CSEC BIOLOGY
MANUAL OF ESSENTIAL NOTES
By Kevin Jared Hosein
Based purely on syllabus requirements.
1
SECTION A (1/2)
LIVING ORGANISMS AND THE ENVIRONMENT
WHAT IS A LIVING ORGANISM?
All living things are made up of CELLS. Thus, there are two types of organisms:
UNICELLULAR - These organisms are only
made of one cell. They usually have simple
structures and do not rely on a transport system
for their nutrients. They instead move dissolved
gases and nutrients around by the process of
diffusion. They do not rely on sexual
reproduction to continue their species, instead
reproducing by splitting in two. Common
examples include: Bacteria, amoeba, yeast
MULTICELLULAR - These organisms
require a more complex structure and
specialized systems may be necessary to
enable to organism to digest and
transport food, escape predators, seek
shelter and find a sexual mate to
continue the species.
All living organisms have specific characteristics, listed in the table below:
Characteristic
Description
GROWTH
Permanent increase in size by increasing dry mass and number of cells.
RESPIRATION
Release of energy through a molecule known as ATP for the metabolism1.
IRRITABILITY
Detection and response to a change in the environment, such as temperature.
MOVEMENT
An action by an organism, causing a change in position or place. 2
NUTRITION
Taking in, utilization and storage nutrients from different sources.
EXCRETION
Removal of metabolic waste, toxic products and excess in the body.
REPRODUCTION
Production of new individuals to continue the species.
1 - Metabolism refers to THE CHEMICAL PROCESSES THAT OCCUR IN THE BODY.
2 - Plants move by orienting their leaves and stems towards sunlight, or through the downward growth of
their roots. While plants can move their body parts or grow in a particular direction, they cannot direct
their bodies from one location to another. When an organism is able to move from one location to
another, this is termed LOCOMOTION (or WHOLE MOVEMENT).
CLASSIFYING SPECIES
2
Each organism belongs to a certain species. Members of the same species:
1. Have very similar physical and biological characteristics.
2. Are able to interbreed and produce viable, FERTILE offspring.
Artificial classification involves categorising by certain features of anatomy. For example, take into
account the organisms below. Find THREE categories to differentiate the ant and termite below.
Characteristic
Flying Ant
Termite
ANTENNAE
Has bowed antennae.
Has straight antennae.
BODY SHAPE
Has a thin division between
Has a wider abdomen.
thorax and abdomen.
WINGS
Has less segments.
Is densely segmented.
List THREE anatomical/physical features that can separate A – E into TWO distinct categories.
1. Only one dorsal fin (A and D). B, C and E have two dorsal fins.
2. Only B has whiskers. The others do not have whiskers.
3. Only B and D have distinctly forked tailfins. A, C and E have more rounded tailfins.
4. C and E have striped tailfins, while the others do not.
Unreliability of Artificial Classification
3
Using artificial classification depends on identifying organisms by physical or anatomical characteristics
(or morphology). This can be problematic for identifying organisms of the same species for several
reasons.
Reason
Explanation
All organisms inherit
Organisms can widely vary in appearance due to characteristics inherited
different genetic traits
from parents. Humans, for example, vary widely in height, weight, skin
from their parents.
colour, hair texture and many other features. Yet we are all the same species,
Homo sapiens.
Maturity causes
Members of the same species change physical appearance during maturity.
changes in appearance.
Examples include tadpoles turning into frogs and chicks shedding their
yellow feathers.
Males and females of a
Different genders of the same species may have differing characteristics.
species may look
Examples include lions, for which the females don’t have manes, and male
different.
peacocks which have large, colourful feathers.
NATURAL CLASSIFICATION
Natural or modern classification is based on an
organism’s DNA base sequences and
evolutionary descent and is structured as a
hierarchy, with each level being called a
TAXON. It is much more accurate than simply
observing a species’ anatomy.
Organisms are identified by a binomial name: a
GENUS and a SPECIES. For example, lions and
tigers belong to the same genus (Panthera), but
have different species names. While a lion is
known as Panthera leo, a tiger is Panthera
tigris. A few more examples of genuses are
shown below.
Genus Name
Example Species within Genus
CANIS
lupus (wolf) | aureus (jackal) | latrans (coyote)
EQUUS
burchellii (zebra) | asinus (donkey) | ferus caballus (horse)
CITRUS
limon (lemon) | paradisi (grapefruit) | sinensis (orange)
HOMO
sapiens (modern) | habilis, neanderthalensis (early)
4
TAXONOMY
According to the Whittaker model, each organism belongs to one of FIVE KINGDOMS:
Kingdom
Description
Example
PLANTAE
Multicellular, able to photosynthesise, have
chlorophyll and cell wall.
Hibiscus, algae, mosses
ANIMALIA
Multicellular, must feed on other organisms to
obtain nutrition, no cell wall.
Humans, corals, birds, snakes
FUNGI
Multicellular, cannot photosynthesise, must
absorb food, has cell wall.
Mushrooms, yeast, mold
PROKARYOTA
or MONERA
Unicellular, no nucleus (prokaryote), either
photosynthesise or ingest food through
absorption.
Bacteria, archaea
PROTISTA
Unicellular, have a nucleus, either
photosynthesise or absorb food.
Amoeba, protozoa
5
Organisms are arranged in the taxa that starts at a kingdom and ends at a species. Take the gray wolf,
Canis lupus, for example below.
Taxon Level
Name
Description
KINGDOM
Animalia
It is a multicellular organism that must feed on others to live.
PHYLUM
Chordata
It has a backbone and nerve running along it.
CLASS
Mammalia
It is a mammal; can regulate its body temperature.
ORDER
Carnivora
It is a carnivore; only eats other animals.
FAMILY
Canidae
It is either a coyote, jackal, fox or wolf.
GENUS
Canis
It is a type of wolf.
SPECIES
Lupus
It is specifically a gray wolf.
NOTE: Viruses are not classed under any kingdom because they are not considered living organisms.
EUKARYOTIC AND PROKARYOTIC CELLS
Characteristic
Unicellular or Multicellular?
Eukaryotic
Can be both unicellular and
Prokaryotic
Only unicellular.
multicellular.
How is the DNA arranged?
Size and examples
Found in a nucleus, in
No nucleus. DNA is in loose
chromosomes.
threads.
Larger. Examples: Amoeba,
Smaller. Examples: Bacteria,
animals, plants
archaea
6
EXERCISE: On this page, draw ONE member of each of the following phylums or classes, give their
binomial names and label TWO major defining characteristics for each.
1. Mollusca
4. Echinoderm
7. Aves
2. Porifera
5. Arthropoda
8. Arachnida
3. Cnidarian
6. Chondrichthyes
7
WHAT IS AN ECOSYSTEM?
An ecosystem is defined as A SYSTEM OF LIVING AND NON-LIVING FACTORS THAT
INTERACT WITH EACH OTHER.
An ecosystem is a combination of two factors:
Factor
Description
Examples
BIOTIC
All organisms that either produce their own
food or consume other organisms for food.
Plants, bacteria, animals
ABIOTIC
The physical features of the environment,
which will affect the types of numbers of the
species populations living in the ecosystem.
Water, sunlight, pH, salinity,
turbidity, climate
Other definitions
Observe the diagram of the food chain:
▪
▪
A POPULATION is a group of one
called its NICHE. This includes its
species within a particular habitat, e.g. the
behaviour, interactions, how it meets its
group of snakes make up a population. Two
needs for food and shelter and how it
plants may be separate species and thus
reproduces. If too many organisms or
comprise two populations.
▪
An organism’s role in its environment is
species occupy the same niche, there will be
A COMMUNITY is all the populations of
COMPETITION.
different species in a particular habitat,
▪
e.g. the grasses, grasshoppers, frogs, snakes
The place where an organism lives is its
HABITAT. In this case, the habitat is a
and hawks all comprise a community.
grassland. Habitats may be classified as
TERRESTRIAL or AQUATIC.
8
FEEDING RELATIONSHIPS
A food chain represents THE FEEDING SEQUENCE OF ORGANISMS TO TRANSFER ENERGY.
There are three main categories of organisms in the food chain, stated below:
Category
Description
AUTOTROPHS
(producers)
Organisms that produce food by photosynthesis. They use sunlight to convert
materials such as oxygen and water into nutrients.
HETEROTROPHS
(consumers)
Organisms that eat other organisms to gain their food. These obtain energy
from other organisms on which they feed.
DECOMPOSERS
Organisms that obtain nutrition by breaking down the dead remains of other
organisms and absorbing nutrients, releasing CO2 as a result.
Examples include: Bacteria and fungi
NOTE: Decomposers are not to be confused with CARRION FEEDERS, which are organisms such as
vultures, and DETRITIVORES, like earthworms that seek and consume already-dead organisms.
ENERGY TRANSFER IN A FOOD CHAIN
Energy moves from organism to organism in a food chain. While materials may be recycled, energy is
described as a unidirectional flow, as it cannot be directly returned to an organism or the Sun.
9
Each stage in the food chain is known as a
TROPHIC level. Energy decreases through
each successive trophic level. For example, the
deer will never get 100% of the energy from the
plants they eat. They only get about 10%
because the other 90% energy is used for the
plants’ life processes (such as growth,
excretion and reproduction).
Imagine the solar energy the plants get is 100%.
This means the plant uses 90% and can only
pass on 10% to the deer. Similarly, when the
tiger eats the deer, it only has 1% of the total
energy and must compensate by EATING
MORE OFTEN OR METABOLIZING MORE
SLOWLY.
SOIL
Soil is described as an important ABIOTIC factor in an ecosystem, as it can affect the lives of plants and
thus affect the trophic levels above it because:
1. It can provide a suitable HABITAT for organisms such as earthworms and insects. A soil habitat
is known as EDAPHIC.
2. It can retain WATER and MINERALS for plant growth and development.
3. It helps provide ANCHORAGE for plants, preventing them from being uprooted.
The top layer of most soils is called HUMUS, which is comprised of the natural decay of materials such
as leaves and animal matter that have accumulated. It is the most fertile layer.
SOIL WATER RETENTION
10
In soil water retention experiments, a fixed mass of soil sample is placed in filter paper folded over a
funnel. A recorded amount of water is then poured into the sample. After a certain amount of time, the
water drains through the soil and into a measuring cylinder below.
NOTE: A fertile mixture of humus, sand and clay is called a LOAM.
11
FOOD WEBS
A food web is a combination of several food chains within a habitat or ecosystem.
Identify a(n):
-
Autotroph: ALGAE
-
Herbivore: TADPOLE
-
Carnivore: FROG
-
Omnivore: SMALL FISH
-
Tertiary Consumer: KINGFISHER
-
Predator/Prey: FROG AND SNAIL
ECOLOGICAL PYRAMIDS
Category
Description
PYRAMID OF
NUMBERS
Represents the number of a certain species at each trophic level in a habitat.
Usually, the shape of the pyramid will be broad at the base and narrow at the top.
However, there are cases where the base is the narrowest. For example, there may be
MANY producers (broad base) or just one (e.g. the only producer might be one tree).
PYRAMID OF
BIOMASS
Represents the total amount of food available in each trophic level at any one
time. In the following food chain: Grass 🡪 Rabbit 🡪 Fox: There is a higher mass of
grass than rabbits, so enough food can be available for the rabbits. Same with the
rabbits and foxes.
PYRAMID OF
ENERGY
Represents the amount of energy retained at each trophic level, with only 10%
being transferred to each successive level. The shape is the same as the pyramid of
biomass.
12
ORGANISM RELATIONSHIPS
Predation
When one animal hunts and eats another animal, the hunter is known as the PREDATOR while the hunted
is known as the PREY. In such a relationship, the number of predators is almost always less than the
number of prey. A typical population size for a predator-prey relationship is depicted below.
Section
What is happening
A
Predator pop. high because prey pop.
is high
B
Prey pop. decreases because predator
pop. is too high; food is depleted.
C
Prey is allowed to reproduce since
predator pop. is low. Predator pop.
then increases once again.
Predators and prey are usually adapted to their roles. Predators will have certain characteristics such as
sharp teeth or the ability to engage their prey with stealth, while prey will be able to burrow, hide or run
away, or employ certain mechanics as CAMOUFLAGE to hide from predators.
Biological controls
In some cases, ecologists prefer to use a predator in order to control a pest population. This is usually
preferable to using agricultural chemicals. There are advantages and disadvantages to this.
13
Advantages of Biological Controls
Disadvantages of Biological Controls
Targets a specific pest.
Can result in disruptions in the food web if the
control becomes a predator.
Does not result in air and land pollution,
such as pesticides.
Takes a long time to work properly, unlike using
chemical control.
Is a long-term solution and less manual
labour is required in the long run.
Research is expensive.
Symbiotic Relationships
Symbiosis refers to RELATIONSHIPS WHERE AT LEAST ONE ORGANISM BENEFITS.
There are THREE main relationships in an ecosystem that can be classified as symbiotic:
Relationship
Description
PARASITISM
One organism is
Examples
harmed while the
other benefits.
COMMENSALISM
One organism benefits
and the other is
neither harmed nor
benefits.
