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UPDATED TO 2023-2025 SYLLABUS
CAIE IGCSE
BIOLOGY
SUMMARIZED NOTES ON THE THEORY SYLLABUS
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1. Characteristics and
Classification of Living
Organisms
1.1. Characteristics of Living Organisms
MRS GREN
Movement: an action by an organism or part of an
organism causing a change of position or place
Respiration: the chemical reactions in cells that break
down nutrient molecules and release energy for
metabolism
Sensitivity: the ability to detect and respond to changes in
the internal or external environment
Growth: a permanent increase in size and dry mass
Reproduction: the processes that make more of the same
kind of organism
Excretion: the removal of the waste products of
metabolism and substances in excess of requirements
Nutrition: the taking in of materials for energy, growth and
development
1.2. Concept and Uses of Classification
System
Organisms are classified into groups by the features they
share.
Sequence of classification: Kingdom → Phylum →Classes
→ Orders → Families → Genus → Species.
Species are a group of organisms which can reproduce to
produce fertile offspring.
The Binomial System of Naming Species is an
internationally agreed system in which the scientific name
of an organism comprises two parts showing the genus
and species.
The format is Genus species. The genus is capitalized,
and the species are not.
The classification of organisms helps show the
evolutionary relationships between them.
Scientists also use the DNA base sequence to help
classify organisms.
The similarity in DNA chains shows how closely related
two organisms are.
Dichotomous keys use visible features to classify
organisms. They give you a choice of two features, and
you follow the one that applies: each choice leads to
another choice until the organism is narrowed down to its
genus and, finally, species.
1.3. The Five Kingdoms
Animals: Multicellular ingestive heterotrophs (eat living
organisms). Ex: cat, ladybird, newt, etc.
Plants: Multicellular photosynthetic autotrophic (make
their food) organism with a cellulose cell wall and
chloroplasts. Ex: cactus, oak tree.
Fungi: Single-celled or multicellular heterotrophic
organisms with cell walls not made of cellulose, spread by
spreading spores in moist/dark/warm environments. Most
have hyphae and mycelium in structure. Ex: yeast,
mushrooms.
Prokaryotes: Single-celled organisms with no true nucleus
or DNA in the cytoplasm. Many also have plasmids. Ex:
E.coli, Salmonella.
Protocists: Single-celled organism with a nucleus.
Eukaryotes. Some are multicellular. Ex: Amoeba,
seaweed.
Main features of all animals:
multicellular
contains a nucleus but no cell walls or chloroplasts
only feed on organic substances made by other living
things
1.4. Animal Kingdom
Mammals
Fur/hair on the skin
External ears (pinna)
Internal fertilisation, giving the birth of young
Mammary glands
Reptiles
Thick, dry, scaly skin
Usually 4 legs
Internal fertilisation, birth from egg
Soft eggs
Fish
Wet scales
Streamlined body shape
External fertilisation and soft eggs
Uses gills to breathe
Amphibians
Smooth, moist skin
External fertilisation and soft eggs
Gills & Lungs can live on land and water
Most have 4 legs
Birds
Feathers on body and scales on legs
Constant internal body temperature
Hard eggs
Internal fertilisation, birth through eggs
1.5. Arthropods
Invertebrates are organisms that do not have a backbone.
All arthropods have three standard features:
1. Exoskeleton
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2. Jointed legs
3. Segmented body
Crustaceans: (e.g. crabs)
Have an exoskeleton 1 pair of compound eyes
3 body segments – head, thorax, abdomen
More than four pairs of legs (10-14 legs)
Arachnids: (e.g. spiders)
2 body segments – cephalothorax and abdomen
Four pairs of legs (8 legs)
Myriapods: (e.g. centipedes)
Segmented body
Additional segments formed
One pair of antennae
10+ pairs of legs – 1 or 2 pairs on each segment
Insects: (e.g. bees)
3 body segments – head, thorax and abdomen
3 pairs of jointed legs (6 legs)
1 pair of antennae
1 or 2 pairs of wings
1.6. Classification of Plants
In IGCSE Biology, the plant kingdom is classified into ferns
and flowering plants.
Ferns:
Do not produce flowers/seeds
They are plants with roots, stems and feathery leaves
Reproduce by spores
Flowering plants:
They are plants with roots, stems and leaves
Reproduce sexually by means of flowers and seeds
Seeds are produced inside the ovary in the flower
Monocotyledons
Dicotyledons
One cotyledon/One-seed leaf Two cotyledons/Two-seed leaf
Parallel veins
Branching veins
Long Narrow Leaf
Broad leaves
3 Flower Parts
4 or 5 Flower Parts
Scattered Vascular Bundles
Ringed Vascular Bundles
2. Organisation of the
organism
2.1. Cell Structure and Organisation
All living things are made of cells.
New cells are produced by the division of existing cells
All typical cells have:
Cell membrane: controls movement in and out of cells
Cytoplasm: where chemical reactions take place
Nucleus: contains DNA and controls the cell
Mitochondria: where aerobic respiration happens
Ribosome: allows protein synthesis
A typical animal cell (e.g., the liver cell) has all above
Plant cells especially also have:
Vacuole: cell sap to keep cell turgid
Cell wall (all cells except for animal and protoctist cells
have cell walls): rigid to keep the shape of the cell,
strengthens the cell
Chloroplasts: contain chlorophyll, which absorbs light
energy for photosynthesis
A typical plant cell (e.g., the palisade cell) has everything
above.
1.7. Viruses
Viruses are not part of any classification system due to
not being considered living things.
They do not carry out the seven life processes for
themselves; instead, they take over a host cell’s metabolic
pathways to make multiple copies of themselves.
Virus structure contains only a genetic material (RNA or
DNA) inside a protein coat.
Example of virus structure below (No mitochondria or
ribosomes)
Prokaryotes DO NOT have mitochondria, rough endoplasmic
reticulum and a nucleus!
A bacterial cell only contains a cell wall, cell membrane,
cytoplasm, ribosomes, circular DNA, and plasmids.
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Other Forms in Magnification Formula
2.2. Levels of Organisation
Actual size = image size / magnification
Image size = magnification x actual size
Key Terms
Cells - Building Blocks of Life
Tissue - Groups of cells with similar structures working
together to perform a shared function
Organ - Group of tissues working together to perform a
specific function
Organ system - Group of organs with related functions
working together to perform body functions.
Cell
Red
blood
cell
Function
Adaptation(s)
Transport of
oxygen
Unit Conversions (μm - micrometre)
1cm = 10mm
1mm = 1000μm
Magnification does NOT have any units (‘x 50’ or ‘x 5000’)
3. Movement In and Out of
Cells
Diagram
Biconcave/Disc
shape
No nucleus
3.1. Diffusion
Flexible
Has haemoglobin
Net movement of particles from a region of their higher
concentration to a region of their lower concentration (i.e.
down a concentration gradient) as a result of their
random movement.
Energy for diffusion comes from the kinetic energy of
random movement of molecules and ions.
The diffusion of gases and solutes is important as without
it, molecules which are needed for life, for example,
glucose and oxygen for respiration, would not be able to
get to the places they are needed. Water is needed as a
solvent.
Factors that influence diffusion:
Concentration gradient
Temperature
Surface area
Distance
Long
Contracts to get
Muscle
structures closer
cell
together
Ciliated
cell
Movement of
mucus in the
trachea and
bronchi
Root
Absorb mineral
hair cell ions and water
Many protein
fibres in
cytoplasm to
shorten cell when
energy available
Tiny hairs called
cilia
Elongated shape
for more surface
area
No cytoplasm so
water passes
freely
3.2. Osmosis
No cross walls so
Xylem Transport water
cells connect to
vessel and support plant
form tube
Lignin makes it
strong and
waterproof
Regular shape so
many can fit in a
Palisade
small space
Photo-synthesises
cell
Many
chloroplasts
2.3. Size of Specimens
M agnification =
size of drawing
image
I
=
=
size of specimen
actual
A
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Net movement of water molecules from a region of
higher water potential (dilute solution) to a region of lower
water potential (concentrated solution) through a partially
permeable membrane
The role of water as a solvent in organisms to aid with
digestion, excretion and transport
Conc. of solute outside cell = conc. inside cell → no change
in size
Conc. of solute outside cell > conc. inside cell → cell
shrinks (Flaccid/Plasmolysis)
Conc. of solute outside cell < conc. inside cell → cell swells
(Turgid)
In animals:
Increasing solute concentration inside a cell can cause
it to burst (lysis) because it has too much water and no
cell wall.
In plants:
Increasing solute concentration inside the cell causes
the cell to become turgid, and the vacuole fills up.
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Decreasing solute concentration inside of the cell
causes the cell to become flaccid, losing water, and
the vacuole gets smaller. The cell body shrinks, pulling
away from the cell wall.
Plants are supported by the water pressure inside the
cells pressing outwards on the cell wall.
3.3. Active Transport
Proteins: Add a few drops of Biuret reagent, +ve result =
purple/lilac colour
Fats: Ethanol Emulsion test; ethanol is added to the
mixture, and this is poured into a test tube with an equal
amount of distilled water, then is shaken, +ve result =
milky-white emulsion
Vitamin C: Decolourisation of DCPIP shows that a vitamin
C is probably present.
Movement of particles through a cell membrane from a
region of lower concentration to a region of higher
concentration (i.e. against a concentration gradient),
using energy from respiration.
Carrier proteins are also used during active transport.
4.3. Structure of a DNA
Chromosomes are made of a molecule called DNA
DNA is also called deoxyribonucleic acid.
It is embedded in the cell membrane to pick up specific
molecules and take them through the cell membrane
against their concentration gradient.
