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UPDATED TO 2023-2028 SYLLABUS

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SUMMARIZED NOTES ON THE THEORY SYLLABUS
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another option until the organism is narrowed down to its

genus and species.
1. Characteristics and
Syllabus 1.2.4: Ensure you can construct and
Classification of Living use dichotomous keys based on identifiable
features
Organisms
1.3. Features of Organisms
By: Zhan Xuan Chong
The Five Kingdoms
1.1. Characteristics of Living Organisms
Animals: Multicellular ingestive heterotrophs (eat living
MRS GREN organisms). Ex: cat, ladybird, newt, etc.
Plants: Multicellular photosynthetic autotrophic (make
Movement: an action by an organism or part of an their food) organism with a cellulose cell wall and
organism causing a change of position or place chloroplasts. Ex: cactus, oak tree.
Respiration: the chemical reactions in cells that break Fungi: Single-celled or multicellular heterotrophic
down nutrient molecules and release energy for organisms with cell walls not made of cellulose, spread by
metabolism spreading spores in moist/dark/warm environments. Most
Sensitivity: the ability to detect and respond to changes in have hyphae and mycelium in structure. Ex: yeast,
the internal or external environment mushrooms.
Growth: a permanent increase in size and dry mass Prokaryotes: Single-celled organisms with no true nucleus
Reproduction: the processes that make more of the same or DNA in the cytoplasm. Many also have plasmids. Ex:
kind of organism E.coli, Salmonella.
Excretion: the removal of the waste products of Protocists: Single-celled organism with a nucleus.
metabolism and substances in excess of requirements Eukaryotes. Some are multicellular. Ex: Amoeba,
Nutrition: the taking in of materials for energy, growth, seaweed.
and development
Guidance: For this section, learn the five
kingdoms' main features.
1.2. Concept and Uses of Classification
System Main Features of All Animals:

Multicellular
Organisms are classified into groups by the features they
It contains a nucleus but no cell walls or chloroplasts
share.
Only feed on organic substances made by other living
Species are a group of organisms which can reproduce to
things
produce fertile offspring.
Sequence of classification: Kingdom → Phylum → Classes
→ Orders → Families → Genus → Species. 1.4. Vertebrates
Funny acronym: King Philip, Come Over For Mammals
Good Soup Fur/hair on the skin
External ears (pinna)
The Binomial System of Naming Species is an
Internal fertilisation, giving the birth of young
internationally agreed system in which the scientific name Mammary glands
of an organism comprises two parts showing the genus Reptiles
and species. Thick, dry, scaly skin
The format is Genus species. The genus is capitalized, Usually four legs
and the species are not. Internal fertilisation, conception from egg
The classification of organisms helps show the Soft eggs
evolutionary relationships between them. Fish
Scientists also use the DNA base sequence to help Wet scales
classify organisms. Streamlined body shape
The similarity in DNA chains shows how closely related External fertilisation and soft eggs
two organisms are. Uses gills to breathe
Dichotomous keys use visible features to classify Amphibians
organisms. They give you a choice of two features, and Smooth, moist skin
you follow the one that applies: each option leads to External fertilisation and soft eggs

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Gills & Lungs can live on land and water Syllabus 1.3.6: You must be able to classify
Most have four legs organisms using the features identified above
Birds
Feathers on body and scales on legs 1.7. Viruses
Constant internal body temperature
Hard eggs Viruses are not part of any classification system due to
Internal fertilisation, birth through eggs not being considered living things.
They do not carry out the seven life processes for
Syllabus 1.3.3: You must be able to classify
themselves; instead, they take over a host cell’s metabolic
organisms using the features identified above
pathways to make multiple copies of themselves.
Virus structure contains only a genetic material (RNA or
1.5. Arthropods DNA) inside a protein coat.
Example of virus structure below (No mitochondria or
Invertebrates: Organisms that do not have a backbone. ribosomes)
All arthropods have three standard features:

1. Exoskeleton
2. Jointed legs
3. Segmented body

Crustaceans (e.g. crabs)

Have an exoskeleton, one pair of compound eyes
Two body segments – cephalothorax, abdomen
More than four pairs of legs (10-14 legs)
Arachnids: (e.g. spiders)
Two body segments – cephalothorax and abdomen
Four pairs of legs (8 legs)
Myriapods: (e.g. centipedes)
Segmented body
One pair of antennae
10+ pairs of legs – 1 or 2 pairs on each segment
Insects: (e.g. bees) 2. Organisation of the
Three body segments – head, thorax and abdomen
Three pairs of jointed legs (6 legs) Organism
One pair of antennae
1 or 2 pairs of wings 2.1. Cell Structure
1.6. Classification of Plants All living things are made of cells.
New cells are produced by the division of existing cells
In IGCSE Biology, the plant kingdom is classified into ferns All typical cells have:
and flowering plants. Cell membrane: controls movement in and out of cells
Cytoplasm: where chemical reactions take place
Ferns: Nucleus: contains DNA and controls the cell
Do not produce flowers/seeds Mitochondria: where aerobic respiration happens
They are plants with roots, stems and feathery leaves Ribosome: allows protein synthesis
Reproduce by spores A typical animal cell (e.g., the liver cell) has all of the
Flowering plants: above
They are plants with roots, stems and leaves Plant cells especially also have:
Reproduce sexually by means of flowers and seeds Vacuole: cell sap to keep cell turgid
Seeds are produced inside the ovary in the flower Cell wall: rigid to keep the shape of the cell,
strengthens the cell
Monocotyledons Dicotyledons
Chloroplasts: contain chlorophyll, which absorbs light
One cotyledon/One-seed leaf Two cotyledons/Two-seed leaf energy for photosynthesis
Parallel veins Branching veins A typical plant cell (e.g., the palisade cell) has everything
Long Narrow Leaf Broad leaves above.
3 Flower Parts 4 or 5 Flower Parts
Scattered Vascular Bundles Ringed Vascular Bundles

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size of drawing image I

M agnification = = =
size of specimen actual
​ ​ ​

A
Other Forms in Magnification Formula

Actual size = image size / magnification

Image size = magnification x actual size

Unit Conversions (μm - micrometre)

1cm = 10mm
1mm = 1000μm

Prokaryotes DO NOT have mitochondria and a true nucleus! Magnification does NOT have any units (‘x 50’ or ‘x 5000’)

A bacterial cell only contains a cell wall, cell membrane,

cytoplasm, ribosomes, circular DNA, and plasmids. 3. Movement In and Out of
Cells
3.1. Diffusion
Diffusion: 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.