14
MUTUALISM
Both organisms
benefit from the
relationship.
How are parasitic relationships different from predator/prey relationships?
15
NATURAL SELECTION
Natural selection is a process that favours species that are BEST ADAPTED to their environments.
Species that that cannot adapt will either die out or have to migrate to another habitat, where they could
adapt. Natural selection is commonly known as “survival of the fittest”.
The above photograph is a popular example of
The black moths were spotted by predators and
natural selection. Biston betularia (peppered
eaten. White moths then reproduced and their
moth) had two variants: white and black.
population size increased.
Before the industrial revolution in Britain, the
However, the industrial revolution caused
white speckled moth was more abundant
pollution which deposited black soot on the
because they were well CAMOUFLAGED on
trunks. This time, the black moth was more
lichen tree trunks.
well-camouflaged than the white moth.
Predators then ate the white moths, leaving the
black variant as the majority of the peppered
moth population.
COMPETITION
FOOD, WATER, SHELTER
Competition can exist between organisms of the
same species or with different species. Usually
the stronger or faster members of the species
survive. The losers either die out or have to
migrate from the habitat.
Competition can be defined as a relationship
If organisms manage to occupy different niches,
where multiple organisms seek the same limited
they can both survive in the same habitat. A
resources they need in order to survive, e.g.
16
good example of this is the Galapagos Island
finches, discovered by Charles Darwin.
17
FACTORS THAT RESULTED IN EVOLUTION IN DARWIN’S FINCHES
Factors
Explanation
Geographical
The finches had no natural predators. They were separated physically from each
isolation
other, limiting competition. They learnt to occupy different habitats.
Diet, variation
Short-beaked finches fed on fruits and nuts while long-beaked ones fed on
and behavioural
worms. They did not have to compete for food as a result. They separated into
differences
various groups and reproduced, amplifying these physical features.
Other species may separate due to being active at different times of day
(temporal), not being physically compatible (mechanical) or having different
mating rituals (behavioural).
Over time, this led to SPECIATION, which is the rise of a new and distinct species.
18
INTERPRETING GRAPHS AND CONSTRUCTING TABLES
Ensure the following when constructing a table:
1.
2.
3.
4.
The table is neatly enclosed.
All units are stated in the headings, if any. Do not repeat units below heading.
Decimal places are consistent, e.g. Don’t use 2 d.p. for one reading 1 d.p. for another.
A title is placed above the table. Ensure it efficiently describes the data represented.
e.g. Table showing Population Count of Frogs and Snakes from 2001 – 2005.
Observe the graph below and construct a table replicating its data.
Construct a table using SIX of the points below.
19
20
ECOLOGICAL STUDIES AND SAMPLING METHODS
Quadrats
It is difficult to survey all the different
organisms in an area, so various sampling
methods are done to assess the biotic factors of a
chosen area. Ecological studies are done to:
● determine population counts over time
●
research species relationships
●
assess damages from a disaster/disease
Most small ecological studies are carried out
using a QUADRAT. A quadrat is a square frame
with a fixed dimension, commonly 1m each
side. Within this frame is usually a series of
wires or strings forming a grid, which can be
labelled for further studies. The quadrat can be
used in two ways:
1. TRANSECT - A straight path is chosen and the quadrat is laid out in intervals along that track,
with the species being counted each time. Transects are especially useful for merging habitats
(ECOTONES), such as when a shoreline merges into a dense woodland. A transect can also be
useful in larger tree areas, because quadrats may too small for these.
2. RANDOM - The quadrat is tossed from a certain point in various directions. Eyes are closed to
prevent bias. Or the quadrat is laid down on random locations on the survey site. Sometimes these
sites can be decided by random numbers for coordinates.
After performing the survey with the quadrats, the species are counted and tallied. Certain factors can be
accounted for in the studied area:
Factor
Description
SPECIES DENSITY
Measured by counting the number of times a chosen species occurs within
the quadrats and calculating the average number per unit area.
SPECIES FREQUENCY
Measured by counting how many times the species was recorded in the
quadrats, e.g. a species that has occurred 2 times in 10 quadrats has a 20%
frequency of occurrence.
COVER
Measured by estimating the area each species covers in the entire quadrat,
e.g. if a quadrat measures 1m2 in area and a shrub takes up 0.5m2 of the
quadrat, it has taken up 50% cover.
21
EXAMPLE QUESTION:
Ten quadrats of 1m2 are randomly placed along the same vegetation. X’s are recorded where the species is
present. The results are recorded as follows:
Species
No. of Recorded Species by Quadrat Number
1
2
3
4
5
6
7
8
9
10
Plant A
0
0
1
0
0
1
0
0
0
2
Plant B
1
1
2
0
0
0
1
1
1
0
Plant C
0
2
3
6
0
0
16
0
2
1
(i)
State the frequency of Plant B. = 60%
(ii)
Calculate the species density of Plant C.
(iii)
Suggest TWO reasons why none of the species was found at quadrat 5.
OTHER SAMPLE COLLECTION METHODS
1. SWEEP NET - where a net is swung from side to side along a transect. The contents of the net are then
emptied into a container and counted. Dip nets can also be used to obtain organisms from water sources,
such as ponds.
2. PITFALL TRAP - A jar is buried in a patch of soil
and camouflaged by foliage to collect insects. The
top of the jar is kept at ground level. In the jar would
be antifreeze to kill the organisms that fall in.
3. POOTER JAR - A device in which insects or
invertebrates can be actively collected in a jar by
sucking through a tube at one end.
4. MARK, RELEASE, RECAPTURE - A small no.
of mobile organisms in a region is captured, marked
and released back into their habitat. A sample is then
22
later recaptured, which is then observed for
previously marked organisms and counted.
SECTION A (2/2)
HUMAN IMPACT ON ENVIRONMENT / PHOTOSYNTHESIS
POPULATION GROWTH
The diagram below shows a typical growth curve for a stable population in an ecosystem.
The growth rate will decelerate, stop or decrease due to a number of factors:
Category
Description
OVERCOMPETITION
Population may be too large and unvaried and resources such as food, water
and shelter are limited.
INVASIVE SPECIES
A new predator migrated into the habitat and reduces the population of many
organisms, e.g. lionfish in Caribbean marine habitats
ECOLOGICAL
DISRUPTION
Natural disasters or human intervention and activity can disrupt the natural
habitats of organisms, displacing them.
DISEASE
If the population has little variation, a disease can wipe out a large subset of
them.
HUMAN POPULATION GROWTH
Why has the human population climbed so much in
23
The last century?
24
RENEWABLE AND NON-RENEWABLE RESOURCES
Category
Definition
Examples
RENEWABLE
Can be reused or replenished in a
relatively short time.
Solar energy, wind energy, water,
forests
NON-RENEWABLE
Are in finite supply and cannot be
replenished in a short time.
Fossil fuels, bauxite, gold
METHODS OF WASTE REDUCTION
One major problem with an expanding population is the increasing amount of waste produced, the limited
space available for disposal and the improper disposal of refuse. Waste can be classed as either:
●
●
BIODEGRADABLE, meaning they can be broken down quickly by microorganisms.
E.g. Paper, wood, food, sewage, cloth
NON-BIODEGRADABLE, meaning they take a very long time to be broken down.
E.g. Glass, plastic, rubber, polystyrene
HUMAN IMPACT ON CORAL REEFS
Activity
Effect
BLAST FISHING
May destroy the reef structure, e.g. using dynamite or cyanide
OVERFISHING
Disrupts marine and coral reef food webs (e.g. Caribbean monk seal).
This allows invasive species such as starfish to destroy coral reefs.
TOURIAM
Coral is depleted when it is harvested to be sold, or by tourists.
25
NOTE: Sewage runoff from coastal communities and hotels also play a big role.
CARBON CYCLE
Three human impacts on carbon cycle:
Activity
Consequence
DEFORESTATION
Less trees means less
photosynthesis is occurring,
meaning atmospheric CO2
levels remain high.
FOSSIL FUEL
COMBUSTION
Raises CO2 levels by
combustion and emission.
SEWAGE RUNOFF
AND OCEAN
POLLUTION
Excess CO2 causes oceans to
become acidified, affecting
marine population life.
●
PHOTOSYNTHESIS - Plants undergo this process and remove CO2 from atmosphere.
●
CONSUMPTION - When animals eat the plants, they gain carbon in their bodies.
●
RESPIRATION - When animals breathe, they exhale CO2.
●
DECOMPOSITION - When animals die, decomposers break them down, also releasing CO2.
●
FOSSILIZATION - Decomposed material become fossil fuels after many years.
●
COMBUSTION - When fossil fuels are burnt, they release CO2 into atmosphere.
AIR POLLUTION AND THE GREENHOUSE GASES
which prevent the Sun’s heat from escaping the
Earth’s atmosphere.
Greenhouse gases are said to be the main cause
of THE GREENHOUSE EFFECT and climate
change, as well as rising sea levels. The main
greenhouse gas is CO2.
▪
Most air pollution occurs mostly due to the
release of combusted emissions from factories
and factories. These include greenhouse gases,
26
When sulphur dioxide and nitrogen
oxide combine, they form a layer of
thick haze called SMOG, which can
cause respiratory diseases, such as .
▪
Sulphur dioxide can also combine with
the rainwater to form ACID RAIN,
which can disrupt habitats such as lakes
and coral reefs.
AGRICULTURAL CHEMICALS AND EUTROPHICATION
Water pollution usually results when untreated sewage and agricultural chemicals or pesticides
leak or run-off into natural water sources. When the NITRATES and PHOSPHATES in
pesticides leak into water ecosystems, they can speed up the growth of underwater plants such as
algae. This is known as EUTROPHICATION or ALGAL BLOOM, and can:
●
Prevent SUNLIGHT from reaching underwater plants, preventing photosynthesis.
●
Cause ASPHYXIATION in aquatic organisms by depleting oxygen resources.
Agricultural chemicals can also lead to LEACHING, where the chemicals dissolve into the soil
and depletes its usable nutrients, making it unsuitable for plant growth.
EFFECTS OF IMPROPER SEWAGE AND GARBAGE DISPOSAL
Effect
Detail
Habitat Loss
The pollution can destroy the living areas of some organisms, causing
them to migrate.
Disease
Animal and insect pests live and feed in garbage, such as flies and
rats. They can carry bacteria that cause cholera and leptospirosis.
27
Flooding
Flooding causes sewage to be brought to the surface of the land,
bringing harmful bacteria with it and contaminating the environment.
28
EFFECTS OF DEFORESTATION
Effect
Reason
Soil erosion
Without tree cover, the force of rain will be greater on the soil.
Without roots to hold the soil together, erosion is more likely.
Flooding
Soil can quickly become compacted and waterlogged without tree
cover and roots, leading to flooding.
Habitat loss
Many birds and insects live in trees. Cutting the trees down causes
these organisms to migrate.
Loss of aesthetic
Trees and plants are used in parks and ‘green spaces’ in urban areas to
beautify the environment. Without them, cities look grey and drab.
CONSERVATION AND RESTORATION
Conservation is the preservation of the Earth’s natural resources so that they are available for
future generations. Conservation is important for two main reasons - to ensure that our demand
for natural resources can continue to be met, and to maintain our quality of life.
Strategy
Detail
Legislation
Moratoriums on hunting certain species. Hunting bans on certain
animals. Laws against poachers.
Proper agricultural
techniques
Using good practices such as crop rotation to keep soil fertile.
Reafforestation
Replanting trees that have been cut down.
Captive breeding
Ensuring that endangered species are kept in sanctuaries and proper
Banning ‘slash and burn’ practices that destroy soil.
breeding grounds, safe from poachers.
29
PHOTOSYNTHESIS
There are TWO main stages to photosynthesis:
Stage
What happens
LIGHT-DEPENDENT
Light energy is captured by chlorophyll in the chloroplast and then
converted into a usable energy called ATP. Light energy causes
PHOTOLYSIS, which splits water molecules into HYDROGEN
and OXYGEN (released as a biproduct)
LIGHT-INDEPENDENT
The HYDROGEN produced in photolysis is used to REDUCE
carbon dioxide to glucose. The ATP required for this process
comes from the light-dependent stage. Enzymes also help speed up
the reactions.
30
TESTING FOR STARCH
1. The simplest carbohydrate is GLUCOSE. It is used for RESPIRATION.
2. If glucose is formed faster than it is used up, the excess is converted to STARCH for
storage. It can occur even in the roots or underground storage organs. To test for
starch, we add IODINE and experience a BLUE-BLACK colour change.
3. In darkness, when photosynthesis stops, enzymes in the leaves change starch to
SUCROSE, which is transported to other parts of the plant. To destarch or remove starch
from the leaves, one can put the plants in darkness for about two days.
4. Why destarch before an experiment? This is because starch is an indicator in a leaf that
photosynthesis has already taken place. To correctly test to see if plants can experience
photosynthesis under certain conditions, one should get rid of this already-formed starch
before the experiment takes place, or results would be inaccurate.
Outline for experiment
31
Remember there are several requirements for photosynthesis. If ONE of these were absent,
photosynthesis will not occur and glucose will not be produced. Thus, no starch will be stored.