Active transport is needed when an organism wants to
optimize the nutrients it can take up - ion uptake by root
hairs cell.
4. Biological Molecules
Carbohydrates: made from Carbon, Hydrogen and
Oxygen (CHO)
Fats and oils: made from Carbon, Hydrogen and Oxygen
(CHO)
Proteins: made from Carbon, Hydrogen, Oxygen, Nitrogen
and sometimes Sulfur (CHON{S})
Smaller molecules
Larger molecules
Simple sugars
Starch, glycogen and cellulose
Fatty acids and glycerol
Fats and oils
Amino acids/peptides
Proteins
4.2. Food Tests
Starch: Add a few drops of iodine solution (+ve result =
blue-black colour, -ve result = remains brown)
Reducing sugars: Add Benedict’s reagent, then the
mixture is heated in a water bath for 2 to 3 minutes
(70°C). (+ve result = brick-red precipitate, -ve result =
remains blue)
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Each chromosome is a very long molecule of tightly coiled
DNA
Two strands coiled together to form a double helix
Each strand contains chemicals called bases
Cross-links between strands are formed by pairs of bases
The bases always pair up in the same way:
A and T
C and G
5. Enzymes
Catalyst: a substance that speeds up a chemical reaction
and is not changed by the reaction
Enzymes are proteins that are involved in all metabolic
reactions, where they function as biological catalysts.
Enzyme lowers the activation energy needed for a
reaction to take place.
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It is important in all living organisms regarding the
reaction rate necessary to sustain life.
Enzymes are unchanged and can be reused
Effect of Temperature
Effect of pH
Lock and Key (model):
6. Plant Nutrition
Substrate: the molecule(s) before they are made to react,
complementary to the active site.
Product: the molecule(s) that are made in a reaction
Different sequences of amino acids may lead to different
shapes of protein molecules, as these slight differences may
be deferred in their function.
5.2. Effect of Temperature on Enzymes
Enzymes have an optimum temperature: the temperature
at which they work best, giving the fastest reaction ≈ at
37°C in animals & humans body.
When temperature increases, molecules move faster,
more effectively, frequent collisions.
Having more kinetic energy makes them more likely to
bind to active sites.
If the temperature is too high, enzyme molecules vibrate
too vigorously; the enzyme is denatured, losing its shape
and no longer binding with a substrate.
When the temperature is too low, there is not enough
kinetic energy for the reaction, so it reacts too slowly.
5.3. Effect of pH on Enzymes
Enzymes are sensitive to pH.
Some enzymes work best in an acid, and others in an
alkaline.
Enzymes work best at their optimum pH.
If the pH changes, the hydrogen bond is broken,
denatures the enzyme, making it no longer fit with the
substrate’s active site; therefore, no reaction occurs.
Pepsin in acidic conditions, Amylase in neutral conditions
and trypsin in alkalinity conditions.
5.4. Graphs for Changes in Enzyme
Activity
Effect of Temperature
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Effect of pH
Photosynthesis: the process by which plants manufacture
carbohydrates from raw materials using energy from light.
C arbonDioxide + Water
6C O2 + 6H2 O
​
​
light+chlorophyll
​
light+cholorophyll
​
Glucose + Ox
+C 6 H12 O6 + 6O2
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​
​
The carbon dioxide diffuses through the open stomata of
a plant leaf, and water is taken up through the roots.
Chlorophyll is a green dye that traps light energy and
converts it into chemical energy to form carbohydrates
and their subsequent storage.
Glucose is used for respiration, energy storage, cellulose
cell wall, making proteins and sugars.
Functions of the carbohydrate made from Photosynthesis
starch as an energy store
cellulose to build cell walls
glucose used in respiration to provide energy
sucrose for transport in the phloem
nectar to attract insects for pollination
6.2. Investigation of Chlorophyll
Take a potted plant with variegated (green and white)
leaves.
De-starch the plant by keeping it in complete darkness for
about 48 hours.
Expose the plant to sunlight for a few days.
Leaf boiled in water for 2 minutes to break down cell
walls, denature enzymes and allow for easier penetration
by ethanol.
Warmed in ethanol until the leaf is colourless to extract
chlorophyll, which would mask the observation
Dipped into the water briefly: to help soften the leaf
The leaf is placed on a white tile, and iodine is added. If
starch is present, the colour will be blue-black; if absent, it
will remain brown.
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6.3. Investigation of Light
De-starch the plant by keeping it in darkness for 48 hours
Place a stencil over part of a leaf
Place the leaf in sunlight for 4-6 hours
Remove the stencil and test for starch
+ve result = parts which received light turn blue-black
-ve result = parts which didn’t receive light remains brown
6.5. Limiting Factors
Limiting Factors: something present in the environment in
such short supply that it restricts life processes.
Light Intensity
As the amount of light
increases, the rate of
photosynthesis increases (ab)
The limiting factor is light
6.4. Investigation of Carbon Dioxide
Take two de-starched potted plants.
Cover both the plants with bell jars and label them A and
B.
Inside A, keep N aHC O3 (Sodium Bicarbonate). It
Increasing the amount of light
after a certain point does not
affect the rate (c)
The limiting factor is now
carbon dioxide or
temperature
​
produces C O2 .
Inside B, keep N aOH (Sodium Hydroxide). It absorbs
C O2 .
Keep both set-ups in the sunlight for at least 6 hours.
Perform the starch test on both plants.
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The leaves of Plant A will turn black after the starch test
The leaves of Plant B will remain brown after the starch
test
Hydrogencarbonate indicator - measures the carbon dioxide
concentration
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6.6. Leaf Structure
Most dicotyledonous plant leaves have a large surface area
and are thin.
Cuticle: the waxy layer that prevents water loss from the
top of the leaf
Upper/Lower Epidermis: transparent cell that allows
sunlight to pass through to the palisade cell
Palisade mesophyll: is found at the top of the cell and
contains many chloroplasts that absorb sunlight.
Spongy mesophyll: irregularly shaped cells which create
air spaces to allow the gaseous exchange to take place;
do not contain many chloroplasts
Vascular Bundles: made up of xylem and phloem
Xylem: vessel which transports water and dissolved
minerals and has lignified walls made of cellulose
Phloem: vessel which transports nutrients
Stomata: little holes that open and close to allow the
gaseous exchange to occur. The stomata are close to
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prevent water loss and open to letting gases in and out.
When guard cells lose water, the stoma close (at night),
while the stoma opens when guard cells gain water &
swell (during the day).
Nutrients
Uses
Calcium
Development and maintenance of
strong bones and teeth
Iron
Making haemoglobin
Fibre (Roughage)
Provides bulk for faeces, helps
peristalsis
Water
Chemical reactions, solvent for
transport
7.3. Deficiencies
Vitamin C: Scurvy; loss of teeth, pale skin & sunken eyes
Calcium/Vitamin D: Rickets, Osteoporosis; weak bones
and teeth
7.4. Human Alimentary Canal
6.7. Mineral Requirements
Nitrate ions
Magnesium ions
Making amino acids
Making chlorophyll
Deficiency: small plant due to
Deficiency: plant lacks
slow/stunted growth
chlorophyll, leaves turn yellow
You need to know the purpose of these required nutrients
.
7. Human Nutrition
Balanced Diet: A diet containing proper proportions of
carbohydrates, fats, proteins, vitamins, minerals and water to
maintain good health and metabolism.
Diet-related to age/gender/lifestyle:
Children Below 12: Require more calcium
Teenagers: Highest calorie intake
Adults: Balanced meal with fewer calories
Pregnant Women: more iron, calcium
Males: Generally, require more energy
7.2. Importance of Dietary Sources
Nutrients
Uses
Carbohydrates
Energy
Fats and oils
Source of energy, building materials,
energy store, insulation, buoyancy,
making hormones
Proteins
Energy, building materials, enzymes,
haemoglobin, structural material
(muscle), hormones, antibodies
Vitamin C
Collagen, resistance to diseases
Vitamin D
Absorption of calcium
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Functions of the Organs
Ingestion: taking substances (e.g. food, drink) into the
body through the mouth.
Physical Digestion: breakdown of food into smaller pieces
without chemical change.
It increases the surface area of food for the action of
enzymes in chemical digestion.
Chemical Digestion: breakdown of large, insoluble food
molecules into small, soluble molecules.
Absorption: the movement of nutrients from the intestines
into the blood
Assimilation: uptake and use of nutrients by cells
Egestion: the removal of undigested food from the body
as faeces
Main Organs in the Alimentary Canal
Mouth: contains teeth used for mechanical digestion, an
area where food is mixed with salivary amylase & where
ingestion takes place
Salivary glands: produce saliva, which contains amylase
and helps food slide down oesophagus
Oesophagus: tube-shaped organ which uses peristalsis
(circular muscle contract and relax) to transport food
from mouth to stomach
Stomach: has pepsin (a protease) to break down proteins
into amino acids and kills bacteria with hydrochloric acid.
They also have elastic walls.
Small intestine: tube-shaped organ composed of two
parts the:
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Duodenum: fats are emulsified by bile and digested by
pancreatic lipase to form fatty acids and glycerol.
Pancreatic amylase and trypsin (a protease) break
down starch.
Ileum: Maltase breaks down maltose to glucose. This
is where absorption takes place, adapted by having
villi and microvilli.
Pancreas: produces amylase, trypsin and lipase.
Liver: produces bile (emulsifies fats, neutralises acidic fat
molecules), deamination and makes urea to be sent to the
kidney. Also, site of the breakdown of alcohol and other
toxins.