Syllabus 2.1.3: You must be able to identify the

cell structures in diagrams and images of
plant, animal and bacterial cells

2.2. Levels of Organisation

The division of existing cells produces new cells.
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 Energy for diffusion comes from the kinetic energy of
specific function random movement of molecules and ions.
Organ system: Group of organs with related functions The diffusion of gases and solutes is important as without
working together to perform body functions. it, molecules that are needed for life, for example, glucose
and oxygen for respiration, would not be able to get to the
Specialised Cells Specific Function places they are required.
Movement of mucus in the Some substances move into and out of cells by diffusion
Ciliated cells
trachea and bronchi through the cell membrane
Root Hair cells Absorption
Factors that influence diffusion:
Palisade Mesophyll cell Undergo photosynthesis
Conduction of electrical Concentration gradient
Neurones
impulses Temperature
Red Blood cells Transport of oxygen Surface area
Distance
Sperm and Egg cells
For reproduction
(gametes)
3.2. Osmosis
2.3. Size of Specimens

fd

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Osmosis: 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.

3.3. Active Transport

The role of water as a solvent in organisms to aid with
digestion, excretion, and transport
Active Transport: Movement of particles through a cell
Water moves into and out of cells by osmosis through the
membrane from a lower concentration region to a higher
cell membrane
concentration region (i.e., against a concentration gradient),
The concentration of solute outside the cell =
using energy from respiration.
concentration inside the cell → no change in size
The concentration of solute outside the cell > Carrier proteins are also used during active transport.
concentration inside the cell → cell shrinks
(Flaccid/Plasmolysis)
The concentration of solute outside the cell <
concentration inside the 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. It is embedded in the cell membrane to pick up specific
Decreasing solute concentration inside of the cell causes molecules and take them through the cell membrane
the cell to become flaccid, losing water, and the vacuole against their concentration gradient.
gets smaller. The cell body shrinks, pulling away from the Active transport is needed when an organism wants to
cell wall. optimise the nutrients it can take up - ion uptake by root
Plants are supported by the water pressure inside the hair cells.
cells pressing outwards on the cell wall.

4. Biological Molecules
4.1. Biological Molecules
Carbohydrates: made from Carbon, Hydrogen and
Oxygen (CHO)
Fats and oils: made from Carbon, Hydrogen and Oxygen
(CHO)
Dialysis Tubing Experiment 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 Proteins

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4.2. Food Tests 5. Enzymes

Starch: Add a few drops of iodine solution (+ve result =
blue-black colour, -ve result = remains brown) 5.1. Enzymes
Reducing sugars: Add Benedict’s solution, then the
mixture is heated in a water bath for 2 to 3 minutes Catalyst: a substance that speeds up a chemical reaction
(70°C). (+ve result = brick-red precipitate, -ve result = and is not changed by the reaction
remains blue) Enzymes: proteins that are involved in all metabolic
Proteins: Add a few drops of Biuret solution, +ve result = reactions, where they function as biological catalysts.
purple/lilac colour Enzyme lowers the activation energy needed for a
Fats and oils: Ethanol Emulsion test; ethanol is added to reaction to take place.
the mixture, poured into a test tube with an equal amount It is essential in all living organisms regarding the reaction
of distilled water, then shaken, +ve result = milky-white rate necessary to sustain life.
emulsion. Enzymes are unchanged and can be reused
Vitamin C: Decolourisation of DCPIP shows that vitamin C
is probably present. Lock and Key Model

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.
4.3. Structure of a DNA
5.2. Temperature on Enzymes
Chromosomes are made of a molecule called DNA
DNA is also called deoxyribonucleic acid. Enzymes have an optimum temperature: the temperature
at which they work best, giving the fastest reaction ≈ at
37°C in animals & human bodies.
When temperature increases, molecules move faster,
more effectively, and frequently collide.
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 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.

Each chromosome is a very long molecule of tightly coiled

DNA 5.3. pH on Enzymes
Two strands coiled together to form a double helix
Each strand contains chemicals called bases Enzymes are sensitive to pH.
Cross-links between strands are formed by pairs of bases Some enzymes work best in an acid, and others in an
The bases always pair up in the same way: alkaline.
A and T Enzymes work best at their optimum pH.
C and G 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.

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Pepsin in acidic conditions, Amylase in neutral conditions The leaf is placed on a white tile, and iodine is added. If
and trypsin in alkalinity conditions. starch is present, the colour will be blue-black; if absent, it
will remain brown.
5.4. Graphs for Changes in Enzyme
Activity
Effect of Temperature Effect of pH

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
6. Plant Nutrition Remove the stencil and test for starch
+ve result = parts which received light turn blue-black
6.1. Photosynthesis -ve result = parts which didn’t receive light remains brown

Photosynthesis: the process by which plants manufacture

carbohydrates from raw materials using energy from light.
light+chlorophyll
C arbonDioxide + Water ​
Glucose + Oxygen
light+cholorophyll
6C O2 + 6H2 O
​ ​ ​ +C 6 H12 O6 + 6O2
​ ​ ​ ​

The carbon dioxide diffuses through the open stomata of

a plant leaf, and water is taken up through the roots. 6.4. Investigation of Carbon Dioxide
Chlorophyll is a green dye that traps light energy and
converts it into chemical energy to form carbohydrates Take two de-starched potted plants.
and their subsequent storage. Cover both the plants with bell jars and label them A and
Glucose is used for respiration, energy storage, cellulose B.
cell walls, and making proteins and sugars. Inside A, keep N aHC O3 (Sodium Bicarbonate). It
​

produces C O2 . ​

Use and Storage of the Carbohydrates Made in Inside B, keep N aOH (Sodium Hydroxide). It absorbs
Photosynthesis C O2 .
​

Keep both set-ups in the sunlight for at least 6 hours.

starch as an energy store
Perform the starch test on both plants.
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. The leaves of Plant A will turn black after the starch test
De-starch the plant by keeping it in complete darkness for The leaves of Plant B will remain brown after the starch
about 48 hours. test
Expose the plant to sunlight for a few days.
Hydrogencarbonate indicator - measures the carbon dioxide
Leaf boiled in water for 2 minutes to break down cell
concentration
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

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prevent water loss and open to letting gases in and out.

When guard cells lose water, the stoma closes (at night),
while the stoma opens when guard cells gain water &
swell (during the day).