These factors that are required are called LIMITING FACTORS and they include:
Light intensity, carbon dioxide concentration, temperature, water availability.
32
Effects of Light Intensity on Photosynthesis
The rate of photosynthesis increases as
light intensity increases, since higher
light intensity excites more electrons.
However, at a certain point all of the
available electrons are excited, and the
maximum rate is reached. This means the
rate will stay constant even when light
intensity is increased past this point.
In the experiment to the left, an aquatic plant
named ELODEA is used. When undergoing
photosynthesis, it releases OXYGEN as a
biproduct, seen as rising bubbles gathering
at the top of the inverted test tube.
As light intensity increases, the NO. OF
OXYGEN BUBBLES will also increase
because photosynthesis occurred at a faster
rate. However, past a certain light intensity,
the oxygen level will be the same
throughout.
Necessity of Carbon Dioxide on Photosynthesis
The necessity of carbon dioxide can be
tested by placing the plant or some of its
leaves in POTASSIUM HYDROXIDE (KOH).
This removes the CO2 from the sample.
Since plants require CO2 to form glucose, an
iodine test will come up negative for the
leaves or plant exposed to KOH (potassium
hydroxide).
33
34
EXTERNAL LEAF STRUCTURE
The diagram below shows the cross-sectional structures of a monocot and dicot leaf.
Many dicot leaves in particular have features that allow them to maximize photosynthesis and
glucose production for the plant. These include:
Feature
How it helps maximize photosynthesis
Large surface area
Allows maximum exposure to sunlight.
Petiole
Orients leaf towards sunlight for maximum exposure.
Dense network of veins
Allows sufficient water to enter leaf for photosynthesis.
Many stomata
Maximizes gaseous exchange of carbon dioxide and oxygen.
35
INTERNAL LEAF STRUCTURE
The diagram below shows the cross-sectional structure of a dicot leaf.
Section
Function/Adaptation
UPPER EPIDERMIS
Has a WAXY CUTICLE above it to prevent water loss. Is
TRANSPARENT to let sunlight into leaf. Contains few to no
stomata.
PALISADE MESOPHYLL
Is densely packed with CHLOROPLASTS. Main site of
photosynthesis.
SPONGY MESOPHYLL
Has many loose AIR SPACES to allow flow of gases and water.
Contains few chloroplasts.
LOWER EPIDERMIS
Contains GUARD CELLS that open and close STOMATA to
allow gaseous exchange of oxygen and carbon dioxide.
VASCULAR BUNDLE
(vein)
Contains the XYLEM and PHLOEM, which allow transport of
water and food respectively in leaf. Also contains the
CAMBIUM, which is the site of growth for stems.
36
SECTION B (1/5) – NUTRITION
CELL STRUCTURE
Organelle
Role
Animal Cell
Plant Cell
NUCLEUS
Contains genetic material (DNA and
RNA) Also regulates activites of other
organelles.
YES
YES
MITOCHONDRION
Site of respiration (energy release).
YES
YES
CYTOPLASM
Holds all organelles together. Also the
site of some chemical reactions.
YES
YES
CELL MEMBRANE
Allows entry and exit of some
substances. Partially permeable.
YES
YES
CHLOROPLAST
Site of photosynthesis (food production
using light).
NO
YES
CELLULOSE CELL
WALL
Support and maintains internal water
pressure in cell, prevents bursting.
NO
YES
VACUOLE
Storage of water and minerals.
Small and
temporary
Large and
permanent
NOTE: Plant cells store glucose as STARCH GRAINS in their cells while animals store it as
GLYCOGEN GRANULES.
37
ARRANGEMENT OF CELLS AND TISSUES
Examples of Systems in the Human Body
System
Purpose
Specialized Cells, Tissues or
Organs
CIRCULATORY
Supplies oxygen and nutrients to the body.
Heart, blood, arteries, veins
DIGESTIVE
Breaks down food and delivers products to the
blood.
Stomach, pancreas, small and large
intestines, teeth
NERVOUS
Sends electrical messages in the body.
Neurones, nerves, brain
RESPIRATORY
The intake and exchange of gases in the air.
Lungs, ribcage, diaphragm
EXCRETORY
Removes wastes and regulates water balance.
Kidneys, nephrons, bladder
IMMUNE
Helps fight disease-causing organisms.
Lymphocytes, phagocytes, spleen
REPRODUCTIV
E
Functions to create offspring.
Ovaries, testes, uterus, prostate
SPECIALIZATION
Specialized or differentiated cells have specific tasks in multicellular organisms and thus, they have
features and adaptations in order to assist in performing that task. Below are just a few examples:
38
DIFFUSION AND ACTIVE TRANSPORT
The opposite of diffusion is Active Transport,
Diffusion is defined as THE MOVEMENT OF
which is defined as THE MOVEMENT OF
MOLECULES FROM A HIGH TO LOW
MOLECULES FROM LOW TO HIGH
CONCENTRATION UNTIL EQUILIBRIUM.
CONCENTRATION, USING ATP.
USES OF DIFFUSION
Location
Description
Lungs
The exchange of O2 and CO2 between the lungs and bloodstream.
Small intestine
The movement of digested nutrients from the intestines to the blood.
Leaves
The movement of CO2 and O2 in and out of the stomata.
USES OF ACTIVE TRANSPORT
Used in
Description
Root hair cells
Used to transport mineral salts into plant.
Nerve cells
Used to transport electrical impulses.
Small intestine
Used to transport sodium into the blood from the intestines.
39
OSMOSIS is defined as THE MOVEMENT OF WATER MOLECULES FROM A HIGH TO LOW
CONCENTRATION ACROSS A PARTIALLY PERMEABLE MEMBRANE.
Like diffusion, osmosis is a passive process, meaning it does not use ATP.
Osmosis Effects on Plant Cells
Observe the three plant cells below. Each one has been placed in a different solution.
Placed in
Movement of Water
Appearance
Cell A
AIR (control)
No change.
Remains turgid.
Cell B
DILUTED
Water flows into the
Becomes more turgid and swells. Vacuole
SOLUTION
cell from solution.
expands as water comes in.
CONCENTRATED
Water flows out of
Becomes plasmolysed. Cell membrane and
SOLUTION
the cell and into
cytoplasm retracts from cell wall. Vacuole
solution.
shrinks as water is lost.
Cell C
40
Osmosis Effects on Animal Cells
The above diagrams show three sets of red blood cells, only found within animals.
The first diagram shows water moving out of the cell because it has been placed in a CONCENTRATED
solution. The cell shrivels and is said to be CRENATED.
The second diagram shows water moving in because it has been placed in a DILUTED solution. As a
result, the cell bursts. The reason why an animal cell bursts, but not a plant cell is because the plant’s
CELL WALL is strong enough to withstand the turgor pressure.
Importance of Osmosis
The table below will show several situations where osmosis is necessary.
Important For
Example
Kidneys
Helps balance the water level in the blood on cold and hot days. Regulates the
amount of water in the urine.
Fish
Regulates how the salt and water balance in fish’s urine that allows them to
survive in either saltwater or freshwater.
Blood
Helps regulate water, salt and glucose levels in the blood. Prevents red blood
cells from bursting or shrivelling.
41
ENZYMES
Enzymes are used in ALL chemical reactions in living things; this includes respiration, photosynthesis,
movement, growth, excretion of toxins in the liver and more. They lower the ACTIVATION energy
required to initiate reactions and speed up reactions in the body. They are called biological catalysts.
●
●
The molecules that enzymes act upon are
called SUBSTRATES. In the end, they turn
these substrates into PRODUCTS. So, for
example, when we eat, the enzyme
AMYLASE found in saliva is used to turn the
substrate STARCH into a sugar called
MALTOSE.
●
Enzymes are made of PROTEINS.
●
Enzymes are SPECIFIC for each chemical
reaction. In terms of the digestive system,
this means that an enzyme can only react
with ONE NUTRIENT, e.g. the enzyme
pepsin in the stomach digests proteins,
but not fats or starch.
Certain enzymes also have to be within a pH to work (e.g. enzymes working in an acidic pH, as in the
stomach, may not work in the intestines).
EXAMPLES OF ENZYMES
Enzyme
Produced by
Substrate 🡪 Product
Amylase
Salivary glands, pancreas
Starch 🡪 Maltose
Pepsin
Stomach
Proteins 🡪 Polypeptides 🡪 Amino acids
Trypsin
Pancreas
Proteins 🡪 Polypeptides 🡪 Amino acids
Lipase
Pancreas, small intestine
Fats 🡪 Fatty acids and Glycerol
42
Catalase
Liver
Hydrogen peroxide* 🡪 Hydrogen and Water
43
FACTORS THAT AFFECT ENZYME ACTIVITY
There are TWO main factors that affect enzyme activity and can denature an enzyme:
1. TEMPERATURE
2. pH (acidity)
Enzymes are easily DENATURED (or
destroyed) by HEAT. Our enzymes work best at
NORMAL BODY TEMP. (37oC).
Too much heat can break down the structure of
the enzyme. When this happens, the substrate no
longer fits because THE ACTIVE SITE
CHANGES. When this happens, the enzyme is
said to be DENATURED.
pH refers to how acidic or alkaline something is.
Certain parts of the body are acidic, such as the
STOMACH, while others are alkaline, such as
SMALL INTESTINE.
pH level goes from 1 – 14.
● Acidic is under 7.
● Alkaline is over 7.
● And neutral is 7.
Optimum pH of pepsin: 3
Optimum pH of trypsin: 7.5
DENATURATION EXPERIMENT
Observe the four test tubes. State the one where
digestion of bread will be successful and explain
why the others will experience no digestion.
44
45
BALANCED DIET
A balanced diet can be defined as A DIET THAT CONTAINS ALL THE REQUIRED NUTRIENTS IN
THE CORRECT PROPORTIONS.
When nutrients are lacking or in excess, this is termed MALNUTRITION This could lead to
nutritional deficiency diseases, or if in excess, could result in physiological diseases such as
DIABETES, HYPERTENSION and CORONARY HEART DISEASE.
MACRONUTRIENTS
NUTRIENT
FUNCTION
SOURCES
EXTRA NOTES
CARBOHYDRATES
Provides energy
for respiration.
Simple: Syrups,
candies, fruits
Carbohydrates are made of
carbon, hydrogen and
oxygen. They are stored as
STARCH in plants and
GLYCOGEN in animals.
Simplest form is
GLUCOSE.
Complex: Rice,
bread, potatoes
PROTEINS
Used for growth
and cell repair.
Meat, eggs, red
beans
Proteins are made of
nitrogen, oxygen, carbon, etc.
They are broken down into
AMINO ACIDS.
LIPIDS (fats and oils)
Helps store energy
for warmth and
insulation.
Olive oil, potato
chips, butter,
avocadoes
‘Good’ fats are termed
unsaturated (e.g. avocadoes)
while ‘bad’ is saturated (e.g.
pizza, cake)
46
47
MAIN VITAMINS AND MINERALS
VITAMIN
FUNCTION
SOURCES
DEFICIENCY
DISEASE
DEFICIENCY
SYMPTOMS
A
Promotes eyesight
in dim light. Helps
maintain skin and
soft tissue.
Carrots, butter,
fish oils, green
leafy vegetables
NIGHT
Inability to see in dim
light.
B
Helps with
respiration.
Bran, cereals
BERI-BERI
Fatigue, fainting.
C
Helps with
repairing linings
and tissues in the
body.
Oranges,
tomatoes, bell
peppers, guavas
SCURVY
Sensitive, bleeding
gums.
D
Helps absorb
calcium for bone
development.
Dairy products,
tuna, salmon,
sunlight
exposure
RICKETS
Bones bend or break
easily.
CALCIU
Helps with bone
and teeth
development.
Dairy products
Same as above.
Same as above.
Helps produce
haemoglobin for
red blood cell
production.
Liver, spinach,
beetroot
ANAEMIA
Reduced production of
haemoglobin in red
blood cells, fatigue,
fainting.
M
IRON
BLINDNESS
The following two minerals are especially important in plants:
NUTRIENT
FUNCTION
EXTRA NOTES
NITROGEN
For growth of shoots
and leaves.
Usable in the nitrate form in the plant. Without it,
plants have stunted growth and small leaves.
MAGNESIUM
For chlorophyll
production.
Without it, plants’ leaves turn yellow and eventually
wither. This is called chlorosis.
48
49
FOOD TESTS
NUTRIENT
REAGANT / PROCEDURE
Reducing
Sugar
(Glucose)
Place food sample in a boiling tube with
BENEDICT’S SOLUTION and place in a
heated water bath until colour changes.
Non-reducing
sugar (Sucrose)
Place food sample in a boiling tube with
HCl and boil for 1 minute. Neutralize HCl
with sodium carbonate. Then heat wwith
BENEDICT’S SOLUTION.
Starch
Add a few drops of IODINE SOLUTION.
Lipid/Fats
COLOUR CHANGE
SPOT TEST: Rub food sample against a
thin piece of paper.
