss, the Sun’s harmful ultraviolet
rays and harmful chemicals in the environment.
Sebaceous glands
Secretes sebum, an oily substance, which helps to keep the skin soft, supple
and waterproof, and inhibits the growth of bacteria.
Nerve endings
Detect various stimuli, e.g. touch, pressure, pain, temperature and hair
movement.
Hairs and hair erector Muscles contract causing hairs to stand upright. This causes ‘goose bumps’
muscles
in humans, but traps a layer of air next to the skin which acts as insulation in
hairy mammals to prevent heat loss.
Arterioles and
Help regulate the body temperature (see page 68).
capillary networks
Sweat glands
Produce sweat by absorbing water, urea and salts from the blood passing
through them. The sweat passes up the sweat ducts and onto the surface of
the skin where the water evaporates and cools the body if it is too hot.
Subcutaneous layer Protects the body against heat loss in low environmental temperatures and
against damage by acting as ‘padding’.
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Homeostasis
Homeostasis is maintaining a constant internal environment.
Conditions surrounding cells must be very carefully controlled; these include the water content
or concentration of blood plasma and body fluids, levels of carbon dioxide in the blood, body
temperature and blood sugar levels.
Feedback mechanisms and homeostasis
Homeostasis is achieved by using negative feedback mechanisms that involve both the nervous system
and hormones. If the level of something in the body changes, receptors in the body detect the change
and send messages to the appropriate effectors causing them to respond and return the level to
normal, i.e. the effectors exert an opposite or negative effect.
level rises
corrective action
taken by appropriate
effector(s), i.e. muscles,
glands or organs
normal level
level drops
level drops
normal level
corrective action
taken by appropriate
effector(s)
level rises
Figure 7.5 The principles of negative feedback mechanisms
If the corrective mechanism fails, the level cannot be returned to normal and will continue to
increase or decrease. This can result in a person’s health being impaired, e.g. diabetes, and may even
cause death.
Osmoregulation
Osmoregulation is the regulation of the water content of blood plasma and body fluids. Their water
content must be kept constant to prevent water moving into and out of body cells unnecessarily.
• If body fluids contain too much water (become too dilute), water will enter body cells by osmosis.
The cells will swell and may burst. Drinking a lot of liquid or sweating very little because of being in
cold weather can cause body fluids to become too dilute.
• If body fluids contain too little water (become too concentrated), water will leave body cells
by osmosis. The cells shrink and the body becomes dehydrated. If too much water leaves cells,
metabolic reactions cannot take place and cells die. Not drinking enough, excessive sweating or
eating a lot of salty foods can cause body fluids to become too concentrated.
The kidneys regulate the water content of body fluids by controlling how much water is reabsorbed
into the blood plasma during selective reabsorption. This determines how much water is lost in urine.
Control involves:
• The hypothalamus of the brain, which detects changes in the concentration of blood plasma.
• Antidiuretic hormone (ADH), which is produced by the pituitary gland at the base of the brain in
response to messages from the hypothalamus. ADH is carried by the blood to the kidneys where it
controls the permeability of the walls of the tubules and collecting ducts to water.
7 Excretion and homeostasis
67
pituitary gland –
releases very little or no
ADH into the blood
hypothalamus –
detects blood plasma
is too dilute
kidneys – tubule and collecting
duct walls remain almost
impermeable to water. Very little
water is reabsorbed from the filtrate.
A lot of dilute urine is produced
water content
of blood rises
water content
of blood drops
water
content of blood
is normal
water
content of blood
is normal
water content
of blood drops
water content
of blood rises
hypothalamus –
detects blood plasma
is too concentrated
kidneys – ADH makes
tubule and collecting duct walls more
permeable to water. Most of the water
is reabsorbed from the filtrate. Very
little concentrated urine is produced
pituitary gland –
releases ADH
into the blood
Figure 7.6 Osmoregulation
Regulation of body temperature
Humans must maintain a constant
internal body temperature of 37 °C
for enzymes to function correctly.
Most heat is gained from metabolic
processes, mainly respiration,
and the blood carries this heat
around the body. Heat is lost
mainly by conduction, convection
and radiation through the skin,
and also by evaporation of water
during exhaling and sweating.
The hypothalamus of the brain
detects changes in temperature
of the blood and sends messages
to appropriate effectors, mainly in
the skin.
68
• Skin produces sweat. Water
evaporates removing heat.
• Vasodilation occurs. Arterioles
supplying the capillaries in the
skin dilate, increasing blood
flow through them and heat loss.
temperature rises • Respiration slows, especially
in liver and muscle cells,
above 37 °C
decreasing heat production.
normal
body temperature –
37 °C
temperature
drops
normal
body temperature –
37 °C
• Skin stops producing sweat.
temperature drops • Vasoconstruction occurs.
temperature
below 37 °C
rises
Arterioles supplying the capillaries
in the skin constrict, decreasing
blood flow through them and
heat loss.
• Respiration speeds up,
especially in liver and muscle
cells, increasing heat production.
• Shivering occurs to generate heat.
Figure 7.7 Control of body temperature
7 Concise Revision Course: Human and Social Biology
Note that heat and temperature are not the same:
• Heat is the total amount of energy an object contains. It is measured in joules or J.
• Temperature is a measure of how hot or how cold an object is. It is measured in degrees Celsius or °C.
Regulation of carbon dioxide levels
Carbon dioxide reacts with water in plasma and forms carbonic acid. As carbon dioxide levels increase
the blood becomes more acidic (its pH decreases). Carbon dioxide levels must be controlled to stop
the blood from becoming too acidic or too alkaline. Receptors, mainly in the medulla of the brain,
detect changes in pH and send messages to the intercostal muscles and diaphragm to adjust the rate
and depth of breathing (see page 40).
Regulation of blood sugar (glucose) levels
The normal concentration of glucose is approximately 80 mg per 100 cm3 of blood. The pancreas
constantly monitors the level of glucose in the blood and secretes two hormones directly into the
blood to keep the level constant:
• If the blood glucose level rises, e.g. after a meal rich in carbohydrates, the pancreas secretes insulin.
Insulin stimulates body cells to absorb glucose for respiration and the liver cells to convert excess
glucose to glycogen, which it stores.
• If the blood glucose level falls, e.g. between meals, or during exercise or sleep, the pancreas
secretes glucagon. Glucagon stimulates liver cells to convert stored glycogen to glucose, which
enters the blood.
ettess
pancreas secretes
insulin into the bblood
l od
loo
od
blood glucose
level increases
normal blood
glucose level
absorb
sooorrbb
body cells ab
glucose for res
respiration
spppirraattiioon
liver cells convert
glucose to glycogen
and store it
blood glucose
level decreases
normal blood
glucose level
blood glucose
level decreases
pancreas secretes
glucagon into the blood
blood glucose
level increases
liver cells break down stored
glycogen into glucose and
release it into the blood
Figure 7.8 Control of blood glucose levels
Diabetes mellitus occurs when a person is unable to regulate his or her blood glucose levels such that
they remain too high (see page 121).
7 Excretion and homeostasis
69
Revision questions
1 a Define ‘excretion’.
b Explain why egestion is not considered to be excretion.
2 Explain what will happen to an organism if excretion does not occur.
3 Construct a table to show the different excretory organs in the human body and what
EACH excretes.
4 Outline how urine is produced in Marissa’s kidneys.
5 A person suffering from kidney failure can be treated using dialysis. Explain why this
treatment must occur at regular intervals.
6 State the function of EACH of the following structures of the skin:
a the epidermis
b the subcutaneous layer
c the sebaceous glands
7 a What is meant by the term ‘homeostasis’?
b Explain why negative feedback mechanisms are important in homeostasis.
8 a Name the process by which the water content of body fluids is regulated.
b Tyler plays tennis all day in the hot sun and drinks very little. What effect will his
behaviour have on the quantity and concentration of his urine? Explain your answer.
9 a Distinguish between heat and temperature.
b Explain the changes that occur in a person’s skin if their body temperature rises
above 37 °C.
100 After a meal rich in carbohydrates, the blood glucose level rises. How does the body
function to return the level to normal?
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8 Coordination and control
Humans must constantly monitor their environment and respond appropriately to any changes in this
environment to help them survive. To do this, two systems are involved, the nervous system and the
endocrine (hormonal) system.
Some important definitions
Stimulus is a change in the internal or external environment of an organism that initiates a response.
Response is a change in an organism or part of an organism which is brought about by a stimulus.
Receptor is the part of the organism that detects the stimulus.
Effector is the part of an organism that responds to the stimulus.
Coordination by the nervous and endocrine systems
Coordination is brought about by receptors detecting stimuli, both internal and external, and passing
messages on to the appropriate effectors causing them to respond. In humans, receptors are the sense
organs, which contain specialised receptor cells, and effectors are muscles and glands. Two systems
are responsible for this coordination, the nervous system and the endocrine (hormonal) system.
Table 8.1 Control by the nervous and endocrine systems compared
Control by the nervous system
Control by the endocrine system
Messages are carried as electrical impulses
Messages are carried by chemicals (hormones) in
along nerves.
the blood.
Messages are transmitted rapidly.
Messages are usually transmitted slowly.
Messages are carried to precise places in
Messages are carried to generalised regions of
the body.
the body.
Messages have an immediate effect on the body. Messages usually have a slow effect on the body.
Messages have a short lasting effect on
Messages usually have a long lasting effect on
the body.
the body.
The nervous system
The human nervous system is composed of neurones
or nerve cells and is divided into two parts:
• The central nervous system (CNS), which consists of
the brain and the spinal cord.
• The peripheral nervous system (PNS), which consists
of cranial and spinal nerves that connect the central
nervous system to all parts of the body. The PNS is
divided into the autonomic nervous system and the
voluntary or somatic nervous system.
Peripheral nervous
system (PNS)
cranial nerves
Central nervous
system (CNS)
brain
spinal cord
spinal nerves
Figure 8.1 Organisation of the human
nervous system
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71
The brain
The human brain is an extremely complex organ. It has five main parts, each concerned with different
functions.
cerebrum –
composed of two
cerebral hemispheres
hypothalamus
pituitary gland
medulla oblongata
cerebellum
spinal cord
Figure 8.2 The main parts of the human brain as seen
in longitudinal section
Table 8.2 Functions of the main parts of the brain
Part of the brain Functions
Cerebrum
• Controls conscious thought, problem solving, decision making, planning
and emotions.
• Responsible for intelligence, memory, learning, speech and language.
• Processes visual, auditory and other external information.
• Coordinates voluntary actions.
Cerebellum
• Controls balance and posture.
• Coordinates movement.
Medulla
• Controls automatic, involuntary actions, e.g. heart rate, breathing rate,
blood pressure, peristalsis.
oblongata
Hypothalamus • Regulates body temperature.
• Regulates the concentration of body fluids by controlling the release of
ADH by the pituitary gland.
• Controls reproduction by controlling the release of FSH and LH by the
pituitary gland.
Pituitary gland • Secretes a variety of hormones, e.g. ADH, GH, FSH, LH (see Table 8.4, page 77).
Neurones
Neurones are specialised cells that conduct nerve impulses throughout the nervous system.
All neurones have a cell body with thin fibres of cytoplasm extending from it called nerve fibres. Nerve
fibres that carry impulses towards the cell body are called dendrites. Nerve fibres that carry impulses
away from the cell body are called axons; each neurone has only one axon. There are three types
of neurones:
• Sensory neurones, which transmit impulses from receptors to the CNS.
• Motor neurones, which transmit impulses from the CNS to effectors.
• Relay or intermediate neurones, which transmit impulses throughout the CNS. They link sensory
and motor neurones.
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receptor
node of Ranvier –
constriction in
the myelin sheath
myelin sheath – fatty sheath to
insulate and protect the nerve
fibre and speed up transmission
of impulses
synaptic
knobs
cell body
axon – short
dendrite – long
direction of
nerve impulse
Figure 8.3 Structure of a sensory neurone
effector – a muscle
or gland
dendrites
myelin sheath
cell body
axon – long
direction of
nerve impulse
node of Ranvier
motor end plate
Figure 8.4 Structure of a motor neurone
sensory neurone
PNS
CNS
receptor
synapse
relay neurone – does
not have a myelin sheath
effector
motor neurone
boundary of
the CNS
Figure 8.5 The connection between a receptor and an effector
Neurones have two major properties:
• Irritability. They can convert a stimulus into an electrical (nerve) impulse.
• Conductivity. They can transmit nerve impulses to other neurones, muscles or glands.
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73
Nerves
Nerves are cordlike bundles of nerve fibres of neurones surrounded by connective tissue through
which impulses pass between the CNS and the rest of the body.
Nerves can be classified into three types based on what they are composed of:
• Sensory nerves (afferent nerves) are composed of the nerve fibres of sensory neurones only and they
carry impulses from receptors to the CNS.
• Motor nerves (efferent nerves) are composed of nerve fibres of motor neurones only and they carry
impulses from the CNS to effectors.
• Mixed nerves are composed of nerve fibres of both sensory and motor neurones and they carry
impulses in both directions, from receptors to the CNS and from the CNS to effectors.
Nerves can be classified into two types based on where they connect to the CNS:
• Cranial nerves connect to the brain.
• Spinal nerves connect to the spinal cord.
Synapses
Adjacent neurones do not touch. There are tiny gaps called synapses between the synaptic knobs
at the end of one axon and the dendrites or cell body of adjacent neurones. Chemicals known as
neurotransmitters are released into the synapses by vesicles (small sacs) in the synaptic knobs. These
chemicals cause impulses to be set up in adjacent neurones. This ensures impulses travel in one
direction only and allows many neurones to interconnect.
Voluntary actions
A voluntary action is an action that is consciously controlled by the brain.
The cerebrum of the brain initiates voluntary actions in one of two ways, both of which involve
conscious thought:
• It can coordinate incoming information from sensory neurones and initiate an action.
• It can spontaneously initiate an action without receiving any incoming information.
To initiate the action, impulses are sent from the cerebrum along relay neurones in the brain and
spinal cord to motor neurones. These motor neurones then carry these impulses to skeletal muscles
(effectors) initiating a conscious response, e.g. talking, writing, running.
Voluntary actions:
• are learned
• are relatively slow
• are complex because a variety of different responses can result from one stimulus.
Involuntary actions
An involuntary action is an action that occurs without conscious thought.
Involuntary actions:
• are not learned
• are rapid
• are simple because the same response always results from the same stimulus.
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There are two types of involuntary actions:
• Actions controlled by the autonomic nervous system.
• Reflex actions.
Actions controlled by the autonomic nervous system
The autonomic nervous system is composed of motor nerves only and regulates the functioning of
internal organs, e.g. it controls breathing rate, heart rate, digestion, peristalsis and blood pressure.
Information from internal receptors passes to the medulla of the brain which sends impulses out
along motor neurones in cranial and spinal nerves to the effectors. The autonomic nervous system is
important in homeostasis (see page 66).
Reflex actions
A reflex action is a rapid, automatic, involuntary response to a stimulus by a muscle or gland.
A reflex action is always initiated by an external stimulus. The pathway between receptor and effector
is known as a reflex arc. It is simple and involves the following:
• A receptor that detects the stimulus.
• A sensory neurone that carries the impulse to the central nervous system.
• A relay neurone in the central nervous system that carries the impulse to a motor neurone.
• A motor neurone that carries the impulse away from the central nervous system.
• An effector that responds to the stimulus.
Simple reflexes are classified as cranial reflexes or spinal reflexes.
Cranial reflexes
In cranial reflexes, impulses pass through cranial nerves and the brain, e.g. the pupil reflex, blinking,
sneezing, coughing and saliva production.
1 Bright light stimulates
light sensitive cells of
the retina of the eye
eye
light
rays
2 Impulses travel along
a sensory neurone
to the brain
iris
boundary of the brain
3 Impulses travel
through a relay
neurone to a
motor neurone
in the brain
pupil
circular
muscles
5 Circular muscles of the iris
contract causing the diameter
of the pupil to decrease
4 Impulses travel along
a motor neurone to
the iris of the eye
Figure 8.6 The pupil reflex
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75
Spinal reflexes
In spinal reflexes, impulses pass through spinal nerves and the spinal cord. Spinal reflexes include the knee
jerk reflex which lacks a relay neurone, and the withdrawal reflex in response to pain, e.g. when the finger
is pricked, pain receptors are stimulated and the hand is rapidly withdrawn from the source of the pain.
neurone –
extensor muscle sensory
in a spinal nerve
stretch receptor
3
knee cap
6
2
1
femur
tibia
dorsal root of
spinal nerve – composed
of sensory fibres
5
motor neurone –
in a spinal nerve
nerve endings
in the extensor
muscle
spinal nerve –
composed of sensory
and motor fibres
1 Stimulus, a tap just below the knee cap.
2 Stretch receptor in the muscle is stimulated.
3 Impulses travel along a sensory neurone into the spinal cord.
4 Impulses travel directly into a motor neurone in the spinal cord.
5 Impulses travel along the motor neurone to the extensor muscle of the leg.
6 The extensor muscle contracts causing the lower leg to rise.
dorsal root ganglion –
contains cell bodies of
sensory neurones
4
white matter –
composed of axons
by
grey matter – surrounded
myelin
sheaths
ventral root of
mainly relay
spinal nerve –
and
composed of motor neurones
cell
bodies
fibres
spinal cord
Figure 8.7 The knee jerk reflex showing the structure of the spinal cord
Revision questions
1 Give THREE differences between coordination by the nervous system and
76
coordination by the endocrine system.
2 Describe the main divisions of the nervous system.
3 Give ONE function of EACH of the following regions of the brain:
a the medulla oblongata
b the cerebellum
c the cerebrum
4 a Distinguish between a neurone and a nerve.
b Name the THREE types of neurones found in the nervous system and indicate the
function of EACH.
c Identify the TWO major properties of all neurones.
5 What is a synapse and why are synapses important in the nervous system?
6 Distinguish between a voluntary action and an involuntary action and give TWO
examples of each.
7 What is the autonomic nervous system and what does it control?
8 What is a reflex action?
9 Jan pricked her finger and immediately withdrew her hand from the source of the
pain. Draw a simple flow diagram to show the pathway along which the impulses
passed in Jan’s body to bring about her response.
8 Concise Revision Course: Human and Social Biology
Sense organs
Sense organs contain specialised receptor cells that detect changes in the environment, i.e. stimuli. The cells
turn these stimuli into electrical impulses which travel along sensory neurones to the CNS. The cerebrum of
the brain then interprets these messages as sensations of seeing, hearing, smelling, tasting and touching.
Table 8.3 Sense organs in the human body
Sense organ Specialised receptor cells
Stimuli detected
Eyes
Rods and cones (photoreceptors) in the retina. Light.
Ears
Mechanoreceptor cells in the inner ear.
Sound waves and the position of the head.
Nose
Olfactory cells (chemoreceptors) in the top Chemicals in the air.
of the nasal cavities.
Tongue
Taste receptor cells (chemoreceptors) in the Chemicals in food.
taste buds.
Four tastes are detected; sweet, sour,
salty and bitter.
Skin
Touch receptor cells.
Touch and texture.
Pressure receptor cells.
Pressure.
Pain receptor cells.
Pain and itching.
Temperature receptor cells.
Hot and cold.
The eye
The eye detects light that has been reflected from an object and converts it into nerve impulses. The
impulses are transmitted along the optic nerve to the brain, which translates them into a precise
picture of the object.
The eyes are situated in bony sockets of the skull called orbits and have muscles attached to move
them. The orbits protect the back of each eye from damage, and the eyelids and eyelashes protect
the front from foreign particles. Tears, produced by tear glands above each eye, keep the eyes moist,
wash away foreign particles and contain an enzyme that destroys microorganisms.
conjunctiva – thin, transparent
layer continuous with the lining
of the eyelids. Protects the cornea
cornea – transparent front
part of the sclera. Refracts
(bends) light rays onto the retina
ciliary body
vitreous humour – jelly-like fluid.
Maintains the shape of the eyeball
sclera – tough, white, fibrous coat.
Protects the eyeball
aqueous humour – colourless fluid.
Maintains the shape of the cornea
choroid – contains blood vessels
which supply the retina with food
and oxygen, and melanin to prevent
reflection of light inside the eye
lens – transparent, elastic, biconvex
structure. Makes fine adjustments
to focus light rays on the retina
fovea – contains cones only. The
most sensitive part of the retina,
most light rays are focused here
pupil – hole in the centre of the
iris. Allows light to enter the eyeball
retina – contains light-sensitive cells
called rods and cones. Where the
image forms
iris – coloured disc composed of
muscle. Controls the amount of
light entering the eye
suspensory ligament – attaches
the lens to the ciliary body
optic nerve – carries impulses from
the retina to the brain
ciliary muscle – circular ring of muscle
running through the ciliary body. Alters
the shape of the lens during
accommodation
blind spot – point where the optic nerve
leaves the eye. No light-sensitive cells
are present
Figure 8.8 Structure and functions of the parts of the human eye, as seen in longitudinal section
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77
Image formation
In order to see, light rays from an object must be refracted (bent) as they enter the eye so that they
form a clear image of the object on the receptor cells of the retina. Being convex in shape, both the
cornea and the lens refract the light rays.
light rays from
the object
3 An image of the object is formed
on the retina. This stimulates the
light-sensitive cells of the retina.
The image is inverted, reversed
and smaller than the object
object
1 The cornea refracts the light rays
2 The lens refracts the light
rays focusing them onto
the retina
4 The optic nerve carries the
impulses to the brain. The brain
turns the image the correct way
up, the correct way round and
forms an impression of size,
shape, colour and distance
away of the object
Figure 8.9 Formation of an image in the eye
Detection of light intensity and colour by the eye
The retina is composed of two types of specialised light-sensitive cells or photoreceptors:
• Rods function in low light intensities. They are responsible for detecting the brightness of light and
are located around the sides of the retina. Images falling on the rods are seen in shades of black
and white only.
• Cones function in high light intensities. They are responsible for detecting colour and fine detail,
and are mainly located around the back of the retina. The fovea is composed entirely of cones
which are packed closely together. There are three types which detect either the red, green or blue
wavelengths of light.
Control of the amount of light entering the eye
The size of the pupil controls the amount of light entering the eye. Muscles of the iris control the
pupil size.
wide pupil – allows as
much light as possible
to enter the eye
circular
muscles relax
radial muscles
contract
circular
muscles contract
radial muscles
relax
a dim light
Figure 8.10 Controlling the amount of light entering the eye
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b bright light
narrow pupil – reduces the
amount of light entering
the eye, preventing
damage to the retina
Focusing light onto the retina – accommodation
By changing shape, the lens makes fine adjustments to focus the light rays onto the retina. Changing
the shape of the lens to focus light coming from different distances onto the retina is called
accommodation and it is brought about by the ciliary muscles in the ciliary body.
ciliary muscle relaxes – its
circumference increases
suspensory ligaments
are pulled tight by the
ciliary muscle
lens is pulled thin by the
suspensory ligaments
cornea bends
the light rays
thin lens bends the light rays
slightly to focus on the retina
light rays from the distant point
focus on the fovea of the retina
light rays from
a distant point
a focusing on a distant object
ciliary muscle contracts – its
circumference decreases
cornea bends
the light rays
suspensory ligaments
slacken
lens is allowed to spring
into a bulged shape
light rays from the near point
focus on the fovea of the retina
light rays from
a near point
bulged lens bends the light
rays a lot to focus on the retina
b focusing on a near object
Figure 8.11 Accommodation
Sight defects and their corrections
Short-sightedness (myopia)
A person with short sight can see near objects clearly, but distant objects are out of focus. Light rays
from near objects focus on the retina; light rays from distant objects focus in front of the retina. It
is caused by the eyeball being too long from front to back or the lens being too curved (thick). It is
corrected by wearing diverging (concave) lenses as spectacles or contact lenses.
light rays from a
distant point
diverging lens bends
light rays outwards
before they enter
the eye
focus of light rays
from the distant
point before correction –
in front of the retina
focus of light rays
from the distant
point after correction –
on the retina
Figure 8.12 The cause and correction of short sight
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79
Long-sightedness (hypermetropia)
A person with long sight can see distant objects clearly, but near objects are out of focus. Light
rays from distant objects focus on the retina; light rays from near objects focus behind the retina.
It is caused by the eyeball being too short from front to back or the lens being too flat (thin). It is
corrected by wearing converging (convex) lenses as spectacles or contact lenses.
light rays from a
near point
converging lens bends light rays
inwards before they enter the eye
focus of light rays from
the near point before
correction – behind the
retina
focus of light rays from
the near point after
correction – on the retina
Figure 8.13 The cause and correction of long sight
Old sight (presbyopia)
A person with old sight finds it increasingly difficult to see near objects clearly. It occurs because the
lens loses its elasticity as a person ages and the ciliary muscles weaken so that the lens is less able to
curve. It is corrected by wearing converging lenses to look at near objects.