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 Syllabus 6.2.3: You must be able to explain how
increases, the rate of the structures above adapt leaves for
photosynthesis increases (a- photosynthesis
b)
The limiting factor is light 6.7. Mineral Requirements
Increasing the amount of light
after a certain point does not Nitrate ions Magnesium ions
affect the rate (c) Making amino acids Making chlorophyll
The limiting factor is now Deficiency: small plant due to Deficiency: plant lacks
carbon dioxide or slow/stunted growth chlorophyll, leaves turn yellow
temperature
Tip! You need to know the purpose of these
6.6. Leaf Structure required nutrients.

Most dicotyledonous plant leaves have a large surface area

and are thin. 7. Human Nutrition
7.1. Diet
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:
Cuticle: the waxy layer that prevents water loss from the Children Below 12: Require more calcium
top of the leaf Teenagers: Highest calorie intake
Upper/Lower Epidermis: transparent cell that allows Adults: Balanced meal with fewer calories
sunlight to pass through to the palisade cell Pregnant Women: more iron, calcium
Palisade mesophyll: is found at the top of the cell and Males: Generally, require more energy
contains many chloroplasts that absorb sunlight.
Spongy mesophyll: irregularly shaped cells that create air 7.2. Nutrition
spaces to allow the gaseous exchange to take place; do
not contain many chloroplasts Nutrients Uses
Vascular Bundles: made up of xylem and phloem
Carbohydrates Energy
Xylem: vessel which transports water and dissolved
minerals and has lignified walls made of cellulose Source of energy, building materials,
Phloem: a vessel that transports nutrients Fats and oils energy store, insulation, buoyancy,
Stomata: little holes that open and close to allow the making hormones
gaseous exchange to occur. The stomata are close to

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Nutrients Uses Stomach: has pepsin (a protease) to break down proteins

Energy, building materials, enzymes, into amino acids and kills bacteria with hydrochloric acid.
Proteins haemoglobin, structural material They also have elastic walls.
(muscle), hormones, antibodies Small intestine: tube-shaped organ composed of two
parts:
Vitamin C Collagen, resistance to diseases
Duodenum: fats are emulsified by bile and digested by
Vitamin D Absorption of calcium pancreatic lipase to form fatty acids and glycerol.
Development and maintenance of Pancreatic amylase and trypsin (a protease) break
Calcium
strong bones and teeth down starch.
Iron Making haemoglobin Ileum: Maltase breaks down maltose to glucose. This
Provides bulk for faeces, helps is where absorption takes place, adapted by having
Fibre (Roughage) villi and microvilli.
peristalsis
Pancreas: produces amylase, trypsin and lipase.
Chemical reactions, solvent for
Water Liver: produces bile (emulsifies fats, neutralises acidic fat
transport
molecules), deamination and makes urea to be sent to the
kidney. Also, it is the site of the breakdown of alcohol and
7.3. Deficiencies other toxins.
Gall bladder: stores bile from the liver
Vitamin C: Scurvy; loss of teeth, pale skin & sunken eyes Large intestine: tube-shaped organ composed of two
Calcium/Vitamin D: Rickets, Osteoporosis; weak bones parts:
and teeth Colon: organ for absorption of minerals and vitamins
and reabsorbing water from waste to maintain the
7.4. Digestive System body’s water levels
Rectum: where faeces are temporarily stored
Anus: a ring of muscle that controls when faeces is
released.
Appendix: is not part of the syllabus, so it doesn’t need to
be known.

7.5. Teeth

Process of Digestion Incisors Canines Premolars Molars

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 Blunt for
Blunt chewing
molecules into small, soluble molecules. Rectangular chewing and
Sharp-pointed and grinding.
Absorption: the movement of nutrients from the intestines shape, sharp grinding, one
for piercing Two or three
into the blood for cutting and or two roots,
and tearing roots, ridges
Assimilation: uptake and use of nutrients by cells biting ridges at the
at the end
Egestion: the removal of undigested food from the body end
as faeces
Structure of Tooth
Main Organs in the Alimentary Canal
Our teeth are embedded in bone, and the gums
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 the oesophagus
Oesophagus: tube-shaped organ that uses peristalsis
(circular muscle contract and relax) to transport food
from mouth to stomach

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Enamel: the strongest tissue in the body made from The small intestine is folded into many villi, increasing the
calcium salts surface area for absorption. One villus will have tiny folds
Cement: helps to anchor tooth on the cells on its outside called microvilli.
Pulp: contains tooth-producing cells, blood vessels, and More surface area means more absorption of nutrients
nerve endings which detect pain. can happen.
Dentine: calcium salts deposited on a framework of Lacteals: absorbs fatty acid and glycerol
collagen fibres Capillaries: provide a better blood supply
Nerves Most water is absorbed from the small intestine, and
Blood vessels some from the colon (large intestine).

7.6. Chemical Digestion 8. Transport in Plants

Chemical Digestion: Enzymes are used to break down large
insoluble substances, such as proteins, into smaller soluble 8.1. Xylem and Phloem
substances, like amino acids so that they can be absorbed.
Functions of Xylem
Amylase: breaks down starch into maltose; it is produced
in the pancreas (but also in the salivary gland) transport water and mineral ions, and support
Maltase: breaks down into glucose in the membrane of
the epithelium lining in small intestines. Functions of Phloem
Protease: breaks down proteins into peptides (done by
transport sucrose and amino acids
pepsin-acidic) and then into amino acids (done by trypsin).
Pepsin comes from the stomach and trypsin comes from Adaptations of Xylem
the pancreas (alkali).
Lipase: breaks down lipids into fatty acids and glycerol, 1. thick walls with lignin (details of lignification are not
produced by the pancreas. required)
Hydrochloric acid in gastric juice: 2. no cell contents
Denaturing enzymes in harmful microorganisms 3. cells joined end to end with no cross walls to form a
Giving the optimum pH for pepsin activity long, continuous tube
Kills pathogens
Bile: an alkaline mixture that neutralises the acid mixture
of food and gastric juices entering the duodenum from
the stomach to provide a suitable pH for enzyme action.

7.7. Absorption & Villus

Absorption: the movement of nutrients from the intestines
into the blood

Syllabus 8.1.2: You must be able to identify in diagrams and

images the position of the xylem and phloem as seen in
sections of roots, stems, and leaves of non-woody
dicotyledonous plants

8.2. Water Uptake

Root Hair Cells

Function: to absorb water and minerals from the soil

They have an elongated shape for a larger surface area,
which increases the water absorption rate by osmosis and
ions by active transport.

The large surface area of root hairs is important as it

The small intestine is the region for absorption of increases the uptake of water and mineral ions.
digested food.