EMULSION TEST: Mix sample with
ethanol and water and shake vigorously.
Protein
BIURET TEST: Add copper sulphate and
sodium hydroxide to food sample and mix.
50
Blue 🡪 Green 🡪 Brick Red
Blue 🡪 Green 🡪 Brick Red
Orange-yellow 🡪 Blue-black
A translucent stain appears.
A cloudy white emulsion if fat
is present.
Blue 🡪 Purple/Violet
THE ALIMENTARY CANAL:
51
SECTION
WHAT OCCURS THERE
ENZYMES PRESENT
MOUTH
Food is broken down MECHANICALLY to
increase surface area for enzyme interaction
AMYLASE
Starch is digested CHEMICALLY by
salivary amylase.
OESOPHAGUS
PERISTALSIS allows food to be carried
into the stomach.
-----------
STOMACH
The chewed food is churned with acids and
enzymes into a mixture called CHYME.
PEPSIN
RENNIN (in babies)
Proteins are broken down by PEPSIN.
LIVER
BILE is secreted, which EMULSIFIES fats.
Bile is eventually stored in the
GALLBLADDER.
CATALASE
PANCREAS
Releases juices to NEUTRALIZE stomach
acid and numerous ENZYMES to digest
carbohydrates, fats and proteins.
AMYLASE
TRYPSIN
LIPASE
DUODENUM
(small intestine)
ILEUM
(small intestine)
COLON
(large intestine)
RECTUM/ANUS
(large intestine)
Allows bile and pancreatic juices and
enzymes to digest food.
Same as above.
Contains villi, which allows the
absorption of food into the blood.
-----------
Helps with absorption of water and
dissolved vitamins.
-----------
Stores solid waste (FECES) before it is
EGESTED from the body.
-----------
52
53
STRUCTURE OF THE HUMAN TOOTH
Tooth
Suited for
INCISORS
Cutting food
CANINES
Tearing meat
PREMOLAR AND
MOLARS
Grinding food into
smaller pieces
Part of Tooth
Purpose
ENAMEL
Protection of inner tooth
DENTINE
Protects pulp cavity
PULP CAVITY
Contains blood vessels and
nerves
CEMENT
Holds tooth to gum
DENTAL HYGIENE
Teeth can rot when carbohydrates or sugars are left on the enamel. Bacteria feed on the sugars and
secrete ACIDS to digest it. These acids wear away the ENAMEL and cause toothaches. Keeping
teeth healthy involves using toothpastes high in FLUORIDE, FLOSSING regularly and avoiding
sugary foods at night before sleep.
FIBRE
Fibre (or roughage) is found in foods such as VEGETABLES, FRUITS AND WHOLEWHEAT.
Most fibres are insoluble and cannot be fully broken down by the human digestive system. These are
used to move digested food through the gut (by the process of PERISTALSIS). Soluble fibre can also
make stools softer and easier to egest.
●
A lack of fibre and water in the diet may lead to a back-up of food in the intestines, leading
to the hardening of the faeces, a condition called CONSTIPATION.
54
●
DIARRHOEA, on the other hand is mostly caused by improper handling of food. Insects
such as FLIES can deposit disease-causing organisms called pathogens on the food. When a person
ingests the food, their body tries to get rid of it by producing excess water.
55
FACTORS AFFECTING DIET
Factor
Reason
Occupatio
Busy lifestyles encourage more purchasing of high-fat fast food.
n
Diseases
Diabetics must consume less carbohydrates. Hypertension sufferers consume less salt.
Pregnancy
Pregnant women must consume more minerals and proteins to aid in the development of the
fetus. They must also consume more food altogether.
ASSIMILATION
After the digested nutrients have been absorbed into the bloodstream from the villi in the small
intestine, they are then transported to cells in various parts of the body by the blood, so they can
be utilized. This process is called assimilation. Here are a few things that occur with assimilated
glucose and amino acids (simple proteins).
1. Glucose is used for RESPIRATION to release ATP. Excess glucose gets stored as FATS
or GLYCOGEN in the liver of humans, or STARCH grains in plant cells.
2. Amino acids are used for GROWTH and REPAIR of cells. They may be used to form
hormones and enzymes as well. Excess gets converted to UREA and are eventually
excreted by the kidneys.
56
NOTE: The hepatic portal vein transports nutrient-rich blood from the alimentary
canal to the liver. The hepatic vein transports blood from the liver to the heart.
57
SECTION B (2/5)
RESPIRATION AND TRANSPORT
BREATHING IS NOT RESPIRATION
o
o
o
Breathing or VENTILATION is the mechanism that moves air in and out of our lungs.
Gaseous exchange is the process in which some of the oxygen in the air in our lungs diffuses
into the blood whilst some of the carbon dioxide in our blood diffuses into the air.
Respiration is the release of energy due to the oxidation of glucose, if oxygen is available.
1. VENTILATION
Body Part
Changes during inspiration
Changes during expiration
Lung volume
Increases
Decreases
Diaphragm
Contracts (flattens)
Relaxes (domes)
Ribcage
Moves upward, outward
Moves downward, inward
Intercostal muscles
Contract.
Relax
2. GASEOUS EXCHANGE
It is important to note that you do NOT breathe in just oxygen and do NOT just breathe out just
carbon dioxide, but other gases as well. The main gases we inhale include:
GAS
INHALED CONTENT (%)
EXHALED CONTENT (%)
NITROGEN
78
78
OXYGEN
21
16
0.04
4
~1
2–3
CARBON DIOXIDE
WATER VAPOUR
While the air is in our lungs, some of the oxygen DIFFUSES into the red blood cells in the blood
and some of the carbon dioxide in the blood cells diffuses into the lungs to be exhaled.
The respiratory tract is prone to infection by
inhalation of foreign bodies. To filter the
inhaled air, tiny hairs called ____________
act as a mechanical barrier against dust and
microbes.
Specialized cells called ___________ cells
produce _____________ to act as a
chemical barrier for microbes.
58
STRUCTURE AND FUNCTION OF ALVEOLI
The alveoli have several adaptations for carrying out their function of gaseous exchange.
Adaptation
Explanation
LARGE SURFACE
There are roughly 600 million alveoli, which collectively occupy a large
AREA
area suited to maximize gaseous exchange.
THIN WALLS
Alveolar membranes are only one cell thick, allowing quick diffusion.
MOISTURE
Gases dissolve more easily in moisture.
MANY CAPILLARIES
There is a dense capillary network around each alveolus.
59
CELLULAR RESPIRATION
There are TWO types of respiration:
Type
Description
Chemical and Word Formulae
AEROBIC
RESPIRATION
ATP is released from glucose by oxygen
(a process called OXIDATION), releasing
carbon dioxide and water as excretory
products.
Oxygen + Glucose -> Carbon dioxide
In the absence of oxygen, ATP is
produced when glucose is converted into
lactic acid. Relatively less ATP is
produced per molecule than aerobic.
Glucose 🡪 Lactic Acid
In plants and yeast, no lactic acid is
produced. Instead, ethanol and carbon
dioxide are released. This is useful for
alcohol fermentation and bread-making.
Glucose 🡪 Carbon dioxide + Ethanol
ANAEROBIC
RESPIRATION
+ Water
6O2 + C6H12O6 -> 6CO2 + 6H2O
C6H12O6 -> 2C3H6O3
C6H12O6 -> 2CO2 + 2C2H5OH
ATP (ADENOSINE TRIPHOSPHATE) is converted to ADP (ADENOSINE DIPHOSPHATE)
and then back again to ATP constantly. It is this that releases the energy from glucose.
OXYGEN DEBT
When one exercises vigorously until the point of anaerobic respiration, a chemical called
LACTIC ACID builds up in the muscles. This can lead to a burning sensation as well as
FATIGUE and MUSCLE CRAMPS.
During exercise, their heart rate also increases. This occurs to supply OXYGENATED BLOOD to
the muscles for respiration. However, the heart continues beating quickly even after exercise
finishes. Why?
Lactic acid must be dissipated from the muscle cells before the respiratory rate returns to
its resting phase.
60
RESPIRATION EXPERIMENTS
The experiment below is to show that organisms produce CO2 when they respire.
Jar
Contains
Note
1
Potassium hydroxide
Removes CO2 from air entering the apparatus.
2
Calcium hydroxide
(limewater)
Tests for CO2; A negative result is needed (limewater remains
clear), so as to ensure no CO2 transfers to Jar 3.
3
Live specimen
When respiring, specimen will release CO2.
4
Calcium hydroxide
(limewater)
Tests for CO2. Will test positive (cloudy white) if Jar 3’s
specimen is respiring.
The experiment below is to show that heat is produced during respiration.
61
●
●
●
●
Boil the peas in sample A to kill them.
Rinse both sets of peas in disinfectant.
Set up apparatus as shown.
Leave peas in flasks for three days.
Read temperatures after that point.
GASEOUS EXCHANGE IN FISHES
consist of a series of filaments that are able
to diffuse oxygen from water into the blood
capillaries, and diffuse carbon dioxide out.
The filaments increase the SURFACE
AREA of the gill.
Fish are notable for not having lungs or
alveoli. Instead, they have GILLS, which
GASEOUS EXCHANGE IN LEAVES
Dicot leaves have structures called guard
cells on their LOWER EPIDERMIS. These
guard cells may become turgid and flaccid to
control an opening called a STOMA. This
can regulate the rate of water loss, and
oxygen and carbon dioxide exchange in the
leaf.
COMPONENTS OF CIGARETTE SMOKE
62
Component
Effect
Nicotine
Acts as a stimulant. Increases heart and breathing rates.
Carcinogens
Cancer-causing agents.
Carbon
Binds to the haemoglobin and limits the uptake of oxygen into the red blood
monoxide
cells.
Tobacco
Contains tar, which would clog the alveoli and result in a decrease in rates of
gaseous exchange.
63
TRANSPORT SYSTEM IN HUMANS
All large animals have circulatory systems. This is
because of their LOW SURFACE AREA : VOLUME
RATIO which means that their surface area is much
less than the volume of their bodies.
Microorganisms can transport materials by
DIFFUSION. This is because their SURFACE
AREA is large compared to their volume.
Substances do not have far to travel.
Unicellular organisms, like amoeba and protozoa, are
flatter in shape and so have a larger surface area to
volume ratio.
The human circulatory system consists of a series of
blood vessels, blood and a pump (heart).
Mammals have a double circulatory system, since the blood travels through the heart twice
on one complete journey around the body. This allows cells and tissues to have a rich
oxygenated blood supply and allows the blood to reach considerable distances due to the
changes in blood pressure in the heart chambers.
Type of
Circulation
Definition
PULMONARY
Deoxygenated blood is
carried to the lungs to be
reoxygenated before
returning to the heart.
SYSTEMIC
Oxygenated blood is
pumped from the heart to
the body and
deoxygenated blood
returns to the heart.
Note the following adjectives that relate to
organs:
64
●
Lungs - Pulmonary
●
Liver - Hepatic
●
Kidney - Renal
●
Stomach - Gastric
●
Heart – Cardiac or Coronary
STRUCTURE OF THE HUMAN HEART
BLOOD PRESSURE
Category
What happens
SYSTOLE
Ventricle muscles contract, forcing blood out of the heart
DIASTOLE
Atria muscles contract and ventricles relax, refilling blood into them.
The usual human blood pressure is given as 120/80 mmHg and the heartbeat is regulated by the
PACEMAKER region of the heart. The pulse rate can be monitored by an EKG.
●
●
Abnormally high blood pressure is called HYPERTENSION.
Abnormally low blood pressure is called HYPOTENSION.
Many factors affect blood pressure including:
Factor
Explanation
Fatty diet
Clogging of arteries by fats and cholesterol (atherosclerosis).*
Excess sodium
Kidneys must work harder to get rid of extra fluid caused by sodium.
Age
Blood vessels become less elastic as we get older (arteriosclerosis).
* If arteries in the heart (coronary arteries) become clogged, bloodflow is restricted. If a blood
clot or thrombus forms, no oxygen can reach the cardiac muscles of the heart and the individual
can undergo CARDIAC ARREST or MYOCARDIAC INFARCTION.
65
BLOOD VESSELS – ARTERIES AND VEINS
ARTERIES
VEINS
Transport of blood
Away from the heart
Into or towards the heart
Oxygenated or
deoxygenated
Oxygenated (except the
pulmonary artery)
Deoxygenated (except the
pulmonary vein)
Outer wall thickness
Thick and elastic muscle
Thin muscular layer
Valves
Absent
Present
Lumen size
Small (high pressure)
Large (low pressure)
Pulse
Present
Absent
CAPILLARIES AND TISSUE FLUID
The blood vessels that connect veins to
arteries and transports material from blood
directly to cells are called CAPILLARIES.
They are ONE CELL THICK, so as to
facilitate quick DIFFUSION. They often
connect organs to the bloodstream (e.g. villi
in the ileum, alveoli in the lungs)
Surrounding the cells is a liquid called
TISSUE FLUID, which help transport
diffused materials between the cells and the
capillaries. Tissue fluid is in direct contact
with the cells, not plasma.