Astigmatism
Both near and distant object appear blurry or distorted to a person who has astigmatism. It occurs if
the cornea or lens is unevenly curved so not all light rays are equally refracted and not all focus on
the retina. It is corrected by wearing unevenly curved lenses that counteract the uneven curvature
in the eye.
Glaucoma
Glaucoma is a condition in which the pressure of the fluid within the eye increases due to the flow of
aqueous humour from the eye being blocked. If left untreated, the optic nerve becomes damaged
and it can lead to blindness. The most common type develops slowly and causes a gradual loss of
peripheral (side) vision. Glaucoma is treated with eye drops to reduce fluid production or improve the
flow of fluid from the eye, or by laser treatment or surgery to open the drainage channels.
Cataract
A cataract is a cloudy area that forms in the lens. It develops
slowly and, as it increases in size, it leads to cloudy or blurred
vision, halos forming around lights, colours appearing faded
and difficulty seeing in bright light and at night. It is usually
caused by ageing and is usually corrected by surgery to remove
the clouded lens and to replace it with an artificial lens.
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Figure 8.14 An eye with a cataract
8 Concise Revision Course: Human and Social Biology
The endocrine system
The endocrine system is composed of endocrine glands or ductless glands which secrete hormones
directly into the blood.
thyroid gland – in
front of the trachea
in the neck
pancreas – in the
loop of the duodenum
testis – in the
scrotal sac in males
pituitary gland – attached to
the hypothalamus on the
underside of the brain
adrenal gland – immediately
above the kidney
ovary – at the end of the
fallopian tube in females
Figure 8.15 The position of the main endocrine glands
Table 8.4 Hormones of the main endocrine glands and their functions
Endocrine gland Hormone(s)
Function(s)
Pituitary gland Antidiuretic
Controls the water content of blood plasma and body
hormone (ADH)
fluids by controlling water reabsorption in the kidney
(see page 63).
Growth hormone • In children: stimulates growth by stimulating protein
synthesis in cells and bone growth.
(GH)
• In adults: helps maintain healthy bone and muscle
masses.
Follicle stimulating • In females: helps regulate the menstrual cycle by
stimulating the development and maturation of the
hormone (FSH)
follicles and ova in the ovaries and stimulating the
ovaries to produce oestrogen (see page 86).
• In males: helps control production of sperm in the
testes.
Luteinising hormone • In females: helps regulate the menstrual cycle by
stimulating ovulation and the development of the corpus
(LH)
luteum in the ovaries (see page 86).
• In males: stimulates the production of testosterone by
the testes.
Thyroid gland
Thyroxine
Controls the rate of metabolism and energy production
in cells, and physical growth and mental development,
especially in children.
Adrenal glands Adrenaline (flight, Released in large amounts when frightened, excited or
fright or fight
anxious. Speeds up metabolism, mainly respiration, and
hormone)
increases blood sugar levels, heartbeat, breathing rate and
blood supply to muscles, i.e. it triggers the fight-or-flight
response and gives the feeling of fear.
Pancreas
Insulin and glucagon Regulate blood glucose levels (see page 69).
8 Coordination and control
81
Endocrine gland Hormone(s)
Ovaries
Oestrogen
(produced by the
Graafian follicle)
Placenta during
pregnancy
Testes
Progesterone
(produced by the
corpus luteum)
Progesterone
Testosterone
Function(s)
Controls the development of female secondary sexual
characteristics at puberty, i.e. development of breasts,
pubic and underarm hair, and a broad pelvis. Helps
regulate the menstrual cycle by stimulating the uterus lining
or endometrium to thicken each month after menstruation
(see page 86).
Helps regulate the menstrual cycle by maintaining a thick
uterus lining after ovulation each month (see page 86).
Maintains a thickened uterus lining during pregnancy,
which prevents menstruation. Stimulates the growth of
milk-producing glands in the breasts during pregnancy.
Controls the development of male reproductive organs and
secondary sexual characteristics at puberty, i.e. development
of a deep voice, facial and body hair, muscles and broad
shoulders. Controls sperm production in the testes.
Revision questions
100 Make a list of the different sense organs in the human body and indicate the stimulus
11
122
133
144
155
166
82
or stimuli detected by EACH.
Construct a table to show the function of EACH of the following parts of the eye: the
conjunctiva, the sclera, the pupil, the choroid, the optic nerve and the
vitreous humour.
Explain how an image is formed in Omari’s eye.
Explain how Samara’s eyes adjust when she:
a walks from a dimly lit room into the bright sunshine
b looks at a book in her hand after watching an aeroplane in the sky.
Malik has his eyes tested and is told that he is short sighted. Explain the possible
cause of his sight defect and how it can be corrected.
What is a cataract and how can it be treated?
For EACH of the following endocrine glands, identify where the gland is located in
the body, name the hormone it produces and outline the functions of the hormone:
a the thyroid gland
b the adrenal glands
c the testes
8 Concise Revision Course: Human and Social Biology
9 The reproductive system
All living organisms must produce offspring in order for their species to survive.
Reproduction is the process by which living organisms generate new individuals of the same kind
as themselves.
There are two types of reproduction, asexual reproduction and sexual reproduction.
Asexual and sexual reproduction compared
Asexual reproduction
Asexual reproduction involves only one parent and offspring are produced by mitosis (see pages 102–3).
All offspring produced asexually from one parent are genetically identical, i.e. they do not show
variation, and are collectively called a clone. The process is rapid because it does not involve gamete
production, finding a mate, fertilisation and embryo development. Asexual reproduction occurs in
unicellular organisms, e.g. Amoeba and bacteria, in fungi, in some plants and in a few animals.
Sexual reproduction
Sexual reproduction involves two parents. Gametes, or sex cells, are produced in reproductive organs
by meiosis (see pages 103–4). A male and a female gamete fuse during fertilisation to form a single cell
called a zygote. The zygote divides by mitosis to form an embryo and ultimately an adult. Offspring
produced sexually receive genes from both parents, therefore they possess characteristics of both
parents, i.e. they show variation. The process is slow because it involves gamete production, finding a
mate, fertilisation and embryo development.
The female and male reproductive systems
The female reproductive system
The female gametes are called ova and they are produced in two ovaries which form part of the
female reproductive system.
fallopian tube or oviduct – narrow
tube with muscular walls lined with cilia.
Transports ova from the ovary to the uterus.
Where fertilisation occurs
ovary – oval-shaped. Produces ova
and secretes female sex hormones
uterus or womb – pearshaped. Where the
foetus grows and develops
during pregnancy
cervix – ring of muscle
around the neck of
the uterus. Keeps the
neck closed during
pregnancy
uterus lining or endometrium – has a rich blood supply.
Where the embryo is implanted
uterus wall – thick and muscular.
Stretches during pregnancy to
accommodate the developing foetus.
Contracts during birth
vagina – thin-walled, muscular passage from the
uterus to the outside. Receives the male penis
and where sperm is deposited during intercourse.
Stretches to let the baby out during birth
Figure 9.1 Structure and function of the parts of the female reproductive system
9 The reproductive system
83
The male reproductive system
The male gametes are called sperm or spermatozoa and they are produced in the testes which form
part of the male reproductive system.
that secrete fluid
seminal vesicle glands
which mixes with sperm
prostate gland to form semen. The fluid
stimulates the sperm to swim
urethra from
the bladder
vas deferens or
sperm duct – muscular tube.
Carries sperm to the urethra
epididymis – series of coiled
tubules. Stores sperm
penis – connective tissue with
many blood spaces surrounding
the urethra. Becomes erect during
intercourse to deposit sperm in
the vagina
urethra – muscular tube. Carries
semen to the outside of the body
testis – oval-shaped, composed of
many coiled seminiferous tubules.
Produces sperm and secretes male
sex hormones
scrotal sac or scrotum – a sac of skin.
Holds the testes at a temperature slightly
below 37 °C to enable sperm to develop
normally and to survive
foreskin – retractable skin.
Protects the head of the penis
Figure 9.2 Structure and function of the parts of the male reproductive system
Production and structure of ova and sperm
At birth, each female ovary contains many thousand immature ova. Each is surrounded by a fluidfilled space that forms a primary follicle. Each month between puberty at about 11 to 13 years old,
and menopause at about 45 to 50 years old, one immature ovum develops into a mature ovum. About
450 immature ova will mature in a woman’s lifetime. To produce a mature ovum, the immature ovum
undergoes meiosis (see pages 103–4). One of the four cells produced develops into a mature ovum
which is released during ovulation.
1 Immature ova
inside fluid-filled
primary follicles
2 An immature ovum undergoes
meiosis. One cell matures and
the fluid-filled space increases
in size forming a Graafian follicle
mature ovum
5 The corpus luteum
breaks down
4 The empty Graafian
follicle forms a
corpus luteum
(yellow body)
3 Ovulation – the Graafian
follicle bursts, releasing the
mature ovum into the oviduct
Figure 9.3 Production of an ovum in an ovary
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9 Concise Revision Course: Human and Social Biology
Sperm cells are produced continuously from puberty in the seminiferous tubules of the testes. Cells in
the tubule walls undergo meiosis and all the cells produced develop into mature sperm. These are
stored in the epididymis until ejaculation.
Table 9.1 Ova and sperm cells compared
Ova
Sperm cells
Structure
layer of follicle cells – act
membrane
as protection
layer of jelly
nucleus
cytoplasm
containing yolk
tail – for
swimming
middle piece – contains mitochondria
to release energy for swimming
nucleus
small amount
of cytoplasm
head acrosome – contains
enzymes to dissolve a
passage into the ovum
Production One is produced each month from
Thousands are produced continuously
puberty to menopause.
from puberty.
Movement Are moved down an oviduct after
Swim actively using their tails when mixed
ovulation by muscular contractions of with secretions from the seminal vesicles
the oviduct walls and beating of the cilia. and prostate gland during ejaculation.
Life span
Live for about 24 hours after ovulation. Can live for about 2 to 3 days in the female
body after ejaculation.
Cancers of the reproductive systems
Cancer is a disease resulting from abnormal cells developing and dividing in an uncontrolled way.
These cells replace normal cells and usually produce a tumour (lump). Some of the cells can also
metastasise, i.e. spread to other parts of the body. Cancer can be treated by surgery to remove the
tumour or the entire organ containing the tumour, radiotherapy or chemotherapy. Cancer can affect
various parts of the reproductive systems.
Table 9.2 Cancers of the reproductive systems
Type of Organ Notes
cancer
affected
Ovarian Ovary Symptoms include abdominal pain and lower back pain.
Cervical Cervix Usually caused by the human papilloma virus (HPV) passed on through
sexual contact and can be detected by a cervical smear test (Pap smear test).
Early stages are free of symptoms. Vaginal bleeding, pain during sexual
intercourse and vaginal discharge are symptoms of the later stages.
Uterine Uterus The most common symptom is abnormal bleeding from the vagina.
Breast
Breast A tumour in a breast can be detected by hand or by a mammogram (X-ray).
Breast reconstruction often follows surgery when the entire breast is
removed.
Prostate Prostate A tumour forms in the gland, which starts to block the urethra causing
gland frequent but slow urination. It can be diagnosed using a prostate specific
antigen (PSA) blood test or a digital rectal examination (DRE).
Testicular Testis A tumour in a testis can be detected by hand. Symptoms may include
testicular discomfort.
9 The reproductive system
85
The menstrual cycle
yravo na ni stneve
This is a cycle of about 28 days comprising two main events:
• Ovulation, which is the release of an ovum from an ovary.
• Menstruation, which is the loss of the uterus lining from the body. This starts to occur about 14 days
after ovulation if fertilisation has not occurred.
The cycle is controlled by four hormones which synchronise the production of an ovum with the
uterus lining being ready to receive it if fertilised. The start of the cycle is taken from the start of
menstruation:
• Follicle stimulating hormone (FSH) is secreted by the pituitary gland at the beginning of the cycle.
FSH stimulates a Graafian follicle to develop in an ovary and an ovum to mature inside the
follicle.
FSH stimulates the follicle to produce oestrogen.
• Oestrogen is produced by the Graafian follicle mainly during the second week of the cycle.
Oestrogen stimulates the uterus lining to thicken and its blood supply to increase after
menstruation.
Oestrogen causes the pituitary gland to stop secreting FSH and to secrete luteinising hormone (LH).
• Luteinising hormone (LH) is
secreted by the pituitary
gland in the middle of the
ovulation corpus luteum
cycle.
corpus luteum
ovum matures inside a Graafian (day 14) develops
breaks down
follicle
A sudden rise in LH
causes ovulation to take
place.
LH stimulates the corpus
1
7
14
21
28
luteum to develop in the
time (days)
ovary after ovulation and
oestrogen secreted
progesterone secreted by
to secrete progesterone.
by Graafian follicle
the corpus luteum
• Progesterone is produced by
the corpus luteum during
the third week of the cycle.
progesterone
Progesterone causes the
level
oestrogen
uterus lining to increase
level
slightly in thickness and
1
7
14
21
28
remain thick.
time (days)
If fertilisation does
progesterone
decrease in progesterone
not occur, the corpus
causes the uterus
causes the uterus lining to
oestrogen
luteum breaks down
stimulates the lining to remain thick begin to break down
uterus lining
during the fourth week
to thicken
and reduces secretion
me
nst
of progesterone. The
r ua
tion
decrease in progesterone
causes the uterus lining
to begin to break down,
and the pituitary gland to
1
7
14
21
28
secrete FSH at the end of
time
(days)
the fourth week.
Figure 9.4 A summary of the events occurring during the
menstrual cycle
senomroh
nairavo fo level
gninil suretu eht fo ssenkciht
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9 Concise Revision Course: Human and Social Biology
Bringing sperm and ova together
When a male becomes sexually excited, blood spaces in the penis fill with blood. The penis becomes
erect and is placed into the female vagina. Semen, composed of sperm and secretions from the
seminal vesicles and prostate gland, is ejaculated into the top of the vagina by muscular contractions
of the tubules of the epididymis and sperm ducts. The sperm swim through the cervix and uterus and
into the fallopian tubes.
From fertilisation to birth
Fertilisation
If an ovum is present in one of the fallopian tubes, one sperm enters, leaving its tail outside. A
fertilisation membrane immediately develops around the ovum to prevent other sperm from entering,
and the nuclei of the ovum and sperm fuse to form a zygote.
Implantation
The zygote divides repeatedly by mitosis using yolk stored in the original ovum as a source of
nourishment. This forms a ball of cells called the embryo, which moves down the oviduct and sinks
into the uterus lining, a process called implantation. Food and oxygen diffuse from the mother’s blood
into the embryo, and carbon dioxide and waste diffuse back into the mother’s blood.
Pregnancy and development
The cells of the embryo continue to divide and some of the cells develop into the placenta. The placenta
is a disc of tissue with finger-like projections called villi which project into the uterus lining and give
the placenta a large surface area. Capillaries run throughout the placenta, including inside the villi. The
embryo is joined to the placenta by the umbilical cord, which has an umbilical artery and umbilical vein
running through it. These connect the capillaries in the embryo with those in the placenta.
muscular wall
of the uterus
placenta – disc-shaped. Provides
a large surface area for the
exchange of substances between
the mother’s and the embryo’s blood.
Secretes progesterone, which maintains
a thickened uterus lining
umbilical cord
thickened lining of
the uterus with a rich
blood supply
embryo or foetus
capillary network
throughout the placenta
umbilical vein – carries
dissolved food and
oxygen to the embryo
umbilical artery – carries
dissolved carbon dioxide and
other waste away from the embryo
food and oxygen diffuse
from the mother’s blood
in the uterus lining into
the embryo’s blood in the
placenta. Carbon dioxide
and waste diffuse from the
embryo’s blood into the
mother’s blood
villi – increase the contact
area between the placenta
and the uterus lining
amnion
support and
protect the
amniotic fluid embryo
plug of mucus in the cervix
vagina
Figure 9.5 The developing human embryo/foetus in the uterus
9 The reproductive system
87
The placenta allows exchange of materials between the mother’s blood and the embryo’s blood, but
prevents mixing of the two bloods, which may be of different types (see Figure 9.5, page 87). It also
prevents certain unwanted substances entering the embryo’s blood from the mother’s blood, e.g.
many bacteria and viruses.
The developing embryo is surrounded by a thin, tough membrane called the amnion, which forms a
sac containing amniotic fluid.
Table 9.3 The development of a human embryo/foetus
Time after
fertilisation
7 to 10 days
4 weeks
Characteristics
A hollow ball of cells, which is implanted in the uterus lining.
The brain, eyes and ears are developing along with the nervous, digestive and
respiratory systems. Limb buds are forming and the heart is beginning to beat.
8 weeks
The embryo has a distinctly human appearance. All the vital organs have been
formed and limbs with fingers and toes are developed.
10 weeks
The embryo is now known as a foetus. External genitals are beginning to appear,
fingernails and toenails form and the kidneys start to function.
11 to 38 weeks The foetus continues to grow and the organs continue to develop and mature.
38 weeks
Birth occurs.
Note that the gestation period (pregnancy) is considered to last for 40 weeks or 280 days since it is
calculated from the first day of the last menstrual cycle and not from the time of fertilisation.
Birth
The foetus turns so it lies head down. Secretion of progesterone by the placenta is reduced and this
stimulates the pituitary gland to secrete the hormone oxytocin. Oxytocin stimulates muscles in the
uterus wall to start contracting, i.e. labour begins. The amnion bursts and the contractions strengthen
and cause the cervix to gradually dilate. When fully dilated, strong contractions push the baby, head
first, through the cervix and vagina. The baby starts to breathe and the umbilical cord is clamped and
cut. The placenta is then expelled as the afterbirth by further contractions of the uterus wall.
The effect of pregnancy on the menstrual cycle
If fertilisation takes place, the corpus luteum remains in the ovary and it secretes increasing amounts
of progesterone. This causes the uterus lining to increase in thickness and it prevents menstruation. As
the placenta develops, it takes over secreting progesterone, which keeps the uterus lining thick and
inhibits the development of mature ova in the ovaries and menstruation throughout pregnancy.
Prenatal and postnatal care
Prenatal or antenatal care
Prenatal care, or care before birth, is essential to ensure the foetus grows and develops normally and
healthily, and that the mother remains healthy throughout her pregnancy. During pregnancy the
mother must:
• Attend regular prenatal checkups with her doctor or clinic to monitor her health and the
development of her baby.
• Eat a balanced diet that contains adequate quantities of protein, carbohydrates, vitamins and
minerals, especially calcium and iron, to ensure the foetus obtains all the nutrients it needs to grow
and develop.
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9 Concise Revision Course: Human and Social Biology
• Not use drugs of any kind, especially alcohol, cigarettes and illegal drugs, which will harm the
developing foetus, and she must protect herself against infectious diseases.
• Exercise regularly to maintain fitness.
• Prepare her body for the birth by attending prenatal classes, which teach correct exercises and
breathing rhythms as well as how to care for her baby after the birth.
Postnatal care
Postnatal care, or care after birth, is essential to ensure the baby grows and develops healthily, and that
the mother remains both physically and emotionally healthy.
• The newborn baby should be breastfed, if possible for a minimum of 6 months, because:
Breast milk contains all the nutrients the baby needs in the correct proportions.
Breast milk contains antibodies, which protect the baby against bacterial and viral diseases.
Breast milk is sterile so reduces the risk of infection, is at the correct temperature and is available
whenever needed.
Breastfeeding lowers the baby’s risk of developing asthma, allergies and other non-communicable
diseases as it grows older.
Breastfeeding creates a strong emotional bond between mother and baby.
• The newborn baby must be kept warm and clean, have plenty of interaction with both parents and
its surroundings, and be taken for regular checkups with the doctor. As the baby grows it must be
vaccinated against infectious diseases, weaned onto semi-solid and solid food, cared for physically
and emotionally, and given continual teaching.
• The mother must continue to eat a balanced diet, not use drugs of any kind, exercise regularly and be
given both physical and emotional support.
Birth control and family planning
Methods of birth control (contraception)
A variety of methods are available to prevent pregnancy from occurring. They are designed to
prevent fertilisation or to prevent implantation, and they can be natural, barrier, hormonal or surgical.
Two methods, abstinence and the condom, also protect against the spread of sexually transmitted
infections (STIs), e.g. HIV. When choosing a method, its reliability, availability, side effects and
whether both partners are comfortable using it, must be considered.
Table 9.4 Methods of birth control
Method
Abstinence
Withdrawal
How the method works
Advantages
• Refraining from sexual • Completely effective.
intercourse.
• Protects against
sexually transmitted
infections.
• Penis is withdrawn
• No artificial device
before ejaculation.
needs to be used
or pills taken, i.e. it
is natural, therefore
is acceptable to all
religious groups.
Disadvantages
• Relies on self-control
from both partners.
• Very unreliable since
some semen is released
before ejaculation.
• Relies on self-control.
9 The reproductive system
89
Method
Rhythm
method
Disadvantages
• Unreliable since the time
of ovulation can vary.
• Restricts the time when
intercourse can occur.
• Unsuitable for women
with an irregular
menstrual cycle.
Spermicides
• Creams, jellies or foams • Easy to use.
• Not reliable if used
inserted into the vagina • Readily available.
alone, should be used
before intercourse.
with a condom or
diaphragm.
• Kill sperm.
• May cause irritation or
an allergic reaction.
Condom
• A latex rubber or
• Very reliable if used
• May reduce sensitivity
polyurethane sheath
correctly.
so interferes with
placed over the erect • Easy to use.
enjoyment.
penis or into the
• Condoms can tear
female vagina before • Readily available.
allowing sperm to enter
intercourse.
• Protects against
the vagina.
sexually transmitted
• Acts as a barrier to
• Latex may cause an
prevent sperm entering infections.
allergic reaction.
the female body.
Diaphragm
• A dome-shaped latex • Fairly reliable if used • Must be left in place
rubber disc inserted
correctly.
for 6 hours after
over the cervix before • Not felt, therefore,
intercourse, but no
intercourse. Should be
not interfere with longer than 24 hours.
used with a spermicide. does
enjoyment.
• Latex may cause an
• Acts as a barrier to
allergic reaction.
•
Easy
to
use
once
the
prevent sperm entering female is taught.
• May slip out of place if
the uterus.
not fitted properly.
Intra-uterine • A T-shaped plastic
• Very reliable.
• Must be inserted by a
medical practitioner.
device (IUD or device, usually
Once fitted, no further
containing copper or • action
coil)
• May cause
progesterone, inserted exceptisanrequired
annual
menstruation to be
into the uterus by a
checkup.
heavier, longer or more
doctor.
painful.
• No need to think
• Prevents sperm
further about
reaching the ova or
contraception.
prevents implantation.
• Few, if any, side effects.
Contraceptive • A hormone pill,
• Almost totally reliable if • Ceases to be effective if
taken daily, which
taken daily.
one pill is missed.
pill
contains oestrogen
is lighter, • May cause side effects
and progesterone, or • Menstruation
shorter
and
less
painful. in some women,
progesterone only.
especially those who
• Prevents ovulation.
smoke.
• Makes cervical mucus
thicker and more
difficult for sperm to
swim through.
90
How the method works
Advantages
• Intercourse is restricted • No artificial device
to times when ova
needs to be used
should be absent from
or pills taken, i.e. it
the oviducts.
is natural, therefore
is acceptable to all
religious groups.
9 Concise Revision Course: Human and Social Biology
Method
Surgical
sterilisation
(vasectomy in
males, tubal
ligation in
females)
How the method works
• The sperm ducts or
oviducts are surgically
cut and tied off.
• Prevents sperm leaving
the male body or ova
passing down the
oviducts.
Advantages
Disadvantages
• Totally reliable.
• Usually irreversible.
• No need to think
further about
contraception.
• No artificial device
needs to be used or
pills taken.
Note that one disadvantage of all methods except abstinence and condoms is that they do not protect
against sexually transmitted infections.
Condoms
Diaphragm
Intra-uterine device (IUD)
Figure 9.6 Methods of birth control
Contraceptive pills
The importance of family planning
Family planning involves making decisions about the number of children in a family and the time
between their births. Contraception plays a major role in family planning. Family planning is
important because:
• If the family is small, parents have more time to spend with each child, so each child receives
greater emotional and physical care and a better education from their parents.
• It is less expensive to have a small family.
9 The reproductive system
91
• It enables parents to decide at what age they wish to have a family, i.e. when they are young or later
in life after pursuing their careers.
• It decreases health risks to women and maternal deaths caused by unintended pregnancies and
unsafe abortions.
• It enables women to complete their education before having a family.
• It enables women to participate fully in society and advance in the workplace by allowing them to
plan when they have a family.