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Factors affecting Rate of Transpiration

Temperature: Higher temperatures increase the water-

holding 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

8.4. Translocation
Translocation: Movement of sucrose and amino acids in the
phloem from regions of production (sources) to regions of
storage or regions of utilisation in respiration or growth
Water enters root hair cells from moist soil via osmosis (sinks).
because water potential is higher in soil than in the
cytoplasm. Translocation in different seasons:
Then it enters into the root cortex cells, xylem, and lastly, Spring: sucrose transported from stores in roots to
the mesophyll cells. leaves
Summer & early autumn: sucrose goes from
photosynthesizing leaves to root stores,
8.3. Transpiration Below is a picture of a girdle in a tree trunk.

Transpiration: loss of water vapour from leaves, and it

evaporates from the surface of the mesophyll cells into the
air spaces and diffuses out of the leaves through the stomata.

Water leaves mesophyll cells into air spaces created by 9. Transport in Animals
an irregular shape of spongy mesophyll cells, then
diffuses out of the stomata.
Water vapour loss is due to the large internal surface 9.1. Circulatory Systems
area provided by the interconnecting air spaces between
mesophyll cells and the size and number of stomata. Circulatory System: a system of tubes (veins, capillaries,
arteries) with a pump (heart) and valves (in heart and veins)
Water moves upwards in the xylem in terms of a
to ensure a one-way flow of blood.
transpiration pull that draws up a column of water
molecules held together by forces of attraction between Single circulation system (fish):
water molecules. Blood flows through the heart once every complete
circuit
Wilting Two heart chambers (Atrium and Ventricle)
Blood absorbs oxygen in the gills
Wilting: occurs if water loss is greater than water uptake –
Released in body cells, then back to the heart
cells become flaccid, tissues become limp, and plants are no
Double circulation system:
longer supported
Four heart chambers

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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

9.2. Heart
Atrial diastole,
The mammalian heart contains a systemic and pulmonary Cardiac diastole: Atrial systole, ventricular systole:
circuit. 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.

Exemplar Past Year Question

Right atrium: collect deoxygenated blood & pump it to the Explain the reasons for changes in pressure seen in arteries
right ventricle (0610/42/F/M/23)
Right ventricle: pumps deoxygenated blood to lungs
Pulmonary artery: carries deoxygenated blood from the caused by contraction of muscles (of the heart/ventricle)
right ventricle to the lungs pressure increases when the heart / ventricles
Septum: separates the left and right sides of the heart contract/pump
and keeps deoxygenated and oxygenated blood separate. pressure decreases when the heart/ventricles relax
Pulmonary vein: carry oxygenated blood from the lungs to
the left atrium 9.4. Exercise on Heart Rate
Left atrium: collect oxygenated blood and pump it to the
left ventricle The heart's electrical activity can be monitored by the
Left ventricle: pumps oxygenated blood to the body via the electrocardiogram (ECG), pulse rate, stethoscope and
aorta listening to the sounds of the valves closing.
Aorta: carries oxygenated blood from the left ventricle to Physical activity makes the heart beat more quickly and
the rest of the body deeply for increased blood circulation so that more
Atrioventricular and semi-lunar valves: prevent backflow oxygen and glucose can get to the muscle.
of blood

Relative Muscle Wall Thickness: Atria < Right Ventricle < Left 9.5. Coronary Heart Disease
Ventricle
The coronary arteries are the heart’s blood supply.

9.3. Cardiac Cycle 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
This can be prevented by not smoking, avoiding fatty food
(a good diet) and exercising regularly

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Arterioles and Venules

The vessels that connect arteries to capillaries are called

arterioles
The vessels that connect capillaries to veins are called
venules

9.7. Blood
Red blood cells: biconcave shape, haemoglobin and
oxygen transport (oxy-haemoglobin)
White blood cells: phagocytosis and antibody production
9.6. Blood Vessels Platelets: allows blood clotting
Plasma: transport of blood cells, ions, nutrients, urea,
Vessel Function Structure hormones and carbon dioxide (mostly water and
dissolved substances)
Elastic tissue walls
stretch and relax as Syllabus 9.4.2: You must be able to identify red
blood is forced out; and white blood cells in photomicrographs and
Transport high-pressure causes pulse diagrams
Arteries
blood away from heart Thick walls to withstand
high pressure
Small lumen maintains
(high) blood pressure.
Valves prevent backflow
of blood.
Blood is at low pressure,
White Blood Cells
but nearby muscles
Transport low pressure Phagocyte Lymphocyte
Veins squeeze veins and help
blood to the heart Phagocyte has lobed/irregular
push blood to the heart Lymphocytes have a circular
C-shaped nucleus and
Large and wide lumen to nucleus and are found in
vesicles containing digestive
reduce resistance to the blood
flow of blood enzymes.
Phagocytosis: engulfs
One cell thick wall for Large nucleus/small
pathogen, vesicles fuse with
easy diffusion cytoplasm, and they produce
the vacuole, enzymes digest
Highly branched; large antibodies,
bacteria.
Allow substances to surface area
Capillaries Antigens:
diffuse into cells Capillary beds
protein/carbohydrate on the Antibodies: Y-shaped proteins
constantly supplied with
surface of the pathogen which bind to label pathogens.
fresh blood, so diffusion
provokes the immune system
occurs
Then, it is either destroyed by
being ingested by phagocytes
Major Blood Vessels
or the antibodies.
Heart: Vena Cava, Aorta, Pulmonary Arteries & Vein
Lungs: Pulmonary Arteries and veins Blood Clotting
Kidney: Renal Arteries and veins
Reduces blood loss and keeps pathogens out
Liver: Hepatic Artery, Hepatic Veins and Hepatic Portal vein