66
BLOOD
COMPONENT
ROLE
APPEARANCE
BLOOD PLASMA
Transports soluble material
Yellow fluid.
(nutrients, hormones, etc.)
RED BLOOD CELLS
Transports O2 and CO2 to
Biconcave disc. Flexible. No nucleus.
and from cells.
PHAGOCYTES (or
Engulfs bacteria and
macrophages)
foreign bodies
Large globular structure. Lobed nucleus.
(phagocytosis)
LYMPHOCYTES
Releases antibodies to
Large round structure. Round nucleus.
combat disease.
PLATELETS (or
Produces blood clots to
thrombocytes)
prevent infection.
Small, irregular fragments.
Blood is a fluid that contains specialised cells. Blood is therefore considered a type of TISSUE.
These are the main components of blood.
ANTIGENS
Antigens are described as foreign substances that stimulate an immune response in a host body.
It leads to the production of ANTIBODIES by lymphocytes, which will eventually travel to and
eradicate the threat. Each antibody is antigen-specific, for e.g. The influenza virus has certain
antigens attached to it. These are detected by the white blood cells. White blood cells then target
the virus with specific antibodies to get rid of it.
67
BLOOD CLOTTING
When a tissue is damaged or wounded:
1. Blood releases PLATELETS and the CLOTTING FACTORS.
2. which converts PROTHROMBIN to THROMBIN, (with calcium and Vitamin K)
3. which causes FIBRINOGEN to form FIBRIN threads around wound,
4. which stops bleeding by forming a mesh of red blood cells and platelets (scab) before
proteins can allow new skin to grow beneath scab.
LYMPHATIC SYSTEM
Aside from blood, another fluid flows
through our body called lymph. Lymph is
formed from proteins and tissue fluid
(located between capillaries and cells).
The purpose of lymph is to fight infection.
It does this by carrying LYMPHOCYTES.
Lymph is filtered through structures called
LYMPH NODES, most of which are located
along the neck and armpits.
STENTS AND ANGIOPLASTY
Angioplasty is the surgical repair or
unblocking of a blood vessel. This is done
by inserting a tiny tube called a catheter with
a balloon, and a wire stent. The balloon
inflates, expanding the vessel’s LUMEN.
Blood flow is then increased in the vessel.
68
STROKE
A stroke occurs when the brain becomes
deprived of oxygen. This is usually due to
a CAROTID artery being clogged
(which leads to the brain).
69
TRANSPORT IN PLANTS
While humans have veins and arteries, the two main transport vessels in plants are known as the
XYLEM and PHLOEM. (which comprise the VASCULAR BUNDLE)
1. PHLOEM
SIEVE TUBES are elongated cells joined
end to end to form a column. Walls between
two cells are perforated, forming sieve
pores.
As they lack the structures needed to carry
out many metabolic processes, they rely on
the COMPANION CELLS, lying close to
them, for their survival.
The phloem transports organic nutrients
such as SUCROSE from leaves and storage
organs to other parts of the plant.
2. XYLEM
70
The xylem transports WATER and dissolved
minerals. Its cells form a continuous hollow
column. This allows the water to flow easily
along the xylem.
The cell walls are thickened with LIGNIN,
which prevents the xylem from collapsing
under tension created by
TRANSPIRATIONAL pull.
CAPILLARY action occurs due to the
xylem tubes being narrow. This occurs
because the water is COHESIVE, meaning
their molecules stick together, and
ADHESIVE, meaning their molecules stick
to surfaces easily.
71
TRANSPIRATION
1. Water is absorbed through the roots
via OSMOSIS. From there it moves
from cell to cell until it gets to the
XYLEM in the stem.
2. Water moves up the xylem vessels
to other branching stems, and the
leaves attached to them. Due to a
changing water potential gradient,
this creates a constant
TRANSPIRATIONAL PULL.
3. Water is stored in the leaf until it is
evaporated through the STOMATA.
Transpiration is defined as
____________________________________
___________________________________.
Factors that Affect Transpiration
Factor
Light
Reason
Stomata open wider to allow entry
of more CO2 for photosynthesis.
Temperature
Evaporation and diffusion of water
occur at faster rates.
Wind speed
Moving air removes water vapour,
increasing rate of water diffusion.
Humidity
Diffusion slows down as
surrouding air is already moist.
72
73
PLANTS ADAPTING TO DRY ENVIRONMENTS
Plants which live in extremely dry environments
are called XEROPHYTES and have special
adaptations to limit their transpiration rate and
conserve water.
Observe the section through the Marram Grass
leaf to the left and note the adaptations.
Adaptation
Purpose
SMALLER LEAVES
Reduces water loss by transpiration due to reduced surface area.
DEEP ROOTS
Better able to locate underground water sources.
SUNKEN STOMATA
Water vapour becomes trapped in sinks and less likely to escape leaf.
WAXY CUTICLE
Prevents water loss along the upper epidermis of leaf.
SUCCULENT TISSUES
Has many large vacuoles to store water and mineral sap.
STORAGE OF FOOD IN THE BODY
Food storage is necessary in both plants and animals due to SCARCITY of resources during times of
drought or harsh climates. It also helps avoid continuous food intake.
●
Animal storage would include GLYCOGEN in the liver and FATS in ADIPOSE tissue.
●
Plant storage would include STARCHES, which can be found in roots, stems, leaves, fruits and
seeds. They may also be needed for the development of ENDOSPERMS in the seeds and for
stages of vegetative reproduction.
74
SECTION B (3/5)
MOVEMENT AND GROWTH
MOVEMENT AND LOCOMOTION IN HUMANS
There are three main functions of the skeleton: MOVEMENT, SUPPORT and PROTECTION.
The skeleton is divided into two sections:
Section
Bones involved
AXIAL
Cranium, vertebral column,
ribcage
APPENDICULA
R
●
Humerus, ulna, radius, femu
tibia, fibula, pelvic girdle, etc
The inorganic content of the bone gives it its
structure and makes it strong. The inorganic
molecule is mostly CALCIUM and
PHOSPHOROUS.
●
The inner part of the bone is known as the
MARROW. RED BLOOD CELLS are
produced there.
Bones and joints in an arm forelimb
JOINTS
Joints are located between bones. Most of them are used for movement. There are three types of joints to
learn at this level.
Name
Movement
Examples
FIXED
No movement is involved here.
Cranium
HINGE
Only along one plane.
Elbow (humerus and radius/ulna) and
knee (femur and tibia/fibula)
BALL and
SOCKET
Can move in full circles.
Shoulder (scapula and humerus) and
hips (pelvic girdle and femur)
75
Both the shoulder and hip, in addition to having a
ball and socket joint, are known as SYNOVIAL
joints. These contain SYNOVIAL FLUID to aid in
lubricating and nourishing the joint.
On the end of each bone, where it touches the other,
is a layer of CARTILAGE which allows the bones
to move past each other with a minimum of
FRICTION.
Ligaments are bundles of connective tissue made of
a type of protein called collagen. They connect
bones to other bones.
BONE STRUCTURE
JOINT HEALTH
Due to the complex nature of ball and socket joints, they are usually the ones that are most subject to
disease and wear. Surgical replacement of the hips and shoulders is not uncommon if the joints become
worn enough that they cause severe pain when used.
Other diseases and problems are characterized by inflammation and/or degeneration, such as
ARTHRITIS.
Wearing SUITABLE FOOTWEAR and having GOOD POSTURE is essential to maintaining bone and
joint health. Wearing high heels everyday can put excess force on the feet and can wear away the cartilage
easily.
76
MUSCLES
Muscle tissue is made of cells that are able to contract and relax. There are three main types of muscle
cells in the mammal:
Type
Features
Example Locations
SKELETAL or
STRIATED
Is connected to bones by tendons. Can
contract and relax voluntarily and are
susceptible to fatigue.
Biceps, triceps, quadruceps,
abdominals
SMOOTH
Usually located around organs. Works
involuntarily.
Oesophagus, small and large
intestine, arteries
CARDIAC
Contracts quickly. Works
involuntarily. Cannot regenerate.
Heart muscle
Muscle cells have protein fibres, which are elastic
and can contract to allow flexing. All muscles
work in PAIRS. Whether they are skeletal muscle,
smooth muscle or cardiac muscle makes no
difference, all muscles must work in pairs.
They rely on the other of the pair to flex or extend.
They are referred to as ANTAGONISTIC as a
result.
The purpose of muscles is to help carry loads and overcome RESISTANCE. The ability for muscles to
remain firm while resting and overcome resistance is called MUSCLE TONE.
During exercise, muscles continuously contract and relax. Muscle fibres become damaged during this
process. When they are repaired and reformed by PROTEINS, they become thicker and denser. Therefore,
muscular growth actually occurs after exercise during rest periods.
Why isn’t locomotion necessary for plants?
Question
Features
How would they get
food and water?
They can absorb water through their roots via osmosis. They store large
amounts of water in their large vacuoles. They photosynthesize to get food.
77
How would they
reproduce?
Plants rely on pollinating agents such as insects or wind. Seeds can also be
dispersed far distances by wind, animals and water.
78
GERMINATION AND DISPERSAL OF SEEDS
A seed contains an embryonic plant and a food
store enclosed in the seed coat or TESTA.
After a period of DORMANCY, the germination
of the seed begins. This is often triggered by the
following factors:
1. Warmth
2. Presence of moisture
3. Presence of oxygen
In a seed, the young root or RADICLE emerges first, followed by the shoot or EPICOTYL (plumule).
These then grow and branch as the young plant develops.
Seeds are displaced a distance away from their parent plants by a various set of mechanisms.
Dispersal Method
Brief Description
WIND
For light seeds, usually with wing or parachute structures.
ANIMAL
Tough-coated seeds that must be broken down through digestion.
WATER
Large, hollow, buoyant seeds.
SELF or
Heavy seeds that are propelled a short distance by their parents.
EXPLOSIVE
79
The COTYLEDONS become the first leaves of
the plant and the first means of the plant to
undergo PHOTOSYNTHESIS. They eventually
decrease in size and fall off when the first “true
leaves” appear from the EPICOTYL of the
seedling.
MOVEMENT IN PLANTS
Even though plants cannot undergo locomotion, they can move individual parts of themselves. The main
responses to stimuli in plants are related to growth. Growth-related mechanisms aid in the plant’s survival
and usually affect the direction of shoot and root growth. The two main environmental stimuli that affect
the growth of a plant are:
1. SUNLIGHT INTENSITY (PHOTOTROPISM)
Plants must always grow towards sunlight to facilitate the process of PHOTOSYNTHESIS in the leaves.
While animals usually use a system of nerves to relay the messages between receptors and effectors, a
plant is more likely to use HORMONES.
80
The hormone that is involved in shoot tip growth is called an AUXIN. Auxins are used to speed up cell
growth in particular sections of the shoot, usually the tip, a section called the MERISTEM. When sunlight
comes into contact with a shoot tip, the auxins spread to the shaded side of the shoot.
81
2. GRAVITY (GRAVITROPISM)
Plants always respond to gravity. Shoots will
always grow upward and roots will always grow
downward. No matter what direction or which
end a germinating seed were to be placed, the
radicle will always grow downwards due to the
influence of gravity.
It should be noted, aside from ABSORPTION
OF WATER, one of the main purposes of roots
is for the ANCHORAGE of the plant.
Plant roots and shoots can grow LATERALLY
(sideways) or LONGITUDINALLY (straight down).
When growth occurs, various zones are taken into
consideration. Cell division occurs near the tip,
which helps increase the number of cells and thus
cause growth. This causes the structure to elongate.
NOTE: Invertebrates such as earthworms, squids and jellyfish lack a bony skeleton but are still able to
experience locomotion through propulsion in their fluid-based bodies or a series of muscles. These type of
skeletons are called HYDROSTATIC skeletons.
82
SECTION B (4/5)
EXCRETION AND RESPONSE
METABOLISM refers to the chemical reactions that occur in the body. Metabolism produces WASTE
products, which can be toxic to the body if allowed to accumulate. EXCRETION is the elimination of
these waste products of metabolism.
EXAMPLES OF EXCRETORY ORGANS AND PRODUCTS IN HUMANS
Excretory Product
Excretory Organ
Notes
Carbon dioxide
Lungs
By-product of respiration, excreted in exhaled air.
Urea
Kidneys, skin
Produced in the liver after removing nitrogen from proteins
(DEAMINATION) and is excreted in urine and sweat.
Water
Kidneys, skin,
lungs
Main constituent of urine and sweat. Expired air also contains
water vapour.
Calcium oxalate
Kidneys
A major constitutent of kidney stones. Also found as
crystalline structures in plants.
Bilirubin
Liver
Formed from the breakdown of red blood cell haemoglobin.
Excreted via the faeces, even though faeces itself is egested.
EXAMPLES OF EXCRETORY ORGANS AND PRODUCTS IN PLANTS
1. The gaseous wastes (CARBON DIOXIDE and WATER VAPOUR) are removed through
STOMATA of leaves.
2. Some waste products collect in the LEAVES and BARK. When the leaves and bark are shed,
the wastes are eliminated.