From a global perspective, the human population is growing rapidly and predictions are that this
will cause shortages of food, water, land and other natural resources, will increase pollution, the
destruction of the environment, unemployment and the spread of disease, and will decrease living
standards. Family planning can reduce population growth which should help maintain a healthy,
productive environment without shortages, and should improve living standards.
Issues related to abortion
Abortion is the termination of a pregnancy. It can occur naturally, known as a spontaneous abortion or
miscarriage, or it can be induced.
Spontaneous abortion
A miscarriage can occur for various reasons:
• The foetus has a chromosomal abnormality.
• The mother has a uterine abnormality so the embryo cannot implant properly in the lining, or she
has a weak cervix that cannot hold the foetus in the uterus as it grows.
• The mother suffers from certain medical conditions, such as diabetes or thyroid disease, that can
make conditions in the uterus difficult for the embryo to survive.
• The mother has an immune system disorder causing the foetus not to be accepted by her body.
• The mother smokes very heavily, drinks too much alcohol or overdoses on illegal drugs during
pregnancy.
Induced abortion
Abortion can be induced by the mother taking an abortion pill containing hormones or undergoing
a surgical procedure. Induced abortion is a very controversial topic and is illegal in many parts of
the world.
Arguments for the use of induced abortion
The following could be put forward as reasons for carrying out induced abortions:
• If the health of the mother or of the foetus is at risk.
• If the foetus has a severe genetic abnormality which would adversely affect the quality of life after
birth and put a strain on other family members.
• If the pregnancy is the result of rape and giving birth to an unwanted child would be a constant
reminder to the mother of the traumatic event.
• If the parents are unable to support a child or the child was conceived as a result of contraceptive
failure or the child is not wanted for other reasons, abortions prevent unwanted children from
being brought into the world.
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9 Concise Revision Course: Human and Social Biology
Arguments against the use of induced abortion
The following could be put forward as reasons against carrying out induced abortions:
• They can be used as a form of contraception and lead to irresponsible behaviour.
• They can give rise to medical complications, e.g. infection, and can lead to infertility, especially if
carried out illegally by unqualified persons (back street abortions).
• They can have a serious impact on a woman’s mental state, causing depression and other
psychological problems, sometimes years after the abortion.
• They are considered to be murder by persons who believe that life begins at conception, and many
religions believe that abortion is morally wrong.
Revision questions
1 Distinguish between sexual and asexual reproduction and suggest ONE possible
advantage and ONE possible disadvantage of EACH.
2 By means of a labelled and annotated diagram, indicate the function of EACH of the
different parts of the female reproductive system.
3 State the function of EACH of the following parts of the male reproductive system:
a the epididymis
b the sperm ducts
c the prostate gland
d the penis
4 a What happens in a person’s body to cause cancer to develop?
b Identify TWO parts of the female reproductive system and TWO parts of the male
reproductive system where cancer may develop.
5 a What happens during ovulation and menstruation?
b Explain the role of oestrogen and progesterone in the menstrual cycle.
6 Outline how ova and sperm are brought together for fertilisation to occur.
7 What role does the placenta play in the development of a human embryo?
8 Outline the steps involved in the birthing process.
9 a Sabrina is 3 months pregnant. Outline some of the steps she should take to ensure
the health of her developing baby.
b After Sabrina gives birth, she is strongly advised to breastfeed her baby for a
minimum of 6 months. Give FOUR reasons to support this advice.
100 Construct a table which explains how EACH of the following methods of birth control
prevents pregnancy, and gives ONE advantage and ONE disadvantage of EACH
method: the contraceptive pill, surgical sterilisation, the rhythm method and
the condom.
11 Suggest THREE reasons why family planning is important.
12 a What is a spontaneous abortion?
b Identify THREE possible causes of a spontaneous abortion.
9 The reproductive system
93
Exam-style questions –
Chapters 3 to 9
Structured questions
1 a) Figure 1 is a diagram of the human digestive system.
1
3
4
2
A
Figure 1 The human digestive system
i) Name the structure labelled 1, and state its function.
(2 marks)
ii) Nikoli is 7 years old and his mother is beginning to worry that his legs are
showing signs of bowing outwards, so she takes him to the doctor and the
doctor suggests he might be lacking vitamin D. Identify ONE way Nikoli
(1 mark)
could increase his intake of vitamin D.
iii) Which numbered structure in Figure 1 would vitamin D have an effect on?
(1 mark)
iv) Explain how increasing his intake of vitamin D would affect the structure
(1 mark)
identified in a) iii) above and help treat Nikoli’s condition.
b) Table 1 gives the body mass index (BMI) of five people. A person with a healthy weight
would have a body mass index between 18.5 and 24.9 kg per m2.
Table 1 Body mass index of five people
Name
Body mass index in kg per m2
Akeem
37.9
Zane
5.4
Alex
28.6
Romain
43.0
Mitchell
22.5
i) Which person has the healthiest body mass index?
ii) Draw a bar graph to represent the data in Table 1.
94
Exam-style questions – Chapters 3 to 9
(1 mark)
(3 marks)
2
iii) Which two people in Table 1 are most likely to be suffering from malnutrition? (2 marks)
iv) Name a disease that EACH person identified in b) iii) might be suffering from and
identify the main factors that could have led to the development of EACH disease
(4 marks)
named.
Total 15 marks
a) Distinguish between respiration and breathing.
(2 marks)
b) Figure 2 shows part of the human respiratory system.
B
C
alveoli
Figure 2 Part of the human respiratory system
i) Name the structures labelled B and C.
(2 marks)
ii) Complete the following sentence by filling in the blank spaces:
To inhale, the external intercostal muscles and diaphragm muscles
causing the ribcage to move upwards and
, and the
(3 marks)
diaphragm to
.
iii) Identify TWO features of the alveoli that make them efficient in carrying
(2 marks)
out gaseous exchange.
c) A study was carried out into the link between smoking levels and lung cancer. The
researchers recorded the number of deaths from lung cancer per 100 000 individuals in the
population, and the smoking levels of each person dying. The results for men aged 60 to
69 years are given in Table 2 below.
Table 2 Death rates from lung cancer among men aged 60 to 69 years related to smoking levels
Death rate per
Level of smoking
100 000 population
Never smoked
12
234
Smoked 20 cigarettes 30 years
per day for:
40 years
487
576
Smoked 40 cigarettes 30 years
per day for:
40 years
608
i) Which individuals are most at risk of dying from lung cancer?
(1 mark)
ii) Give TWO conclusions that the researches could have drawn from the results. (2 marks)
Exam-style questions – Chapters 3 to 9
95
d) Tamara used to be a very good sprinter; however, she started to smoke
heavily and now finds that whenever she tries to run she quickly becomes
breathless and at times she even collapses.
i) Write a word equation to summarise what causes Tamara to collapse.
ii) Other than lung cancer, suggest TWO ways that Tamara’s heavy smoking
contributes to her breathlessness.
(1 mark)
(2 marks)
Total 15 marks
3 a) Figure 3 shows the internal structure of the heart.
aorta
anterior
vena cava
Q
R
S
Figure 3 The internal structure of the heart
i) Identify the parts labelled R and S.
ii) What is the function of the structure labelled Q?
iii) Complete Table 3 to compare the aorta with the anterior vena cava.
Table 3 Differences between the aorta and the anterior vena cava
Aorta
Anterior vena cava
Pressure of blood
carried
Thickness of the walls
(2 marks)
(1 mark)
(2 marks)
(2 marks)
iv) Humans have a double circulation. Explain what this means.
b) Jerome is rushed to hospital complaining of a tight feeling and pain in his chest
and pain in his arms, shoulders and neck.
i) What might Jerome be suffering from?
(1 mark)
ii) Explain what could have led up to Jerome’s current situation.
(3 marks)
c) Sabrina spends all day sitting working at her computer and by the end of the day
she notices that her feet and ankles appear swollen.
i) By reference to her lymphatic system, explain why Sabrina’s feet and ankles
(3 marks)
are swollen.
ii) What suggestion would you give to Sabrina to avoid the same thing
(1 mark)
happening again?
Total 15 marks
96
Exam-style questions – Chapters 3 to 9
4 a) State TWO functions of the skeleton, other than movement.
b) Figure 4 is a diagram of a knee joint.
(2 marks)
F
5
Figure 4 A knee joint
i) Name the type of joint shown in Figure 4.
(1 mark)
ii) Identify F and state its main function.
(2 marks)
iii) How does movement of the knee joint differ from movement at the hip joint? (2 marks)
iv) Jordan is told by his doctor that he needs to have one of his knees replaced.
(2 marks)
Suggest TWO reasons why this might be necessary.
c) Shakira works as a shop assistant and goes to the gym each day after work.
i) Explain how Shakira’s elbow joint works as she bends and straightens it
(4 marks)
repeatedly during her daily workout using dumbbells.
ii) Shakira wears high-heeled shoes to work each day. Suggest TWO adverse
(2 marks)
effects this might have on her body.
Total 15 marks
a) i) What is meant by the term ‘excretion’?
(2 marks)
ii) Name ONE excretory organ, other than the kidney, found in the human body
(2 marks)
and identify ONE substance that it excretes.
b) Figure 5 is a diagram of a nephron found in a human kidney.
Y
H
G
Z
J
Figure 5 Diagram of a nephron
i) Identify the structures labelled G, H and J in Figure 5.
ii) Briefly describe the process that takes place in EACH of the structures
labelled Y and Z.
(3 marks)
(4 marks)
Exam-style questions – Chapters 3 to 9
97
6
c) Table 4 shows the composition of Andrew’s urine 1 hour after he drank 2 large glasses of
water and again 1 hour after he played a 90-minute game of football in the heat of the day,
without drinking.
Table 4 Composition of Andrew’s urine
in Andrew’s urine % in Andrew’s urine
Component %
after drinking
after playing football
Urea
2.0
6.0
Salt
0.3
1.0
Water
95
90
i) Which activity caused Andrew’s urine to have the HIGHEST concentration?
(1 mark)
ii) Name the hormone secreted by Andrew’s pituitary gland when there is not
(1 mark)
enough water in his body fluids.
iii) Explain how the hormone named in c) ii) above functioned to prevent
Andrew losing too much water in his urine when his body fluids became too
(2 marks)
concentrated.
Total 15 marks
a) Complete the following sentence:
The nervous system can be divided into the
nervous system
(2 marks)
and the
nervous system.
b) Figure 6 is a diagram of a neurone.
K
L
M
Figure 6 A neurone
i) Name the parts labelled K and L.
(2 marks)
ii) State the function of L.
(1 mark)
iii) How do impulses travel from the structures labelled M to adjacent neurones
(1 mark)
in the brain?
c) Complete Table 5 below, which gives information about three different regions of the brain.
Table 5 Functions of three regions of the brain
Region of the brain One function
Medulla oblongata •
• Controls conscious thought
Cerebellum
•
(3 marks)
98
Exam-style questions – Chapters 3 to 9
d) i) Dana’s dress has a hole in it that needs mending, so she cuts a piece of cotton thread
and threads her needle. Are her actions voluntary or involuntary? Give ONE reason to
(2 marks)
support your answer.
ii) Dana starts to mend the hole, but accidently pricks her finger causing her to
immediately pull her hand away from the needle. Complete Figure 7 below by drawing
(3 marks)
and labelling THREE neurones involved in bringing about Dana’s action.
pain receptors
in the skin
spinal cord
biceps muscle
in the upper arm
Figure 7 Parts of the nervous system
iii) What term is used to describe Dana’s action in d) ii) above?
(1 mark)
Total 15 marks
7 a) Figure 8 shows the male and female reproductive systems.
III
IV
I
II
Figure 8 Male and female reproductive systems
i) Complete Table 6 below by writing the name and ONE function of EACH of the
structures labelled I and III
Table 6 Name and function of parts of the human reproductive systems
Name of structure
One function
I
III
ii) Suggest TWO reasons why structures labelled II and IV in Figure 8 may be
described as having similar functions.
iii) Place arrows on the male reproductive system to show the pathway taken
by sperm as it travels out of the male body.
(4 marks)
(2 marks)
(2 marks)
Exam-style questions – Chapters 3 to 9
99
b) Figure 9 shows the number of births to teenage mothers aged 16 and 17 years over five-year
periods from 1980 to 2009 in a certain Caribbean territory.
400
16 year olds
350
17 year olds
300
shtrib fo rebmuN
250
200
150
100
50
0
80–84
85–89
90–94
Years
95–99
00–04
05–09
Figure 9 Number of births to mothers aged 16 and 17 years between 1980 and 2009
i) In which five-year period was the total number of births the HIGHEST?
(1 mark)
ii) Between which two five-year periods was the GREATEST decrease in the
(1 mark)
number of births recoded?
iii) Describe TWO trends shown in Figure 9.
(2 marks)
iv) It is thought that increased use of contraception among teenagers, particularly
condoms, could possibly account for the overall trend in teenage pregnancy
numbers in the country. Explain how condoms act as a method of birth control
(3 marks)
and give ONE advantage and ONE disadvantage of their use.
Total 15 marks
Structured essay questions
8 a) Alexa is advised by her doctor that after her baby is born she should feed him on breast
milk for the first 6 months of his life because breast milk is a complete food for babies.
i) Why is breast milk considered to be a complete food for babies?
(2 marks)
ii) Alexa takes her doctor’s advice and breastfeeds her baby, Jay, from birth.
Describe how the milk is digested as it passes through Jay’s digestive system. (6 marks)
iii) There is a tendency for babies fed on powered milk to gain weight more
(2 marks)
rapidly than breastfeed babies. Suggest TWO reasons for this.
b) Alexa is also told that Jay must develop teeth before he can digest solid foods properly.
i) Explain why Jay needs to develop teeth before he can properly digest any
(3 marks)
solid food in his diet.
ii) Why is it important that the enamel of Jay’s teeth is the hardest substance
(2 marks)
found in his body?
Total 15 marks
100
Exam-style questions – Chapters 3 to 9
9 a) Define the term ‘homeostasis’ and outline how negative feedback mechanisms
(4 marks)
play an important role in homeostasis.
b) Jason goes on a hiking expedition into the mountains and loses his way as it
begins to get dark. He is forced to spend the night high up in the mountains
and begins to get very cold. Explain how his body responds to conserve as
(6 marks)
much heat as possible.
c) On Sports Day Britnee runs a 200 m race. After crossing the finish line she
realises that she is breathing much faster and deeper than normal. Explain what
(5 marks)
is taking place in her body to bring about the changes in her breathing.
Total 15 marks
10 a) Give THREE differences between control by the nervous system and control
(3 marks)
by the endocrine system.
b) i) Describe the changes that occur in Aiden’s eyes as he looks up from the
(4 marks)
smart phone in his hand to watch a bird in the top of a tree.
ii) As Aiden gets older, he finds it harder and harder to focus on his smart
phone. Suggest the possible cause of Aiden’s difficulty and explain what
(4 marks)
he must do to correct it.
c) Aiden is also found to have developed an underactive pituitary gland. By referring
to TWO different hormones produced by Aiden’s pituitary gland, explain how this
(4 marks)
reduced activity could affect his body.
Total 15 marks
11 a) i) Describe the events taking place in Rasheeda’s ovaries and uterus during one
(5 marks)
complete menstrual cycle.
ii) Name TWO hormones, other than those secreted by Rasheeda’s pituitary gland,
(4 marks)
that control her menstrual cycle and outline the role played by EACH.
b) Rasheeda misses her period and decides to go to the doctor because she thinks
she might be pregnant. Her doctor confirms her suspicions. Outline the role that
the placenta, umbilical cord and amniotic fluid play in the development of
(6 marks)
Rasheeda’s baby during her pregnancy.
Total 15 marks
Exam-style questions – Chapters 3 to 9
101
Section C – Heredity and variation
10 Cell division and variation
Cells contain all the information they need to control their activities coded as genetic information
in their genes. These genes are passed on to new cells during cell division. Living organisms show
variation and much of this variation is passed on from one generation to the next via genes.
An introduction to chromosomes and genes
Chromosomes
Chromosomes are present in the nuclei of all living cells. Each chromosome is composed of a single
deoxyribonucleic acid (DNA) molecule wrapped around proteins called histones. DNA molecules contain
genetic information in the form of genes. In any cell that is not dividing, chromosomes exist as long, thin
strands known as chromatin threads, which are spread throughout the nucleus. Chromosomes become
visible when a cell begins to divide, due to them becoming shorter and thicker.
Chromosomes are passed on from one generation to the next in gametes and each species has
a distinctive number of chromosomes per body cell; every human cell has 46 chromosomes. The
number of chromosomes in each cell is known as the diploid number or 2n number. Chromosomes
exist in pairs known as homologous pairs. Every human cell has 23 pairs, one member of each pair
being of maternal origin and the other of paternal origin. With the exception of the pair of sex
chromosomes, members of each homologous pair are similar in shape, size and genetic composition.
Genes
Genes are specific sections of chromosomal DNA molecules and are the basic units of heredity. Each
human body cell has over 30 000 genes and each gene controls a particular characteristic. Genes
work by controlling the production of proteins in cells, mainly the production of enzymes. Each gene
controls the production of a specific protein.
All the cells of one individual contain an identical combination of genes. It is this combination which
makes each individual unique since no two individuals, except identical twins or organisms produced
asexually, have the same combination of genes. Within any cell some genes are active while others
are inactive, e.g. in a nerve cell, genes controlling the activity of the nerve cell are active and genes
that would control the activity of a muscle cell are inactive.
Cell division
When a cell divides, chromosomes with their genes are passed on to the cells produced, known as
daughter cells. There are two types of cell division: mitosis and meiosis.
Mitosis
Mitosis is the type of cell division that results in the formation of two daughter cells, each with the
same number and kind of chromosomes as the parent cell.
Mitosis occurs in all body (somatic) cells except in the formation of gametes. During mitosis, two
genetically identical cells are formed. Each cell contains the diploid number of chromosomes. All cells
produced by mitosis from a single parent cell are collectively called a clone.
Mitosis is important because:
• It ensures that each daughter cell has the same number and type of chromosomes as the parent cell.
• It ensures that each daughter cell has an identical combination of genes.
• It is the method by which all cells of a multicellular organism are formed, hence it is essential for
growth and to repair damaged tissues.
• It is the method by which organisms reproduce asexually, forming offspring that are identical to
each other and to the parent.
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10 Concise Revision Course: Human and Social Biology
nuclear membrane
centrioles
chromatin threads
composed of DNA
centromere
two chromatids
spindle fibres
centromere – attached
to the equator of the spindle
spindle fibres
chromatids separating
spindle fibres
disintegrate
chromosomes
new cell membranes
form
When the cell is not dividing,
the chromosomes are not visible;
they exist as long, thin strands
called chromatin threads
The chromosomes shorten, thicken,
duplicate themselves and become visible;
each consists of two identical chromatids
joined at the centromere. The centrioles
separate forming spindle fibres between them
The nuclear membrane disintegrates
and a spindle forms between the centrioles.
The chromatid pairs line up around the
equator of the spindle
The centromeres split and the spindle fibres
pull the chromatids, by their centromeres,
to opposite poles of the cell
The chromatids reach the opposite
poles and are now called chromosomes.
The spindle fibres disintegrate, and the
cell constricts at the equator
A nuclear membrane forms around
each group of chromosomes. The cell
divides forming two, identical daughter
cells each with the diploid number of
chromosomes. The chromosomes then
become long and thin so they are no
longer visible
Figure 10.1 The process of mitosis in an animal cell with four chromosomes; two of paternal origin
(blue) and two of maternal origin (red)
Meiosis (reduction division)
Meiosis is the type of cell division that results in the formation of four daughter cells, each with half
the number of chromosomes as the parent cell.
Meiosis occurs only in the reproductive organs during the production of gametes. During meiosis,
four genetically non-identical cells are formed. Each cell contains the haploid number or n number of
chromosomes, i.e. half the diploid number.
10 Cell division and variation
103
Meiosis is important because it ensures that:
• Each daughter cell or gamete has the haploid number of chromosomes. The diploid number can
then be restored at fertilisation.
• Each daughter cell or gamete has a different combination of genes. This leads to variation among
offspring (see page 105).
two chromosomes
of maternal origin
centrioles
two chromosomes
of paternal origin
centromere
centrioles
separating
nuclear membrane
crossover point
spindle fibres
spindle
exchanged
segments of
crossed over
chromatids
bivalents
separating
nuclear membrane
The chromosomes
shorten, thicken and
become visible
pair of homologous
chromosomes forming
a bivalent
The homologous
chromosomes pair forming
bivalents. The centrioles
separate forming spindle
fibres between
Each chromosome
duplicates itself forming
two chromatids joined by
a centromere. Adjacent
chromatids cross over
each other
The nuclear membrane
disappears and the
bivalents arrange
themselves around the
equator of the spindle.
The chromatids break at
the crossover points and
rejoin with opposite
chromatids thus
exchanging genetic
material
The homologous
chromosomes of the
bivalents separate and
the spindle fibres pull the
chromosomes, each
composed of two
chromatids, to opposite
poles of the cell
A nuclear membrane
forms around each group
of chromosomes. The
spindle fibres disintegrate
and the centrioles divide.
The cell constricts at the
equator forming two cells
The centrioles in each cell separate
forming two new spindles at right angles
to the first spindle
The nuclear membranes disappear. The
chromosomes, each composed of two
chromatids, line up around the equators
of the spindles
chromatids
separating
The centromeres split, and the spindle
fibres pull the chromatids to opposite
poles of the cells
The chromatids reach the opposite poles
of the cells and are now called
chromosomes. The spindle fibres
disintegrate. A nuclear membrane forms
around each group of chromosomes and
each cell divides. Four daughter cells are
formed, each with the haploid number of
chromosomes whose compositions are
different. The chromosomes then
become long and thin, so they are no
longer visible
Figure 10.2 The process of meiosis in an animal cell with four chromosomes
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10 Concise Revision Course: Human and Social Biology
immature ovum 2n
in an ovary
in the wall of a
2n cell
seminiferous tubule
in the testis
meiosis
meiosis
one cell develops n
into a mature ovum n
n
n
fertilisation
n
n
n
n
sperm cells
2n a zygote
mitosis
embryo composed
2n 2n an
of two cells
mitosis
an embryo composed of
2n 2n four cells – by mitosis
2n 2n continuing; an adult is eventually
formed with all cells containing the
2n number of chromosomes
Figure 10.3 The relationship between mitosis and meiosis
Variation
No two living organisms are exactly alike, not even identical twins. Variation refers to the differences
that exist between individuals and it arises from a combination of genetic causes and environmental
causes.
The observable characteristics of an individual make up the individual’s phenotype, and the composition
of genes within the cells of an individual makes up the individual’s genotype. The phenotype of an
individual is determined by his or her genotype and the influences of his or her environment:
phenotype = genotype + environmental influences
Genetic and environmental causes of variation
Genetic variation
Genetic variation is controlled by genes and can be passed on from one generation to the next, i.e. it
can be inherited. It arises in several ways:
• Meiosis. Every gamete produced by meiosis has a different combination of genes as a result of:
Chromatids of homologous chromosomes crossing over and exchanging genes.
Chromosomes arranging themselves around the equators of the spindles in totally random ways.
• Sexual reproduction. During fertilisation, male and female gametes fuse in completely random ways
to create a different combination of genes in each zygote.
• Mutations. A mutation is a change in the structure of a single gene, the structure of part of a
chromosome containing several genes or in the number of chromosomes in a cell. Mutations cause
new characteristics to develop in organisms. Mutations occurring in body cells cannot be inherited,
whereas mutations occurring in a gamete or zygote can be inherited. Many mutations are harmful;
however, a few produce beneficial characteristics which help the organism survive. Examples of
mutations include:
Albinism, which is caused by a mutation in a gene controlling the production of melanin. People
with albinism produce very little or no melanin in their skin, eyes and hair (see page 108).
10 Cell division and variation
105
Down’s syndrome, which occurs when an individual has an extra chromosome 21 in each of their
cells because pair 21 fails to separate properly during meiosis and both chromosomes pass into
one gamete. Individuals with Down’s syndrome usually have flattened facial features, a short
wide neck, small ears, a bulging tongue, slanted eyes, short stocky arms and legs, poor muscle
tone and slow learning capabilities.
Antibiotic resistance, which can arise in bacteria from a mutation occurring in some bacterial cells
that makes them resistant to certain antibiotics. When exposed to these antibiotics, the resistant
organisms are more likely to survive and reproduce than the non-resistant ones, passing their
resistance on to the next generation.
Environmental variation
Environmental variation is caused by different factors in an organism’s environment. It is not caused
by genes and cannot be passed on from one generation to the next. Environmental factors affecting
humans include:
• The type and quantity of food they eat.
• The diseases they suffer from.
• The drugs they take.
• The climate they are exposed to, especially the amount of sunlight.
• Their upbringing and living conditions.
• The education they receive.