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Fibrinogen (inactive) turns to fibrin (activated), forms a To destroy a pathogen, antibody molecules must be made
mesh to trap red blood cells, and eventually dries to form that are exactly the right shape to fit into molecules
a scab. (antigens) outside the pathogen.
Antibodies lock onto antigens, leading to the destruction
of pathogens/marking of pathogens for phagocytes to
10. Diseases and Immunity engulf.
If a pathogen enters the body, it meets many
10.1. Pathogens lymphocytes. One of these will recognise the pathogen
and divide rapidly by mitosis.
Pathogen: a disease-causing organism.
These lymphocytes then secrete antibodies, creating active
Transmissible disease: a disease in which the pathogen
immunity.
can be passed from one host to another.
The pathogen for a transmissible disease may be
Active Immunity
transmitted either:
Direct contact e.g., through blood, body fluids Active Immunity: defence against a pathogen by antibody
Indirect contact e.g., contaminated surfaces/food, production in the body.
from animals, from air
Active Immunity is gained after infection by a pathogen or
by vaccination.
10.2. Body Defences
Vaccines immunise children against diseases caused by
pathogens
The human body has many natural defences against
pathogens. Process of Vaccination:
weakened pathogens or their antigens are put into the
Mechanical barriers: body
Nostrils contain hairs that help trap dust the antigens stimulate an immune response by
The skin has a thick outer layer of dead cells lymphocytes which produce antibodies
Chemical barriers: memory cells are produced that give long-term
Sticky mucus which can trap pathogens immunity
In the stomach, hydrochloric acid is secreted, which
kills many of the bacteria in food Passive Immunity
Cells: Pathogens that manage to get through all these
defences are destroyed by white blood cells: Passive Immunity: short-term defences against a pathogen by
Some of these cells take in and digest the pathogens antibodies acquired from another individual.
by phagocytosis
Memory cells are NOT made in passive Immunity
Others produce antibodies that incapacitate or kill the
Babies get passive immunity by breastfeeding.
pathogen
Breast milk contains antibodies from the mother,
Vaccination against disease helps antibodies to be
which are passed on to her baby.
made very quickly
Useful because a young baby’s immune system is not
well developed; the mother’s antibodies can protect it
Ways of Controlling the Spread of Diseases
against any diseases.
a clean water supply Some diseases are caused by the immune system
hygienic food preparation targeting and destroying body cells (Auto-immune
disease)
good personal hygiene
waste disposal
sewage treatment 10.4. Cholera
Diarrhoea: loss of watery faeces
10.3. Active & Passive Immunity
To cure this, is oral rehydration therapy
Antibody: proteins that bind to antigens leading to the direct One of these is infectious by a bacterium, “Vibrio chlorae”,
destruction of pathogens or marking pathogens for causing cholera.
Cholera is a disease caused by a bacterium transmitted in
destruction by phagocytes.
contaminated water.
Pathogen molecules are called antigens, and they have The cholera bacterium produces a toxin that causes the
specific shapes secretion of chloride ions into the small intestine, causing
Specific antibodies have complementary shapes which fit lower osmotic water movement into the gut, causing
specific antigens diarrhoea, dehydration and loss of salts from the blood.

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Physical activity increases the breathing rate – more

11. Gas Exchange in Humans respiration - and higher CO2 concentration in the blood.
This is measured with a spirometer to produce a
11.1. Gas Exchange Surfaces spirogram.
During exercise, tissues respire at a higher rate; the
change in breathing volume and rate helps keep CO2
Properties Reasons
concentration and pH safe.
Short distance to diffuse (one cell
Thin surface
thick)
Many molecules can diffuse at
11.4. Breathing
Large surface area
once/More alveoli
Inspiration Expiration
Regular fresh air supplies keep up
Good ventilation concentration gradients for oxygen External intercostal muscles External intercostal muscles
and carbon dioxide. contract – pulls ribcage relax – ribcage falls
upwards and outwards downwards and inwards
Gases can be carried to/from the
Good blood supply Diaphragm muscles contract Diaphragm muscles relax –
cells that need/produce them
– the diaphragm moves return to a dome shape, and
downwards, and the volume the volume of the thorax
11.2. Structure of the Lungs of the thorax increases decreases
Atmospheric Pressure > Atmospheric Pressure <
The lung contains a diaphragm, ribs, intercostal muscles,
Pressure in Thorax Pressure in Thorax
larynx, trachea, bronchi, bronchioles, alveoli and associated
capillaries
Air moves into the lungs Air moves out of the lungs

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 expand
and contract (and efficient breathing). Internal intercostal muscles are used in coughing and
Intercostal (internal & external) muscles: situated sneezing.
between the ribs that create and move the chest wall. Mucus & cilia: goblet cells produce sticky mucus to trap
Diaphragm: produces volume and pressure changes in and eliminate particulate matter and microorganisms.
the thorax, leading to the ventilation of the lungs. Ciliated cells have cilia, little hairs which sweep/beat back
and forward in a coordinated way to brush mucus up the
Composition of Breathing Dry Air lungs into the mouth.

Inspired Air Expired Air

Oxygen 21% 16%
12. Respiration
Carbon Dioxide 0.04% 4%
Nitrogen 78% 78% 12.1. Respiration
Water Vapour Lower Higher
Respiration: Chemical reactions that break down nutrient
molecules in living cells to release energy.
Test for CO2: Add CO2 through limewater. +ve result =
turns cloudy Uses of energy in the body of humans: muscle
contraction, protein synthesis, cell division, active
11.3. Physical Activity on Breathing

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transport, growth, the passage of nerve impulses and the

12.4. Comparison of Aerobic and
maintenance of a constant body temperature.
Respiration involves the action of enzymes in cells to Anaerobic Respiration
speed up the reaction.
Aerobic Anaerobic
Effect of Temperature on Respiration in Yeast Oxygen Needed Not needed
Breakdown of
Complete Incomplete
Glucose
Animals: Lactic Acid
Carbon Dioxide
Products & Yeast: Carbon
and Water
Dioxide and Ethanol
Amount of Energy
More Less
Released

13. Excretion in Humans

Exam Tip! In the exam, always state that
energy is released; it is NEVER made, 13.1. Excretion
produced, or created.
Excretion: the removal from organisms of toxic materials, the
12.2. Aerobic Respiration waste products of metabolism (chemical reactions in cells
including respiration) and substances in excess of
Aerobic Respiration: chemical reactions in cells that use requirements.
oxygen to break down nutrient molecules to release energy
Substances should include carbon dioxide (lungs), urea,
Glucose + Oxygen → C arbonDioxide + Water excess water and ions (kidney).
The importance of excretion is due to the toxicity of the
C 6 H12 O6 + 6O2 → 6C O2 + 6H2 O
​ ​ ​ ​ ​ ​
urea.

12.3. Anaerobic Respiration 13.2. Function of Liver

Anaerobic Respiration: chemical reactions in cells break down The role of the liver is in the assimilation of amino acids by
nutrient molecules to release energy without using oxygen. converting them to proteins.
Recap: Do remember assimilation is the uptake and use of
In muscles (vigorous exercise): nutrients by cells. \n
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. Deamination: removal of the nitrogen-containing part of
Oxygen Debt is removed by:
amino acids to form urea.
continuation of fast heart rate to transport lactic acid
in the blood from the muscles to the liver Urea is formed in the liver from excess amino acids.
continuation of deeper and faster breathing to supply Alcohol, drugs & hormones are broken down in the liver.
oxygen for aerobic respiration of lactic acid
aerobic respiration of lactic acid in the liver 13.3. Function of Kidney

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Removal of urea and excess water and the re-absorption by osmosis because of the low water potential of the
of glucose and some salts 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. Mammalian Nervous System
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 travel through the neurones.
The nervous system helps with the coordination and
regulation of body functions.