Gall bladder: stores bile from the liver
Large intestine: tube-shaped organ composed of two
parts:
Colon: organ for absorption of minerals and vitamins
and reabsorbing water from waste to maintain the
body’s water levels
Rectum: where faeces are temporarily stored
Anus: a ring of muscle which controls when faeces is
released.
Appendix: is not part of the syllabus, so it doesn’t need to
be known.
7.5. Teeth
Incisors
Canines
Premolars
Molars
Dentine: calcium salts deposited on a framework of
collagen fibres
Nerves
Blood vessels
7.7. Chemical Digestion
Where enzymes are used to break down large insoluble
substances such as proteins into smaller soluble
substances like amino acids so that they can be absorbed.
Amylase: breaks down starch into maltose; it is produced
in the pancreas (but also in the salivary gland)
Maltase: breaks down into glucose in the membrane of
the epithelium lining in small intestines.
Protease: breaks down proteins into peptides (done by
pepsin-acidic) and then into amino acids (done by trypsin).
Pepsin comes from the stomach and trypsin from the
pancreas (alkali).
Lipase: breaks down lipids into fatty acids and glycerol,
produced by the pancreas.
Hydrochloric acid in gastric juice:
Denaturing enzymes in harmful microorganisms
Giving the optimum pH for pepsin activity
Kills pathogens
Bile: an alkaline mixture that neutralises the acidic
mixture of food and gastric juices entering the duodenum
from the stomach to provide a suitable pH for enzyme
action.
7.8. Absorption & Villus
Absorption: the movement of nutrients from the intestines
into the blood
Blunt for
Blunt chewing
Rectangular
chewing and
Sharp-pointed
and grinding.
shape, sharp
grinding, one
for piercing
Two or three
for cutting and
or two roots,
and tearing
roots, ridges
biting
ridges at the
at the end
end
7.6. Structure of a Tooth
Our teeth are embedded in bone and the gums
Enamel: the strongest tissue in the body made from
calcium salts
Cement: helps to anchor tooth
Pulp: contains tooth-producing cells, blood vessels, and
nerve endings which detect pain.
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The small intestine is the region for absorption of
digested food.
The small intestine is folded into many villi, increasing the
surface area for absorption. One villus will have tiny folds
on the cells on its outside called microvilli.
More surface area means more absorption of nutrients
can happen.
Lacteals: absorbs fatty acid and glycerol
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Capillaries: provide a better blood supply
Most water is absorbed from the small intestine, and
some from the colon (large intestine).
8.2. Root Hair Cell
The small intestine absorbs 5–10 dm3 per day
The colon absorbs 0.3–0.5 dm3 per day
8. Transport in Plants
Functions of Xylem
transport water and mineral ions, and support
Functions of Phloem
transport sucrose and amino acids
Adaptations of Xylem
Function: to absorb water and minerals from the soil
They have an elongated shape for a larger surface area,
which increases water absorption rate by osmosis and
ions by active transport.
8.3. Pathway Taken by Water
The large surface area of root hairs is important as it
increases the uptake of water and mineral ions.
1. thick walls with lignin
2. no cell contents
3. cells joined end to end with no cross walls to form a
long continuous tube
Water enters root hair cells from moist soil via osmosis
because water potential is higher in soil than in the
cytoplasm.
Then it enters into the root cortex cells, xylem, and lastly,
the mesophyll cells.
8.4. Transpiration
Transpiration: loss of water vapour from leaves, and it
evaporates from the surface of the mesophyll cells into the
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air spaces and diffuses out of the leaves through the stomata.
Caused by water loss in leaves which lowers their water
potential
Water moves from the xylem to leaf tissues via osmosis
Water moves up the stem in the xylem due to tension
(because of the cohesion of water molecules to each
other) caused by water loss from the leaves
Ends with the gain of water through roots
This upwards flow of water is called the transpiration
stream
8.6. Factors Affecting Rate of
Transpiration
\n
Water leaves mesophyll cells into air spaces created by
an irregular shape of spongy mesophyll cells, then
diffuses out of the stomata.
Water vapour loss is due to the large internal surface
area provided by the interconnecting air spaces between
mesophyll cells and the size and number of stomata
Water moves upwards in the xylem in terms of a
transpiration pull that draws up a column of water
molecules held together by forces of attraction between
water molecules
Wilting
occurs if water loss is greater than water uptake – cells
become flaccid, tissues become limp, and plants are no
longer supported
Temperature: Higher temperatures increase the waterholding capacity of air and increase the transpiration rate
Humidity: Low humidity increases the water potential
gradient between the leaf and the atmosphere hence
increasing the transpiration rate
Wind speed: Removing water molecules to maintain a
steep concentration gradient
8.7. Translocation
Translocation: Movement of sucrose and amino acids in the
phloem; from regions of production (sources) to regions of
storage or regions of utilization in respiration or growth
(sinks).
Translocation in different seasons:
Spring: sucrose transported from stores in roots to
leaves
Summer & early autumn: sucrose goes from
photosynthesizing leaves to root stores,
Below is a picture of a girdle in a tree trunk.
Investigating Transpiration
A potometer is used to measure the rate of water uptake
However, it may not be accurate as some water is used
for photosynthesis.
8.5. Uptake of Water
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9. Transport in Animals
Circulatory system: a system of tubes (veins, capillaries,
arteries) with a pump (heart) and valves (in heart and veins)
to ensure a one-way flow of blood.
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9.2. Transport Systems
Single circulation system (fish):
Blood flows through the heart once every complete
circuit
Two heart chambers
Blood absorbs oxygen in the gills
Released in body cells, then back to the heart
Right atrium: collect deoxygenated blood & pump it to the
right ventricle
Right ventricle: pumps deoxygenated blood to lungs
Pulmonary artery: carries deoxygenated blood from the
right ventricle to the lungs
Septum: separates the left and right sides of the heart
and keeps deoxygenated and oxygenated blood separate.
Pulmonary vein: carry oxygenated blood from the lungs to
the left atrium
Left atrium: collect oxygenated blood and pump it to the
left ventricle
Left ventricle: pumps oxygenated blood to the body via the
aorta
Aorta: carries oxygenated blood from the left ventricle to
the rest of the body
Atrioventricular and semi-lunar valves: prevent backflow
of blood
Relative Muscle Wall Thickness: Atria < Right Ventricle < Left
Ventricle
9.4. Cardiac Cycle
Double circulation system:
Four heart chambers
Blood passes through the heart twice every complete
circuit
Oxygenated in the lungs, to the heart, to the body, and
back to the heart
Advantages: delivers greater blood flow rate to tissues
around the body as the heart pumps the rich
oxygenated blood to it from the lungs
9.3. The Heart
The mammalian heart contains a systemic and pulmonary
circuit.
Atrial diastole,
Cardiac diastole:
Atrial systole,
ventricular systole:
all chambers are ventricular diastole: after the atria relax,
relaxed, and
atria contract,
the ventricles
blood flows into
pushing blood into
contract, forcing
the heart
the ventricles
blood out of the
heart
Physical activity makes the heart beat faster and more
deeply for increased blood circulation so that more
oxygen and glucose can reach the muscles.
Explain the reasons for changes in pressure seen in arteries
(0610/42/F/M/23)
caused by contraction of muscles (of the heart/ventricle)
pressure increases when the heart / ventricles
contract/pump
pressure decreases when the heart/ventricles relax
9.5. Exercise on Heart Rate
The heart's electrical activity can be monitored by the
electrocardiogram (ECG), pulse rate, stethoscope and
listening to the sounds of the valves closing.
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Physical activity makes the heart beat more quickly and
deeply for increased blood circulation so that more
oxygen and glucose can get to the muscle.
Vessel
Function
Large and wide lumen to
reduce resistance to the
flow of blood
9.6. Coronary Heart Disease
One cell thick wall for
easy diffusion
The coronary arteries are the heart’s blood supply.
The coronary artery becomes blocked, interrupting blood
supply to the heart muscle.
Part of the heart muscle stops contracting, causing a
heart attack
Risk factors are diet, lack of exercise, stress, smoking,
genetic predisposition, age and sex
Can be prevented by not smoking, avoiding fatty food (a
good diet) and exercising regularly
Structure
Capillaries
Allow substances to
diffuse into cells
Highly branched; large
surface area
Capillary beds
constantly supplied with
fresh blood, so diffusion
occurs
Major Blood Vessels
Heart: Vena Cava, Aorta, Pulmonary Arteries & Vein
Lungs: Pulmonary Arteries & Veins
Kidney: Renal Arteries & Veins
Liver: Hepatic Artery, Hepatic Veins and Hepatic Portal vein
Arterioles and Venules
The vessels that connect arteries to capillaries are called
arterioles
The vessels that connect capillaries to veins are called
venules
9.8. Blood
Arteries, Veins and Capillaries
9.7. Structural Adaptations of Vessels
Vessel
Arteries
Function
Structure
Elastic tissue walls
stretch and relax as
blood is forced out;
causes pulse
Transport high-pressure
blood away from heart Thick walls to withstand
high pressure
Small lumen maintains
(high) blood pressure.
Veins
Red blood cells: haemoglobin and oxygen transport (oxyhaemoglobin)
White blood cells: phagocytosis and antibody production
Platelets: allows blood clotting
Plasma: transport of blood cells, ions, nutrients, urea,
hormones and carbon dioxide (mostly water and
dissolved substances)
Transport low pressure Valves prevent backflow
blood to the heart
of blood.
Blood is at low pressure,
but nearby muscles
squeeze veins and help
push blood to the heart
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9.9. White Blood Cells
Phagocyte
Lymphocyte
Phagocyte has lobed/irregular
Lymphocytes have a circular
C-shaped nucleus and
nucleus and are found in
vesicles containing digestive
blood
enzymes.