• The amount of exercise they get and their daily activities.
Continuous and discontinuous variation
There are two basic types of variation within a species: continuous variation and
discontinuous variation.
Continuous variation
slaudividni fo rebmun
Continuous variation is where characteristics show
continuous gradation from one extreme to the other without
a break. Most individuals usually fall in the middle of the
range with fewer at the two extremes, i.e. the characteristics
show a normal distribution. Examples include height,
weight, foot size, hand span, hair colour, skin colour
and intelligence.
Characteristics showing continuous variation are
usually controlled by many genes and can be affected by
environmental factors.
mean height
height
Figure 10.4 A normal distribution
curve showing height
Discontinuous variation is where characteristics show clear cut differences with no intermediates.
Individuals can be divided into distinct categories. Examples include gender, ABO blood groups,
rhesus blood groups and tongue-rolling ability. Characteristics showing discontinuous variation are
usually controlled by a single gene and environmental factors have little, if any, influence on them.
Discontinuous variation
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10 Concise Revision Course: Human and Social Biology
The importance of variation to living organisms
Within any species, individuals with variations that make them best suited to their environment
have a better chance of survival than the others. More of these individuals will survive to reproduce
and when they do, they pass on the genetic information for their beneficial characteristics to their
offspring. This process is known as natural selection. Over time, this enables species to remain well
adapted to their environment or to gradually change and improve by becoming better adapted, i.e.
it enables species to evolve. For example, some species of bacteria have become resistant to almost
all commonly available antibiotics, enabling them to survive when antibiotics are used to treat a
bacterial infection.
Revision questions
1 Define the following terms:
a mitosis
b meiosis
2 Outline the process of mitosis.
3 Give THREE reasons why mitosis is important to living organisms.
4 In what ways does meiosis differ from mitosis?
5 Give TWO reasons why meiosis is important to living organisms.
6 Distinguish between genetic and environmental variation.
7 a What is a mutation?
b By reference to albinism and Down’s syndrome, explain how mutations cause
variation.
8 Identify FOUR environmental factors that can cause variation in humans.
9 Outline the differences between continuous and discontinuous variation.
100 Explain why variation is important to living organisms. Support your answer by
referring to antibiotic resistance in bacteria.
10 Cell division and variation
107
11 Inheritance and genetic
engineering
The branch of science which seeks to understand how characteristics are passed on from one
generation to the next is known as genetics. For over 200 years humans have selected and crossed
plants and animals to produce improved varieties due to the mixing of genetic material. Since the
structure of DNA was discovered in 1953, gene technology has moved at an ever-increasing pace to
improve food production and the production of medicinal drugs.
Monohybrid inheritance
Monohybrid inheritance is the inheritance of a single characteristic. Like chromosomes, genes exist in
pairs. One gene of each pair is of maternal origin and one is of paternal origin, and the pairs occupy
equivalent positions on homologous chromosomes. A gene controlling a particular characteristic can
have different forms known as alleles. Each gene usually has two different alleles.
Example: albinism
People with albinism produce very little or no melanin in their skin, eyes and hair. The gene
controlling the production of the pigment melanin has two different alleles which can be represented
using letters:
• N stimulates melanin production
• n fails to stimulate melanin production
The allele stimulating melanin production, N, is dominant, i.e. if it is present it shows its effect on the
phenotype. The allele for albinism, n, is recessive, i.e. it only has an effect on the phenotype if there is
no dominant allele present. Three combinations of these alleles are possible; NN, Nn and nn. If the
two alleles are the same, the organism is said to be homozygous. If the two alleles are different, the
organism is said to be heterozygous. Heterozygous individuals are carriers because they can pass on a
recessive allele.
Table 11.1 Possible combinations of the alleles controlling melanin production
Genotype
How the alleles appear on
Phenotype (appearance)
(combination of alleles) homologous chromosomes
N
NN
Normal pigmentation of the skin, eyes
and hair
Homozygous dominant
(pure breeding)
N
N
Nn
Normal pigmentation of the skin, eyes
and hair
Heterozygous (carrier)
nn
Homozygous recessive
(pure breeding)
n
n
n
Albino – very pale skin that does not tan,
white or light blond hair and very pale
blue eyes
Gametes produced in meiosis contain only one chromosome from each homologous pair. As a result,
they contain only one allele from each pair. When fertilisation occurs, chromosomes and the alleles
they carry recombine to form pairs in the zygote.
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11 Concise Revision Course: Human and Social Biology
Results of possible crosses
1 If one parent is homozygous dominant and one is homozygous recessive:
Parental phenotypes
Parental genotypes (2n)
normal pigmentation
NN
Gametes (n)
N
N
n
n
Nn
Nn
Nn
Nn
albino
nn
Random fertilisation
First filial generation (F1) genotypes
First filial generation (F1) phenotypes
normal pigmentation
All the offspring have normal pigmentation
2 If one parent is heterozygous and one is homozygous recessive, showing the use of a Punnett square
to predict the outcome of the cross:
Parental phenotypes normal pigmentation
Nn
Parental genotypes
Gametes
N n
gametes
n
n
N
Nn
Nn
n
nn
nn
Random fertilisation
F1 genotypes
albino
nn
n n
Nn
Nn
nn
normal pigmentation
F1 phenotypes
50% of the offspring have normal pigmentation
50% of the offspring have albinism
nn
albino
3 If both parents are heterozygous, i.e. carriers:
Parental phenotypes
Parental genotypes
Gametes
normal pigmentation
Nn
F1 genotypes
n
N
Random fertilisation
NN
n
N
gametes
N
n
N
NN
Nn
n
Nn
nn
Nn
nn
Nn
F1 phenotypes
normal pigmentation
75% of the offspring have normal pigmentation
25% of the offspring have albinism
Co-dominance
normal pigmentation
Nn
albino
Sometimes neither allele dominates the other, such that the influence of both alleles is visible in the
heterozygous individual. These alleles show co-dominance. Examples include sickle cell anaemia and
ABO blood groups.
109
11 Inheritance and genetic engineering
Sickle cell anaemia
The blood of a person with sickle cell anaemia contains abnormal haemoglobin S instead of normal
haemoglobin A. The disease is caused by an abnormal allele. The normal allele HbA stimulates the
production of normal haemoglobin A, the abnormal allele HbS stimulates the production of abnormal
haemoglobin S. These alleles show co-dominance.
Table 11.2 Possible combinations of alleles controlling haemoglobin production
Genotype Haemoglobin produced
Phenotype
HbA HbA
Normal.
100% haemoglobin A
A
S
Hb Hb
Sickle cell trait. Usually no symptoms. Symptoms of
55–65% haemoglobin A
35–45% haemoglobin S
sickle cell anaemia may develop in very low oxygen
concentrations, e.g. at high altitude or during
extreme physical exercise. People with the trait are
resistant to malaria.
S
S
Hb Hb
Sickle cell anaemia. Symptoms of sickle cell anaemia
100% haemoglobin S
develop which include painful crises, anaemia,
increased vulnerability to infections and jaundice.
For example, if both parents have sickle cell trait:
Parental phenotypes
sickle cell trait
sickle cell trait
Parental genotypes
HbAHbS
HbAHbS
Gametes
HbA
HbA
HbAHbA
F1 phenotypes
normal
HbS
gametes
HbA
HbS
HbA
HbAHbA
HbAHbS
HbS
HbAHbS
HbSHbS
Random fertilisation
F1 genotypes
HbS
HbAHbS
HbAHbS
sickle cell trait
25% of the offspring are normal
50% of the offspring have the sickle cell trait
25% of the offspring have sickle cell anaemia
ABO Blood groups
ABO blood groups are controlled by three alleles, IA, IB and IO.
• IA and IB are both dominant to IO.
• IA and IB are co-dominant, i.e. there is no dominance between them.
Only two alleles are present in any cell.
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11 Concise Revision Course: Human and Social Biology
HbSHbS
sickle cell anaemia
Table 11.3 Possible combinations of alleles controlling ABO blood groups
Genotype Phenotype
IA IA
Blood group A
IA IO
Blood group A
B
B
II
Blood group B
IB IO
Blood group B
IA IB
Blood group AB
O
O
I I
Blood group O
For example, if one parent is heterozygous with blood group A and the other is heterozygous with blood
group B:
Parental phenotypes
Parental genotypes
Gametes
blood group A
I A IO
IA IO
blood group B
I B IO
IB I O
gametes
IB
IO
IA
I A IB
I A IO
IO
I B IO
I O IO
Random fertilisation
F1 genotypes
F1 phenotypes
I A IB
I A IO
blood
blood
group AB
group A
25% of the offspring have blood group AB
25% of the offspring have blood group A
25% of the offspring have blood group B
25% of the offspring have blood group O
I B IO
blood
group B
I O IO
blood
group O
The inheritance of sex in humans
In each cell, one pair of chromosomes is composed of the sex chromosomes. There are two types, X and Y,
and they determine the individual’s sex. Genotype XX is female; genotype XY is male. Only the male can
pass on the Y chromosome, consequently the father is the parent who determines the sex of his offspring.
Parental phenotypes
female
XX
Parental genotypes
Gametes
male
XY
X
X
X
Y
XX
female
XY
male
XX
female
XY
male
Random fertilisation
F1 genotypes
F1 phenotypes
50% of the offspring are female
50% of the offspring are male
11 Inheritance and genetic engineering
111
Sex-linked characteristics
Sex-linked characteristics are characteristics determined by genes carried on the sex-chromosomes
that have nothing to do with determining the sex of the offspring. These are known as sex-linked
genes. Since chromosome X is longer than chromosome Y, it carries more genes. Males only have one
X chromosome and any allele carried on this chromosome only, whether dominant or recessive, will
be expressed in the phenotype. Examples of sex-linked characteristics include haemophilia and colour
blindness.
Haemophilia
Haemophilia is a sex-linked condition where the blood fails to clot at a cut. The dominant allele, H,
causes blood to clot normally; the recessive allele, h, causes haemophilia. These alleles are carried
on the X chromosome only. Males are much more likely to be haemophiliacs than females; if the
single X chromosome in a male carries the recessive allele he will have the condition, whereas both X
chromosomes must carry the recessive allele in a female for her to have the condition.
Table 11.4 Possible combinations of alleles controlling blood clotting
Genotype Phenotype
XH XH
Female, normal blood clotting
XH Xh
Female, normal blood clotting (carrier)
Xh Xh
Female, haemophiliac
H
XY
Male, normal blood clotting
Xh Y
Male, haemophiliac
Example
A cross between a female with normal blood clotting who is a carrier, and a male with normal
blood clotting.
Parental phenotypes
Parental genotypes
female, normal clotting
XHXh
Gametes
F1 genotypes
F1 phenotypes
Xh
XH
Random fertilisation
XHXH
male, normal clotting
XHY
XH
gametes
XH
Y
XH
XHXH
XHY
Xh
XHXh
XhY
XHY
female,
male,
normal clotting
normal clotting
All the female offspring have normal blood clotting
50% of the male offspring have normal blood clotting
50% of the male offspring have haemophilia
112
Y
XHXh
XhY
female,
normal clotting
male
with haemophilia
11 Concise Revision Course: Human and Social Biology
Colour blindness
Colour blindness (also known as red–green colour blindness) is a sex-linked condition where the
sufferer is unable to distinguish differences between certain colours. The dominant allele, R, allows
normal vision and the recessive allele, r, causes colour blindness. These alleles are carried on the X
chromosome only, so colour blindness is inherited in the same way as haemophilia.
Some important genetic terms
Chromosome: a thread-like structure composed of deoxyribonucleic acid (DNA) and protein, which
contains genetic information in the form of genes.
Gene: the basic unit of heredity which is composed of DNA, occupies a fixed position on a
chromosome and determines a specific characteristic.
Allele: either of a pair (or series) of alternative forms of a gene that occupy the same position on a
particular chromosome and that control the same characteristic.
Dominant allele: the allele which, if present, produces the same phenotype whether its paired allele is
identical or different.
Recessive allele: the allele that only shows its effect on the phenotype if its paired allele is identical.
Dominant trait: an inherited characteristic that results from the presence of a single dominant allele. It
is seen in an individual with one or two dominant alleles.
Recessive trait: an inherited characteristic that results from the presence of two recessive alleles. It is
only seen in an individual with no dominant allele.
Co-dominance: neither allele dominates the other such that the influence of both alleles is visible in
the heterozygous individual.
Genotype: the combination of alleles present in an organism.
Phenotype: the observable characteristics of an organism.
Homozygous: having two identical alleles in corresponding positions on a pair of
homologous chromosomes.
Heterozygous: having two different alleles in corresponding positions on a pair of
homologous chromosomes.
Genetic engineering
Genetic engineering or recombinant DNA technology involves changing the traits of one organism by
inserting genetic material from a different organism into its DNA. The organism receiving the genetic
material is called a transgenic organism or genetically modified organism (GMO).
Genetic engineering is used to:
• Improve the quality of a food product, e.g. by increasing nutritional value.
• Improve yields of livestock and crops, e.g. by increasing size or growth rate, or by making
organisms hardier.
• Protect agricultural crops against environmental threats, e.g. pathogens, pests, herbicides and low
temperatures.
• Make organisms produce materials that they do not usually produce, e.g. vaccines and drugs.
Genetic engineering and food production
Genetic engineering is used to improve food production. Some examples follow.
11 Inheritance and genetic engineering
113
Golden rice
By inserting two genes into rice plants, one from
maize and one from a soil bacterium, the rice grains
are stimulated to produce beta-carotene which the
body converts to vitamin A. Golden rice should help
fight vitamin A deficiency, which is a leading cause
of blindness, and often death, of children in many
developing countries.
Bovine somatotrophin (BST) hormone
By transferring the gene which controls the production
of BST hormone from cattle into bacteria, the bacteria
produce the hormone, which is then injected into
cattle to increase milk and meat production.
Figure 11.1 Golden rice
Chymosin (rennin)
By transferring the gene which controls the production of chymosin from calf stomach cells into
bacteria or fungi, the microorganisms produce chymosin, which is used in cheese production. This
has considerably increased the production of cheese worldwide.
Genetic engineering and medical treatment
Genetic engineering is used to produce many drugs used in medical treatment. Some examples follow.
Insulin
By transferring the gene that controls insulin production in humans into bacteria, the bacteria
produce human insulin which is used to treat diabetes.
bacterium
human pancreas cell
plasmid –
ring of DNA
chromosome with
insulin-producing gene
in its DNA
plasmid DNA is
removed and cut using
restriction enzymes
insulin-producing
gene is cut out
insulin-producing gene is
inserted into the plasmid DNA
forming recombinant DNA
recombinant DNA is
reintroduced into a bacterium
the bacterium multiplies and
all the cells produce insulin
insulin is separated
and purified
Figure 11.2 Recombinant DNA technology to produce insulin
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Human growth hormone (HGH)
By transferring the gene controlling the production of HGH into bacteria, the bacteria produce the
hormone which is used to treat growth disorders in children.
Hepatitis B vaccine
By transferring the gene controlling the production of hepatitis B antigens by the hepatitis B virus
into yeast, the yeast produces the antigens, which are used as a vaccine.
Other drugs produced by genetic engineering
• Blood clotting drugs for haemophiliacs.
• Follicle stimulating hormone (FSH) used to stimulate the ovaries to release ova in women that are
infertile.
• Interferons used to treat viral infections and certain cancers.
• Anticoagulants used to prevent the development of life-threatening blood clots in heart patients.
• Human papilloma virus vaccine.
Possible advantages of genetic engineering
• Yields can be increased by genetic engineering, which should increase the world food supply and
reduce food shortages.
• The nutritional value of foods can be increased by genetic engineering, which should reduce
deficiency diseases worldwide.
• The need for chemical pesticides that harm the environment can be reduced by genetically
engineering crops to be resistant to pests.
• Vaccines produced by genetic engineering are generally safer than vaccines containing live and
weakened, or dead pathogens.
• Larger quantities of drugs in a safer and purer form can be produced than were previously
produced from animal sources, resulting in more people worldwide having ready access to safe,
life-saving drugs.
• It overcomes ethical concerns of obtaining certain drugs from animals, e.g. insulin used to be
obtained from pigs and cows.
Possible disadvantages of genetic engineering
• Plants genetically engineered to be toxic to a pest may also be toxic to useful organisms, e.g. insects
which bring about pollination. This could reduce reproduction in crops, reducing food production.
• Plants genetically engineered to be resistant to pests and herbicides could create unpredictable
environmental issues, e.g. they could lead to the development of pesticide-resistant pests and
herbicide resistant ‘superweeds’.
• Once a genetically modified organism is released into the environment it cannot be contained or
recalled. Any negative effects are irreversible.
• The number of allergens in foods could be increased by transferring genes causing allergic
reactions between species.
• As yet unknown health risks may occur as a result of eating genetically modified plants and animals.
• Large companies with funds and technology to develop genetically modified organisms could
make large profits at the expense of smaller companies and poorer nations.
• Future steps in genetic engineering might allow the genetic makeup of higher organisms, including
humans, to be altered, e.g. to produce ‘designer babies’. Difficult moral and ethical issues then arise,
e.g. how far should we go in changing our own genes and those of other animals?
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11 Inheritance and genetic engineering
Revision questions
1 Distinguish between the following pairs of terms:
a genotype and phenotype
b gene and allele
c homozygous and heterozygous
2 PTC is a chemical that tastes bitter to some people and is tasteless to others. The
allele for tasting PTC, T, is dominant. Draw a Punnett square to show how a couple
who can both taste PTC could produce a child who is unable to taste PTC.
3 What is the chance that a couple who both have sickle cell trait will have a child who
suffers from neither the trait nor sickle cell anaemia? Use a genetic diagram to
explain your answer.
4 Is it the mother or the father that determines the sex of their children? Explain your
answer by means of a genetic diagram.
5 What are sex-linked characteristics?
6 Colour blindness is caused by an X-linked, recessive allele. Is it possible for a mother
with normal vision and a father with colour blindness to have a colour-blind child? Use
a Punnett square to explain your answer (XR = normal vision; Xr = colour blindness).
7 What is meant by the term ‘genetic engineering’?
8 Outline TWO ways genetic engineering is being used to improve food production.
9 Outline how genetic engineering can be used to produce insulin to treat diabetes.
10 Discuss THREE possible advantages and THREE possible disadvantages of using
genetic engineering.
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11 Concise Revision Course: Human and Social Biology
Exam-style questions –
Chapters 10 to 11
Structured questions
1 a) Distinguish between a chromosome and a gene.
(2 marks)
b) Figure 1 shows a dividing cell.
X
2
Figure 1 A dividing cell
i) Name the structure labelled X.
(1 mark)
ii) Identify the type of cell division that the cell in Figure 1 is undergoing.
(1 mark)
iii) Give TWO reasons for your answer to b) ii) above.
(2 marks)
iv) Name ONE place in the human body where the type of cell division shown in
(1 mark)
Figure 1 would occur.
v) How many chromosomes would each daughter cell possess when the cell
(1 mark)
shown in Figure 1 has finished dividing?
vi) Give TWO reasons why this type of cell division is important.
(2 marks)
c) i) All living organisms show variation. What is meant by the term ‘variation’?
(1 mark)
ii) Distinguish between continuous variation and discontinuous variation.
(2 marks)
iii) Explain what happens to cause a person to be born with Down’s syndrome. (2 marks)
Total 15 marks
Some people can roll the edges of their tongues upwards to form a tube, other people
cannot do this. The allele for rolling the tongue is dominant, and tongue-rolling is NOT
sex-linked. Selena can roll her tongue whereas her husband, Ario, cannot roll his.
Figure 2 below shows the phenotypes of Selena, Ario and their five children.
Selena
Ano
Key
Male Female
Cannot roll tongue
Can roll tongue
Figure 2 The inheritance of tongue rolling in Selena and Ario’s family
a) i) What is meant by the term ‘dominant allele’?
(2 marks)
ii) Complete the following Punnett square to show the possible genotypes of Selena and
Ario’s children.
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Exam-style questions – Chapters 10 to 11
Use R to represent the dominant allele for being able to roll the tongue and r to
represent the recessive allele for not being able to roll the tongue.
gametes
(4 marks)
iii) What is the chance that Selena and Ario’s next child will be unable to roll his
(1 mark)
or her tongue?
iv) What term is used to describe Selena’s genotype?
(1 mark)
b) i) Identify the type of variation shown in Figure 2.
(1 mark)
ii) Identify ONE other human characteristic that shows the same type of variation. (1 mark)
iii) Tara and Ashlee are identical twins. Explain, using suitable examples, how it is
possible for them to have differences in their phenotypes even though they
(3 marks)
have the same genotypes.
iv) Why is it important that living organisms show variation?
(2 marks)
Total 15 marks
Structured essay question
3 a) i) Haemophilia is caused by an X-linked recessive allele. Use a Punnett square to
determine the genotype of the offspring of a cross between a female carrier of
haemophilia and a normal male.
Use XHXh to denote the genotype of the female carrier and XHY to denote the
(4 marks)
genotype of the normal male.
ii) State the phenotype of EACH offspring in a) i) above.
(4 marks)
b) i) Kemar suffers from Type 1 diabetes. Explain how genetic engineering is used
to help treat Kemar’s condition. Your answer must include the name of the
product produced by genetic engineering and an explanation of how the
(5 marks)
product is made.
ii) Give TWO concerns that people might have about the use of genetic
(2 marks)
engineering to change the traits of organisms.
Total 15 marks
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Exam-style questions – Chapters 10 to 11
Section D – Disease and its impact
on humans
12 Health and disease
According to the World Health Organisation (WHO), healthy people are able to function well physically,
their minds are free from worry and depression, and they are able to show care and concern for others.
Health is a state of complete physical, mental and social wellbeing and not merely the absence of
disease and infirmity.
A disease is a condition that impairs the normal functioning of part or all of an organism, and leads to a
loss of good health.
Types of disease
Diseases may be classified into the following two types:
• Communicable (infectious) diseases
• Non-communicable diseases
Communicable diseases
Communicable diseases are caused by pathogens (organisms that cause disease) and can be passed from
one person to another. They are also known as infectious diseases and include sexually transmitted
infections (STIs), air-borne diseases, water-borne diseases, food-borne diseases and vector-borne
diseases (see Tables 12.3, 12.4 and 12.5).
Non-communicable diseases
Non-communicable diseases are not caused by pathogens and cannot be passed from one person to
another. Many are chronic, i.e. they are long-term medical conditions that often get worse over time.
Non-communicable diseases include:
• Nutritional deficiency diseases (see page 23).
• Degenerative diseases, which are conditions that cause a breakdown of body tissues or organs over
time which prevents them from functioning normally, e.g. Alzheimer’s disease, Parkinson’s disease
and osteoporosis.
• Inherited disorders, which are passed on from one generation to the next via genes, e.g. cystic
fibrosis and sickle cell disease.
• Lifestyle-related diseases (see page 121).
Signs and symptoms of disease
Diseases are detected by signs and symptoms.
• Signs can be detected by someone other than the person affected by the disease, e.g. a rash, high
body temperature and low blood pressure.
• Symptoms are experienced by the person affected by the disease. They are what the person feels,
e.g. pain, fatigue and nausea.
Asthma
Asthma is a non-communicable disease that affects the respiratory system. During an asthma attack,
the muscles surrounding the bronchi and bronchioles contract, causing these airways to become
narrower. The bronchial lining also becomes inflamed and there is increased mucus secretion.
12 Health and disease
119
air trapped
in alveoli
relaxed
smooth
muscles
normal airway
tightened
smooth
muscles
wall inflamed
and thickened
asthmatic airway
asthmatic airway
during attack
Figure 12.1 The effects of asthma on the respiratory system
Main causes of asthma
The main causes of asthma include:
• a family history of asthma
• lung infection
• childhood exposure to tobacco
• a mother who smoked during pregnancy.
Certain substances or conditions trigger an asthma attack. The triggers vary from person to person,
and include:
• allergens, e.g. pollen, dust mites and animal fur
• airborne irritants, e.g. smoke and fumes
• respiratory infections
• anxiety or stress
• sudden temperature changes
• exercise.
Primary symptoms of asthma
Symptoms of asthma include:
• shortness of breath
• coughing
• wheezing
• chest pain.
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12 Concise Revision Course: Human and Social Biology
Possible treatment of asthma
There is no cure for asthma. However, asthma can be controlled by avoiding exposure to allergens and
other asthma triggers. Two types of medication are used to treat asthma:
• Quick relief medications – administered using an inhaler to relax the muscles around the airways
during an asthma attack.
• Long-term control medications – inhaled steroids that are generally taken daily for long-term relief of
inflammation of the bronchial tubes.