Cortex: contains Bowman’s capsules and coiled tubules 14.2. Types of Neurones
Ureter: carries urine from the kidney to the bladder
Medulla: has loops of Henlé and collecting ducts Nerve Impulse: an electrical signal that passes along the
Urethra: carrying urine from the bladder to the outside. nerve cells called neurones
Bladder: stores urine
Renal artery: brings wastes and water from the blood Motor Neurone
Renal vein: reabsorbs water and functional molecules and
leaves wastes behind

13.4. Structure and Function of the

Nephron

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
nephron by active transport. These substances are Relay Neurone
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

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neurotransmitter

14.3. Simple Reflex Arc

Reflex Action: automatically and rapidly integrates and The synapses ensure that impulses travel in one direction
coordinates the stimuli with the responses of effectors only.
(muscles and glands). Synaptic cleft: the small gap between each pair of
neurones
E.g. quickly removing your hand from the hot metal Inside the neurone’s axon, there are 100s of tiny vacuoles
surface (vesicles, each containing a chemical called
They involve three neurones: a sensory neurone, a relay neurotransmitter)
neurone and a motor neurone. When an impulse arrives, the vesicles move to the cell
The gap between neurones is called a synapse. membrane and empty their content into the synaptic cleft.
How the simple reflex arc works: The neurotransmitter quickly diffuses across the tiny gap
A stimulus affects a receptor (cell or organ that and attaches to receptor molecules in the cell membrane
converts a stimulus into an electrical impulse) of the relay neurone.
A sensory neurone carries impulses from the receptor This can happen because the neurotransmitter
to the CNS molecules' shape complements the receptor molecule's
Connector/relay neurone carries impulse slowly shape.
(because it has no myelin sheath) across the spinal
cord
The motor neurone carries impulses from the CNS to
14.5. Sense Organs
the effector
Sense organ: groups of receptor cells responding to specific
The effector (either a muscle or a gland) carries out
stimuli: light, sound, touch, temperature and chemicals.
the response

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
14.4. Synapse different colours (Rods and cones)
Optic nerves: carry impulses to the brain
Synapse: a junction between two neurones, consisting of a
gap across which impulses pass by diffusion of a 14.6. Pupil Reflex

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Adjusting for high and low light intensity Rods Cones

An involuntary response
Packed most tightly around
Most tightly packed at the
the edge of the retina, so you
Low Light Intensity High Light Intensity retina's centre, objects are
can see things most clearly
Radial muscles (straight lines) seen most clearly when
Circular muscles (circular when not looking directly at
contract and become shorter directly looking at them.
lines) contract and become them.
to pull the pupil (black dot),
shorter to reduce pupil size
making it wider to let more
and protect the retina from Fovea:
light enter to form a clear
bleaching. Part of the retina where the receptor cells are pushed
image on the retina
most closely together
Where light is focused when you look straight at an
14.7. Accommodation object
Distribution of Rods and Cones
Accommodation: Adjusting for near and distant objects.

14.9. Hormones
Hormones: A chemical substance produced by a gland and
carried by the blood, altering the activity of one or more
specific target organs.
Near Object Distant Object
Ciliary muscles contract Ciliary muscles relax Endocrine Glands
Suspensory Ligaments slack Suspensory Ligaments tighten
adrenal glands and adrenaline
The lens becomes short and The lens becomes long and
pancreas and insulin
fat thin testes and testosterone
ovaries and oestrogen
Exemplar Past Year Question
Adrenaline
Explain why a person cannot focus on distant objects if the
suspensory ligaments become permanently overstretched. A hormone secreted by the adrenal gland.
(0610/42/F/M/23) It increases pulse rate, heart rate and pupil diameter.
Increases blood glucose concentration for respiration.
1. ciliary muscles relax
Adrenaline is secreted, for example, bungee jumping or
2. suspensory ligaments can no longer become tight
riding a rollercoaster.
3. the lens is not stretched/remains wide
4. the angle of refraction remains unchanged Gland Hormone Function
Prepares the body for vigorous
14.8. Rods and Cones Adrenal gland Adrenaline
action
Reduces the concentration of
Rods Cones Pancreas Insulin
glucose in the blood
Provide low detail, black & Causes the development of
Provide detailed, coloured Testes Testosterone
white images, suitable for male sexual characteristics
images; they work in high light
seeing in low-intensity light (at
intensity. Causes the development of
night). Ovary Oestrogen
female sexual characteristics

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Gland Hormone Function

Increases concentration of
Pancreas Glucagon
glucose in the blood

14.10. Nervous and Hormonal Control

Comparison Nervous system Endocrine system When the control of blood glucose does not work, a
Speed of action Very rapid Can be slow person is said to have diabetes
Chemical
Electrical impulses messengers Type 1 Diabetes
Nature of message travelling along (hormones)
nerves travelling in the Type 1 Diabetes: caused by the death of the cells that secrete
bloodstream insulin.

Duration of Usually within It may take years Symptoms: hyperglycaemia (feeling unwell, dry mouth,
response seconds (puberty) blurred vision, and feel thirsty) or hypoglycaemia (tired,
Localized response Widespread showing confusion and irrational behaviour)
Area of response (only one area response (in many Treatment: eating little and often and avoiding large
usually) organs) amounts of carbohydrates, injecting insulin to reduce
Development of the blood glucose concentration
Example of Reflexes such as
reproductive
process-controlled blinking
system 14.13. Thermoregulation

14.11. Homeostasis
Homeostasis: The maintenance of a constant internal
environment.

Insulin decreases blood glucose concentration.