83
3. Some waste products are rendered harmless and then stored in the plant body as solid bodies,
such as RESINS and TANNINS.
KIDNEY STRUCTURE
They are reddish-brown bean-shaped organs situated towards the back of the abdominal cavity just above
the waist. Inside the kidney, it is divided into an outer area called the CORTEX and an inner layer called
the MEDULLA. The kidney narrows to form the renal pelvis and URETER.
FUNCTIONS OF KIDNEYS
4. Regulates WATER and SALT balance of
body fluids.
1. These are main excretory organs to
remove unwanted metabolic wastes,
including urea, excess water and mineral
salts from blood, in the form of URINE.
2. The kidneys act as a filter to remove
water, salts, urea, while leaving LARGE
SOLUTES in the blood. This is called
ULTRAFILTRATION.
3. Useful substances (such as GLUCOSE)
are reabsorbed from the nephrons back
into blood. This is called SELECTIVE
REABSORPTION.
84
KIDNEY NEPHRONS
85
ANTI-DIURETIC HORMONE (ADH)
Sensors in the brain detect amount of water in the blood and responses are sent to balance it if there is too
much or too little. Water levels in the body may be affected by environment temperature and exercise.
These responses involve the hormone ADH, also called anti-diuretic hormone. It is secreted by the
PITUITARY gland in the brain. ADH makes the collecting duct’s walls more permeable to water. More
water can then pass back into the blood stream.
Scenario
Action of pituitary gland
What happens
Hot day
Secretes ADH
More water reabsorbed into blood. More sweat. Concentrated urine.
Cold day
Suppresses ADH
Less water reabsorbed into blood. Less sweat. Diluted urine.
86
THE SKIN AND HOMEOSTASIS
The skin is the largest organ of the human body. It acts as a natural barrier against outside bacteria and
particles. However, the skin plays a crucial role in regulating body temperature. Heat is produced within
the body as a result of metabolic activities. This heat has to be excreted somehow, or our metabolism
would be affected and even death could occur.
Skin’s Role in Temperature Regulation
Section of Skin
Warm Environments
Cold Environments
Blood vessels
Become larger and move towards
surface (VASODILATION).
Become smaller and move away from
surface (VASOCONSTRICTION)
Sweat glands and muscles
Releases sweat, which cools the
body upon evaporation.
Muscles vibrate rapidly (shivering) to
produce heat.
Hair
Remains flattened.
Hair erector muscle contracts. Hair
stands up to trap heat.
87
HOMEOSTASIS AND REGULATION OF BLOOD GLUCOSE LEVEL
Blood glucose level rises anytime sugary or starchy foods are digested and absorbed into the blood.
However, the glucose is then taken in by the body cells for RESPIRATION, allowing the level to drop.
The excess glucose is converted to GLYCOGEN and stored in the LIVER.
▪
The hormone that allows this to happen is called INSULIN, which is secreted by the PANCREAS
from a region called the Islets of Langerhans, when blood glucose level is too high.
▪
When blood glucose level is too low, regions of the pancreas secrete GLUCAGON which
converts GLYCOGEN back into GLUCOSE, to be re-released into the bloodstream.
The diagrams below show homeostasis in two NEGATIVE FEEDBACK mechanisms in the body.
88
STIMULUS AND RESPONSE
A DETECTABLE change in the external environment that enacts a response in an organism is called a
STIMULUS. Stimuli could include changes in temperature, pressure against skin, light intensity and
sound level.
Most organisms are adapted to detect these stimuli through cells called RECEPTORS and respond to
them through EFFECTORS, e.g. skin receptors detect heat and pituitary gland (effector) responds by
secreting ADH.
RESPONSE IN INVERTEBRATES
Invertebrates, such as snails, jellyfish and earthworms, tend to respond to the following.
Stimulus Response
Reason
Away from light
To avoid being seen by predators. Also to avoid drying out.
Away from coldness
To maintain their internal body temperatures and avoid freezing.
Towards moisture
To avoid desiccation (drying out).
EXPERIMENT
Two petri-dishes are placed side by side with a
drying agent (desiccant) in one and a moist
tissue in the other. An equal number of maggots
are placed in each dish, with a small passage to
cross over. Which petri-dish would have a
greater no. of maggots after an hour?
How could this experiment be altered to test
response to the stimulus of light?
Remove the moist tissue and drying agent and cover only ONE of the petri dishes with black paper.
89
RESPONSE IN HUMANS
Responses in humans occur via two systems: the NERVOUS system and the ENDOCRINE system.
Sections of the nervous system
Section
Consists of
Central nervous system (CNS)
Brain and spinal cord
Peripheral nervous system (PNS)
Peripheral nerves and cranial nerves
NEURONE CELLS
There are three types of neurone cells:
Type
Function
SENSORY
To connect the receptors to the CNS.
MOTOR
To connect the CNS to effectors (muscles or glands).
RELAY (intermediate)
To connect the sensory and motor neurones in the spinal cord.
Nerves carry information via electrical IMPULSES along the AXON. The branching ends of the nerves
(called dendrites) do not touch. There is a tiny gap called a SYNAPSE between the nerve cells. A
chemical called a NEUROTRANSMITTER is released which connects these synapses and increases
conductivity to make the electrical impulse pass through.
90
REFLEX ARCS (CRANIAL AND SPINAL)
Why are some actions automatic when others are not? If you have ever touched a hot object, you would
notice you would pull away immediately. These are done by reflex arcs. Reflex arcs are:
1. AUTOMATIC
2. INVOLUNTARY
3. A DEFENSE MECHANISM
Usually, sensory information gets sent to the CEREBRUM to be filtered and analyzed and then returned
to the spinal cord and muscles. A reflex arc bypasses the brain process and the receptor sends a rapid
response directly to the spinal cord and THEN to an effector, which is usually a muscle or gland, which
acts immediately.
Cranial reflex arcs operate in the same manner, with the message being sent directly to the brain stem
and with no conscious thought involved. They occur involuntarily, as with all reflexes. An example would
be: BLINKING.
THE BRAIN
91
Section
Function
CEREBRUM
Memory, emotion, judgment,
senses (e.g. sight, hearing)
CEREBELLUM
Movement and coordination
MEDULLA (brain
stem)
Autonomic nervous system
(breathing, heart rate, reflexes,
etc.)
HYPOTHALAMU
S
Regulation of body temperatu
PITUITARY
GLAND
Regulates release of hormone
RESPONSE IN HUMANS – ENDOCRINE SYSTEM
A hormone is defined as a CHEMICAL SECRETED BY A GLAND THAT TARGETS A CERTAIN
ORGAN AND STIMULATES A SPECIFIC ACTION.
There are two types of glands in the body.
Type
Description
Examples
ENDOCRINE
Transports substances directly into
the blood. Glands have no ducts.
Sweat glands, tear glands, salivary glands
EXOCRINE
Glands have ducts. Usually
ransports substances to areas outside
of the bloodstream.
Adrenal glands, thyroid gland, ovaries
NOTE: The pancreas is known as BOTH an exocrine gland and endocrine gland because:
The pancreas secretes hormones such as insulin directly into the bloodstream, but also secretes
enzymes into the small intestine through its duct.
Name of Gland
Hormone produced
Effect of Hormone
Pituitary
GROWTH HORMONE
Stimulates growth of tissue and bones.
ADH
Regulates water reabsorption in the kidneys.
FSH
Forms follicles around egg cells; sperm development
LH
Triggers ovulation during menstrual cycle.
Thyroid
THYROXINE
Regulates metabolic activity.
Adrenal
ADRENALINE
Heightens awareness during stressful situations, raises
heart + breathing rate, increases rate of digestion.
Pancreas
INSULIN
Converts glucose to glycogen to be stored in cells.
GLUCAGON
Converts glycogen to glucose when blood sugar is low.
92
Ovaries
Testes
OESTROGEN
Releases eggs from ovary; secondary sex characteristics
PROGESTERONE
Thickens uterus lining during ovulation
TESTOSTERONE
Sperm development; secondary sex characteristics
Diagram showing location of various endocrine glands.
RESPONSES TO BRIGHT AND DIM LIGHT STIMULI
In order to see, an image must be formed on the retina of the eye after light enters the pupil and is focused
by the lens.
Light Exposure
What Happens in Eye
Why
Bright
The pupil CONSTRICTS. In the iris, radial muscles
relax and circular muscles contract.
To limit light entering the eye,
which would damage the
retina
Dim
The pupil DILATES. In the iris, the radial muscles
contract and circular muscles relax.
To allow more light into the
eye to form a clear image.
RODS AND CONES
Rods and cones are specialized receptors in the retina, at the back of the eye.
●
Rods enable vision in DIM LIGHT and mainly form outlines of images.
93
●
Cones enable vision in BRIGHT LIGHT and mainly form colours.
94
ACCOMMODATION
The process of accommodation in the eye involves changing the shape of the lens in order to focus on
near and distant objects.
OTHER EYE CONDITIONS
1. ASTIGMATISM - The deformation of the cornea; requires special lenses.
2. GLAUCOMA - High fluid pressure near optic nerve causes blurry vision.
3. CATARACT - Clouding of the lens in the eye. Can be surgically removed.
GLAUCOMA
This is the section that contains AQUEOUS humour. As
a result, fluid buildup occurs and pressure persists
through the VITREOUS humour and OPTIC nerve.
Due to the strain of the nerve, electrical impulses are
interrupted and vision becomes blurry. The condition
also causes considerable discomfort in the patient.
When a person has glaucoma, it means that a drainage
canal at the front of the eye is blocked.
95
THE HUMAN EYE
SECTION
FUNCTION
CORNEA
Focuses the entrance of light into the eye.
PUPIL
The entryway of light into the eye.
IRIS
Changes the size of the pupil size to regulate how much light enters the eye.
RETINA
Has photoreceptors called rods and cones that detect light and forms images.
FOVEA
Contains the highest concentration of cones. Develops sharpest vision.
LENS
Can adjust thickness to focus light on the retina to create sharp images.
CILIARY MUSCLES
Contract and relax to adjust thickness of lens.
SUSPENSORY
LIGAMENTS
Allows ciliary muscles to pull lens and adjust thickness.
OPTIC NERVE
Sends images from the retina to the brain via electrical impulses. No image or
photoreceptors are found here, so it is also called the BLIND SPOT.
CHOROID
Prevents internal reflection of light in the eye.
SCLERA
Serves as the outermost protective layer; the white of the eye.
96
VITREOUS
HUMOUR
Gel-like material that keeps the shape of the eye.
97
SECTION B (5/5)
DISEASE AND DRUGS
Disease can be put into FOUR distinct categories:
Category
Cause
Prevention Method /
Examples
Treatment
PATHOGENIC or
INFECTIOUS
Disease-causing organisms
called pathogens enter the
body and can be spread in
various ways.
NUTRITIONAL
DEFICIENCY
The absence of a certain
nutrient from the diet, which
can have negative effects on the
body.
HEREDITARY
A disease that is passed on
from parent to offspring
through the genes.
Somatic gene therapy
and genetic screening.
Sickle cell anaemia,
cystic fibrosis,
haemophilia.
PHYSIOLOGICA
L or LIFESTYLE
Results from the malfunction of
an organ, due to poor eating
habits, lack of exercise or
misuse of drugs.
Balanced diet. Regular
exercise. Reduction of
substance abuse.
Diabetes, coronary
heart disease, obesity.
Quarantine. Face masks.
Vaccination and antisera.
Antibiotics, antiviral
drugs, antifungals.
Having a balanced diet.
Nutritional supplements.
Cholera, malaria,
dengue fever, typhoid,
leptospirosis, tetanus.
Scurvy, rickets,
beri-beri, anaemia,
kwashiorkor.
Disease can be divided into COMMUNICABLE and NON-COMMUNICABLE.
-
Communicable diseases are infectious, meaning that they can be spread to other individuals,
whether by contact, mediums such as water or air, or through vectors (animals/insects that carry
pathogens). These are PATHOGENIC.
-
-
Non-communicable diseases cannot be spread to other individuals through means of infection.
These are classed as nutritional deficiency, physiological and hereditary.
98
PATHOGENS AND VECTORS
●
A PATHOGEN is a disease-causing microorganism. They are usually one of three types of
organisms: BACTERIA, VIRUS, FUNGUS (and PROTOZOA)
●
A VECTOR is an organism that can transmit a pathogen but is mostly unaffected by it.
Vector
Pathogen
Disease
Signs/Symptoms
Anopheles mosquito
Protozoa
Malaria
High fever, headaches, low rbc count.
Aedes aegypti
Virus
Dengue
Joint pain, high fever, headaches.
Housefly
Bacteria
Cholera
Vomiting, diarrhoea, dehydration.
Rat
Bacteria
Leptospirosis
Nervous system failure, red eyes, jaundice.
TYPICAL LIFE CYCLE OF AN ANOPHELES MOSQUITO
Stage
Control Method
Egg
Draining of stagnant water sources.
Larva
Introduction of predators to water sources. Spraying larvacide on water.
Pupa
Draining of stagnant water sources. Pesticide-resistant at this stage.