Lifestyle-related diseases
Lifestyle-related diseases are non-communicable diseases. They are said to be lifestyle-related because
certain practices and behaviours, including poor eating habits, smoking and inactivity, contribute to
persons developing these diseases. Other factors such as age, gender and inherited traits have an
impact. Lifestyle-related diseases include obesity, diabetes mellitus and cardiovascular disease (CVD).
Obesity
When persons consume more food than the body requires, the excess is converted to fat and is
stored under the skin and around organs. Obesity is a form of malnutrition in which persons have
accumulated so much body fat that it has a negative effect on their health. Obese persons are very
overweight, i.e. they have a BMI greater than 30 kg per m2 (see page 26).
• Causes: Excess carbohydrate and fat intake, especially animal fats that are rich in saturated fatty acids,
and a lack of physical activity.
• Signs/symptoms: Breathing difficulties, increased sweating, back and joint pains, inability to cope
with physical exercise, chronic fatigue and elevated blood pressure. Persons who are obese are
also at increased risk of having other serious health problems, such as type II diabetes, hypertension,
stroke and coronary heart disease.
• Treatment and prevention: Changing to a low-carbohydrate and low-saturated fat diet, and doing
more physical activity (exercise) are important measures used in the prevention and treatment of
obesity.
Diabetes mellitus
Diabetes mellitus is a condition in which the blood sugar level is consistently high over a prolonged
period. The blood glucose level is so high that the kidneys are unable to reabsorb all of the
glucose from the filtrate (see page 69) and some is passed out in the urine. There are two types of
diabetes mellitus:
• Type I (insulin-dependent diabetes) – This is the less common type of diabetes mellitus, accounting
for 5–10% of the total cases of diabetes worldwide. It develops mainly in young children.
• Type II (non-insulin-dependent diabetes) – This accounts for 90–95% of diabetes cases worldwide,
and is most often seen in adults. Being overweight or obese and having a close relative with Type II
diabetes increase a person’s chances of developing the condition.
12 Health and disease
121
Table 12.1 Causes, signs/symptoms, treatment and prevention of diabetes mellitus
Type I diabetes
Type II diabetes
Causes
The pancreas does not produce insulin. The pancreas does not produce
enough insulin or the body cells
do not respond to the insulin.
Signs/symptoms
• Higher than normal blood glucose level
• Excessive thirst
• Frequent urination
• Glucose present in the urine
• Extreme hunger
• Unexplained weight loss
• Fatigue
• Blurred vision
• Slow-healing wounds
Treatment and
• Insulin treatment by means of regular • Oral medication to help lower
prevention
insulin injections or using an insulin
blood glucose levels
pump
• Weight management
• Regular monitoring of blood glucose • A healthy diet low in sugar
levels
and saturated fats and high in
• A healthy diet low in sugar and
dietary fibre
saturated fats and high in dietary fibre • Regular exercise
• Regular exercise
• Regular medical checkups
• Regular medical checkups
Cardiovascular disease (CVD)
Cardiovascular disease refers to a group of conditions that affects the heart and blood vessels, such as
hypertension and coronary heart disease.
• Hypertension (high blood pressure) occurs when the blood pressure in the arteries is consistently
high (≥140/90 mmHg). Obesity increases the risk of hypertension developing. This is called
secondary hypertension, as it results from another medical condition.
• Coronary heart disease (CHD) is a condition caused
by a build-up of fatty material (plaque) inside
coronary arteries. These are arteries that supply
oxygenated blood to the heart muscle cells. The
process by which plaque is deposited in the lining
blood
clot
of the arteries is called atherosclerosis. The plaque
plaque
reduces the internal diameter of the coronary
buildup
arteries and causes the blood pressure in the arteries
to increase. A blood clot may then form in one of the
blocked
narrow arteries.
coronary artery
dying muscle
Figure 12.2 Atherosclerosis
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12 Concise Revision Course: Human and Social Biology
Table 12.2 Causes, signs/symptoms, treatment and prevention of cardiovascular disease (CVD)
Hypertension
Coronary heart disease (CHD)
Causes
• Being overweight or obese
• A diet high in saturated fats
• Alcohol use
• Lack of exercise
• Smoking
• Smoking
• Stress
• Lack of exercise
• A diet rich in salt
Signs/symptoms
• Higher than normal blood pressure • Chest pain (angina)
(≥140/90 mmHg)
• Heart attack (myocardial
• In many cases, there are no warning infarction)
signs/symptoms (‘silent killer’)
• Heart attack (myocardial infarction)
• Stroke
Treatment and
• Prescription drugs to lower blood • Coronary artery bypass surgery
prevention
pressure
(heart bypass surgery)
• Weight management
• A daily low-dose aspirin tablet to
help prevent blood clot formation
• Stress management
• Weight management
• Reduced alcohol consumption
• A diet low in saturated fats and salt • A diet low in saturated fats and salt
• Regular exercise
• Regular exercise
• Stopping smoking
• Stopping smoking
The importance of diet and exercise to lifestyle-related diseases
Diet and exercise are important components of the treatment and prevention measures for all of
the lifestyle-related diseases discussed above. Eating a healthy, balanced diet ensures that excess
carbohydrates and fats, which contribute to these diseases, are not consumed. This limits weight gain
and helps in the maintenance of normal heart rate and blood pressure. In particular, the diet should
be low in saturated fats and high in dietary fibre supplied by fresh fruits, vegetables and whole grains.
Regular, aerobic exercise also limits weight gain, promotes more efficient gaseous exchange, a faster
metabolic rate, a lower heart rate and an increase in muscle size and strength. Exercise has the additional
benefit of improving mental health, as it helps to reduce depression and anxiety, and boosts self-esteem.
Revision questions
1 Define the terms:
a health
b disease
2 Using examples, distinguish between the following terms as they relate to disease:
a communicable and non-communicable
b signs and symptoms
3 Explain how asthma affects the respiratory tract.
4 a Describe FOUR signs/symptoms of obesity.
5
6
b Identify TWO other diseases that may affect persons who are obese.
Describe the treatment measures for Type I and Type II diabetes.
Discuss the importance of diet and exercise in the prevention and treatment of
lifestyle-related diseases.
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123
Infectious diseases (communicable diseases)
Infectious diseases or communicable diseases are caused by pathogens such as viruses, bacteria,
protozoans and fungi. These pathogens can be spread directly or indirectly from one person to
another in a variety of ways (see Tables 12.3, 12.4 and 12.5).
When controlling any of these diseases, the aim is to prevent further development and spread of the
disease so that its incidence in the population is gradually reduced. Vaccinating individuals against
a disease (see page 136) and treating their symptoms are two important methods that can be used to
control infectious diseases. The aim of treating a disease is to relieve the symptoms experienced by the
person suffering from the disease and to cure the disease if possible.
Table 12.3 Examples of air-borne, water-borne and food-borne infectious diseases
Disease
Causative agent Method of
Signs
Symptoms
Prevention and
transmission
control measures
Influenza
Virus
Air-borne
• Cough
• Headache • Influenza
droplets from • Shivering • Sore throat
vaccination
the respiratory
• Treat with
• Elevated
• Muscle
system
painkillers,
body
aches
fever reducers,
temperature
bed rest and
(fever)
antiviral drugs
• Stuffy or
• Avoid
runny nose
overcrowded
areas
• Good
ventilation
Bronchitis
Virus
Air-borne
• Cough with • Chest
• Treat with bed
(acute)
droplets from mucus
discomfort
rest and lots of
the respiratory • Wheezing
fluids to drink
system
• Avoid
• Shortness of
overcrowded
breath
areas
• Fever
• Avoid lung
irritants
• Good
ventilation
Pneumonia Bacterium
Bacterial
• Cough
• Chest pain • Treat with
(most
spores in
antibiotics
• Fever
• Nausea
common) –
air-borne
• Avoid
Streptococcus droplets from • Shortness of • Fatigue
overcrowded
pneumoniae the respiratory breath
areas
system
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12 Concise Revision Course: Human and Social Biology
Disease
Causative agent Method of
Signs
Symptoms
transmission
Tuberculosis Bacterium – Air-borne
• Chronic
• Loss of
Mycobacterium droplets from cough
appetite
tuberculosis the respiratory • Blood in
• Fatigue
system
sputum
• Fever
• Weight loss
• Lung
tubercles
(nodules)
Ringworm
Fungus – Tinea Spores on
• Red patches • Itching
surfaces, skin, on the body
animals
Cholera
Typhoid
Prevention and
control measures
• BCG
vaccination
• Treat with
antibiotics
• Avoid
overcrowded
areas
• Treat with
fungicide
ointments,
creams or
lotions
• Ensure the skin
is kept dry
• Avoid sources
of infection
Bacterium –
Contaminated • Severe
• Stomach
• Cholera
watery
pain
vaccination
Vibrio cholera water
diarrhoea • Muscle
• Treat with
• Vomiting
cramps
antibiotics and
by drinking
• Dark• Thirst
rehydration
coloured
(associated
fluids
urine
with
(associated
dehydration) • Chlorination of
with
drinking water
dehydration)
• Proper disposal
of faeces
Bacterium – Contaminated • Fever
• Stomach
• Typhoid
Salmonella
water and
pain
vaccination
•
Rash
typhi
food
with
• Diarrhoea • Headache • Treat
antibiotics
• Loss of
appetite
• Chlorination of
drinking water
• Weakness
• Wash fruits
and vegetables
thoroughly
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125
Disease
Causative agent Method of
Signs
transmission
Gastroenteritis Viruses – e.g. Contaminated • Diarrhoea
rotavirus,
water and
• Vomiting
norovirus
food
• Fever
Bacteria – e.g.
E. coli
Prevention and
control measures
• Abdominal • Rotavirus
pain
vaccination
• Fatigue
• Treat by
drinking
• Nausea
rehydration
fluids
• Chlorination of
drinking water
• Proper disposal
of faeces
• Frequent hand
washing
• Good food
hygiene
Note that influenza, acute bronchitis and pneumonia are classified as acute respiratory infections. An
acute infection is one that comes on rapidly, has distinct symptoms and lasts for a short time. Chronic
bronchitis is a long-lasting inflammation of the bronchi and bronchioles that is associated with
smoking (see page 42). It is not a communicable disease.
Sexually transmitted infections (STIs)
Symptoms
Sexually transmitted infections (STIs) are passed from one person to another during sexual intercourse.
Examples of STIs are gonorrhoea, syphilis, genital herpes and HIV/AIDS.
Table 12.4 Examples of sexually transmitted infections
Infection Causative agent
Method of
Signs
Symptoms Prevention
transmission
and control
measures
Gonorrhoea Bacterium
• Unprotected • Pus
• Itching • Treat with
– Neisseria
sexual
discharge
and
antibiotics
gonorrhoeae
intercourse
from the
burning • Condom use
with an
vagina or
sensation during sexual
infected
penis
when
person
urinating intercourse
• Blindness
• Public
• Mother to the in babies
education
eyes of her
infected
• No vaccine
baby during
during
exists
childbirth
childbirth
• Sterility
Syphilis
Bacterium –
• Unprotected • Painless
• Muscle • Treat with
sexual
round
aches
antibiotics
Treponema
intercourse
sores on
pallidum
of • Condom use
with an
the genitals • Loss
appetite
during sexual
infected
lasting 3 to 6
intercourse
person
weeks
• Public
• Mother to
• Body rash
education
foetus across and sores
• No vaccine
the placenta • Stillbirths
exists
• Brain damage
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12 Concise Revision Course: Human and Social Biology
Infection
Causative agent
Method of
transmission
Signs
Symptoms
Prevention
and control
measures
Genital
Viruses – herpes • Unprotected • Recurrent
• Genital • Treat with
herpes
simplex virus
sexual
genital
itching
antiviral
type 1 (HSVintercourse
blisters and
drugs to
1) and herpes
with an
ulcers
reduce
simplex virus type
infected
symptoms
2 (HSV-2)
person
• Condom use
during sexual
intercourse
• Public
education
• No cure or
vaccine exists
AIDS –
Virus – human
• Unprotected • Rapid weight • Extreme • Treat using
acquired immunodeficiency sexual
loss
tiredness antiretroviral
immune
virus (HIV)
intercourse • Recurring
to slow
• Headache drugs
deficiency
with an
reproduction
fever
syndrome
infected
of the virus
•
Night
sweats
person (main
• Condom use
method in the • Swelling of
during sexual
Caribbean)
lymph glands
intercourse
• Using
• Prolonged
• Use sterile
infected
diarrhoea
needles
needles
and cutting
• Skin rash
or cutting
instruments
instruments • Sores around
• Test blood for
the mouth,
• Transfusions
HIV prior to
anus or
of infected
transfusion
genitals
blood
• Public
• Infected
education
mother to
• No cure or
baby during
vaccine exists
pregnancy
and
breastfeeding
Mode of action of HIV/AIDS
When the human immunodeficiency virus (HIV) enters the blood, the virus particles bind to certain
specialised white blood cells of the immune system known as T lymphocytes. They then enter these
cells and begin to make copies of themselves. The new HIV particles burst out of the lymphocytes,
destroying them. The new particles go on to attack more lymphocytes and this starts to weaken the
body’s immune system.
When a person is first infected, flu-like symptoms lasting 1 to 2 weeks may develop 2 to 6 weeks
after infection. The person may then remain without symptoms for 10 years or more, but the virus
is continuing to weaken their immune system. When the immune system is weakened to a point
that it cannot destroy invading pathogens, the person becomes ill and develops AIDS. People with
AIDS display signs and symptoms outlined in Table 12.4 and are susceptible to other infections,
known as opportunistic infections, such as pneumonia, tuberculosis and some types of cancer,
e.g. Kaposi’s sarcoma.
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The significance of HIV/AIDS
There is major concern worldwide regarding the spread of HIV/AIDS. HIV was first identified in 1983.
At the end of 2016, the WHO estimated that 36.7 million people worldwide were living with HIV and
that 35 million people have already died from AIDS. The Caribbean is the second most-affected region
in the world after Africa.
The spread of HIV/AIDS is very difficult to control for several reasons.
• There is currently no vaccine or cure for HIV/AIDS.
• The virus has a long incubation period between when it enters the body and when symptoms
develop. This can be 10 years or more. During this time, the infected person can pass on the virus
without knowing it.
• It can be very difficult to convince persons to change their sexual behaviour.
• Anti-retroviral drugs are relatively expensive and have to be taken daily for the remainder of the
infected person’s life. Side effects are severe in some persons and include fatigue, nausea and
vomiting, diarrhoea, headaches and insomnia.
• There is still a social stigma associated with HIV/AIDS so persons who have the disease may not
disclose this to others or seek medical assistance.
The effects of STIs on a pregnant mother and her foetus
Many STIs can infect the foetus during pregnancy or the baby during birth. Syphilis can pass from
mother to foetus across the placenta and can result in stillbirths or premature births and syphilitic
babies can develop serious problems with many internal organs. HIV can also pass across the
placenta, or from mother to baby during birth or while breastfeeding, causing the baby to become
HIV positive. Gonorrhoea can infect the eyes of the baby during birth, leading to eye infections and
blindness. Active herpes blisters on the genitals can infect the baby with the virus as it is being born.
Vectors and vector-borne infectious diseases
Vector-borne diseases are infectious (communicable) diseases that are transmitted by a vector.
A vector is an organism that carries pathogens in or on its body and transmits the pathogens from one
host to another.
The vector is not usually harmed by the pathogen. Rats, mosquitoes and houseflies are examples of
vectors. Rats transmit leptospirosis; mosquitoes transmit several diseases including malaria, dengue,
chikungunya and zika; and houseflies transmit gastroenteritis.
Table 12.5 Examples of vector-borne diseases
Disease
Causative
Method of
Signs and
Treatment
Prevention and
agent
transmission symptoms
control measures
Malaria
Protozoan – Mosquito
• High fever
• Drugs
• Measures to
such as
control the
Plasmodium – Anopheles and sweating
quinine
and
Anopheles
• Feeling cold
chloroquine
mosquito (see
and shivering
page 131)
• Weakness
• Antimalarial
• Can lead to
drugs to protect
death
against infection
• Protect against
mosquito bites,
e.g. long sleeves,
insect repellents,
mosquito nets
• Public education
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12 Concise Revision Course: Human and Social Biology
Disease
Causative
Method of
agent
transmission
Viruses
Mosquito
– DEN-1,
– Aedes
DEN-2, DEN-3 aegypti
and DEN-4
Signs and
Treatment
Prevention and
symptoms
control measures
Dengue
• High fever
• Painkillers • Measures to
fever
and fever
control the Aedes
• Severe
reducers
aegypti mosquito
headache
(not aspirin) (see page 131)
• Severe joint • Bed rest
• Protect against
and muscle
mosquito bites
pains
• Increase
(see malaria
fluid intake
• Skin rash
above)
• Bleeding from
• Public education
the nose,
gums and
beneath the
skin (dengue
haemorrhagic
fever)
Leptospirosis Bacterium Rat urine
• Headache
• Antibiotics • Rodent control
– Leptospira Urine of
(see page 132)
• Muscle pains • Painkillers
domestic and • High fever
and fever • Vaccination of
farm animals
reducers
domestic animals
• Nausea and
• Avoid contact
vomiting
with animal urine,
• Jaundice
infected animals
(yellowing of
and contaminated
the skin)
soil and water
• Red eyes
• Public education
• Liver and
kidney failure
The life cycle of a mosquito
There are four distinct stages in the life cycle of a mosquito:
• Egg: The adult female lays eggs in standing water. The eggs float on the surface of the water.
• Larva: When eggs hatch, the larvae emerge. Larvae hang from the surface of the water and breathe
air through breathing tubes. This is the feeding and growing stage of the mosquito life cycle. The
larvae feed on microorganisms and organic matter in the water.
• Pupa: The larva develops into a pupa. Pupae live in the water and also breathe air through breathing
tubes. This is the non-feeding stage of the mosquito life cycle in which the larval tissue re-organises
into adult tissue.
• Adult (imago): The adult emerges from the pupa. The adults are able to fly and they feed on nectar
and sugars from plants. This is the reproductive stage of the mosquito life cycle. After mating, the
female needs a blood meal to mature her eggs before she lays them. This blood is usually taken
from a human when the female mosquito flies and feeds in the evenings. During the day, the adults
rest in cool, dark places around human residences.
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129
breathing tube
antenna
larva
surface
of water
egg
feeding
brushes
breathing tube
compound
eye
developing
limb
adult
pupa
Figure 12.3 The life cycle of a mosquito
The mosquito as a vector
Humans are the primary hosts of the pathogens that are transmitted by mosquitoes. Mosquitoes are
the secondary hosts. The pathogens cause disease in the primary hosts, but the secondary hosts are
not harmed by them.
When a female mosquito bites an infected person, she sucks up blood that contains pathogens.
The pathogens pass through the walls of her intestines and move into her salivary glands. When she
bites another person, the pathogens are transmitted to that person when she injects saliva into that
person’s blood to prevent it from clotting.
The life cycle of a housefly
There are four distinct stages in the life cycle of a housefly:
• Egg: The adult female lays eggs in faeces, compost or other decomposing organic material, e.g. the
bodies of dead animals.
• Larva (maggot): When eggs hatch, the larvae emerge. This is the feeding and growing stage of the
housefly life cycle. Maggots feed and grow rapidly and then burrow deep into the organic material
they were feeding on.
• Pupa: The larva develops into a pupa which has a hard, brown protective covering. This is the nonfeeding stage of the housefly life cycle in which larval tissue re-organises into adult tissue.
• Adult (imago): The adult emerges from the pupa. The adults have legs and wings and are able to
fly. They feed on decaying organic matter and human food. This is the reproductive stage of the
housefly life cycle. After mating, the female lays eggs.
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12 Concise Revision Course: Human and Social Biology
adult
the adult house fly feeds on
human food, faeces or other
waste material
pupa
egg
eggs are laid in faeces,
compost or other
decomposing
organic matter
larvae live in
organic matter
larva
Figure 12.4 The life cycle of a housefly
The housefly as a vector
Houseflies transmit several pathogens that cause food poisoning while they are feeding. A housefly
feeds using its proboscis (an elongated sucking mouthpart) which it lowers onto its food. Digestive
juices are released through the proboscis onto the food to digest it externally. The dissolved food is
then sucked up into the fly’s gut.
Houseflies collect pathogens on their legs, body and mouth parts when they feed on organic waste
and faeces, and also take them into their gut in the food consumed. The flies then transfer these
pathogens onto human food while walking on the food and feeding, or they pass them onto the food
in faeces or vomit spots.
Methods of controlling vectors
The control of vectors is very important in order to control the spread of diseases transmitted by these
vectors. Studying the life cycle of a vector helps in the control of that vector, as this knowledge can be
used to determine at which stage or stages control will be easiest, cheapest and most effective.
The control of mosquitoes
Mosquito larvae and pupae can be controlled by:
• Draining all areas of standing water.
• Adding insecticides to breeding areas to kill the larvae and pupae.
• Introducing fish into breeding areas to feed on the larvae and pupae (biological control).
• Spraying oil onto the surface of standing water to prevent the larvae and pupae from breathing.
Adult mosquitoes can be controlled by:
• Spraying with insecticides to kill the adults.
• Removing dense vegetation to remove the adult’s protection.
The control of houseflies
Houseflies can be controlled by:
• Proper disposal of human and animal waste.
• Covering food so that flies cannot land on it.
• Spraying adults with insecticides to kill them.
• Using fly traps to kill adults.
• Treating all sewage.
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The control of rats
Rats can be controlled by:
• Using traps and/or bait to kill them.
• Introducing cats or other animals that prey on rats (biological control).
• Rodent-proofing buildings (exclusion).
The impact of diseases on the human population
Diseases have several socio-economic impacts on the human population including:
• Increased demand on health services.
• Job losses and loss of earnings for affected people.
• Reduced productivity of businesses.
• Reduced foreign exchange earnings for the country.
• Lowered standards of living.
• Shortened life expectancies.
Revision questions
7 Name the causative agent of each of the following diseases:
a influenza
b ringworm
c typhoid
d tuberculosis
8 Heavy rain resulted in flooding in a rural community. This was followed by an
9
100
11
122
133
144
155
132
outbreak of cholera.
a Identify FOUR signs/ symptoms that will be experienced by affected community
members.
b Outline the measures that should be taken to prevent further spread of the
disease.
Describe the causative agent, signs/symptoms and treatment measures
of gonorrhoea.
There is great concern in the Caribbean regarding the spread of HIV/AIDS. Discuss
FOUR reasons for this.
Describe TWO ways in which STIs may be passed from a mother to her baby.
a What is a vector?
b Identify TWO vector-borne diseases and the vector responsible for their
transmission.
Using a labelled diagram, describe the life cycle of a housefly.
Describe control measures for ANY TWO stages in the life cycle of a mosquito.
Discuss the impact of diseases on the human population.
12 Concise Revision Course: Human and Social Biology
13 Hygiene and defences against
disease
The human body is always surrounded by microorganisms, some of which are pathogens. However,
there are measures that can be taken in order to reduce the likelihood of these pathogens entering
the body and causing disease. The body also has natural defences against pathogens, such as a
healthy, functioning immune system.
Personal hygiene
Personal hygiene refers to practices that are carried out by individuals in order to maintain cleanliness
and good grooming of the body.
Maintaining personal hygiene is important because it helps to:
• Ensure good health.
• Prevent the spread of infections.
• Eliminate body odours.
• Prevent dental caries.
• Promote social acceptance.
Skin and hair hygiene
When people are active or the air temperature is high, sweat is produced in order to cool the body.
Evaporation of the water in sweat leaves salts, urea and dead skin cells on the surface of the skin.
Bacteria feed on these substances and produce an unpleasant odour, called body odour (BO). They
can also cause infections.
In order to reduce body odour and the likelihood of infections, the following measures should be
carried out:
• Regular washing of the body, especially the armpits, genitalia and between the toes.
• Regular washing of the hair.
• Drying the skin and hair thoroughly after washing.
• Applying a deodorant to clean, dry skin of the armpits.
• Changing and washing clothing frequently.
Genital hygiene
Genital hygiene is maintained by:
• Thorough cleaning of the genitalia, especially during menstruation in females.
• Wiping the female genitalia from front to back to prevent faeces entering the vagina.
• Male circumcision (removal of the foreskin) or pulling back the foreskin and washing the area with
soap and water.
Hands hygiene
Hands hygiene is maintained by:
• Washing hands before preparing and eating meals.
• Washing hands after using the toilet.
• Keeping fingernails short and clean.
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133
Dental hygiene
Dental hygiene is outlined in page 30.
Controlling the growth of microorganisms
Sterilisation
Sterilisation is the complete destruction of all of the microorganisms present in a specified region.
Methods of sterilisation include:
• Ultra-high temperature treatment (UHT) – This method is used for the sterilisation of liquid food
items such as milk, soups, sauces and baby food and can affect the flavour. The food is heated to
temperatures higher than 135 °C for 1 to 2 seconds, cooled rapidly and packaged in pre-sterilised
containers.