The concept of homeostatic control by negative feedback
with reference to a set point
Constant body temperature is maintained by:
Negative Feedback
Insulation: provided by fatty tissue retains heat. Hairs
Negative Feedback: controls the production of hormones and become erect to trap warm air by contracting erector
regulates their own production muscles and vice versa.
Vasodilation: when it is hot, arterioles, which supply blood
A negative feedback control is when the change in to the skin-surface capillaries, dilate (become wider) to
hormone level acts as a signal to cancel out that change, allow more blood near the skin surface to increase heat
so when the blood hormone level is low, hormone loss (face redder)
production is stimulated; when it is high, it is inhibited. Vasoconstriction: when it is cold, arterioles, which supply
blood to the skin-surface capillaries, constrict (become
14.12. Glucoregulation smaller) to allow less blood near the skin surface to
decrease heat loss
Blood glucose levels are monitored and controlled by the Sweating: the water evaporates, giving a cooling effect
pancreas Skin receptors: sense heat, and sensory neurons send
The pancreas produces and releases different hormones impulses to the hypothalamus
depending on the blood glucose level Shivering: muscular activity generates heat
Insulin is released when blood glucose levels are high – Thermoregulatory Centre: the hypothalamus controls
the liver stores excess glucose as glycogen corrective mechanisms (e.g. sweating and shivering).
Glucagon is released when blood glucose levels are low –
the liver converts stored glycogen into glucose and
releases it into the blood

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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.

15.2. Antibiotic-Resistant Bacteria

Antibiotic-resistant bacteria can be reproduced through
natural selection, where it begins from:

Mutation - giving rise to variation

Antibiotics kill bacteria without changing genes
Competition for food space, etc
14.14. Tropic Responses
Reproduce via binary fission
Auxin: Then, alleles are passed on to offspring to reproduce.
Plant hormones or growth substances
Controls tropisms
It is produced by cells at the tip of the roots and shoots
16. Reproduction
of plants
16.1. Asexual Reproduction
Gravitropism: a response in which a plant grows towards
(positive) or away (negative) from gravity. Asexual Reproduction: the process resulting in the production
of genetically identical offspring from one parent.
Auxins’ role in gravitropism:
Made in the shoot tip Bacteria:
Then, it diffuses through the plant from the shoot tip Reproduced by binary fission, each bacterium divides
Auxin is unequally distributed in response to light and into two.
gravity The generation time is the time taken for a cell to
Auxin stimulates cell elongation divide into 2.

Phototropism: a response in which a plant grows towards Advantages Disadvantages

(positive) or away (negative) from the direction light is
Fast: no need to find a mate,
coming. No variation/biodiversity
fertilise, etc.
Auxins’ role in phototropism: Good characteristics are kept Harmful genes transferred
If the sun shines on the right side of a plant’s shoot, Overcrowding- fighting for
auxins accumulate on the dark opposite left side.
Do not need to carry offspring
food
Auxins accumulating makes cells on the left side grow
Prone to extinction
faster than cells on the right.
When the left side of the shoot starts growing faster
Syllabus 16.1.2: You must be able to identify
than the right side, the shoot will start to bend to the
examples of asexual reproduction in diagrams,
right side towards sunlight.
images and information provided

15. Drugs 16.2. Sexual Reproduction

Drugs: Any substance taken into the body that modifies or Sexual reproduction: a process involving the fusion of the
affects chemical reactions in the body. nuclei of two gametes (sex cells) to form a zygote and the
production of offspring that are genetically different from
each other
15.1. Antibiotics
Fertilisation: the fusion of gamete nuclei
Antibiotics work by disrupting the cell wall formation of The nuclei of gametes are haploid, and the nucleus of a
the bacteria you are trying to get rid of, but not of human zygote is diploid
cells. Diploid: Full Set of Chromosomes
Some bacteria are resistant to antibiotics, which reduces Haploid: Half Set of Chromosomes
the effectiveness of antibiotics.
Advantages Disadvantages

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Advantages Disadvantages Agents of pollination: insects, birds, mammals, water and

wind
Produces genetically different It takes lots of time and
offspring energy Fertilisation occurs when a pollen nucleus fuses with a
nucleus in an ovule
Reduced risk of extinction Mate required
Energy on improving Insect Pollinated Wind Pollinated
appearances or pollen Bright, colourful petals –
volume for pollination (plants) Dull petals
attract
Sweetly scented No scent
16.3. Sexual Reproduction in Plants Contains nectar No nectaries
A moderate amount of pollen Huge amount of pollen
Insect Pollinated Flowers Pollen is spiky/sticky Pollen round and smooth
Flowers are the reproductive organ of the plant Anther & stigma inside the
Anther and Stigma hang out
flower
Sticky stigma Feathery stigma

Pollen tube: pollen grain lands on the stigma and creates

a tunnel down the style, through the micropyle, to the
ovules.
Ovule - seed
Ovary - fruit

Wind Pollinated Flowers Self Pollination

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 Increases competition
pollination between plants
Functions Susceptible to the same
Fast and saves time
disease
Sepal: protect the flower bud.
Petal: brightly coloured and scented and may have
nectarines, which are all used to attract insects petals in
Cross-Pollination
wind-pollinated flowers are tiny and used for pushing the
Cross-pollination: the transfer of pollen grains from the
bracts (leaf-like structures) apart from exposing stamens
anther of a flower to the stigma of a flower on a different
and stigma.
plant of the same species.
Anther: has pollen sacs with pollen grains that contain the
Advantages Disadvantages
male nucleus (male gamete).
Stigma: platform on which pollen grains land Increases variation Reliance on pollinators
Ovary: hollow chamber, ovules grow from the walls. Quick to adapt to surroundings Wastage of pollen
Less susceptible to diseases More energy required
Syllabus 16.3.1 and 16.3.2: You must be able to
identify in diagrams and images and draw the
following parts of an insect-pollinated flower:
sepals, petals, stamens, filaments, anthers,
carpels, style, stigma, ovary and ovules,
together with its function.

16.4. Pollination
Pollination: transfer of pollen grains from the male part of the 16.5. Germination
plant (anther of stamen) to the female part of the plant
(stigma). Germination: A process controlled by enzymes

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Water: activates enzymes to turn insoluble food stores Oviduct (fallopian tube): carries the ovum to the uterus
into soluble substances, and makes tissues swell so that Uterus (womb): where the fetus develops.
the testa splits Cervix: neck of the uterus: a robust and rigid muscle,
Oxygen: enters through the gaps in the testa (along with moist by mucus with a small opening
water), and is used in aerobic respiration. Vagina: receives the penis during intercourse and way out
Temperature: must be suitable for enzymes to work (at for baby at birth. Moist tube of muscle, flexible and
optimum temperature). secretes mucus

16.6. Sexual Reproduction In Humans 16.7. Fertilisation & Early Development

Male Reproductive System Fertilisation: 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.
The 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: The zygote is changed through
growth (mitosis) and development (organization of cells
into tissues and organs)
Umbilical cord: contains the umbilical artery, which
Testes: have many coiled tubes that produce sperm, and carries deoxygenated blood and waste products from the
the cells between tubes produce testosterone. fetus to the placenta and the umbilical vein, which carries
Scrotum: holds testicles oxygenated blood and soluble food from the placenta to
Sperm duct: carries sperm from testicles to urethra. the fetus. (Contains fetus’ blood)
Prostate gland: makes seminal fluid Placenta: organ for exchange of soluble materials such as
Urethra: carries semen from the sperm duct to the tip of foods, wastes and oxygen between mother and fetus;
the penis physical attachment between uterus and fetus. (Contains
Penis: male sex organ used to transfer semen to the mother’s blood)
female. Amniotic sac: membrane which encloses amniotic fluid,
broken at birth.
Female Reproductive System 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.