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Phagocyte
Lymphocyte
Phagocytosis: engulf
pathogen, vesicles fuse with
the vacuole, enzymes digest
bacteria.
Large nucleus/small
cytoplasm, and they produce
antibodies,
Antigens:
protein/carbohydrate on the Antibodies: Y-shaped proteins
surface of the pathogen which
bind to label pathogens.
provokes the immune system
Then either destroyed by
being ingested by phagocytes
or the antibodies do it.
9.10. Blood Clotting
Reduces blood loss and keeps pathogens out
Fibrinogen (inactive) turns to fibrin (activated), forms a
mesh to trap red blood cells, and eventually dries to form
a scab.
10. Diseases and Immunity
10.1. Pathogens
Pathogen: a disease-causing organism.
Transmissible disease: a disease in which the pathogen
can be passed from one host to another.
The pathogen for a transmissible disease may be
transmitted either:
Direct contact e.g. through blood, body fluids
Indirect contact e.g. contaminated surfaces/food, from
animals, from air
10.2. Body Defences
The human body has many natural defences against
pathogens.
Mechanical barriers:
Nostrils contain hairs that help trap dust
The skin has a thick outer layer of dead cells
Chemical barriers:
Sticky mucus which can trap pathogens
In the stomach, hydrochloric acid is secreted, which
kills many of the bacteria in food
Cells: Pathogens that manage to get through all these
defences are usually destroyed by white blood cells:
Some of these cells take in and digest the pathogens
by phagocytosis
Others produce antibodies that incapacitate or kill the
pathogen
Vaccination against disease helps antibodies to
produce very quickly
10.3. Ways of Controlling the Spread of
Diseases
a clean water supply
hygienic food preparation
good personal hygiene
waste disposal
sewage treatment
10.4. The Immune System
An antibody is a protein molecule which fits into another
molecule
Pathogen molecules are called antigens.
To destroy a pathogen, antibody molecules must be made
which are exactly the right shape to fit into molecules
(antigens) outside the pathogen.
Antibodies lock onto antigens leading to the destruction of
pathogens/marking of pathogens for destruction by
phagocytes
If a pathogen enters the body, it meets many
lymphocytes. One of these will recognise the pathogen
and divide rapidly by mitosis
These lymphocytes then secrete antibodies, destroying the
pathogens
Active immunity: defence against a pathogen by antibody
production in the body.
Active immunity is gained after infection by a pathogen or
by vaccination.
Vaccines immunise children against diseases caused by
pathogens
Process of vaccination:
Harmless pathogen given which has antigens by
injection
Antigens trigger an immune response by lymphocytes
which produce antibodies
Memory cells are produced that give long-term
immunity
Passive immunity - short-term defences against a pathogen
by antibodies acquired from another individual.
Memory cells are NOT produced in passive immunity
Babies get passive immunity by breastfeeding.
Breast milk contains antibodies from the mother,
which are passed on to her baby.
Useful because a young baby’s immune system is not
well developed; the mother’s antibodies can protect it
against any diseases.
Some diseases are caused by the immune system
targeting and destroying body cells (Auto-immune
disease)
10.5. Cholera
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Diarrhoea: loss of watery faeces
To cure this is to give oral rehydration therapy
One of these is infectious by a bacterium, “Vibrio chlorae”,
causing cholera.
Cholera is a disease caused by a bacterium transmitted in
contaminated water.
The cholera bacterium produces a toxin that causes the
secretion of chloride ions into the small intestine, causing
lower osmotic water movement into the gut, causing
diarrhoea, dehydration and loss of salts from the blood.
11. Gas Exchange in Humans
11.1. Gas Exchange Surfaces
Properties
Reasons
Thin surface
Short distance to diffuse (one cell
thick)
Large surface area
Many molecules can diffuse at
once/More alveoli
Good ventilation
Regular fresh air supplies keep up
concentration gradients for oxygen
and carbon dioxide.
Good blood supply
Gases can be carried to/from the
cells that need/produce them
11.2. Structure of the Lungs
The lung contains a diaphragm, ribs, intercostal muscles,
larynx, trachea, bronchi, bronchioles, alveoli and associated
capillaries
Cartilage (in the trachea): prevents the trachea from
collapsing during the absence of air and protects it by
keeping it open.
Ribs: to protect vital organs and blood vessels and
expands and contract (and efficient breathing).
Intercostal (internal & external) muscles: situated
between the ribs that create and move the chest wall.
Diaphragm: produces volume and pressure changes in
the thorax leading to the ventilation of the lungs.
Composition of Breathing Dry Air
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Inspired Air
Expired Air
Oxygen
21%
16%
Carbon Dioxide
0.04%
4%
Nitrogen
78%
78%
Water Vapour
Lower
Higher
Test for CO2: Add CO2 through limewater. +ve result =
turns cloudy
11.3. Effect of Physical Activity on
Breathing
Physical activity increases the breathing rate – more
respiration - higher CO2 concentration in the blood
This is measured with a spirometer to produce a
spirogram.
During exercise, tissues respire at a higher rate, the
change in breathing volume and rate helps to keep CO2
concentration and pH at safe levels.
11.4. Breathing
Inspiration
Expiration
External intercostal muscles
contract – pulls ribcage
upwards and outwards
External intercostal muscles
relax – ribcage falls
downwards and inwards
Diaphragm muscles contract Diaphragm muscles relax –
– the diaphragm moves
return to a dome shape, and
downwards, and the volume
the volume of the thorax
of the thorax increases
decreases
Atmospheric Pressure >
Pressure in Thorax
Atmospheric Pressure <
Pressure in Thorax
Air moves into the lungs
Air moves out of the lungs
Internal intercostal muscles: are used in coughing and
sneezing.
Mucus & cilia: goblet cells produce sticky mucus to trap
and eliminate particulate matter and microorganisms.
Ciliated cells have cilia: little hairs which sweep/beat back
and forward in a coordinated way to brush mucus up the
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lungs into the mouth.
12. Respiration
Respiration: Chemical reactions that break down nutrient
molecules in living cells to release energy.
Uses of energy in the body of humans: muscle
contraction, protein synthesis, cell division, active
transport, growth, the passage of nerve impulses and the
maintenance of a constant body temperature.
Respiration involves the action of enzymes in cells to
speed up the reaction.
In the exam, always state that energy is released; it is
NEVER made, produced, or created.
12.2. Aerobic Respiration
Chemical reactions in cells that use oxygen to break down
nutrient molecules to release energy
Glucose + oxygen → carbondioxide + water
C 6 H12 O6 + 6O2 → 6C O2 + 6H2 O
​
​
​
​
​
​
12.3. Anaerobic Respiration
Chemical reactions in cells break down nutrient molecules
to release energy without using oxygen.
In muscles (vigorous exercise):
Aerobic
Anaerobic
Oxygen
Needed
Not needed
Breakdown of
Glucose
Complete
Incomplete
Products
Carbon Dioxide
and Water
Animals: Lactic Acid
& Yeast: Carbon
Dioxide and Ethanol
Amount of Energy
Released
More
Less
13. Excretion in Humans
Excretion: the removal from organisms of toxic materials, the
waste products of metabolism (chemical reactions in cells
including respiration) and substances in excess of
requirements.
Substances should include carbon dioxide (lungs), urea,
excess water and ions (kidney).
The importance of excretion is due to the toxicity of the
urea.
13.2. Function of Liver
The role of the liver is in the assimilation of amino acids by
converting them to proteins.
Glucose → Lactic Acid
In yeast (single-cell fungi):
Glucose → Ethanol + C arbon Dioxide
C 6 H12 O6 → 2C 2 H5 OH + 2C O2
​
​
​
​
​
​
Disadvantages of anaerobic respiration:
Only produces 1/20 of the energy per glucose
molecule that aerobic respiration would
Produces poisonous lactic acid
Lactic acid:
Builds up in muscles and blood during vigorous
exercise
The heart, liver and kidneys need extra oxygen to do
this which causes you to continue breathing heavily
after exercise.
The extra oxygen is called the oxygen debt.
Oxygen Debt is removed by:
continuation of fast heart rate to transport lactic acid
in the blood from the muscles to the liver
continuation of deeper and faster breathing to supply
oxygen for aerobic respiration of lactic acid
aerobic respiration of lactic acid in the liver
12.4. Comparison of Aerobic and
Anaerobic Respiration
Aerobic
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Anaerobic
Deamination is removing the nitrogen-containing part of
amino acids to form urea.
Urea is formed in the liver from excess amino acids.
Alcohol, drugs & hormones are broken down in the liver.
13.3. Function of Kidney
Removal of urea and excess water and the re-absorption
of glucose and some salts
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nephron by active transport. These substances are
reabsorbed back into the blood capillary.
3. Loop of Henlé: this part is permeable to water but not
salt. Water is drawn out of the filtrate in the nephron
by osmosis because of the low water potential of the
medulla tissue fluid.
4. Collecting duct: the remaining substances move
through the second coiled tubule into the collecting
duct, forming urine. The permeability of this part of
the nephron to water is controlled.
14. Coordination and
Response
14.1. Nervous Control in Humans
Cortex: contains Bowman’s capsules and coiled tubules
Ureter: carries urine from the kidney to the bladder
Medulla: has loops of Henlé and collecting ducts
Loop of Henlé: selectively absorbs water/solutes
Collecting ducts: reabsorbs water into blood and stores
wastes until it is passed into the ureter.
Urethra: carrying urine from the bladder to the outside.
Bladder: stores urine
Renal capsule: filters water, glucose, urea and salts from
the blood.