• Pasteurisation – This method kills most of the microorganisms in food and drinks while maintaining
the quality of the product. It is a commonly used method for sterilising milk. The process involves
heating the milk to 72 °C for 15 to 25 seconds and then cooling it very quickly.
• Canning – This method is used to protect a wide variety of foods from the action of microorganisms.
Containers are filled with the food, covered with lids and placed into a boiling water bath or
a steam bath. The heat kills the microorganisms in the food and the lids are sealed onto the
containers after removal from the bath, preventing further entry of microorganisms.
• Autoclaving – This method is also referred to as steam sterilisation, and involves the use of
pressurised steam in an autoclave to kill microorganisms in and on liquids, equipment and
instruments such as hospital equipment and surgical instruments. An autoclave is similar to a
pressure cooker. Inside the autoclave, the high pressure ensures that high temperatures of above
121 °C are maintained in order to destroy all microorganisms and their spores.
• Boiling – This method involves boiling materials to be sterilised, such as surgical instruments, in
water at 100 °C for 15 to 30 minutes. It is also used for the purification of drinking water. Boiling kills
all bacteria and some spores.
Disinfection
Disinfection involves the use of chemicals to reduce the number of microorganisms that are present in
a specified region to a level that cannot cause infection.
Disinfection can be carried out by using disinfectants or antiseptics:
• Disinfectants are chemicals used to destroy microorganisms in or on non-living objects, e.g. in water
and on counter tops and floors. Examples of disinfectants are chlorine and ethanol.
• Antiseptics are chemicals used to destroy microorganisms on living tissues, e.g. on the surface of the
skin and in the mouth. Examples of antiseptics are hydrogen peroxide, rubbing alcohol and iodine.
Disinfectants are stronger and more toxic than antiseptics and can be harmful to living tissues.
Antiseptics are milder and cause little or no harm to living tissues.
Antibiotics and antifungal agents
Antibiotics are chemicals that are used to kill bacteria or to slow their growth. Many antibiotics are
produced by living organisms. The first antibiotic to be discovered was penicillin, which is produced
by the Penicillium fungus. Scientists are now able to make synthetic antibiotics to treat or prevent
different bacterial infections.
Antifungal agents (fungicides) are chemicals that are used in the treatment of fungal infections such as
athlete’s foot and ringworm.
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Defence against disease
The immune system protects the body from infections in different ways. Some white blood cells are
able to engulf and digest pathogens by the process of phagocytosis. Other white blood cells, called
lymphocytes, produce antibodies.
An antibody is a specific protein produced by lymphocytes in response to a specific antigen.
An antigen is a substance that is recognised as foreign to the body and stimulates lymphocytes to
produce antibodies.
An antitoxin is an antibody that is produced in response to a specific toxin and that is able to
neutralise this toxin.
Antigens include toxins and bacterial,
different types of antibody –
fungal and viral proteins. These proteins
each antibody is produced in
are usually displayed on the surface of the
response to a specific antigen
pathogen, as shown in Figure 13.1.
When antigens are detected in the body,
antigen – a specific
the appropriate lymphocytes multiply
protein displayed
on the surface
quickly and produce specific antibodies
of the pathogen
for these antigens. These antibodies bind
to the antigens and cause the pathogens
antigen-antibody
interaction – the
to clump together so that the phagocytes
pathogenic
specific antibody
microorganism
can engulf them, or they cause the
causes destruction
of
the
pathogen
pathogens to disintegrate. Antibodies can
also neutralise the toxins produced by
Figure 13.1 The antibody–antigen interaction
the pathogens.
Types of immunity
Immunity is the body’s temporary or permanent resistance to a disease.
Immunity can be innate or acquired:
• Innate immunity refers to the
Acquired immunity
inborn ability of the body to
resist disease. It is inherited
genetically and is present from
Natural
Artificial
birth.
(Antigens or antibodies
(Antigens or antibodies are
enter the body in a
deliberately introduced into the
• Acquired immunity refers to the
natural way)
body to stimulate an immune
response or to provide protection)
immunity that the body gains
over time. It is not present at
birth. There are four different
Active
Passive
Active
Passive
types of acquired immunity.
(Antibodies are
(Antibodies pass
(Antibodies are
(Antibodies in
Natural active immunity
made in response
to antigens that
entered the
body naturally)
from mother to
the foetus via the
placenta or to the
baby in breast milk)
made in response
to antigens
introduced
in vaccines)
serum are
injected into
the body)
Natural active immunity is
acquired by a person exposed to Figure 13.2 The types of acquired immunity
a pathogenic disease. When the
antigen is recognised, the
lymphocytes begin to produce the specific antibody. While antibody production is taking place, the
person experiences signs and symptoms of disease. When enough antibodies have been produced,
13 Hygiene and defences against disease
135
noitartnecnoc ydobitna
they destroy the pathogens or neutralise the toxins, and the person recovers. The antibodies
gradually disappear from the blood and some lymphocytes develop into lymphocyte memory cells
that remember the specific antigen.
When the same pathogen re-enters
first exposure
the body, the memory cells recognise
to the pathogen
the antigen, multiply and produce
second exposure
antibodies build up slowly.
to the pathogen
large amounts of the specific antibody
This gives the pathogen time
rapidly. The antibodies destroy the
to cause symptoms of the disease
pathogen or neutralise its toxins so
antibodies slowly
large quantities of
quickly that the person does not
disappear from the
antibodies are made
blood after recovery
develop any signs or symptoms of the
rapidly. The pathogen
is destroyed before
disease, i.e. the person is immune to
symptoms develop
the disease. This is known as active
immunity because the antibodies are
produced by the body of the person
time
exposed to the pathogen. This type
of immunity may provide short-term
Figure 13.3 Antibody production during the acquisition of
protection, e.g. against the common
active immunity
cold, or long-term protection, e.g.
chicken pox is rarely caught twice.
Natural passive immunity
Natural passive immunity is acquired by the transfer of antibodies from the mother to the foetus or
baby. Antibodies are passed from the mother to the foetus across the placenta and from the mother
to the baby in breast milk, especially colostrum, the first breast milk formed after birth. This is known
as passive immunity because antibodies are produced by another organism’s body. The protection
provided is short-term as no memory cells have been produced in the baby’s body, and the antibodies
will gradually disappear from the blood.
Artificial active immunity
Artificial active immunity is acquired by the deliberate introduction of a small amount of the
weakened or dead pathogen, or the antigen itself into a person’s body. This process is known as
vaccination and the preparation that is injected is called a vaccine. The antigen or toxin present in
the vaccine does not cause disease, but it stimulates lymphocytes in the person’s body to produce
the specific antibody needed. Lymphocyte memory cells also develop and provide protection against
future infection by that pathogen. Vaccines that provide long-term protection have been developed
for several infectious diseases including tuberculosis, typhoid and polio.
Immunisation is the process by which a person is made immune or resistant to an infectious disease.
Immunisation is usually carried out by administering a vaccine.
Artificial passive immunity
Artificial passive immunity is acquired when serum containing antibodies or antitoxins produced in
the body of another organism is injected into a person’s body for immediate relief of symptoms of
infection. The immunity provided is short-term as the antibodies will eventually disappear from the
blood. For example, serum containing antibodies against tetanus is used if tetanus is suspected.
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13 Concise Revision Course: Human and Social Biology
Revision questions
1 Why is it important to maintain personal hygiene?
2 Outline THREE measures used to maintain EACH of the following:
a skin and hair hygiene b dental hygiene
c hands hygiene
3 Distinguish between the following terms:
4
5
6
7
a sterilisation and disinfection
b disinfectant and antiseptic
c antibiotic and antifungal agent
Describe THREE methods of sterilisation.
Define the terms ‘antibody’ and ‘antigen’.
Name the cells that produce antibodies and describe how antibodies work to protect
the body.
Identify and explain the type of immunity that is gained in the situations described:
a Kryssie contracted chicken pox when she was a child. She does not get sick several
years later when there is another outbreak of chicken pox.
b Enrique was injected with a serum after being bitten by a snake.
c Shiann got the influenza vaccine before travelling abroad.
13 Hygiene and defences against disease
137
14 Drug use and misuse
A drug is any chemical substance that affects the functioning of the body.
Some drugs are used to treat medical conditions and to improve health while others are illegal. All
drugs can have harmful effects on the body if they are used incorrectly.
Drug dependence
Drug dependence takes place when a person takes a drug over a period of time and needs the
drug in order to function. The person is said to be addicted to the drug. Drugs affect the body in
different ways. Some drugs affect the physical functioning of parts of the body, and are said to have
physiological effects. Some drugs affect the brain and cause changes in mood and behaviour. These
are described as psychological effects. Drug dependence can be physical or psychological:
• Physical dependence occurs when the body adapts to the drug and the body’s cells cannot function
without it. The person will experience withdrawal symptoms if drug use stops suddenly; these are
often painful and include tremors, nausea, diarrhoea and body aches.
• Psychological dependence occurs when the person feels the constant need for the drug. The drug
becomes the central focus of their lives and they feel they cannot function without it.
Drug misuse refers to the use of a drug for purposes for which it was not intended or using a drug in
excessive quantities.
Prescription drugs
A prescription drug is a drug that legally requires a prescription from a medical practitioner to be
dispensed. Some prescription drugs have very strong effects, and persons may develop dependence
on these drugs. Prescription drug abuse is an area of growing concern.
Examples of prescription drugs that can be abused include:
• Sedatives – These are drugs that are used to treat anxiety and insomnia. They slow down body
functions, cause the user to feel calm and induce sleep. Examples include sleeping pills and
tranquillisers. Sedatives are depressants of the central nervous system. They slow the heart rate,
breathing rate and the speed of transmission of nerve signals. Sedative misuse can lead to poor
muscular coordination, slurred speech, blurred vision and mental confusion.
• Painkillers – These drugs interfere with the transmission of nerve signals and reduce the perception
of pain. Examples include paracetamol, aspirin and morphine. They also reduce anxiety and promote
muscle relaxation. Some painkillers have similar effects to depressants, slowing the breathing rate,
lowering the blood pressure and causing drowsiness. Misuse of painkillers may result in nausea,
vomiting, mental confusion, dizziness and fluctuations in the heart rate.
• Antibiotics – These are drugs that are used to treat bacterial infections, as they either kill or inhibit
the growth of bacteria. Examples include penicillin and streptomycin. Misuse of antibiotics may
result in the development of antibiotic-resistant strains of bacteria. Some persons are also allergic to
antibiotics, in which case their use can be fatal.
Non-prescription drugs
Some non-prescription drugs are legal and can be obtained over-the-counter at a pharmacy (without
a prescription from a medical practitioner). Other non-prescription drugs, e.g. alcohol, may only be
used legally by persons who are of a certain age. This age limit differs in different countries. Some
non-prescription drugs are illegal, e.g. cocaine and heroin.
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Cocaine
Cocaine is a white powdery substance that is usually inhaled through a tube. It is a highly addictive
illegal drug which is a powerful stimulant of the central nervous system. Misuse of cocaine causes
increased heart rate, breathing rate, blood pressure and body temperature. These can lead to sudden
death by a heart attack or stroke. Cocaine use may also result in weight loss, destruction of the
septum of the nose, reduced need for sleep, paranoia, anxiety, depression and, later, schizophrenia
and other mental illnesses.
LSD (acid)
LSD, also known as acid, is a very powerful hallucinogenic illegal drug. It is taken as a pill or on blotting
paper, and causes the user to go on a ‘trip’ or a state of altered consciousness, during which colours
seem more intense and lights seem brighter. The pupils become dilated and the body temperature and
blood pressure increase. Users may also become disoriented, anxious and have impaired judgement.
Heroin
Heroin is a highly addictive, illegal narcotic obtained from the opium poppy. It is taken by sniffing
or by injections into the limbs or directly into veins. It is a depressant of the central nervous system,
which initially reduces stress and anxiety by slowing the heart rate, breathing rate and the speed of
transmission of nerve impulses. Dependence is established very quickly and withdrawal symptoms
are severe, including diarrhoea, vomiting, muscle pain and cold flashes with goose bumps. Injection
of heroin is also associated with the transmission of HIV and other pathogens, as drug users often
share unsterilised needles.
Figure 14.1 Heroin and pills can kill
Ecstasy
Ecstasy is a hallucinogenic drug that is taken in tablet form. It causes heightened perception, sexual
stimulation and reduced appetite. Ecstasy users experience mood changes and the reduction of
inhibitions, which may result in unprotected sexual intercourse. It also causes increased heart rate,
blood pressure and body temperature. Heat exhaustion may occur as a result of the elevated body
temperature, which could lead to death. Long-term ecstasy use often results in an irregular heartbeat,
brain damage and kidney failure.
14 Drug use and misuse
139
Marijuana (cannabis)
Marijuana (also known as
cannabis, ‘ganja’, ‘herb’ and ‘pot’)
is a hallucinogen that is usually
smoked. It is the most commonly
used illegal drug. Marijuana
produces a feeling of wellbeing
(a ‘high’) followed by a feeling
of despair (a ‘low’). Short-term
effects include dilated pupils,
red eyes due to dilation of
capillaries in the eyes, dizziness,
increased appetite, slowed
reflexes, increased heart rate and
hallucinations. Heavy marijuana
use may cause long-term lung and
heart problems, mental disorders
Figure 14.2 Marijuana leaves are dried, rolled into a cigarette
in vulnerable individuals and
and smoked
reduced fertility in males.
Alcohol
Alcohol is a legal drug that is a depressant of the central nervous system. It slows down the passage
of nervous impulses. It is a very commonly used and misused drug which acts on the body quickly,
as it is rapidly absorbed into the bloodstream. Persons who are dependent on alcohol are called
alcoholics. Alcoholism is considered to be a disease. Misuse of alcohol has short-term and long-term
effects on the body.
Short-term effects of alcohol use
• Slowed reflexes and reduced muscular coordination.
• Impaired concentration and judgement.
• Lack of self-control and aggression.
• Slurred speech, distorted vision and hearing.
• Dehydration due to frequent urination.
• Memory lapses (blackouts).
• Vomiting.
• Drowsiness.
• Loss of consciousness.
Long-term effects of alcohol use
• Fatty liver disease and cirrhosis (scarring) of the liver.
• Increased blood pressure, heart attack and stroke.
• Cancer of the mouth, throat and oesophagus.
• Ulcers and other intestinal disorders.
• Permanent brain damage.
• Long-term memory loss.
• Alcohol poisoning.
• Malnutrition.
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14 Concise Revision Course: Human and Social Biology
Alcohol can be passed across the placenta from the mother’s blood into the blood of the foetus.
Babies that were exposed to large quantities of alcohol prior to birth may develop foetal alcohol
syndrome (FAS), which is characterised by mental retardation.
The social effects of drug misuse
Drug misuse has a devastating impact on individuals, families and communities. Addiction may lead
to broken relationships, loss of parents from households, personal neglect and neglect of family
members. Higher suicide rates and antisocial behaviour are associated with drug use. Babies born to
drug addicts may have developmental problems or they may be addicted to the drug as well.
Drug addicts may suffer the negative health effects associated with the misuse of drugs and require
treatment and rehabilitation. The cost to society to provide these services is very high. Drug use may
also lead to loss of jobs and reduced productivity. This affects families directly and the society as a
whole. In the case of Caribbean countries, it may mean reduced foreign exchange earnings.
Criminal acts such as murder, burglary and prostitution are often carried out in order for drug addicts
to obtain money to buy drugs. Thus, the crime rate tends to be higher in areas where drug misuse
is prevalent. There are also more automobile accidents when people drive under the influence
of drugs.
Revision questions
1
2
3
4
5
6
7
8
9
What is a drug?
Define drug dependence.
Distinguish between physical and psychological dependence.
What is the function of EACH of the following prescription drugs?
a antibiotics
b sedatives
Describe FIVE effects of cocaine use on the human body.
Name TWO hallucinogenic drugs and describe their effects on the human body.
Why is alcohol considered a drug?
Describe FIVE short-term and FIVE long-term effects of alcohol misuse.
Discuss the social effects of drug misuse in your country.
14 Drug use and misuse
141
Exam-style questions –
Chapters 12 to14
Structured questions
1 a) i) Define the term ‘non-communicable disease’.
2
142
(1 mark)
ii) Name TWO non-communicable lifestyle-related diseases that are prevalent
(2 marks)
in the Caribbean.
iii) Explain why diet and exercise are important measures in the prevention
(3 marks)
and treatment of the diseases named in a) ii) above.
b) Dengue fever is a vector-borne disease that has affected many countries in
the Caribbean.
i) Name the vector that is responsible for the spread of dengue fever.
(1 mark)
ii) State TWO signs/symptoms of dengue fever, other than fever.
(2 marks)
iii) Describe THREE measures that can be taken by community members to
(3 marks)
control the spread of dengue fever.
c) Scientists recently announced the development of a dengue vaccine. Explain
(3 marks)
how this vaccine will work to provide immunity to dengue fever.
Total 15 marks
a) i) What is meant by the term ‘drug misuse’?
(1 mark)
ii) Name THREE drugs, other than heroin, which are commonly misused in the
(3 marks)
Caribbean.
b) A study was carried out in a particular country to assess heroin use within various age
groups. Table 1 below shows the results of the study.
Table 1 Heroin addicts in various age groups
Age group
Number of addicts
15–24
475
25–34
1035
35–44
354
45–54
198
55 or older
81
i) Construct a bar graph using the data in Table 1.
(3 marks)
ii) Compare the number of heroin addicts in the various age groups.
(3 marks)
iii) Discuss THREE socio-economic implications of the findings of the study
(3 marks)
for the country.
c) The spread of HIV/AIDS is often associated with drug use. State TWO ways in
(2 marks)
which HIV/AIDS is transmitted, other than by sharing drug needles.
Total 15 marks
Exam-style questions – Chapters 12 to14
Structured essay question
3 a) Sterilisation and disinfection are both methods that are used to prevent harmful
microorganisms from affecting us.
i) Describe TWO differences between sterilisation and disinfection.
(4 marks)
ii) Suggest how sterilisation and disinfection could be used when caring for
(2 marks)
a patient in a hospital. Provide ONE situation for EACH method.
iii) Your classmate, Jordan, suggests that antiseptics are the same as disinfectants.
Explain to Jordan that they are different, stating ONE difference between
(2 marks)
them.
b) Your new friend, Jess, has poor hygiene and it is affecting her self-esteem. Advise Jess on
measures she should take to maintain good personal hygiene. Include in your answer:
• THREE reasons for maintaining good personal hygiene
• TWO methods of skin hygiene
(7 marks)
• TWO methods of dental hygiene
Total 15 marks
Exam-style questions – Chapters 12 to14
143
Section E – The impact of health
practices on the environment
15 Pollution and its effects
Pollution is the unfavourable alteration of the environment by the release of harmful substances or
forms of energy into the environment.
A pollutant is a harmful substance or form of energy that causes unfavourable changes to the
environment.
Based on their origin, pollutants can be classified into domestic, agricultural and industrial pollutants.
• Domestic pollutants – These are pollutants that are released from homes. They include sewage from
the kitchen, the bathroom and the laundry room, as well as food waste.
• Agricultural pollutants – These are mainly associated with modern agricultural practices, and
include pesticides and fertilisers.
• Industrial pollutants – These are pollutants that are released from industry. They include oxides of
carbon, oxides of nitrogen, smoke, dust and other particulate matter.
Air pollution
Air pollution results from the release of harmful substances or forms of energy into the atmosphere.
Many cities experience air pollution associated with industrial activities, such as energy production
in power plants and processing of materials, as well as the operation of numerous motor vehicles in
cities. Air pollution in rural areas is often associated with agricultural practices such as land clearance
by slash and burn.
Table 15.1 Examples of air pollutants and their effects
Pollutant
Origin
Harmful effects
Carbon dioxide
• Burning fossil fuels in • Builds up in the atmosphere and enhances the
industry, motor vehicles greenhouse effect which contributes to global
(CO2)
warming (see page 145).
and power plants
• Some is absorbed by oceans and causes ocean
acidification. This is a lowering of the pH of
ocean water, which harms aquatic organisms.
Carbon monoxide • Burning fossil fuels in • Combines with haemoglobin in the blood more
industry and motor
readily than oxygen. This reduces the amount of
(CO)
vehicles
oxygen being carried to body cells and results
in headaches, dizziness, loss of consciousness
• Cigarette smoke
and death.
Sulfur dioxide
• Burning fossil fuels in • Combines with water vapour, smoke and other
industry and power
air pollutants to form smog, which causes
(SO2)
plants
respiratory problems, e.g. asthma, bronchitis
and lung disease, and irritates the skin and eyes.
• Dissolves in rain water to form acid rain. Acid rain
lowers the pH of the soil and bodies of water
such as lakes, streams and rivers, and makes them
unsuitable for organisms. It also damages plants,
harms animals and corrodes buildings.
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15 Concise Revision Course: Human and Social Biology
Pollutant
Origin
Harmful effects
Oxides of nitrogen • Combustion at high
• Combine with water vapour, smoke and other
temperatures in
air pollutants to form smog (see above).
industry, motor vehicles • Reduce plant growth.
and power plants
• Dissolve in water to form acid rain (see above).
Volatile organic
• Vehicle exhaust fumes • Combine with water vapour, smoke and other
air pollutants to form smog (see above).
compounds (VOCs) • Industrial waste
Dust and other
• Combustion in industry • Cause respiratory problems, e.g. asthma,
bronchitis and lung disease.
particulate matter • Mining and quarrying
• Coat leaves, which reduces photosynthesis.
• Domestic fires
The greenhouse effect and global warming
Greenhouse gases, e.g. carbon dioxide, water vapour and methane (CH4), in the atmosphere allow heat
energy from the Sun to pass through them and to warm the Earth. However, they trap much of this
heat in the atmosphere by reflecting it back towards the surface of the Earth. The trapped heat also
warms the Earth. This is similar to how a greenhouse traps heat, so it is called the greenhouse effect.
2 The Earth reflects some
radiation back into
space.
Sun
3 Greenhouse gases absorb some
radiation and radiate it back to
Earth. This also warms the Earth.
1 Radiation from the Sun
passes through the Earth’s
atmosphere and warms
the Earth.
Earth
Earth’s atmosphere
containing greenhouse
gases
Figure 15.1 The greenhouse effect
Human activities that release carbon dioxide, such as burning fossil fuels and deforestation, enhance
the greenhouse effect and contribute to an increase in the Earth’s temperature over time. This is
called global warming. Global warming is also leading to global climate change, which is having several
effects on the environment, including:
• Melting of polar ice caps and glaciers.
• Rising sea levels.
• Flooding of low-lying coastal areas.
• Changes in global weather patterns.
• Extreme weather and severe natural hazards.
• Rising sea temperatures.
• Wider spread of some infectious diseases.
Water pollution
Water pollution results from the release of harmful substances or forms of energy into a body of
water. These pollutants make the water unsuitable for organisms to live in and for human use.
15 Pollution and its effects
145
Table 15.2 Examples of water pollutants and their effects
Pollutant
Origin
Harmful effects
Suspended solids • Soil erosion, which causes silt • Reduce light penetration, which reduces
and soil to wash into bodies of photosynthesis in aquatic plants.
water when it rains
• Block rivers and lakes.
• Domestic and industrial waste
Plant nutrients
• Chemical fertilisers
• Cause eutrophication (see below).
(e.g. nitrates and • Sewage
• Make water unsuitable for consumption.
phosphates)
High nitrate levels in water make it
• Manure and other farm waste
poisonous for babies to drink.
• Detergents
Organic matter • Sewage
• Reduces the amount of oxygen dissolved
in water, leading to the death of fish and
• Manure and other farm waste
other aquatic organisms.
• Industrial waste
Pesticides
• Used in agriculture to control • Can harm beneficial organisms as well as
pests, pathogens and weeds
harmful ones.
• Become higher in concentration up food
chains and can harm top consumers.
Heavy metal ions • Industrial waste
• May be toxic to organisms and kill them
directly.
(e.g. mercury and
lead)
• May become higher in concentration up
food chains and can harm top consumers.
• Damage many body tissues and organs,
especially parts of the nervous system.
Pathogens
• Sewage
• May cause various infectious diseases, e.g.
typhoid, cholera and dysentery.
• Animal manure
Heat
• Factories and power plants,
• May kill organisms directly.
which release waste heat into • Makes organisms more susceptible to
bodies of water
pathogens.
• Reduces the amount of oxygen dissolved
in water, leading to the death of fish and
other aquatic organisms.
Radioactive waste • Nuclear power plants
• Causes genetic defects (mutations).
• Hospital waste
• Can lead to death.