99
Adult
Spraying pesticides. Electrical zappers. Sleep under net to prevent infection.
100
WHAT ARE SOME IMPACTS OF DISEASES ON SOCIETY?
Factor
Economy
Explanation
Impact of State-funded medical care. Reduced labour force. Quarantine can result
in businesses closing down.
Trade relations
Reduced income from exports and tourism sectors.
Food
Reduced food availability if agricultural sector is affected.
Household income
Cost of privatized healthcare and medical bills. Reduced income from
unemployment.
Quality of living
Emotional toll of illness, death and being quarantined for lengthy periods.
AIDS/HIV
Question
Answer
What do AIDS and HIV
stand for?
HIV – Human Immunodeficiency Virus
Why is there no cure?
HIV is very difficult to detect and produce a vaccine for.
Antibiotics useless against viruses. Virus mutates constantly.
How is HIV transmitted?
Via the exchange of bodily fluids such as semen, vaginal fluids,
breast milk and blood transfusions.
How can HIV spread be
prevented or reduced?
Use of barrier contraception (condoms). Limiting sexual partners.
Regular HIV blood screening. Education on safe sex for young
people. Anti-HIV drugs for pregnant women.
AIDS – Acquired Immune Deficiency Syndrome
NOTE: The drug AZT does not cure AIDS, only minimizes its
impact.
101
WHAT IS A DRUG?
A drug is defined as a: SUBSTANCE THAT IS EXTERNALLY ADMINISTERED TO THE BODY,
WHICH AFFECTS ITS METABOLISM.
A drug may be beneficial the body or harmful to it depending on how we use it. Usually, problems arise
when people become addicted or dependent on a particular drug. Drugs can be classified in three social
categories:
1. PHARMACEUTICAL drugs (e.g. Penicillin, Quanine)
2. SOCIALLY ACCEPTABLE drugs (e.g. Nicotine, Alcohol)
3. SOCIALLY UNACCEPTABLE or ILLICIT drugs (e.g. Crystal meth, Cocaine, Heroin)
DRUG ABUSE
Drug abuse is the taking of drugs excessively; or not under a doctor’s prescription. Drug abuse can cause
either TOLERANCE, where the person has to keep on taking more and more of the drug to achieve the
same initial effect, or ADDICTION, where a person feels a strong urge to take the drug and experiences
WITHDRAWAL symptoms if they don’t. These symptoms include: nausea, trembling, depression, acute
anxiety attacks).
TYPES OF DRUGS
Type
Effect
Examples
STIMULANT
Increases blood pressure and heart rate
Caffeine, nicotine, cocaine.
DEPRESSANT
Decreases blood pressure, heart rate and
reaction time.
Alcohol, codeine, benzodiazepine
HALLUCINOGE
Used as an escape from reality, amplifies
emotions
Cannabis, LSD, Ecstasy
Used to numb pain, disrupt
neurotransmitters.
Morphine, heroin
N
ANALGESIC
102
EFFECTS OF DRUG ABUSE ON THE INDIVIDUAL AND SOCIETY
Category
Family
Effect
Loss of income from rehab or addiction, especially if breadwinner is involved. Child
neglect and domestic violence. Isolation and stigma.
Finances
Loss of income from purchasing drugs and paraphernalia. Loss of employment. Cost of
rehab.
Health
Long-term physiological and psychological damage to organs. Risk of overdose and
contracting infections from sharing needles.
Economy
Reduced labour force. Rise of the black market and crime if drug trade is involved.
Isolation of certain crime-ridden areas.
EFFECTS OF ALCOHOL
Effect
Description
Nervous system
Acts as a depressant, reduces reaction time to stimuli.
Circulatory system
Lowers heart rate and blood pressure.
Water balance
Suppresses the release of ADH, allowing less water to be reabsorbed into
bloodstream. Frequent urination and dehydration. Higher body temp.
Long-term health
Impact of addiction and cirrhosis of the liver.
Social issues
Loss of income. Domestic abuse and child neglect. Drunk driving.
103
MISUSE OF ANTIBIOTICS
Although antibiotics are highly effective drugs against bacterial infections, their misuse has led to severe
problems in the health and medical industry.
•
•
•
Patients who take antibiotics for too short a duration, for example, if they do not complete the full
course of the prescription, will run the risk of having ANTIBIOTIC-RESISTANT bacteria
develop in their bodies.
When they take the same antibiotic next time, it will not be effective against the resistant bacteria.
Some antibiotics also have ADDICTIVE, properties, which can make the user experience
WITHDRAWAL when the course of treatment ends.
NATURAL PREVENTION OF INFECTION
Part
Function
Skin
Acts as a mechanical barrier to keep microbes out of the body.
Cilia and mucus
A mechanical and chemical barrier that filters microbes or traps them.
Platelets
Clots wounds to prevent infection.
Stomach acids (HCl)
Denatures enzymes in bacteria that end up there.
White blood cells (leucocytes)
Engulfs foreign bodies or produces antibodies to attach to antigens of
microbes, of which effect can be boosted by vaccines.
104
IMMUNITY AND IMMUNIZATION
Immunity can be defined as AN ORGANISM’S ABILITY TO RESIST INFECTION. The process of
making an individual resistant to a disease is called IMMUNIZATION. Specialized cells called
MEMORY CELLS are produced when exposed to active immunity to provide long-term immunity.
They are not produced during passive immunity.
Type of Immunity
Description
Natural passive
Occurs when a child pre-natally receives antibodies from its mother
through the placenta or through breast milk post-natally.
Naturally acquired
Occurs when a person is exposed to a pathogen, which stimulates the
active
production of antibodies. Can prevent a future infection.
Artificial passive
Occurs when an antiserum containing antibodies is administered to
the body in order to treat an infection and kill pathogens in the short
term. Cannot be used as a preventative measure.
Artificially acquired
Occurs when a vaccine containing a weakened or deactivated version
active
of a pathogen is introduced to the body. This stimulates the
production of antibodies and memory cells to prevent future
infections in the long term. Cannot be used as a treatment.
BACTERIAL STRUCTURE
105
SECTION C
REPRODUCTION, CONTINUITY AND VARIATION
Term
Definition or Explanation
DNA
A nucleic acid that contain all genetic information. It stands for:
DEOXYRIBONUCLEIC ACID
GENE
A segment of DNA that carries information to code for a trait, or to
produce a specific protein.
CHROMOSOME
A strand of DNA and proteins (histones).
ALLELE
Each of an alternative form of a gene, coding for a different aspect of a
trait, e.g. eye colour could have brown or blue alleles.
GENOTYPE
The set of genetic code in the DNA, represented as letters, e.g. BB codes
for brown eyes while bb codes for blue eyes.
HOMOZYGOUS
When the genotype code has two of the same alleles, e.g. BB, bb
HETEROZYGOUS
When the genotype code has two different alleles, e.g. Bb
PHENOTYPE
A physical characteristic expressed by the genotype, e.g. if BB codes for
brown eyes, the genotype is ‘BB’ and the phenotype is ‘brown eyes’.
DOMINANT
A phenotype is expressed even if only one allele is present.
RECESSIVE
Phenotypes are only expressed if both alleles are present, e.g. Brown (B)
is dominant to blue (b). If a person is Bb, their eye colour will be brown
despite carrying a blue gene.
GAMETE
A sex cell that is used for fertilization, e.g. sperm and eggs.
ZYGOTE
A fertilized egg, which will divide to form an embryo and fetus.
DIPLOID
The chromosome number in a cell that is not a gamete. Represented as
‘2n’. Humans have 46 chromosomes.
HAPLOID
The chromosome number in a gamete. Represented as ‘n’. A human egg
or sperm has 23 chromosomes.
106
MITOSIS AND MEIOSIS
Mitosis and meiosis are both processes that are involved with replication or cell division. Cells usually
reproduce by splitting into two or more cells. There are, however, major differences between these two
processes.
●
Mitosis allows cells to divide without
exchanging DNA and so all daughter
cells are clones. It is used in GROWTH
and ASEXUAL reproduction. Mitosis
occurs in every cell (besides to form
gametes).
●
Meiosis only occurs to produce
gametes. Meiosis allows the genetic
material or DNA to ‘cross-over’ and
create new sets of DNA in the daughter
cells. Since genes undergo independent
assortment in the gametes, there is a
different DNA combination in each
gamete, promoting genetic variation for
sexual reproduction.
CHARACTERISTIC
MITOSIS
MEIOSIS
Number of cell divisions
One
Two
Number of daughter cells produced
Two
Four
DNA of daughter and parent cells
Identical (clones).
Genetically varied.
Chromosome number
Diploid (2n)
Haploid (n)
Example of cell formed
Any somatic cell.
Sperm and eggs.
107
STAGES OF MITOSIS (excluding interphase)
108
SEXUAL REPRODUCTION AND DEVELOPMENT
REPRODUCTION IN ANIMALS
The purpose of reproduction is to carry on the species of the organisms across generations over time. If
a species cannot reproduce as fast as its population decreases, it will become extinct.
There are two types of reproduction:
Type
Description
ASEXUAL
Involves one parent. Typically occurs in bacteria, protozoa, some plants and
animals, e.g. starfish, sea anemones and yeast. The offspring are identical to
their parents because they only obtain one set of chromosomes.
SEXUAL
Involves two parents. Two gametes, produced by reproductive organs or
gonads, fuse to form a zygote. Occurs in most animals and plants that have
male and female parts.
Diagrams of female reproductive system (above) and male reproductive system (below).
109
CONCEPTION AND PREGNANCY
During __________________, sperm are
released from the ___________. Once in the
vagina, they swim towards the ______________
and into the ______________.
Most will die before they get to this point. The
rest continue to swim towards the
___________________ tubes and to the
______________. Many millions of sperm are
110
Section
Description
PLACENTA
Contains many blood vessels that collects nutrients, oxygen and antibodies
from the mother to be delivered to the fetus. *
UMBILICAL CORD
Allows the transfer of materials from the placenta to the fetus.
AMNIOTIC SAC or
AMNION
Acts as a shock absorber to prevents the fetus from being injured by external
collisions and trauma.
* Unfortunately, there are some toxins and pathogens that can be transferred across the placenta, such as
nicotine and the rubella virus.
111
CONTRACEPTION
Contraception or birth control refers to any method that prevents pregnancy.
Category
Examples
How they work
BARRIER
Condoms
Prevents sperm from entering the vagina
Caps/Diaphragms
Prevents sperm from entering the uterus
Rhythm method
Pinpoint the time of ovulation and avoid intercourse
NATURAL
at this time. Least reliable method.
Vasectomy
Prevents sperm from reaching the penis
Tubal ligation
Prevents eggs from reaching the uterus
HORMONAL
Birth control pill
Contains sex hormones which suppress ovulation
MECHANICAL
Intra-uterine devices
A small piece of moulded plastic in the uterus which
(IUD’s)
interferes with implantation
SURGICAL
Why use contraception?
For individual families, the main purpose of contraception is to avoid financial strain and to increase
quality of life for all individuals. Too many children may lead to cases of neglect. For countries, family
planning is important to maintain a stable population and to avoid economic strain, such as from welfare.
Contraceptive Pills
Progesterone-only female contraceptive pills typically work by:
1. Preventing OVULATION by suppressing the hormone OESTROGEN.
2. Thickening the MUCUS around the CERVIX to prevent sperm from entering.
Male contraceptive pills are not yet on the market but are being researched. Listed below are several ways
in which they could work.
(i) By reducing testosterone levels and sperm count
(ii) by thickening mucus around the sperm duct and preventing release of sperm
(iii) by making the sperm immobile
112
OVULATION AND MENSTRUATION
Phase
Description
Follicle Phase
The follicle develops around the ovum after an increase of FSH.
Ovulation
An increase of oestrogen and LH causes ovum to be released from follicle.
Luteal Phase
The decayed follicle (corpus luteum) secretes progesterone, which leads to
the thickening of the uterus wall for implantation.
Menstruation
If pregnancy does not occur,progesterone level drops and the uterus wall
sheds.
Hormone
Function
FSH
Stimulates the growth and maturation of the ovarian follicle.
LH
Releases the ovum from the follicle; stimulates ovulation.
Oestrogen
Helps with thickening uterus lining; stimulate LH secretion.
Progesterone
Thickens uterus lining for implantation.
113
ASEXUAL REPRODUCTION IN PLANTS
Natural Vegetative Propagation
Vegetative propagation is a form of ASEXUAL reproduction found in plants. It can occur naturally and
usually involves the growth of a new part of a plant, usually a bud or stem, which eventually becomes
separated from the parent plant to form a new individual. In this way, several plants can be produced from
a single parent plant.
Other examples of natural vegetative propagation include:
1. Rhizomes (e.g. ginger and lily of the valley)
2. Tubers (e.g. potato and yam)
3. Bulbs (e.g. onions and garlic)
Artificial Vegetative Propagation
114
Tissue Culture (micropropagation)
Cutting and Grafting
115
SEXUAL REPRODUCTION IN PLANTS – STRUCTURE OF A FLOWER
Most plants can reproduce sexually AND asexually. But some can only reproduce sexually and others can
only reproduce asexually. To recap, sexual reproduction involves the fusion of special cells called
GAMETES. In flowering plants, sexual reproduction takes place in the flowers, which are the plants'
reproductive organs.