Kidney tubule: reabsorbs 100% of glucose; most of the
water and some salts back into the blood (red), leading to
urea concentration in the urine and loss of excess water
and salts into the tubule.
Renal artery: brings wastes and water from the blood
Renal vein: reabsorbs water and useful molecules and
leaves wastes behind
The mammalian nervous system consists of two parts:
Central nervous system (CNS) consists of the brain
and spinal cord, which are the areas of coordination.
Peripheral nervous system (PNS) comprises nerves
and neurones, which coordinate and regulate body
functions.
Electrical impulses are travelled through the neurones.
The nervous system helps with the coordination and
regulation of body functions.
14.2. Types of Neurones
Nerve impulse: an electrical signal that passes along the
nerve cells called neurones
Motor Neurone:
13.4. Structure of the Kidney
Sensory Neurone:
1. Ultrafiltration: blood from the renal artery enters the
glomerulus. Water, urea, salts and glucose are forced
into the Bowman’s capsule. Blood cells and large
proteins cannot pass through.
2. Selective reabsorption: in the tubule, two-thirds of the
salt and water and all the glucose move out of the
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Relay Neurone:
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Synaptic cleft: the small gap between each pair of
neurones
Inside the neurone’s axon, there are 100s of tiny vacuoles
(vesicles, each containing a chemical called
neurotransmitter)
When an impulse arrives, the vesicles move to the cell
membrane and empty their content into the synaptic cleft.
The neurotransmitter quickly diffuses across the tiny gap
and attaches to receptor molecules in the cell membrane
of the relay neurone.
This can happen because the neurotransmitter
molecules' shape complements the receptor molecule's
shape.
14.3. Simple Reflex Arc
A reflex action automatically and rapidly integrates and
coordinates the stimuli with the responses of effectors
(muscles and glands).
E.g. quickly removing your hand from the hot metal
surface
They involve three neurones: a sensory neurone, a relay
neurone and a motor neurone.
The gap between neurones is called a synapse.
How the simple reflex arc works:
A stimulus affects a receptor (cell or organ that
converts a stimulus into an electrical impulse)
A sensory neurone carries impulses from the receptor
to the CNS
Connector/relay neurone carries impulse slowly
(because it has no myelin sheath) across the spinal
cord
The motor neurone carries impulses from the CNS to
the effector
The effector (either a muscle or a gland) carries out
the response
14.5. The Eye
Sense organ: groups of receptor cells responding to specific
stimuli: light, sound, touch, temperature and chemicals.
Cornea: refracts light
Iris: controls how much light enters the pupil
Lens: focuses light onto the retina
Retina: contains light receptors, some sensitive to light of
different colours (Rods and cones)
Optic nerves: carries impulses to the brain
14.6. Accommodation
Adjusting for near and distant objects.
14.4. Synapses
Synapse: a junction between two neurones, consisting of a
gap across which impulses pass by diffusion of a
neurotransmitter
The synapses ensure that impulses travel in one direction
only.
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Near Object
Distant Object
Ciliary muscles contract
Ciliary muscles relax
Suspensory Ligaments slack Suspensory Ligaments tighten
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Near Object
Distant Object
The lens becomes short and
fat
The lens becomes long and
thin
Distribution of Rods and Cones
Explain why a person cannot focus on distant objects if the
suspensory ligaments become permanently overstretched.
(0610/42/F/M/23)
1. ciliary muscles relax
2. suspensory ligaments can no longer become tight
3. the lens is not stretched/remains wide
4. the angle of refraction remains unchanged
14.7. Pupil Reflex
14.9. Hormones
Adjusting for high and low light intensity
An involuntary response
Low Light Intensity
High Light Intensity
Radial muscles (straight lines)
Circular muscles (circular
contract and become shorter
lines) contract and become
to pull the pupil (black dot),
shorter to reduce pupil size to
making it wider to let more
protect the retina from
light enter to form a clear
bleaching.
image on the retina
14.8. Rods and Cones
Rods
Cones
Provide low detail, black &
Provide detailed, coloured
white images, good for seeing images; they work in high light
in low-intensity light (at night).
intensity.
Packed most tightly around
the edge of the retina, so you
can see things most clearly
when not looking directly at
them.
Most tightly packed at the
retina's center, objects are
seen most clearly when
directly looking at them.
Fovea:
Part of the retina where the receptor cells are pushed
most closely together
Where light is focused when you look straight at an
object
Hormones: A chemical substance produced by a gland and
carried by the blood, altering the activity of one or more
specific target organs.
Endocrine Glands
adrenal glands and adrenaline
pancreas and insulin
testes and testosterone
ovaries and oestrogen
14.10. Adrenaline
A hormone secreted by the adrenal gland.
It increases pulse rate, heart rate and pupil diameter.
Increases blood glucose concentration for respiration.
Adrenaline is secreted, for example, bungee jumping or
riding a rollercoaster.
Gland
Hormone
Adrenal gland Adrenaline
Function
Prepares the body for vigorous
action
Pancreas
Insulin
Reduces the concentration of
glucose in the blood
Testes
Testosterone
Causes the development of
male sexual characteristics
Ovary
Oestrogen
Causes the development of
female sexual characteristics
Pancreas
Glucagon
Increases concentration of
glucose in the blood
14.11. Nervous and Hormonal Systems
Comparison
Nervous system
Endocrine system
Speed of action
Very rapid
Can be slow
Electrical impulses
Nature of message travelling along
nerves
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Chemical
messengers
(hormones)
travelling in the
bloodstream
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Comparison
Nervous system
Endocrine system
Duration of
response
Usually within
seconds
It may take years
(puberty)
Area of response
Example of process
controlled
blood glucose concentration
14.15. Thermoregulation
Localized response
Widespread
(only one area
response (in many
usually)
organs)
Reflexes such as
blinking
Development of the
reproductive
system
14.12. Homeostasis
Homeostasis: The maintenance of a constant internal
environment.
Homeostasis is the control of internal conditions within
set limits.
14.13. Negative Feedback
Feedback controls the production of hormones – the
hormones regulate their own production.
A negative feedback control is when the change in
hormone level acts as a signal to cancel out that change,
so when blood hormone level is low, hormone production
is stimulated, when it is high, it is inhibited.
14.14. Glucoregulation
Blood glucose levels are monitored and controlled by the
pancreas
The pancreas produces and releases different hormones
depending on the blood glucose level
Insulin is released when blood glucose levels are high –
the liver stores excess glucose as glycogen
Glucagon is released when blood glucose levels are low –
the liver converts stored glycogen into glucose and
releases it into the blood
Constant body temperature is maintained by:
Insulation: provided by fatty tissue retains heat. Hairs
become erect to trap warm air by contracting erector
muscles and vice versa.
Vasodilatation: when it is hot, arterioles, which supply
blood to the skin-surface capillaries, dilate (become
wider) to allow more blood near to skin surface to
increase heat loss (face redder)
Vasoconstriction: when it is cold, arterioles, which supply
blood to the skin-surface capillaries, constrict (become
smaller) to allow less blood near to skin surface to
decrease heat loss
Sweating: the water evaporates, giving a cooling effect
Skin receptors: sense heat, and sensory neurons send
impulses to the hypothalamus
Shivering: muscular activity generates heat
Thermoregulatory centre: the hypothalamus controls
corrective mechanisms (e.g. sweating and shivering).
14.16. Tropic Responses
When the control of blood glucose does not work, a
person is said to have diabetes
Type 1 diabetes is caused by the death of the cells that
secrete insulin.
Symptoms: hyperglycaemia (feeling unwell, dry
mouth, blurred vision, and feel thirsty) or
hypoglycaemia (tired, showing confusion and
irrational behaviour)
Treatment: eating little and often and avoiding large
amounts of carbohydrates, injecting insulin to reduce
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Auxin:
Plant hormones or growth substances
Controls tropisms
It is produced by cells at the tip of the roots and shoots
of plants
Gravitropism: a response in which a plant grows towards
(positive) or away (negative) from gravity.
Auxins’ role in gravitropism:
Made in the shoot tip
Then it diffuses through the plant from the shoot tip
CAIE IGCSE BIOLOGY
Auxin is unequally distributed in response to light and
gravity
Auxin stimulates cell elongation
Phototropism: a response in which a plant grows towards
(positive) or away (negative) from the direction light is
coming.
Auxins’ role in phototropism:
If the sun shines on the right side of a plant’s shoot,
auxins accumulate on the dark opposite left side.
Auxins accumulating makes cells on the left side grow
faster than cells on the right.
When the left side of the shoot starts growing faster
than the right side, the shoot will start to bend to the
right side towards sunlight.
15. Drugs
Drugs: Any substance taken into the body that modifies or
affects chemical reactions in the body.
15.2. Antibiotics
Antibiotics work by disrupting the cell wall formation of
the bacteria you are trying to get rid of, but not of human
cells.
Some bacteria are resistant to antibiotics which reduces
the effectiveness of antibiotics
The development of resistant bacteria such as MRSA can
be minimized by limiting antibiotics only when essential
and ensuring treatment is completed.
Antibiotics don’t work on viruses because they do not have
a cell wall and make the host cell perform their tasks.
15.3. Antibiotic-Resistant Bacteria
Antibiotic-resistant bacteria can be reproduced through
natural selection, where it begins from:
The generation time is the time taken for a cell to
divide into 2.
Advantages
Disadvantages
Fast: no need to find mate,
fertilise etc.