Eutrophication
Excess nutrients in water, especially nitrates
and phosphates, cause an overgrowth of
aquatic plants and algae, which gives the
water a green appearance. When the plants
and algae die, decomposers in the water
break them down. These decomposers are
aerobic bacteria, which multiply quickly and
use up the dissolved oxygen in the water. This
causes other aquatic organisms, e.g. fish, to
suffocate and die.
146
Figure 15.2 Eutrophication
15 Concise Revision Course: Human and Social Biology
Methods of controlling pollution
Controlling air pollution
The following are measures that can be used to reduce the amount of air pollution:
• Reduce the use of fossil fuels by using alternative energy sources, e.g. solar and wind energy, which
do not cause air pollution.
• Pass laws with strict penalties that limit the release of air pollutants by industry, e.g. a Clean Air Act.
• Clean gaseous emissions from factories before releasing them into the atmosphere.
• Equip motor vehicles with pollution control devices and modify engines to make them more fuel
efficient. Burning less fuel means less air pollutants will be released.
• Ban smoking or restrict the activity to specific locations.
• Put public education programmes in place.
Controlling water pollution
The following are measures that can be used to reduce the amount of water pollution:
• Carry out proper treatment of sewage before releasing it into bodies of water.
• Compost plant waste, such as vegetable peelings and crop residues.
• Use farm waste and waste from the food industry to produce biogas.
• Use organic fertilisers instead of inorganic chemical fertilisers.
• Use biodegradable detergents.
• Use biological control or natural, biodegradable pesticides instead of synthetic pesticides.
• Pass laws with strict penalties that limit the release of water pollutants by industry, e.g. a Clean
Water Act.
• Put public education programmes in place.
Revision questions
1 Define the terms:
a pollution
b pollutant
2 Several air pollutants are released into the atmosphere when fossil fuels are burned
3
4
5
6
7
in industry. Name THREE such pollutants and outline the harmful effects of EACH.
Explain what is meant by the term ‘global warming’.
Dawn wants to know why her teacher said that agriculture contributes to water
pollution. Explain to her how the overuse of chemical fertilisers and pesticides
affects aquatic environments.
Identify the sources and outline the harmful effects of the following water pollutants:
a suspended solids
b organic matter
c heavy metal ions
List FOUR methods of controlling air pollution.
Discuss FOUR methods of controlling water pollution.
15 Pollution and its effects
147
16 The cycling and treatment
of water
All living organisms need water for survival and there is a great demand on water resources by the
human population for various purposes. Most of the freshwater withdrawn from water bodies is used
in agriculture for irrigation and to provide water for farm animals. A large amount of water is also
used in industry, as well as for domestic purposes.
The water cycle
The water cycle, also known as the hydrological cycle, shows how water moves on, above and below
the surface of the Earth. It also shows the changes of the state of water as it moves.
The cycling of water ensures that all living organisms have a continuous supply of water to keep their
cells hydrated and to act as a solvent for chemical reactions. Plants also need a steady supply of water
for photosynthesis. The water cycle also ensures that aquatic organisms have a constant environment in
which to live.
condensation
evaporation
precipitation
transpiration
exhalation
surface
runoff
infiltration
percolation
Figure 16.1 The water cycle
The following processes are involved in the water cycle:
• Evaporation – Heat from the Sun causes liquid water in bodies of water, e.g. oceans, lakes, ponds,
rivers and streams, and in the soil to change into water vapour, which enters the atmosphere.
• Transpiration – Heat from the Sun also causes water from plants to be lost to the atmosphere as
water vapour.
• Respiration – When organisms respire aerobically, water is produced as a by-product and some of
this is released into the atmosphere as water vapour when the organisms exhale.
• Condensation – As water vapour rises, it cools and becomes water droplets that form clouds.
• Precipitation – Water returns to the surface of the Earth in the form of rain, hail or snow.
• Surface runoff – Some water flows across the surface of the ground into bodies of water.
• Infiltration – Some water moves downwards through the soil.
• Percolation – The water then moves through rocks into groundwater and may eventually return to
bodies of water.
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16 Concise Revision Course: Human and Social Biology
Water purification
Water may become polluted in different ways as it moves through the environment, as outlined in
Chapter 15. As a result, various forms of purification are required to make water safe for human use.
Water that is safe to drink or to use in food preparation is called potable water.
The aim of water purification is to ensure that drinking water:
• Is safe for human consumption.
• Is clear and not discoloured.
• Has an acceptable taste.
• Has an acceptable smell.
In order to achieve this aim, drinking water from rivers, streams and lakes, as well as rainwater
collected using gutters, needs thorough treatment. Treatment methods include the small-scale
measures often used in the home and large-scale measures that provide water for cities and towns.
Small-scale domestic water purification
Filtration
Muslin cloth can be used as a filter to remove suspended material from water. This does not make
the water safe for drinking, but it can be used for other domestic purposes, such as bathing and
washing clothes. Domestic filters can be attached to taps. Their pore sizes are tiny enough to remove
suspended material, including bacteria and protozoa.
Boiling
This is the oldest method and is still satisfactory for purifying water on a small scale. For it to be
effective, water must be brought to a ‘rolling boil’ for 10–20 minutes. This kills bacteria, spores, cysts
and ova of intestinal parasites. It also removes hardness of water, producing soft water.
Chlorination
Chlorine tablets are very effective for disinfecting small quantities of water. One 500 mg tablet
can be used to kill microorganisms in 20 litres of water. Chlorine bleach is also effective for killing
microorganisms in water. One teaspoon of bleach should be added to one litre of water.
Large-scale water purification
There are four steps involved in the large-scale purification of water:
1 Screening – Water from rivers, lakes and reservoirs passes through grid screens to remove large
floating materials and suspended solids.
2 Sedimentation – The water is then pumped to a settlement tank where fine suspended solid
particles coagulate (clump together) and settle.
3 Filtration – The clear water from the settlement tank passes through sand filters containing
microorganisms. These microorganisms remove organic matter from the water by feeding on it.
4 Chlorination – The filtered water is treated with chlorine to kill all harmful microorganisms that are
still in the water. Fluoride is sometimes added at this stage to reduce tooth decay. The water is then
pumped to storage tanks for distribution to consumers.
16 The cycling and treatment of water
149
river, lake or reservoir
screen
pump
sedimentation
clean water
distributed
to homes
and factories
storage tank
pump
chlorination
filtration
Figure 16.2 Large-scale water purification
Testing water for bacteria
The presence of pathogenic coliform bacteria in water can
be determined by using agar plates. The agar is a liquid
when hot and forms a gel when cooled. It has nutrients in it
that will allow bacteria to grow rapidly. Water that is safe for
drinking will have no colonies of coliform bacteria.
The steps involved in testing water for bacteria are
outlined below:
1 Collect a sample of the water to be tested in a
sterile container.
2 Pour a small amount of the water onto an agar plate. Cover
the plate and tape the lid to ensure it does not come off.
3 Incubate the plate at 35 °C for 24 hours.
Figure 16.3 Bacterial colonies on
an agar plate
4 Count the number of colonies of bacteria.
The impact of human activities on water supplies
Humans are having a negative impact on water supplies in several ways:
• They harvest freshwater for agricultural, industrial and domestic use, and as the human population
grows, the demands for freshwater increase.
• They carry out deforestation, which reduces the amount of transpiration and precipitation that take
place to replenish water sources.
• They release different types of waste and harmful substances into bodies of water.
By carrying out the above activities, humans:
• Reduce the amount of freshwater available for agricultural, industrial and domestic purposes.
• Contaminate water sources, leading to a loss of potable water.
• Increase the cost of water treatment, as multiple steps have to be used in the purification of heavily
contaminated water.
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16 Concise Revision Course: Human and Social Biology
Harmful effects of contaminated water on human health
Contaminated water is detrimental to human health because it may contain:
• Pathogens that cause diseases such as typhoid, cholera and gastroenteritis.
• Pesticides that may harm the nervous and endocrine systems.
• Heavy metal pollutants, e.g. mercury and lead, that affect many body tissues, especially those of the
nervous system, resulting in mental illnesses and brain damage.
• Nitrates, which are especially harmful to infants and pregnant women because they reduce the
amount of oxygen carried in the blood and can lead to blue baby syndrome.
• Radioactive waste that may result in genetic defects and even death.
Revision questions
1 Draw and label a diagram of the water cycle, including the following processes:
2
3
4
5
6
evaporation, transpiration, condensation, respiration and infiltration.
Describe TWO simple ways of purifying water in the home.
Outline the processes involved in large-scale water purification.
Your teacher asks you to outline the steps used to test water for the presence of
bacteria. List the steps you would include in your answer.
Discuss THREE impacts of human activities on water supplies.
Explain, giving at least THREE reasons, why contaminated water is detrimental
to humans.
16 The cycling and treatment of water
151
17 The treatment and disposal of
human waste
Human activities produce waste material that must be properly treated and disposed of in order to
keep the environment clean and to reduce the spread of disease. Some of this waste is in liquid form
with suspended solids known as sewage, and some of the waste is solid waste, also known as refuse
or garbage.
Sewage disposal
Sewage consists of human faeces and urine, household wastewater, wastewater from some industries
and rainwater.
Improper sewage disposal
Improper sewage disposal takes place when untreated sewage:
• is released directly onto the land
• is released directly into open water
• leaks from cracked sewage pipes.
Improper disposal of sewage has a negative effect on human health and the environment:
• Untreated sewage is directly responsible for the spread of infectious diseases such as cholera,
typhoid and dysentery.
• Untreated sewage that is released onto the land promotes the breeding of vectors, such as flies and
rats, which transmit diseases.
• Untreated sewage that is released into water may float on the surface of the water and reduce
the amount of light that is absorbed by aquatic plants. This reduces the amount of photosynthesis
taking place in the water and affects aquatic food chains. It may also reduce the amount of oxygen
dissolved in the water, leading to the death of aquatic organisms.
• Nutrients in untreated sewage may contribute to eutrophication of water bodies (see page 146).
• Sewage gives off a foul odour that contaminates the environment.
Proper sewage disposal
Sewage is disposed of properly when it is removed from houses and other buildings through
underground pipes or sewers, which take it to sewage treatment plants (see page 152) or into areas
that are far enough from homes and water sources so as to not be problematic. Flush toilets and pit
latrines are commonly used in the Caribbean to dispose of human faeces and urine.
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17 Concise Revision Course: Human and Social Biology
Flush toilets
water tank
water from piped
mains supply
valves control water flow
into and out of the tank
handle
water in the tank
lid
seat
water runs down this pipe
and into the bowl when
the toilet is flushed
water that is flushed into
the bowl washes the waste
down to the sewers or
a septic tank
toilet bowl
this bend keeps some water
in the toilet, which prevents
odours and microorganisms
coming up from the sewers
Figure 17.1 A flush toilet
Faeces and urine are passed out into the toilet bowl, and water from the tank is used to flush them
out of the building and into the sewers. The bend in the toilet keeps some water in the toilet and
prevents unpleasant odours and microorganisms from coming up from the sewers. Flush toilets are
very effective means of disposing of sewage, however, they generally require a large amount of water.
New low-flow toilets are now available which use significantly less water.
Pit latrines
Pit latrines are used in areas with
fly screen made of
galvanised
limited water supply or where
wire mesh
iron roof
there is no sewage treatment
wire mesh-covered
ventilation pipe to allow
system in place. They should
vent to allow air
gases and odours produced
circulation
during decomposition in
be carefully sited and used to
the pit to escape into the
ensure that water sources are not door
atmosphere
contaminated and to reduce the
lid to keep
base made of smooth
likelihood of health hazards. The
out vectors
material for easy cleaning
following guideline should be
concrete cover
cement pit collar prevents
followed when siting pit latrines:
slab to prevent
the side from caving in
entry of vectors
• They should be dug to at least
deep pit to reduce odours
three metres (3 m) deep in order drop hole
escaping and to allow the
to reduce odours coming up
pit latrine to be used for a
long time
at
least
3
m
from the pit and to ensure that
they can be used for a long
human waste
time before they fill up.
porous soil allows liquids
to drain from the pit
• They should be placed in sandy
soil because bacteria in the
latrines break down the faeces Figure 17.2 A pit latrine
and convert them into liquids.
Sandy soil will allow the liquids to drain away.
• They should also be placed downhill and far enough away from wells and other sources of drinking
water so that they do not contaminate these water sources.
17 The treatment and disposal of human waste
153
While the pit latrine is in use, no disinfectants should be added as these will kill bacteria, thereby
preventing them from decomposing the faeces. When the pit is full, it should be covered and left for
at least six months before the land can be used for another purpose.
Advantages of pit latrines
Pit latrines have been very effective for disposal of sewage in the Caribbean.
• They require less water than flush toilets.
• They are relatively cheap to construct.
Disadvantages of pit latrines
• They contribute to the risk of water and food contamination.
• They can contribute to the spread of infectious diseases.
• The rapid growth of the Caribbean population makes it difficult to site pit latrines. There is now
limited land space available in appropriate locations.
As a result of these disadvantages, pit latrines are due to be phased out throughout the Caribbean and
replaced with modern disposal methods and sewage treatment systems.
Sewage treatment
There are two methods that are usually used in the treatment of sewage:
• biological filter method
• activated sludge method
The initial treatment steps for both processes are as follows:
1 Screening – Large objects, e.g. plastic bottles, rags, paper and twigs, are removed from the sewage
by using screens.
2 Grit settling – The sewage passes slowly through a grit pit, and the grit and sand settle out.
3 Sedimentation – The sewage flows slowly through sedimentation tanks where the remaining solid
material settles and forms sludge. The sludge is removed from the bottom of the tanks and is used
to make methane in a sludge digester or to make fertiliser.
The liquid from the sedimentation tanks still contains suspended organic matter and is known as
effluent. This effluent is then either passed into a biological filter, or into an aeration tank for treatment
using the activated sludge method.
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17 Concise Revision Course: Human and Social Biology
sewage in sewer pipes
screen – large objects
are removed
grit pit – grit and
sand settle out
sedimentation tank – solid material
settles and forms sludge
Biological filter method
side view of percolating filter
sprinkler
effluent
in
bed of stones
covered with a film
of microorganisms
effluent
out
sludge removal
Activated sludge method
side view of aeration tank
effluent
in
mixing
paddle
effluent
out
air bubbles
final settlement tank
compressed
air
final settlement tank
water bodies, e.g. a river or the sea
Figure 17.3 Sewage treatment
Biological (percolating) filter method
The effluent is sprayed onto small stones that are covered with a film of aerobic bacteria and protozoa.
The microorganisms feed on the organic matter in the effluent, breaking it down. The effluent is
then passed to a final settlement tank to allow any remaining solids to settle, after which it is safe for
release into bodies of water, e.g. a river or the sea.
Activated sludge method
The effluent is passed into aeration tanks where compressed air is forced through it. Paddles are also
used to help with the mixing of air and effluent. This ensures that enough oxygen is present for
aerobic bacteria in the tank to decompose the organic matter. The effluent from the tank is then
passed to a final settlement tank to allow any remaining solids to settle, after which it is safe for
release into bodies of water.
Domestic refuse disposal
Domestic refuse refers to all the unwanted solids that accumulate after use in the home, including
organic matter such as waste food and garden waste, and other solid waste such as plastics, paper, glass
and other materials. It is important that domestic refuse is disposed of properly. Disposal in landfills,
incineration, composting and recycling are some of the main ways to dispose of domestic refuse.
Before collection, refuse should be placed into bins with tight-fitting lids to prevent the entry of rats
and flies. The refuse should be collected at least once per week, and the bins should be inspected
and cleaned regularly.
155
17 The treatment and disposal of human waste
Table 17.1 Evaluation of some of the methods of domestic refuse disposal
Method
How method Advantages
Disadvantages
works
Landfill
(see below) • Once constructed, it is
• Requires continuous
convenient and relatively easy
maintenance to prevent
to use to dispose of refuse.
leachate and toxic gases
entering the environment.
• Many different types of waste
can be disposed of.
• Waste gases can contribute to
air pollution and unpleasant
• Methane can be used as a fuel
odours if allowed to escape.
to generate electricity.
can contaminate soil
• The site can be re-landscaped • Leachate
and water sources if allowed to
and put to good use once the
escape.
landfill is full.
• Uses up valuable land.
• Unsightly when in operation.
Incineration Solid
• Reduces the volume of solid • Incinerators are relatively
waste entering landfills.
expensive to build and operate.
combustible
waste is
• High temperatures kill harmful • Energy requirements to
burned in
pathogens in the waste.
operate incinerators are high.
incinerators • Heat produced can be used to • Waste gases are produced
at very high
generate electricity or to heat
which can contribute to air
temperatures. water and nearby buildings.
pollution and cause respiratory
problems.
• Incinerators do not take up a
lot of land.
Composting Biodegradable • Reduces the volume of solid • Can be time consuming to
waste entering landfills.
‘turn’ the compost daily.
waste is
broken down • Produces organic fertiliser
• Compost heaps can give off
by aerobic
rich in mineral ions which is
unpleasant odours.
bacteria in
beneficial to soil.
• Compost heaps can attract
compost heaps • Reduces the demand for
pests and vectors of disease.
or composters. synthetic chemical fertilisers
which can harm soil.
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17 Concise Revision Course: Human and Social Biology
Figure 17.4 An incinerator
Landfills
Landfills consist of large, deep pits in which compacted solid waste is buried to isolate it from the
surrounding environment. Domestic refuse is often disposed of in a landfill.
To make a landfill, topsoil is removed and a large, deep pit is dug into the ground. The pit is lined with
an impermeable material which forms the bottom liner to prevent liquids from the waste, known a
leachate, seeping into the ground and contaminating soil and water. Two sets of pipes are installed,
one to help drain off any leachate and carry it to a treatment plant, and the other to remove any waste
gases, e.g. methane, which can be used as a fuel to produce electricity.
On arrival at the landfill, the refuse is sorted to remove materials that can be recycled. The remaining refuse
is then compacted to make it difficult for vectors to penetrate and to reduce its volume so the landfill can be
used for a long time. The compacted refuse is then placed into the landfill and is covered with a layer of soil
at the end of each day so it is not exposed to the wind and vectors, and to reduce smells.
Figure 17.5 A landfill site
17 The treatment and disposal of human waste
157
Any biodegradable organic material in the refuse is broken down by soil bacteria and fungi. It is
during this decomposition that gases such as methane are given off. Any non-biodegradable refuse
remains, and when a landfill is full, it is capped to seal it, the topsoil is replaced and vegetation is
grown so that the land can be used in a variety of ways, e.g. recreational purposes or building.
Landfills are the most cost-effective means of solid waste disposal in the Caribbean. However, finding
suitable sites for landfills is becoming difficult.
The impact of solid waste on the environment
If solid waste is not disposed of properly it becomes a threat to the environment:
• Toxic chemicals in the waste can leach out and contaminate the soil, aquatic environments and
water sources.
• Greenhouse gases, e.g. methane and carbon dioxide, can be released into the atmosphere where
they contribute to the greenhouse effect (see page 145).
• Hydrogen sulfide gas can be released into the air. This gas is extremely toxic, and even low
concentrations irritate the eyes and respiratory system.
• Plastics can enter waterways and oceans where they are harmful to aquatic organisms.
• Refuse attracts rodents, which can spread disease.
• Refuse creates an eyesore, which impacts negatively on tourism, especially eco-tourism.
Controlling the volume of solid waste
The volume of solid waste to be disposed of can be controlled by using ‘The Three Rs’ of waste
management – reduce, reuse and recycle.
Reduce means to cut down on the purchase and use of materials.
Manufacturers can reduce the amount of waste to be discarded by using less packaging material.
Individuals can also reduce waste by using electronic mail (e-mail) rather than paper mail and
carrying shopping bags to the supermarket so that plastic bags are not taken.
Reuse means to use again for the same or for a different purpose.
Items that can be reused include glass bottles, clothing, old tyres and old newspapers.
Recycling involves the separation and reprocessing of a resource into new products.
Materials that can be recycled include paper, glass, metals and some plastics. Paper can be repulped
and reused to make new paper, glass and metal can be melted and recast, and some plastics can
be melted and reformed to make plastic wood, fibres for clothing and other useful materials.
Composting recycles organic material into fertilisers.
The Three Rs have several advantages:
• They allow materials and energy resources to last longer, as they reduce the need for new products
to be made.
• They reduce the amount of waste to be disposed of in landfills and by incineration.
• They reduce the amount of pollution that would result from manufacturing and waste disposal
measures.
One disadvantage of The Three Rs to consumers is that they must spend additional time separating
waste into the different categories for disposal or recycling.
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17 Concise Revision Course: Human and Social Biology
Biodegradable and non-biodegradable waste
Waste can be classified as biodegradable and non-biodegardable:
• Biodegradable waste is waste that can be broken down by microorganisms into harmless materials
that can be recycled into the environment, e.g. food waste, paper, garden and farmyard waste, and
a few plastics.
• Non-biodegradable waste is waste that cannot be broken down by microorganisms, so it remains in
the environment, e.g. most plastics, rubber, metal and glass.
Revision questions
1
2
3
4
Name THREE components of sewage.
Distinguish between proper and improper sewage disposal practices.
Discuss THREE impacts of improper sewage disposal practices.
Identify ONE similarity and ONE difference between the biological filter and
activated sludge methods of sewage treatment.
5 Outline the function of EACH of the following parts of a pit latrine:
a ventilation pipe
b lid
c cement lining
6 Your neighbour is planning to construct a pit latrine in her yard. Explain to her some
factors to consider when siting and constructing the pit latrine.
7 Discuss TWO advantages and TWO disadvantages of the use of pit latrines in
the Caribbean.
8 Identify THREE methods of disposal of domestic refuse.
9 Describe a landfill and the operations that take place there.
100 Discuss THREE impacts of solid waste on the environment.
11 Define EACH of the following terms, as it relates to waste management:
a reduce
b reuse
c recycle
122 Distinguish between the terms biodegradable and non-biodegradable materials,
giving TWO examples of EACH.
17 The treatment and disposal of human waste
159
Exam-style questions –
Chapters 15 to 17
Structured questions
1 Community members were advised by the health authorities to avoid polluted floodwater
after a tropical storm.
a) i) What is meant by the term ‘pollutant’?
ii) Name TWO examples of water pollutants.
b) i) Describe a test the health authorities could use to determine if the
community’s water supply is contaminated with bacteria.
ii) Describe ONE small-scale method of water purification that community
members would be encouraged to use.
c) Outline THREE methods of controlling water pollution.
d) Discuss THREE impacts of human activities on water supplies.
2 a) i) Complete the following statement by filling in the blank spaces.
Sewage consists of
,
(1 mark)
(2 marks)
(4 marks)
(2 marks)
(3 marks)
(3 marks)
Total 15 marks
and
(3 marks)
.
ii) Describe ONE improper sewage disposal practice.
(1 mark)
iii) Explain how the practice described in a (ii) above poses a threat to the health of
(3 marks)
communities in the Caribbean.
b) Your neighbour thinks that pit latrines are inappropriate for sewage disposal.
(3 marks)
Outline THREE advantages of the use of pit latrines in the Caribbean.
c) Biological filter and activated sludge are two methods used in sewage treatment.
i) Which stage in the sewage treatment process is done immediately before the
(1 mark)
biological filter?
ii) Compare the treatment of sewage by biological filter and activated sludge
(4 marks)
methods, giving TWO similarities and TWO differences between them.
Total 15 marks
Structured essay question
3 a) Solid waste may be classified as biodegradable or non-biodegradable.
160
i) What is meant by the term ‘biodegradable’?
(1 mark)
ii) Give ONE example of a biodegradable waste material and ONE example of a
(2 marks)
non-biodegradable waste material.
b) Solid waste is sometimes disposed of in a landfill.
i) Describe how a landfill is made.
(3 marks)
ii) Describe the daily operations at a landfill.
(4 marks)
c) A small village in your country does not have a garbage collection system in place.
You visit the village as a Health Inspector, and notice there is solid waste strewn all
over the village. What advice would you give to the villagers about the proper
(5 marks)
disposal of this solid waste?