Sepals – Sepals are modified leaves
which enclose and protect the other
parts of the flower in the bud stage. All
the sepals together make up the
CALYX. They also help hold the flower
upright.
Petals – Petals are modified leaves and
are usually brightly coloured in
insect-pollinated flowers. All the petals
combined form the COROLLA. Petals
attract insects as well as act as a landing
platform for them.
FLOWER REPRODUCTIVE PARTS
Section
Comprised of
Notes
STAMEN
Anther
Produces pollen grain, containing male gametes.
Filament
Holds the anther in place.
Stigma
Usually allows pollen to stick to it.
Style
Holds the stigma in place. Leads to ovary.
Ovary
Contains ovules, containing the egg cell.
PISTIL
116
POLLINATION
Flowering plants reproduce sexually by producing seeds. The seeds are formed from structures in the
flowers. The male sex cells of plants are inside POLLEN GRAINS. The egg cell is the female sex cell and
is found in the OVULES. When these two sex cells fuse, they form a ZYGOTE. But first:
Plants must transfer the pollen grains from an ANTHER to a STIGMA. This is called POLLINATION.
It usually occurs between flowers on diferent plants of the same species.
●
Pollination between two different flowering plants of same species is called
CROSS-POLLINATION.
●
Pollination within the same flowering plant is called SELF-POLLINATION.
Cross-pollination takes place in one of two main ways. Some flowers use the wind to transfer pollen –
they are wind-pollinated flowers. Others use insects to transfer the pollen – they are insect-pollinated
flowers.
CROSS-POLLINATION
Continued in-breeding or self-pollination results in the production of offspring that are weaker and less
adaptable to changes in the environment. Cross-pollination is necessary for species survival.
Feature
Insect-Pollinated
Wind-Pollinated
Petals
Large and colourful
Small and dull, or absent
Nectary or Scent
Present
Mostly absent
Stamens or Stigma
Usually short stigmas
Usually long filaments
Pollen Production
A variable amount
Much more than insect-pollinated
117
FERTILIZATION AND DOUBLE FERTILIZATION
Following pollination, the following occurs:
1. The pollen grain grows a tube down
through the style to one of the ovules
inside the ovary. The nucleus of the
pollen grain passes down the tube.
2. When it reaches the opening to the
ovule, the pollen grain nucleus passes
into the ovule and fuses with the egg
cell nucleus in the ovule. This is called
FERTILIZATION.
An EMBRYO is formed.
3. The fertilized ovule develops into a
SEED.
4. The ovary becomes a FRUIT and these
may contain several seeds or just one.
Changes that occur in the flower after fertilization
Before Fertilization
After Fertilization
118
Ovary
Fruit
Ovary wall
Pericarp
Ovule
Seed
Zygote
Embryo
Endosperm nucleus
Endosperm
119
MONOHYBRID INHERITANCE
Characteristics, such as the colour of our eyes or skin, height and blood type are passed on to us
by our parents. They are referred to as GENETIC characteristics. It was only until the 19th century
an Austrian monk named Gregor Mendel carried out breeding experiments with garden peas to
give an explanation of the mechanism of heredity. Monohybrid inheritance refers to the study of
the passing down of only one genetic characteristic.
For Mendel's experiments, he carefully selected several varieties of garden peas that differed in
easily observable characteristics, such as height, flower colour and seed colour.
In one of his experiments, Mendel crossed
tall plants with dwarf plants. He used
pure-bred varieties, which are plants that are
self-fertilized (asexually), so they produce
identical offspring.
He cross-pollinated the tall plants with
pollen from the dwarf plants and vice versa.
The offspring resulted in the first filial
generation or F1 generation. These F1 plants
then self-pollinated and produced to the F2
generation. The results of his experiment is
shown in the diagram.
In his experiments, Mendel noticed that his F1 plants always resulted in the same tall height,
while the other "dwarf" trait seemed to disappear or "recede". Mendel then noticed the dwarf
characteristic reappeared in the F2 generation only. Mendel called the trait that appeared
unchanged in the F1 hybrid a DOMINANT trait and the other a RECESSIVE trait.
Thus, it can be said that:
●
Dominant traits are always expressed over recessive traits.
●
Recessive traits are ONLY expressed if no DOMINANT allele is present.
120
CODOMINANCE AND INCOMPLETE DOMINANCE
Type
Description
Example
CODOMINANCE
Two alleles are equally dominant and
Red and white camellia flowers
thus, produces a combined phenotype.
produce red-and-white spotted.
INCOMPLETE
Where one allele is not completely
Red and white snapdragons
DOMINANCE
expressed in the phenotype.
produce pink.
GENETIC TEST CROSSES AND PUNNETT SQUARES
Diploid organisms will have two copies of
Usually letters are used to represent alleles:
each gene in each cell. These copies are
capital letters for dominant alleles and
called ALLELES. The alleles may be the
common letters for recessive alleles. For
same or they may be different.
example, the allele for tallness in pea plants
may be designated "T" while the allele for
dwarfness may be designated "t".
●
If both alleles are the same (e.g. TT), the organism is said to be HOMOZYGOUS
●
If they are different (e.g. Tt), the organism is said to be HETEROZYGOUS.
121
122
SEX DETERMINATION AND SEX-LINKED (X-LINKED) DISEASES
●
Among the 46 chromosomes that humans have, one pair typically codes for a person’s
sex or gender. A male’s sex genotype is XY while a female’s is XX.
●
The egg cell always has an X chromosomes, while the sperm cell can carry either an X or
a Y chromosome.
Some diseases, such as HAEMOPHILIA and genetic COLOUR BLINDNESS. are more
prevalent in males than in females. This is because these diseases only are carried in the X
chromosome. Since males only have one X chromosome, they have a higher chance of getting the
disease from childbirth. For instance, if the a normal healthy gene is XH and the haemophilia gene
is Xh, the Punnett square below will show how a male has a higher chance of getting the disease.
123
124
SICKLE CELL ANAEMIA
Sickle cell anaemia is a condition where the red
blood cells are crescent-shaped due to abnormal
haemoglobin. As a result, they cannot efficiently
absorb OXYGEN, leading to fatigue and
fainting. Because of their shape, they also tend
to form blood clots and limit blood flow. This
can lead to death.
A person with the disease has two recessive
alleles. The alleles for sickle cell are given as:
1. HbA is the healthy allele.
2. HbS is the sickle cell allele.
Complete the Punnett square to the right show
how a mother and father who don’t have sickle
cell anaemia can produce a child who has.
MULTIPLE ALLELES IN HUMAN BLOOD GROUPS
In a population, there may be more than two alleles for a given trait. If a gene exists in more than two
alleles, it is said to have multiple alleles. The occurrence of blood groups is an example of multiple
alleles. There are four blood groups in human populations: A, B, AB and O.
The alleles for A group, B group and O group may be designated IA, IB and IO respectively.
o
IA and IB are dominant over IO
o
IA and IB are co-dominant, therefore individuals with these two alleles will have an AB blood
group.
o
The only way blood type O can be obtained is if both genes are IO
125
EXAMPLE QUESTION:
In the diagrams below, show how a father of
blood type B and a mother of blood type A
can produce a child of blood type O.
VARIATION
Variation can also seen within organisms of the same species. A number of factors contribute to variation
such as genetic exchange during sexual reproduction, sunlight exposure, diet, water, fertilizer.
Variation is important to species to:
1. Resist diseases or pests (e.g. the Gros Michel banana was nearly wiped out by a fungus)
2. Prevent overcompetition for resources
3. Encourage species survival if there is a sudden environmental change
Type
Description
Example
GENETIC
Mostly occurs through sexual
A brother and sister will both be
VARIATION
reproduction. Because there are two
genetically different because they
sets of DNA that cross-over and
would have different random
recombine during meiosis and fuse
assortments of genes from their
through fertilization, new genotypes
mother and father.
and phenotypes are produced in the
offspring.*
ENVIRONMENTA
Occurs through factors external to
Two plants of similar genes can
L VARIATION
genetics, such as lifestyle, diet and
still grow at different rates if
surrounding environment.
planted in two different soils and
given different amounts of water.
*The only way genetic variation can occur through asexual reproduction is via MUTATIONS.
126
Variation of characteristics can also occur in two other categories.
Type
Description
Examples
CONTINUOUS
Occurs due to the influence of
many alleles, can have possibilities
across a spectrum.
Height, body mass, skin colour
DISCONTINUOUS
Occurs due to one or a few alleles
typically. Only a distinct few
possibilities of phenotype.
Eye colour, ability to roll tongue,
presence of widow’s peak, blood
type
NATURAL AND ARTIFICIAL SELECTION
Recall the case of the peppered moth, where only the moths of certain colours survived based on their
environment (black moths survived in the soot, white moths survived on light-coloured lichen on trees).
This was the process of natural selection, where organisms survived based on their ability to ADAPT TO
THEIR SURROUNDINGS.
Artificial selection involves the selective breeding of organisms in order to preserve or attain favourable
genotypes or traits. Organisms are selected to mate based on desirable traits, e.g. breeding cows to
produce more milk, chickens to produce larger eggs, or crops to resist disease and have higher yields.
The Belgian Blue Cow is a good example. The
cattle with increased muscle mass have a
recessive gene, caused by a mutation, which
increases their muscle mass more than normal.
These cattle with these recessive genes are then
selected to breed to produce offspring that
contain the gene. It is different from genetic
engineering, since the gene was not directly
inserted into the cow.
How is artificial selection different from natural selection?
Artificial selection is done in a CONTROLLED environment and is a FASTER process than natural
selection. However, the trait the organism is bred for may not always be advantageous to the organism
127
itself. In natural selection, the trait is always BENEFICIAL since it allows survival in the wild.
128
MUTATION
Mutations occur when the chromosomal set of an organism changes unexpectedly, or there is some
alteration to a genotype. It is VERY important to remember that mutations are RANDOM, though
substances called MUTAGENS (e.g. radioactive exposure) can increase the risk of mutations.
Examples of common mutations in humans include:
Condition
Description
Albinism
Occurs when a recessive mutant allele prevents the production of
MELANIN, causing very pale skin and eyes.
Down’s Syndrome
Occurs when one of the chromosomes divides one extra time, forming a total
of 47.
Sickle Cell Anaemia
Recessive mutation that produces abnormal haemoglobin and thus changes
the shape of red blood cells. O2 is thus not able to be transported properly.
MUTATION AND SPECIATION
A single mutation in an individual cannot lead
to a new species arising. However, if a mutation
occurs throughout a population and that
mutation is beneficial to the species and allows
it to better survive in its environment, those
mutated species will be able to reproduce and
form a new species.
An interesting example of mutation leading to
thus would have survived over their legged
the formation of a new species is the snake. A
counterparts.
long time ago, snakes had legs.
A mutation would’ve caused some snakes to
have small legs or have no legs. These snakes
would have had greater mobility in underground
regions and were better able to escape predators,
129
130
GENETIC ENGINEERING
Genetic engineering involves THE ALTERATION OF THE ORGANISM’S GENOME OR THE
EXTRACTION AND TRANSFER OF A GENE FROM ONE ORGANISM INTO ANOTHER.
It is a controversial process that has caused many ethical debates, mainly due to religious consequences or
the wide possibility of situations that can occur due to mishaps. However, genetic engineering has ensured
great steps in biotechnology, medicine and agriculture.
Field
Examples
Medicine and
The production of insulin using recombined DNA in E. coli bacteria.
Biotechnology
Agriculture
Gene therapy for inherited disorders. Research of stem cell techniques.
The production of Golden Rice (which produces beta-carotene and Vitamin A).
The production of crops that produce their own pesticides and crops that grow
faster and resist harsh weather conditions. The “Flavr-Savr” tomato, which had
a longer shelf-life than regular tomatoes.
There are, however, numerous disadvantages to genetic engineering. These include:
Factor
Explanation
Social & Ethical
Changing the genome of an organism can be seen as ‘playing God’. The
chances of producing ‘designer babies’. The impact of ‘cloning humans’. The
risk of biological weapons.
Physiological
It is possible for ALLERGENS can be transferred from one food crop to
another through genetic engineering. Another concern is that pregnant women
eating GMO products may endanger their offspring.
Environmental
The release of a GMO species would have the possibility of causing an
ECOLOGICAL IMBALANCE. The main concern is that crops can spread their
genes to wild plants through pollination.
131
INSULIN PRODUCTION WITH RECOMBINANT DNA
Differentiating Artificial Selection and Genetic Engineering
Factor
Artificial Selection
Genetic Engineering
Method
Done by selecting two animals to breed
DNA is transferred from one organism to
to pass on their genes that code for their
another using plasmids and enzymes.
desirable traits.
Trait selection
Timespan
Expressions for traits are selected but
Individual genes are transferred from one
usually not individual alleles.
organism to another. Very specific.
May take a few generations to achieve
Achieves results as soon as the process is
optimum results.
done. Much faster.
132