No variation/biodiversity
Good characteristics are kept
Harmful genes transferred
Do not need to carry offspring
Overcrowding- fighting for
food
Prone to extinction
16.2. Sexual Reproduction
Sexual reproduction: process involving the fusion of the
nuclei of two gametes (sex cells) to form a zygote and the
production of offspring that are genetically different from
each other
Fertilisation: the fusion of gamete nuclei
Nuclei of gametes are haploid and that the nucleus of a
zygote is diploid
Diploid - Full Set of Chromosomes
Haploid - Half Set of Chromosomes
Advantages
Disadvantages
Produces genetically different
Takes lots of time and energy
offspring
Reduced risk of extinction
Mate required
Energy on improving
appearances or pollen
volume for pollination (plants)
16.3. Sexual Reproduction in Plants
Insect-pollinated, dicotyledonous flowering plant: foxglove
Flowers are the reproductive organ of the plant
Mutation - giving rise to variation
Antibiotics kill bacteria without changing genes
Competition for food space, etc
Reproduce via binary fission
Then alleles are passed on to offspring to reproduce.
16. Reproduction
Wind-pollinated flower structure: grass
16.1. Asexual Reproduction
Asexual Reproduction: the process resulting in the
production of genetically identical offspring from one
parent.
Bacteria:
Reproduce by binary fission, each bacterium divides
into two.
16.4. Functions
Sepal: protect the flower bud.
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Petal: brightly coloured and scented and may have
nectarines which are all used to attract insects, petals in
wind pollinated flowers are tiny, and used for pushing the
bracts (leaf-like structures) apart to expose stamens and
stigma
Anther: has pollen sacs with pollen grains which contain
the male nucleus (male gamete).
Stigma: platform on which pollen grains land
Ovary: hollow chamber, ovules grow from the walls.
16.5. Pollination
Pollination: transfer of pollen grains from the male part of
the plant (anther of stamen) to the female part of the
plant (stigma).
Agents of pollination: insects, birds, mammals, water and
wind
Insect Pollinated
Wind Pollinated
Bright, colourful petals – attract
Dull petals
Sweetly scented
No scent
Contains nectar
No nectaries
A moderate amount of pollen
Huge amount of pollen
Pollen is spiky/sticky
Pollen round and smooth
Another & stigma inside the
flower
Anther & stigma hangs out
Sticky stigma
Feathery stigma
Pollen tube: pollen grain lands on stigma and creates a
tunnel down the style, through the micropyle, to the
ovules.
Ovule - seed
Ovary - fruit
Self-Pollination
the transfer of pollen grains from the anther of a flower to
the stigma of the same flower or a different flower on the
same plant.
Advantages
Disadvantages
Genetically identical
Lack of genetic variation
High chance of successful
pollination
Increases competition
between plants
Fast and saves time
Susceptible to the same
disease
Cross-Pollination
the transfer of pollen grains from the anther of a flower to
the stigma of a flower on a different plant of the same
species.
Advantages
Disadvantages
Increases variation
Reliance on pollinators
Quick to adapt to surroundings
Wastage of pollen
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Advantages
Disadvantages
Less susceptible to diseases
More energy required
16.6. Germination
A process controlled by enzymes
Water: activates enzymes to turn insoluble food stores
into soluble substances, and makes tissues swell so that
the testa splits
Oxygen: enters through the gaps in the testa (along with
water), and is used in aerobic respiration.
Temperature: must be suitable for enzymes to work (at
optimum temperature).
16.7. Sexual Reproduction In Humans
Male reproductive system:
Testes: have many coiled tubes which produce sperm,
and the cells between tubes produce testosterone.
Scrotum: holds testicles
Sperm duct: carries sperm from testicles to urethra.
Prostate gland: makes seminal fluid
Urethra: carries semen from the sperm duct to the tip of
the penis
Penis: male sex organ used to transfer semen to the
female.
Female reproductive system:
CAIE IGCSE BIOLOGY
4. Released once per month containing 23 chromosomes
Features
Functions
Energy storage
Development of zygote
Jelly coat
Changes at fertilisation
16.9. Menstrual Cycle
Ovary: contains follicles that develop into the ova and
produces progesterone and oestrogen
Oviduct (fallopian tube): carries the ovum to the uterus
Uterus (womb): where the fetus develops.
Cervix: neck of the uterus: a strong rigid muscle, moist by
mucus with a small opening
Vagina: receives the penis during intercourse and way out
for baby at birth. Moist tube of muscle, flexible and
secretes mucus
16.8. Adaptive Features of Gametes
Sperm (Male Gamete)
1. Small in size
2. Elongated and streamlined with energy storage
3. Millions in numbers containing 23 chromosomes
Features
Functions
Flagellum
Propels the sperm to swim
Mitochondria
Respiration to release energy
for swimming
Enzymes in the acrosome
Release digestive enzymes to
digest the jelly coat
Egg Cell (Female Gamete)
1. Larger in size
2. Spherical, protein/fat in the cytoplasm
3. Moved with the help of Cillia
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Day 1 to 5:
In the ovary, FSH secreted by the Pituitary Gland to
stimulate the maturation of ONE follicle in the ovary.
In the uterus: the endometrium breaks down;
menstruation
Day 5 to 12:
In the ovary, the follicle keeps maturing
In the uterus, oestrogen is secreted by follicle and the
ovarian tissues to prepare the endometrium
Day 13/14/15:
In the ovary, LH is also secreted by the Pituitary Gland
to trigger the release of the egg from the follicle into
the fallopian tube. Ovulation happens on Day 14.
Day 15 to 28:
CAIE IGCSE BIOLOGY
In the ovary, LH triggers the formation of Corpus
Luteum
In the uterus: progesterone is secreted by Corpus
Luteum to keep endometrium thick, waiting for
possible embryo implants.
Day 28 – Scenario 1: Egg not fertilised
No implantation takes place, the Corpus Luteum
degenerates, causing a lack of progesterone.
This means that endometrium is no longer thick, back
to Day 1
Day 28 – Scenario 2: The egg is fertilised
Implantation occurs.
This makes the hormones keep the Corpus Luteum
maintained which means that progesterone is high.
This keeps the Endometrium thick for pregnancy
The fusion of the nuclei from a male gamete (sperm) and
a female gamete (egg cell).
Development of zygote:
One sperm penetrates
The ovum membrane alters to form a barrier against
sperm
The head of the sperm (male nucleus) approaches
and then fuses with the nucleus of the ovum.
Zygote divides over and over to make a ball of cells
called an embryo.
It implants itself in the nucleus's (implantation) wall,
followed by conception.
Development of fetus: zygote is changed through growth
(mitosis) and development (organization of cells into
tissues and organs)
Umbilical cord: contains the umbilical artery, which
carries deoxygenated blood and waste products from the
fetus to the placenta and the umbilical vein, which carries
oxygenated blood and soluble food from the placenta to
the fetus. (Contains fetus’ blood)
Placenta: organ for exchange of soluble materials such as
foods, wastes and oxygen between mother and fetus;
physical attachment between uterus and fetus. (Contains
mother’s blood)
Amniotic sac: membrane which encloses amniotic fluid,
broken at birth.
Amniotic fluid: protects the fetus against mechanical
shock, drying out and temperature fluctuations
Some pathogens and toxins can pass across the placenta
and affect the fetus.
16.12. Sex Hormones
16.10. Hormones in Menstrual Cycle
Oestrogen is secreted by the ovaries. It stops FSH from
being produced - so that only one egg matures in a cycle,
and it stimulates the pituitary gland to release the
hormone LH.
Progesterone is a hormone secreted by ovaries. It
maintains the lining of the uterus during the middle part
of the menstrual cycle and pregnancy.
Follicle-stimulating hormone (FSH) is secreted by the
pituitary gland. It causes an egg to mature in an ovary and
stimulates ovaries to release the hormone oestrogen.
Luteinizing hormone (LH): is also secreted by the pituitary
gland and causes mature eggs to be released from the
ovary.
16.11. Fertilisation
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Primary sexual characteristics: present during
development in the uterus and are the differences in
reproductive organs etc, between males and females
Secondary sexual characteristics: are the changes that
occur during puberty as children become adolescents
At puberty, the pituitary gland starts to stimulate the
primary sex organs; the testes in males and the ovaries in
females.
Sex hormones – testosterone in males and oestrogen in
females are released into the bloodstream.
They only affect the target organs, which have receptors
which can recognize them.
Causes secondary sexual characteristics such as the
growth of pubic hair and maturation of sexual organs.
16.13. Sexually Transmitted Infections
Human Immunodeficiency virus (HIV) is one example of a
sexually transmitted infection.
Transmission: Intercourse, blood transfusion, organ
transplant or sharing a needle with an infected person
Prevention:
Avoid intercourse with many partners
Use a condom
CAIE IGCSE BIOLOGY
Don’t come in contact with other people’s blood
How it affects the immune system:
Infects and destroys lymphocytes
Decreases the efficiency of the immune system
The body becomes liable to infection by other
pathogens
This may leads to AIDS and dies from infection
17. Inheritance
Inheritance: The transmission of genetic information from
generation to generation.
17.2. Chromosomes, Genes and Proteins
Chromosomes: made of DNA, which contains genetic
information in the form of genes
Gene: a length of DNA that codes for a protein
Allele: an alternative form of a gene
Inheritance of sex in humans is used with X and Y
chromosomes.
Haploid nucleus: a nucleus containing a single set of
unpaired chromosomes (e.g. sperm and egg)
Diploid nucleus: a nucleus containing two sets of
chromosomes (e.g. in body cells)
The sequence of bases in a gene determines the
sequence of amino acids used to make a specific protein.
Different sequences of amino acids give different shapes
to protein molecules.