Total 15 marks
Exam-style questions – Chapters 15 to 17
Index
A
ABO blood groups, 49, 110–111, 111t
abortion
defined, 92
induced, 92–93
spontaneous, 92
absorption
in colon, 35
defined, 34
in small intestine, 34
acids, 29
amino, 6, 10, 20, 35
fatty, 20, 36
lactic, 44
acquired immunity, 135, 135f
active transport, 8, 34
adenosine diphosphate (ADP), 43
adenosine triphosphate (ATP), 43
ADH. see antidiuretic hormone (ADH)
adipose (fat) tissue, 35
ADP. see adenosine diphosphate (ADP)
aerobic bacteria, 146
aerobic respiration, 1, 37, 43
agricultural pollutants, 144
air pollution, 144–145, 144t–145t
controlling, 147
albinism, 105, 108
alcoholic beverages, anaerobic respiration and, 44
alcoholism, 140–141
alimentary canal, 27
movement of food through, 34
allele, 113
alleles, 108, 108t
alveoli, 37, 42
gaseous exchange in, 40f
walls of, 39
amino acids, 6, 10, 20, 35
amylase, 30
anaerobic respiration, 1, 43
industrial and domestic uses of, 44
anal sphincter, 35
animal cells, 1–2, 2f, 3t
anorexia, 26
antagonistic pair, 59
anterior vena cavae, 51
antibiotic resistance, 106
antibiotics, 134, 138
antibodies, 35
antibody, 135
antidiuretic hormone (ADH), 67
antifungal agents, 134
antigen, 135
antigens, 49
antiseptics, 134
antitoxin, 135
anus, 27, 35
aorta, 51
appendicular skeleton, 57, 57f
arteries, 49f, 50, 50t
coronary, 53
artificial active immunity, 136
artificial pacemaker, 51
artificial passive immunity, 136
asexual reproduction, 1, 83
assimilation, 35–36
asthma, 119–121, 120f
causes of, 120
effects on respiratory system, 119, 120f
symptoms of, 120
treatment of, 121
astigmatism, 80
atheromas, 53
atherosclerosis, 53, 122, 122f
ATP. see adenosine triphosphate (ATP)
atria, 51
atrial systole, 52
autoclaving, 134
autonomic nervous system, 71, 75
autotrophs, 1
axial skeleton, 56–57
axons, 72
B
bacteria, 4, 4f, 29, 44
aerobic, 146
denitrifying, 14
nitrifying, 14
nitrogen-fixing, 14
balanced diet, 25–26
ball and socket joints, 59, 59f
biceps, 60
biconcave discs, 47
biodegradable waste, 159
biogas, 44
birth, 88
birth control, 89
methods, 89t–91t, 91f
Biuret test, 21t
Index
161
blood
cells, 46, 47t–48t, 58
clotting, 48–49, 53, 122
deoxygenated, 51, 52
groups, 49
oxygenated, 51, 52
plasma, 46–47, 54
blood pressure, 52
blood sugar (glucose) levels, regulation of,
69–70, 69f
blood vessels, 49–50, 49f, 50t, 53f
teeth, 28
BMI. see body mass index (BMI)
body mass index (BMI), 26, 26t, 121
body temperature, regulation of, 69, 69f
bones, 56
bovine somatotrophin (BST) hormone, 114
Bowman’s capsule, 64
brain, 72
functions of, 72t
involuntary actions, 74–75
nerves, 74
neurones, 72, 73f
parts of, 72, 72f
reflex actions, 75–76
synapses, 74
voluntary actions, 74
bread making, 44
breathing, 37, 58
cigarette smoking and, 41–42
mechanism of, 39, 39f
rate, factors affecting, 40
rescue, 41
bronchioles, 37, 42
bronchus, 37
BST hormone. see bovine somatotrophin (BST)
hormone
bulimia, 26
C
cancerous tumours, 42
cancers, of reproductive systems, 85, 85t
canine tooth, 28, 28t, 29f
cannabis, 140
canning, 134
capillaries, 34, 49f, 50, 50t
carbohydrates, 19, 19f
functions of, 22, 22t
laboratory tests to identify, 21, 21f, 21t
properties of, 20t
sources of, 22, 22t
types of, 19, 19f
162
Index
carbon (C) atoms, 13
carbon-containing compounds, 13
carbon cycle, 13, 13f
carbon dioxide, 6, 37, 44
levels, regulation of, 68
carbon monoxide, 42
cardiac arrest, 54
cardiac cycle, 52
cardiac muscle, 51
cardiovascular disease (CVD), 122, 123t
cardiovascular system
blood. see blood
blood vessels, 49–50, 49f, 50t
heart. see heart
Caribbean food groups, 25
carnivores, 11
cartilage, 56
cartilaginous joints, 59
catalase, 30
cataract, 80, 80f
cell division, 102
meiosis, 103–104, 104f
mitosis, 102, 103f
cell membrane, 1, 2f, 7, 36
cells
animal, 1–2, 2f, 3t
bacteria, 4, 4f
blood, 46, 47t–48t, 58
defined, 1
egg (ovum), 4t, 5f
epithelial, 4t, 5f
muscle, 4t, 5f, 44
nerve (neurone), 4t, 5f
plant, 1–2, 2f, 3t
specialised, 4–5, 4t, 5f
sperm (spermatozoon), 4t, 5f
yeast, 44
cell sap, 2f
cell wall, 2f, 8
central nervous system (CNS), 71. see also brain
CHD. see coronary heart disease (CHD)
chemical digestion, 27, 30–34
digestive system and, 32f, 33t
chitin, 4
chlorination, 149
chlorophyll, 10
chloroplasts, 2f, 10
chromatin threads, 102
chromosomes, 102, 113
sex, 111
chronic obstructive pulmonary disease (COPD),
42, 42f
chymosin, 114
cigarette smoking, 41–42
components of, 41f
and lungs, 42
cilia, 42
ciliary muscles, 79
circulation, 52–53, 52f
double, 52, 52f
pulmonary, 52
systemic (body), 52
circulatory system, 46–55
blood. see blood
blood vessels, 49–50, 49f, 50t
heart. see heart
lymphatic system, 54–55, 54f
need for, 46
clone, 83
clotting, blood, 48–49, 53, 122
CNS. see central nervous system (CNS)
cocaine, 139
co-dominance, 109, 113
ABO blood groups, 110–111, 111t
sickle cell anaemia, 110
colon, absorption in, 35
colour blindness, 113
combustion, 13
communicable/infectious diseases, 119, 124
examples of, 124t–126t
sexually transmitted infections, 126–128,
126t–127t
vector-borne, 128, 128t–129t
cones, 78
constipation, 24, 24t
consumers, food chains, 11
contaminated water, 151
continuous variation, 106
contraception. see birth control
contraction, 52
coordination, by nervous and endocrine systems,
71–76
COPD. see chronic obstructive pulmonary disease
(COPD)
coronary arteries, 53
coronary heart disease (CHD), 122
coronary thrombosis, 53
cranial nerves, 74
cranial reflexes, 75
crown, teeth, 28
CVD. see cardiovascular disease (CVD)
cytoplasm, 1, 2f, 7
D
decomposers, 13, 14
deficiency diseases, 23, 23t
degenerative diseases, 119
denature enzymes, 31
dendrites, 72
dental hygiene, 134
dentine, 28
deoxygenated blood, 51, 52
deoxyribonucleic acid (DNA) molecule, 102
dermis, 65, 66f, 66t
diabetes mellitus, 70, 121, 122t
dialysis, 65
diaphragm, 37, 39
diarrhoea, 24, 24t
diastole, 52
diet, 19–24
balanced, 25–26
carbohydrates. see carbohydrates
dietary fibre, 24
and lifestyle-related diseases, 123
lipids. see lipids
minerals, 22–23, 22–23t
proteins. see proteins
unbalanced, 61
vitamins, 22–23, 22–23t
water, 23–24
dietary fibre, 24
diffusion, 6, 34
digestion
chemical, 27, 30–34
defined, 27
mechanical, 27, 28–30
digestive enzymes, 32, 32t
digestive system, 27
and chemical digestion, 32f, 33t
disaccharides, 19, 19f
discontinuous variation, 106
diseases
communicable/infectious. see communicable/
infectious diseases
defence against, 135–136
defined, 119
degenerative, 119
hygiene as defences against, 133–134
impact on human population, 132
non-communicable. see
non-communicable diseases
signs/symptoms of, 119
disinfectants, 134
disinfection, 134
domestic pollutants, 144
Index
163
domestic refuse disposal, 155–159, 156t
landfills, 157–158
dominant allele, 113
dominant trait, 113
double circulation, 52, 52f
Down’s syndrome, 106
drug misuse, 138
social effects of, 141
drugs
defined, 138
dependence, 138
misuse, 138
non-prescription. see non-prescription drugs
prescription, 138
E
ecological pyramids, 13, 13f
ecstasy, 140
effector, 71, 73f
egestion, 35, 63
egg (ovum), 4t, 5f
elbow joint, movement of, 60, 60f
emphysema, 42
Emulsion test, 21t
enamel, 28
endocrine (hormonal) system, 81, 81f, 81t–82t
coordination by, 71–76
energy, 11, 25
transfer in food chains, 12, 12f
environmental variation, 106
enzymes, 30, 35, 43. see also proteins
denature, 31
digestive, 32, 32t
properties of, 31
epidermis, 65, 66f, 66t
epithelial cells, 4t, 5f
epithelium, 34
erythrocytes. see red blood cells
eutrophication, 146, 146f
excretion, 1, 35
defined, 63
kidneys and, 63–65
excretory products, 12
exercise, 89
effect on skeletal system, 60–61
and lifestyle-related diseases, 123
exhaled air, 41
extensor muscle, 59
eyelashes, 77
eyelids, 77
eyes, 77
astigmatism, 80
164
Index
cataract, 80, 80f
colour detection by, 78
glaucoma, 80
image formation, 78, 78f
light detection by, 78
light entering, 78, 78f
long-sightedness, 80, 80f
old sight, 80
parts, structure and functions of, 77f
retina, 78, 79, 79f
short-sightedness, 79, 79f
F
faeces, 35, 154
family planning, importance of, 91–92
fat, 25, 36
fat soluble vitamins, 22
fatty acids, 20, 36
fatty substances, 34
feeding, 1
female reproductive system, 83, 83f
fermentation, 44
fertilisation, 87
fibrin fibres, 49
fibrinogen, 47
fibrous connective tissue, 59
filtration, water, 149
fixed/fibrous joints, 59
flexor muscle, 59
flush toilets, 153, 153f
follicle stimulating hormone (FSH), 86
food chains, 11, 11f
energy transfer in, 12, 12f
food poisoning, 24
food production, genetic engineering and, 113–114
food webs, 12, 12f
fossil fuels, 13
FSH. see follicle stimulating hormone (FSH)
fungi, 4, 4f
G
gametes, 83, 102, 103, 108
gaseous exchange, 37
in alveolus, 40f
mechanism of, 39, 40f
gaseous exchange surface, 37
gastroenteritis, 24
genes, 102, 113
gene technology, 108
genetically modified organism (GMO), 113
genetic engineering, 113–115
advantages of, 115
disadvantages of, 115
and food production, 113–114
and medical treatment, 114–115
genetics, 108
genetic variation, 105–106
genital hygiene, 133
genotype, 105, 113
girdles, 57
glands, 81f, 81t–82t
glaucoma, 80
global warming, 145
glomerulus, 64
glucagon, 69
glucose, 6, 10, 35
glycerol, 20, 36
glycogen, 69
grease spot test, 21t
greenhouse effect, 145, 145f
greenhouse gases, 145
growth, 1
H
haemophilia, 112
hair hygiene, 133
hands hygiene, 133
health, 119
heart
blood pressure, 52
cardiac cycle, 52
chambers, 51
circulation, 52–53, 52f
functions of, 51f
pacemaker, 51
heart attack, 51
causes and effects of, 53–54
risk factors, 53–54
symptoms of, 54
heartbeat, 52
heat, 69
hepatic portal vein, 35
herbivores, 11
heroin, 139
heterotrophs, 1
heterozygous individuals, 108, 109, 109f, 113
HGH. see human growth hormone (HGH)
high blood pressure, 52
hinge joints, 59, 59f
histones, 102
HIV/AIDS (human immunodeficiency virus/acquired
immune deficiency syndrome)
mode of action of, 127
significance of, 128
homeostasis, 63, 67–70
blood sugar (glucose) levels, regulation of,
69–70, 69f
body temperature, regulation of, 69, 69f
carbon dioxide levels, regulation of, 68
defined, 67
feedback mechanisms and, 67, 67f
osmoregulation, 67, 68f
homozygous individuals, 108, 109, 109f, 113
hormones, 35
bovine somatotrophin, 114
follicle stimulating, 86
human growth, 115
luteinising, 86
progesterone, 86
housefly
control of, 131
life cycle of, 130, 131f
as vector, 131
human brain. see brain
human diet. see diet
human growth hormone (HGH), 115
human papilloma virus (HPV), 85t
human skeleton, 56–58, 56f
appendicular skeleton, 57, 57f
axial skeleton, 56–57
bones, 56
cartilage, 56
ligaments, 58
tendons, 58
humerus, 57f
hydrolysis, 30
hygiene, personal, 133–134
hypermetropia, 80, 80f
hypertension, 52, 53, 122
hypha, 4f
hypothalamus, 67, 69
I
immunisation, 136
immunity
acquired, 135, 135f
artificial active, 136
artificial passive, 136
innate, 135
natural active, 135–136, 136f
natural passive, 136
implantation, 87
improper sewage disposal, 152
incisors, 28, 28t
induced abortion, 92–93
industrial pollutants, 144
Index
165
inheritance
co-dominance. see co-dominance
monohybrid, 108
of sex in humans, 111
innate immunity, 135
insulin, 114, 114f
intercostal muscles, 37, 39
intermediate neurones, 72
involuntary actions, 74–75
ions
mineral, 8
nitrate, 14
irritability, 1
J
joints
defined, 59
types of, 59
K
kidneys, 67
dialysis, 65
and excretion, 63–65
nephrons, 64, 64f
kwashiorkor, 26, 26f
L
lacteals/lymph capillaries, 34
lactic acid, 44
landfills, 157–158
larynx, 37
leucocytes. see white blood cells
LH. see luteinising hormone (LH)
lifestyle-related diseases
diabetes mellitus, 121, 122t
diet and, 123
exercise and, 123
obesity, 121
ligaments, 58
limbs, 57
movement of, 59–60
pentadactyl, 57, 57f
lipids, 10, 20, 20f
functions of, 22, 22t
laboratory tests to identify, 21, 21f, 21t
sources of, 22, 22t
living organisms
active transport importance in, 8
characteristics of, 1
dependence on plants, 12
diffusion importance in, 6
osmosis importance in, 8
166
Index
variation in. see variation
locomotion, 1, 61
long-sightedness, 80, 80f
LSD (acid), 139
lungs, 37, 63
cigarette smoking and, 42
vital capacity, 40–41, 41f
luteinising hormone (LH), 86
lymph, 54, 54f
functions of, 54
lymphatic system, 54–55, 54f
functions of, 54–55
lymph nodes/glands, 54
functions of, 55
lymphocytes, 48t, 54
lymph vessels, 54
M
male reproductive systems, 84, 84f
malnutrition, 25
maltose, 30
marasmus, 26, 26f
marijuana (cannabis), 140
mechanical digestion, 27
teeth and. see teeth
meiosis, 103–104, 104f, 105
mitosis and, 105f
menstrual cycle, 86, 86f
menstruation, 86
microbes/microorganisms
bacteria, 4, 4f
defined, 3
fungi, 4, 4f
growth, controlling, 134
viruses, 3, 3f
microvilli, 34
milk teeth, 28
mineral ions, 8
minerals, 22, 22t–23t
deficiency diseases, 23, 23t
mitochondrion, 2f
mitosis, 102, 103f
meiosis and, 105f
mixed nerves, 74
molars, 28, 28t
molecules
lipid, 20, 20f
protein, 20, 20f
monohybrid inheritance, 108
albinism, 108
co-dominance, 109–111
monosaccharides, 19, 19f, 35
mosquitos
control of, 131
life cycle of, 129, 130f
as vector, 130
motor nerves, 74
motor neurones, 72, 73f
mouth, 27, 37
mouth-to-mouth resuscitation, 41
moveable/synovial joints, 59
movement, 1
active transport, 8
diffusion, 6
joints, 59
of limbs, 59–60
osmosis, 7–8, 7–8f
skeletal muscles, 58, 58f
multicellular, 1
muscles
cells, 4t, 5f, 44
ciliary, 79
extensor, 59
flexor, 59
insertion of, 60
intercostal, 37, 39
origin of, 60
skeletal, 58, 58f
muscle tone, 60
mutations, 105
mycelium, 4f
myocardial infarction. see heart attack
myogenic heart, 51
myopia, 79, 79f
N
nasal cavities, 37
natural active immunity, 135–136, 136f
natural passive immunity, 136
nephrons, 64, 64f
nerve (neurone), 4t, 5f
nerve fibres, 72
nerves, 74
nerves, teeth, 28
nervous system
central, 71
coordination by, 71–76
organisation of, 71f
peripheral, 71
neurones
defined, 72
properties, 73
types of, 72, 73f
nicotine, 42
nitrate ions, 14
nitrogen (N) atoms, 14
nitrogen-containing compounds, 14
nitrogen cycle, 14, 14f
non-biodegradable waste, 159
non-communicable diseases, 119
asthma, 119–121, 120f
lifestyle-related diseases, 121–123
non-prescription drugs, 138
alcohol, 140–141
cocaine, 139
ecstasy, 140
heroin, 139
LSD (acid), 139
marijuana (cannabis), 140
nucleoid, 4, 4f
nucleus, 2f
nutrients, 19
nutrition, 1, 19–36
absorption, 34–35, 34f
assimilation, 35–36
defined, 19
digestion and. see digestion
egestion, 35
human diet and. see diet
O
obesity, 25, 61, 121, 122
oestrogen, 86
old sight, 80
omnivores, 11
optimum pH, 31, 31f
optimum temperature, 31, 31f
orbits, 77
organelles, 1
organic compounds, 22. see also carbohydrates;
lipids; proteins; vitamins
organism, 5
organs, 5
excretory, 63
sense, 77, 77t
organ systems, 5, 5t
osmoregulation, 63, 67, 68f
osmosis
defined, 7
demonstrating, 7f
explanation of, 7f
overnutrition, 25
ovulation, 86
ovum, 87
production and structure of, 84–85, 84f
oxygen, 6, 10, 37
Index
167
oxygenated blood, 51, 52
oxygen debt, 44
oxytocin, 88
P
pacemaker, heart, 51
pain killers, 138
pasteurisation, 134
pathogens, 119, 124
PEM. see protein-energy malnutrition (PEM)
pentadactyl limb, 57, 57f
periodontal membrane, 28
peripheral nervous system (PNS), 71
peristalsis, 24, 34, 34f
permanent teeth, 28
personal hygiene, 133–134
dental hygiene, 134
genital hygiene, 133
hands hygiene, 133
skin and hair hygiene, 133
pH, 68
phagocytes, 48t, 54
pharynx, 37
phenotype, 105, 113
photosynthesis, 1
defined, 10
pit latrines, 153–154, 153f
pituitary gland, 67
placenta, 87, 88
plant cells, 1–2, 2f, 3t, 8, 8f
plaque, 29
plasma, 46, 54
composition of, 47
functions of, 47
serum, 47
plasmids, 4, 4f
platelets (thrombocytes), 46, 48t
pleural fluid, 37
pleural membranes, 37
PNS. see peripheral nervous system (PNS)
pollutant, 144
pollution, 144
air, 144–145, 144t–145t
methods of controlling, 147
water, 145–146, 146t
polysaccharides, 19, 19f
poor posture, 61
posterior vena cavae, 51
postnatal care, 89
posture, 61
pregnancy, and development, 87–88, 87f, 88t
premolars, 28, 28t
168
Index
prenatal care, 88–89
presbyopia, 80
prescription drugs, 138
primary consumer, food chains, 11
producers, food chains, 11
progesterone, 86
proper sewage disposal, 152
flush toilets, 153, 153f
pit latrines, 153–154, 153f
protein-energy malnutrition (PEM), 26
proteins, 20, 20f, 26, 35. see also enzymes
functions of, 22, 22t
laboratory tests to identify, 21, 21f, 21t
sources of, 22, 22t
pulmonary artery, 37, 51
pulmonary circulation, 52
pulmonary vein, 37
pulp cavity, 28
pupil reflex, 75, 75f
Q
quaternary consumer , food chains, 11
R
rats, control of, 131
receptor, 71, 73f
recessive allele, 113
recessive trait, 113
recycling, 158
red blood cells, 46, 46f, 47
reduce, 158
reflex actions, 75–76
reflex arc, 75
relaxation, 52
reproduction
asexual, 1, 83
defined, 1
sexual, 1, 83, 105
reproductive systems
cancers of, 85, 85t
female, 83, 83f
male, 84, 84f
rescue breathing, 41
respiration, 10, 13, 36, 43–44
aerobic, 1, 37, 43
anaerobic, 1, 43–44
defined, 1, 43, 83
respiratory system, 37–44
breathing. see breathing
gaseous exchange. see gaseous exchange
parts, functions of, 38t–39t
structure of, 37, 37f
response , defined, 71
retina, 78, 79, 79f
reuse, 158
rhesus system, 49
ribosomes, 2f
ribs, 37, 57
rods, 78
root, teeth, 28
rough endoplasmic reticulum, 2f
S
saprophytes, 13
secondary consumer, food chains, 11
sedatives, 138
selective reabsorption, 65, 65f
sense organs, 77, 77t
sensitivity, 1
sensory nerves, 74
sensory neurones, 72, 73f
septum, 51
serum, 47
sewage disposal, 152–154
improper, 152
proper, 152
sewage treatment, 154–155, 155f
sex chromosomes, 111
sex-linked characteristics, 112–113
colour blindness, 113
haemophilia, 112
sexually transmitted infections (STIs), 126–128,
126t–127t
sexual reproduction, 1, 83, 105
short-sightedness, 79, 79f
sickle cell anaemia, 110
signs, of diseases, 119
sinoatrial node, 51
skeletal muscles, 58, 58f
skeletal system
effect of exercise on, 60–61
factors adversely affect, 61
functions of, 58
human skeleton, 56–58, 56f
skin, 63, 65
functions of, 66t
hygiene, 133
structure of, 66f
skull, 56
small intestine, absorption in, 34
smooth endoplasmic reticulum, 2f
solid waste
impact on environment, 158
volume, controlling, 158
somatic nervous system., 71
specialised cells, 4–5, 4t, 5f, 51
sperm (spermatozoon), 4t, 5f, 84, 87
production and structure of, 84–85
spinal nerves, 74
spinal reflexes, 76, 76f
spontaneous abortion, 92
spores, 4f
starch, 10, 30
sterilisation, 134
stimulus, 71
STIs. see sexually transmitted infections (STIs)
stomach, 5
subcutaneous layer, 65, 66f, 66t
sugars, 29
symptoms, of diseases, 119
synapses, 74
synovial joints, 59
systemic (body) circulation, 52
systole, 52
T
tears, 77
teeth
care, guidelines for, 30
importance in digestion, 28
milk, 28
permanent, 28
structure, 28, 29f
types of, 28, 28t
temperature, 69
tendons, 58, 60
tertiary consumer, food chains, 11
thorax, 37
structure of, 38f
“Three Rs” of waste management, 158
thrombin, 48
thrombocytes, 46, 48t
thrombokinase, 48
tissue fluid, 54
tissues, 5
tooth decay
causes of, 30
process of, 29, 29f
trachea, 37
transgenic organism, 113
triceps, 60
trophic level, 11, 11f
U
UHT. see ultra-high temperature treatment (UHT)
ultra-filtration, 65, 65f
Index
169
ultra-high temperature treatment (UHT), 134
unbalanced diet, 61
unicellular, 1
urinary system, 63
structure of, 64f
urine, 153
production of, 65, 65f
V
vacuoles, 2f
valves, 51, 54
variation
continuous, 106
defined, 105
discontinuous, 106
environmental, 106
genetic, 105–106
importance to living organisms, 107
vector-borne infectious diseases, 128, 128t–129t
vectors, 128
housefly, 130–131, 131f
methods of controlling, 131–132
mosquitos, 129–130, 130f
veins, 49f, 50, 50t
ventricles, 51
ventricular systole, 52
venules, 50
vertebral column, 57, 58
villi, 34, 34f
viruses, 3, 3f
vital capacity, 40–41, 41f
vitamins, 22, 22t–23t
deficiency diseases, 23, 23t
voluntary actions, 74
voluntary nervous system, 71
170
Index
W
waste
biodegradable, 159
domestic refuse disposal, 155–159, 156t
non-biodegradable, 159
sewage disposal, 152–154
substances, 46, 63
water, 8, 23–24
contaminated, effects on human health, 151
cycle, 148, 148f
supplies, impact of human activities on, 150–151
water molecules, 7
water pollution, 145–146, 146t
controlling, 147
water purification, 149
large-scale, 149, 150f
small-scale domestic, 149
testing water for bacteria, 150
water-soluble substances, 34
water soluble vitamins, 22
white blood cells, 46, 48t
word equation, photosynthesis, 10
Y
yeasts, 4, 44
yoghurt, 44
Z
zygote, 87
About the Publisher
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CSEC® CONCISE REVISION COURSE
Get ready to succeed in CSEC® Human and Social Biology with this full-colour Concise Revision
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