17.3. DNA & Protein Synthesis
DNA: controls cell function by controlling the production of
proteins, including enzymes, membrane carriers and
receptors for neurotransmitters
DNA has 2 long strands and 4 nucleotides, AT and CG
Protein synthesis has two stages:
Transcription (rewriting the base code of DNA into
bases of RNA)
Translation (using RNA base sequence to build amino
acids into a sequence in a protein)
How proteins are made:
the gene coding for the protein remains in the nucleus
messenger RNA (mRNA) is a copy of a gene
mRNA molecules are made in the nucleus and move
to the cytoplasm
the mRNA passes through ribosomes
the ribosome assembles amino acids into protein
molecules
the specific order of amino acids is determined by the
sequence of bases in the mRNA
All body cells in an organism contain the same genes, but
many genes in a particular cell are not expressed
because the cell only makes the specific proteins it needs
17.4. Mitosis
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The nuclear division giving rise to genetically identical
cells
Mitosis is needed for:
Growth: in animals each tissue provides its own new
cells when they are needed.
Repair of damaged tissues: for example, when you cut
your skin, mitosis provides new cells to cover up cut.
Replacement of worn out cells
Asexual reproduction: in plants
Exact replication of chromosomes occurs before mitosis
During mitosis, the copies of chromosomes separate,
maintaining the chromosome number in each daughter
cell
Stem cells: unspecialized cells that divide by mitosis to
produce daughter cells that can become specialized for
specific functions
17.5. Meiosis
Reduction division in which the chromosome number is
halved from diploid to haploid
Meiosis is involved in the production of gametes
Meiosis results in genetic variation, so the cells produced
are not all genetically identical.
17.6. Monohybrid Inheritance
Genotype: the genetic makeup of an organism in terms of
the alleles present (e.g. Tt or GG)
Phenotype: the observable features of an organism (e.g.
tall plant or green seed)
genotype + environment + random variation → phenotype
Homozygous: having two identical alleles of a particular
gene (e.g. TT or gg). Two identical homozygous individuals
that breed together will be pure-breeding
Heterozygous: having two different alleles of a particular
gene (e.g. Tt or Gg), not pure-breeding
Dominant: an allele that is expressed if it is present (e.g. T
or G)
Recessive: an allele that is only expressed when there is
no dominant allele of the gene present (e.g. t or g)
Pedigree diagrams:
CAIE IGCSE BIOLOGY
IA and IB are co-dominant giving blood group AB or IAIB,
and both dominant to IO.
Sex-linked characteristic: a characteristic in which the
gene responsible is located on a sex chromosome, and
this makes it more common in one sex than in the other
Red-green colour blindness is an example of sex
linkage.
18. Variation & Selection
18.1. Variation
Genetic diagrams:
1:1 Monohybrid Crosses
Variation: differences between individuals of the same
species
Phenotypic variation is caused by both genetic and
environmental factors
Continuous variation results in a range of phenotypes
between two extremes; examples include body length and
body mass
Discontinuous variation results in a limited number of
phenotypes with no intermediates (e.g. you are either
blood group O, A, B or AB, nothing else)
Discontinuous variation is usually caused by genes only,
and continuous variation is caused by both genes and the
environment.
3:1 Monohybrid Crosses
18.2. Genetic Mutation
Mutation is a genetic change.
Gene mutation: a change in the base sequence of DNA
Mutation is the way in which new alleles are formed
Mutation, meiosis, random mating and random
fertilisation are sources of genetic variation in populations
Ionising radiation and some chemicals increase the rate
of mutation
Co-dominance: when both alleles in heterozygous
organisms contribute to the phenotype
There are three alleles for the blood group given by the
symbols IA, IB and IO.
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CAIE IGCSE BIOLOGY
Variation leads to survival of the fittest since the
variations in certain organisms give that organism an
advantage over the others in its species in that area.
The development of strains of antibiotic-resistant bacteria
is an example of natural selection.
The surviving organisms reproduce since they don’t get
eaten up, so variation has caused the species to evolve.
Adaptation is the process of natural selection by which
populations become more suited to their environment
over many generations.
18.5. Artificial Selection
Mutation is a source of variation e.g. in Down’s syndrome,
where a parent’s chromosomes are unevenly distributed
in meiosis. In fertilisation, a zygote with a number of
chromosomes that is not 46 is created (e.g. 23 + 24).
Characteristics: broad forehead, short neck, downwardsloping eyes, short nose and mental retardation.
18.3. Adaptive Features
Adaptive feature: an inherited feature that helps an organism
to survive and reproduce in its environment
Xerophytes: live in deserts where water is scarce, and
evaporation is rapid or in windy habitats. Their features
are:
Deep roots reach the water far underground
Leaves reduced spines with minimum surface area for
transpiration
Shallow spreading roots to collect occasional rain
Rolled leaves, leaf hairs and stomata sunk in pits to
trap moist air
Waxy leaf cuticle, impermeable water
Stomata open at night and closed at midday when
evaporation is highest
E.g. cactus and marram grass
Hydrophytes: live wholly or partly submerged in water.
Their features are:
Leaves are highly divided to create a large surface
area for absorption and photosynthesis
Very little cuticle formation
Lack of xylem tubes, no stomata underside of leaves
Stomata are on the upper surface and have a thick
waxy layer to repel water and to keep the stomata
open and clear
Roots are often reduced, and root hairs are often
absent
18.4. Natural Selection
The greater chance of passing on genes by the bestadapted organisms.
Variation is natural or random changes in all living
organisms.
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It is breeding organisms with valued characteristics
together to try to produce offspring which share those
useful characteristics (selective breeding).
It can be used to produce organisms that are more
economically valued
For example, cows that produce more milk, wheat that is
easier to separate from grain, dogs which have a better
appearance
Selective breeding:
Selecting by humans of individuals with desirable
features
Crossing three individuals to produce the next
generation
Selection of offspring showing the desirable features
Selective breeding by artificial selection is carried out
over many generations to improve crop plants and
domesticated animals.
19. Organisms and their
Environment
19.1. Food Chains and Food Webs
The sun is the principal source of energy input to
biological systems.
Energy flow is NOT a cycle; it starts from the sun, and then
that energy is harnessed by plants which are eaten by
animals which other animals eat.
At each step, energy is lost to the environment.
Food chain: a chart showing the flow of energy (food) from
one organism to the next beginning with a producer, for
example:
Mahogany tree → caterpillar → song bird → hawk
Food web: showing a network of interconnected food
chains.
Energy is transferred between organisms in a food
chain by ingestion
Producer: an organism that makes its organic nutrients,
usually using energy from sunlight through
photosynthesis
CAIE IGCSE BIOLOGY
Consumer: an organism that gets its energy by feeding on
other organisms.
Consumers may be classed as primary, secondary,
tertiary and quaternary according to their position in a
food chain
Herbivore: an animal that gets its energy by eating plants
Carnivore: an animal that gets its energy by eating other
animals
Decomposer: an organism that gets its energy from dead
or waste organic matter (i.e. a saprotroph)
Trophic level: the position of an organism in a food chain,
food web or ecological pyramid.
Primary consumer: eat vegetables
Secondary consumer: eat meat/drink milk
Tertiary consumer: eat a predatory fish, salmon
Food chains usually have fewer than five trophic levels
because energy transfer is inefficient:
Sun produces light, and less than 1% of the energy falls
onto leaves.
Producers ‘fix’ only about 5-8% of that energy because of:
transmission, reflection and incorrect wavelength.
Primary consumers only get between 5-10% because
some parts are indigestible (e.g., cellulose) and do not eat
the whole plant.
Secondary consumer gets between 10-20% because the
animal matter is more digestible & has a higher energy
value.
At each level, heat is lost by respiration.
Humans eating plants is more efficient than humans eating
animals because:
We need only a couple of vegetables to have one meal,
but to have the meat; we must feed the animal a lot of
plant material to get far less meat.
When raising an animal, plants lose energy in the
environment. Then the animal loses energy to the
environment and does not use up all the plant material, so
it is inefficient.
Pyramid of Numbers
Pyramid of Biomass
Carbon is taken from the atmosphere by photosynthesis
(plants)
It is passed on to animals and decomposers by feeding.
It is returned by respiration; in plants, in animals and
being decomposed by microorganisms.
(Fossilisation is NOT needed anymore - 2023-2025 syllabus)
19.3. Nitrogen Cycle
Nitrogen-fixing bacteria provide usable nitrogen for
plants, these may exist in the root nodules where they live
in symbiosis with the plants (nitrogen fixation), or this can
happen because of lightning, or microorganisms provide
them through decomposition.
Nitrifying bacteria convert nitrogen-containing substances
into better nitrogen-containing substances for the plants
(nitrification).
Plants absorb these substances and convert them into
proteins
Death and decay happen at each trophic level leading to
stage one
Denitrifying bacteria carry out denitrification: they convert
nitrogen-containing substances into atmospheric nitrogen
19.4. Population
Shows the number of each
organism in a food chain
Pyramid, which shows the
biomass
When moving up the pyramid,
(number of individuals × their
the number of individuals
individual mass)
decreases
The pyramids of biomass are ALWAYS pyramid-shaped.
19.2. Carbon Cycle
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Population: a group of organisms of one species living in
the same area at the same time.
Community: all of the populations of different species in
an ecosystem.
Ecosystem: a unit containing the community of organisms
and their environment interacting together.
19.5. Factors Affecting the Rate of
Population Growth
CAIE IGCSE BIOLOGY
Food supply: quantity and quality; snails need calcium to
reproduce to make a shell.
Predation: if the predator population falls, the prey
population will rise.
Disease: causes organisms to die, so a high death rate
partly cancels out the birth rate meaning less population
growth, especially if the organism dies before giving birth,
or even population decline.
19.6. Sigmoid Population Growth Curve
20.1. Food Supply
Humans have increased food production because:
Agricultural machinery to use larger areas of land and
improve efficiency
Chemical fertilisers help crops grow better
Insecticides: a type of pesticide that kills insects
Herbicides: a type of pesticide that kills weeds
Selective breeding to improve production by crop plants
and livestock
Large-scale Monoculture: the continuous production of one
type of genetically identical crop.
Lag phase: number of mature, reproducing individuals is
low and they may be widely dispersed
Exponential (Log) phase: exponential growth occurs, the
conditions are ideal and the maximum growth rate is
reached. Limiting factors do not limit growth much.
Stationary phase: limiting factors slow growth as the
population has reached the “carrying capacity” of its
environment; when mortality rate = birth rate, the curve
levels off and fluctuates around this maximum population
size.
Death phase: death rate > birth rate due to lack of food,
competition, etc.
19.7. Human Population Growth
Factors favouring growth
Factors controlling growth
Lower infant mortality
Disease
Higher life expectancy
famine
Better nutrition
War
Better housing
Better sanitation
Medicine
Vaccination
The human population is becoming stable (stagnation)
due to:
better education (particularly for women), so they
work instead of getting married and having children
better living conditions, fewer people die, fewer births
needed
cities, reduced need for physical labour on farms
family planning
But overall, the population is still increasing.
20. Human Influences on
Ecosystems
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Negative Impacts of Large-scale Monoculture
If a natural disaster occurs, the whole crop could be
wiped out.
If pests & diseases attack crops, they could harm them
easily
Using large fields and pesticides reduces the variety
of species. This hinders biodiversity.
When insecticides are used persistently, the pests
may eventually become resistant to them, reducing
their effectiveness
Negative Impacts of Intensive Livestock Production
Welfare issues for the livestock
Diseases can spread easily among them
Waste can pollute land and waterways nearby
20.2. Habitat Destruction
Biodiversity: the number of different species that live in an
area.
Reason for habitat destruction
Increased area for food crop growth, livestock
production and housing
Extraction of natural resources
Freshwater and Marine pollution
By altering food webs, and food chains, humans can have
a negative impact on habitats.
Effects of deforestation
Reduced biodiversity/destroys habitats/extinction
Loss of CO2 fixation, thus increase in CO2, thus global
warming
Soil erosion: tree roots cannot retain soil and go into
rivers making the water dirty & cause blockages, and
the soil becomes less fertile
Flooding: 75% of water is usually absorbed by foliage,
root systems or evaporates. After deforestation, water
accumulates in valleys.
20.3. Pollution
Pollution due to pesticides:
CAIE IGCSE BIOLOGY
Insecticides (kill insects): meant to kill insects which eat
crops, but can kill other, useful insects such as bees which
are pollinators, or by bioaccumulation (the increase in
dose of toxin from one level of the food chain to the next)
Herbicides (kill weeds): can be harmful to animals which
eat the plants
Non-biodegradable plastics:
Choke birds, fish and other animals
Fill up the animals’ stomachs so that they can’t eat food
Collect in rivers, and get in the way of fish
Global Warming:
Increase in average temperature of the Earth
Methane from burping of cows
Started at the same time as humans began burning fossil
fuels
Scientists believe fossil fuels are causing this – not proven
yet
Increase in carbon dioxide and methane concentrations in
the atmosphere cause an enhanced greenhouse effect
the leads to climate change
Eutrophication: when water plants receive too many
nutrients.
Fertilisers put in soil by farmers
Fertilisers with nitrates / detergents with phosphates
leach into rivers and lakes after rain
Water plants grow more than usual
They block sunlight and kill plants underneath
They die and sink to bottom
Bacteria/fungi decompose remains using the O2 and
decreasing the O2 concentration
Fish and other creatures die from oxygen starvation
20.4. Conservation
Sustainable resource: one which is produced as rapidly as it is
removed from the environment so that it does not run out
Some resources can be conserved and managed
sustainably, limited to forests and fish stocks.
1. Forests can be conserved using: education, protected
areas, quotas and replanting.
2. Fish stocks can be conserved using: education, closed
seasons, protected areas, controlled net types and
mesh size, quotas and monitoring.
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Natural resources:
Water: used to grow food, keep it clean, provide power,
control fires, and drink. We get water constantly through
rainfall but we are using up the planet’s fresh water faster
than it can be replenished.
Fossil fuels: need to be conserved as they will soon run
out, they should be therefore replaced with green forms
of energy.
Recycling:
Water: water from sewage can be returned to the
environment for human use by sanitation and sewage
treatment
Paper: sent to special centres where it is pulped to make
raw materials for industry
Plastic: fossil fuels, bottles → fleece clothing
Metal: mining takes a lot of energy, so recycling saves
energy
Species and habitats: need to be conserved because:
Organisms have value in themselves (ethical value)
Value to medicine (new molecules from exotic plants =
new drugs)
Genetic resources are useful to humans as well and are
lost when species disappear (DNA for genetic
engineering)
Each species has its role in its ecosystem; if it is removed,
then the whole ecosystem could collapse
The use of artificial insemination (AI) and in vitro
fertilisation (IVF) in captive breeding programmes
Endangered species:
How they become endangered: climate change, habitat
destruction, hunting, pollution and introduced species
If the population size drops, variation decreases
Endangered species can be conserved by: monitoring and
protecting species and habitats, education, captive
breeding programmes and seed banks
Reasons for conservation programmes include:
reducing extinction
protecting vulnerable environments
maintaining ecosystem functions by nutrient cycling
and resource provision, e.g. food, drugs, fuel and
genes
increase biodiversity
21. Biotechnology & Genetic
Modification
Bacteria are useful in biotechnology and genetic
engineering due to their rapid reproduction rate and their
CAIE IGCSE BIOLOGY
ability to make complex molecules
Lipases: break down stains containing fats and oil
Amylases: break down carbohydrate-based stains, such
as starch
Cellulases: break down cellulose fibres
Lactase:
The enzyme that breaks down lactose (the sugar found in
milk); people can stop making lactase naturally, therefore,
can’t digest lactose. \n
Why are bacteria useful in biotechnology and genetic
modification?
1. few ethical concerns over their manipulation and
growth
2. the presence of plasmids
21.2. Biofuel
Use plants to make sugars which yeast then breaks down
to make ethanol.
This process also uses anaerobic respiration.
Bread Making
Flour, sugar, water and salt are mixed with yeast to make
the dough.
Amylase breaks down some starch to make maltose and
glucose. This is used by yeast in respiration.
The dough is kept warm, moist (28°C). Yeast ferments
sugar making carbon dioxide which creates bubbles, so
bread rises.
Cooking (at 180°C) – kills yeast, evaporates alcohol and
hardens the outer surface.
21.3. Uses of Enzymes
Lactose-free milk production
Lactase made from yeast
Lactase bound to the surface of alginate beads
Milk passed down beads
Lactose is broken down into glucose and galactose
Immobilized enzymes are reused
21.4. Making Penicillin
Pectinase:
Fruit juices are extracted using pectinase (breaks down
pectin)
Pectin helps plant walls stick together
If pectin is broke down, it’s easier to squeeze juice from
the fruit
Extraction of juice from fruit, making juice clear, not
cloudy
Biological Washing powders:
Biological washing powders and liquids contain enzymes
that help remove the stain
The enzymes are coated with a special wax that melts in
the wash releasing the enzyme
Once the stains have been broken down, they are easier
for detergents to remove
Proteases: break down proteins in stains, e.g., grass,
blood
WWW.ZNOTES.ORG
Penicillin: an antibiotic produced by a fungus called
Penicillium.
They require proper temperature, pH, oxygen, nutrient
supply and waste products.
The stainless steel fermentation vessel contains medium
containing sugars and ammonium salts.
Penicillium is added to produce penicillin. They use sugar
for respiration and ammonium salts to make protein and
nucleic acids
CAIE IGCSE BIOLOGY
The fermentation vessel consists of ‘PAWS’
Probes monitor temperature and pH
Air provides oxygen for aerobic respiration in fungus
A water-cooled jacket removes heat to maintain a
temperature of 24°C.
Stirrer keeps the microorganism suspended (allowing
access to nutrients and oxygen) while maintaining an
even temperature.
Filtered to remove fungus and then can be crystallized to
make capsules.
21.5. Genetic Modification
Genetic Modification: changing the genetic material of an
organism by removing, changing or inserting individual genes
Examples of genetic modification:
the insertion of human genes into bacteria to produce
human insulin
the insertion of genes into crop plants to confer
resistance to herbicides
the insertion of genes into crop plants to confer
resistance to insect pests
the insertion of genes into crop plants to provide
additional vitamins
Human Insulin in Bacteria
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Isolation of the DNA making up a human gene using
restriction enzymes, forming sticky ends
Cutting of bacterial plasmid DNA with the same restriction
enzymes, forming complementary sticky ends.
Insertion of human DNA into bacterial plasmid DNA using
DNA ligase to form a recombinant plasmid – insertion of
the plasmid into bacteria.
Replication of bacteria containing recombinant plasmids,
which make human protein as they express the gene
21.6. Genetically Modified Crops
Advantages
Disadvantages
Uniform in shape – easy to
transport/appeal to
consumers
Natural species may die
Growing season shorter
Decrease biodiversity/genetic
diversity
Led to the development of
Drought resistant – less water superweeds – stronger than
GM
Higher yields
No one knows the long-term
effects on humans
Solve global hunger
Expensive seeds
CAIE IGCSE
Biology
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