16.8. 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

Ovary: contains follicles that develop into the ova and

produces progesterone and oestrogen

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Features Functions
Flagellum Propels the sperm to swim
Respiration to release energy
Mitochondria
for swimming
Release digestive enzymes to
Enzymes in the acrosome
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
4. Released once per month containing 23 chromosomes

Day 1 to 5:
In the ovary, FSH secreted by the Pituitary Gland to
stimulate the maturation of ONE follicle in the ovary.
Features Functions
In the uterus: the endometrium breaks down;
Energy storage Development of zygote menstruation
Jelly coat Changes at fertilisation Day 5 to 12:
In the ovary, the follicle keeps maturing
16.9. Sex Hormones in Humans In the uterus, oestrogen is secreted by follicle and the
ovarian tissues to prepare the endometrium
The roles of testosterone and oestrogen in the development Day 13/14/15:
and regulation of secondary sexual characteristics during In the ovary, LH is also secreted by the Pituitary Gland
puberty to trigger the release of the egg from the follicle into
the fallopian tube. Ovulation happens on Day 14.
Primary sexual characteristics: present during Day 15 to 28:
development in the uterus and are the differences in In the ovary, LH triggers the formation of Corpus
reproductive organs etc., between males and females Luteum
Secondary sexual characteristics: are the changes that In the uterus: progesterone is secreted by Corpus
occur during puberty as children become adolescents Luteum to keep endometrium thick, waiting for
At puberty, the pituitary gland starts to stimulate the possible embryo implants.
primary sex organs; the testes in males and the ovaries in Day 28 – Scenario 1: Egg not fertilised
females. No implantation takes place, the Corpus Luteum
They only affect the target organs, which have receptors degenerates, causing a lack of progesterone.
which can recognize them. This means that endometrium is no longer thick, back
Causes secondary sexual characteristics such as the to Day 1
growth of pubic hair and maturation of sexual organs. Day 28 – Scenario 2: The egg is fertilised
Implantation occurs.
16.10. Menstrual Cycle This makes the hormones keep the Corpus Luteum
maintained which means that progesterone is high.
This keeps the Endometrium thick for pregnancy

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DNA: controls cell function by controlling the production of

16.11. Hormones in Menstrual Cycle
proteins, including enzymes, membrane carriers and
Oestrogen is secreted by the ovaries. It stops FSH from receptors for neurotransmitters
being produced - so that only one egg matures in a cycle, DNA has 2 long strands and 4 nucleotides, AT and CG
and it stimulates the pituitary gland to release the Protein synthesis has two stages:
hormone LH. Transcription (rewriting the base code of DNA into
Progesterone is a hormone secreted by ovaries. It bases of RNA)
maintains the lining of the uterus during the middle part Translation (using RNA base sequence to build amino
of the menstrual cycle and pregnancy. acids into a sequence in a protein)
Follicle-stimulating hormone (FSH) is secreted by the How proteins are made:
pituitary gland. It causes an egg to mature in an ovary and the gene coding for the protein remains in the nucleus
stimulates ovaries to release the hormone oestrogen. messenger RNA (mRNA) is a copy of a gene
Luteinizing hormone (LH): is also secreted by the pituitary mRNA molecules are made in the nucleus and move
gland and causes mature eggs to be released from the to the cytoplasm
ovary. the mRNA passes through ribosomes
the ribosome assembles amino acids into protein
16.12. Sexually Transmitted Infections molecules
the sequence determines the specific order of amino
Human Immunodeficiency virus (HIV) is one example of a acids of bases in the mRNA
sexually transmitted infection. All body cells in an organism contain the same genes, but
many genes in a particular cell are not expressed
Transmission: Intercourse, blood transfusion, organ because the cell only makes the specific proteins it needs
transplant or sharing a needle with an infected person
Prevention:
Avoid intercourse with many partners
17.3. Mitosis
Use a condom
Mitosis: The nuclear division gives rise to genetically identical
Don’t come in contact with other people’s blood
cells
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 lead to AIDS and dies from infection

17. Inheritance
Mitosis is needed for:
Growth: in animals, each tissue provides its own new
17.1. Chromosomes, Genes and Proteins cells when needed.
Repair damaged tissues: for example, when you cut
Chromosomes: made of DNA, which contains genetic
your skin, mitosis provides new cells to cover up cuts.
information in the form of genes
Replacement of worn-out cells
Gene: a length of DNA that codes for a protein
Asexual reproduction: in plants
Allele: an alternative form of a gene
The exact replication of chromosomes occurs before
Inheritance of sex in humans is used with X and Y
mitosis
chromosomes.
During mitosis, the copies of chromosomes separate,
Haploid nucleus: a nucleus containing a single set of
maintaining the chromosome number in each daughter
unpaired chromosomes (e.g., sperm and egg)
cell
Diploid nucleus: a nucleus containing two sets of
chromosomes (e.g., in body cells) Stem cells: unspecialized cells that divide by mitosis to
The sequence of bases in a gene determines the produce daughter cells that can become specialized for
sequence of amino acids used to make a specific protein. specific functions
Different sequences of amino acids give different shapes
to protein molecules.
17.4. Meiosis
17.2. DNA & Protein Synthesis Meiosis: Reduction division in which the chromosome number
is halved from diploid to haploid

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Meiosis is involved in the production of gametes.

Meiosis results in genetic variation, so the cells produced
are not all genetically identical.

17.5. Monohybrid Inheritance 3:1 Monohybrid Crosses

Inheritance: The transmission of genetic information from

generation to generation.

Terminologies

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
Co-dominance: when both alleles in heterozygous organisms
no dominant allele of the gene present (e.g. t or g)
contribute to the phenotype

Pedigree Diagram There are three alleles for the blood group given by the
symbols IA, IB and IO.
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, making it more
common in one sex than in the other.

Genetic Diagrams

1:1 Monohybrid Crosses

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Red-green colour blindness is an example of sex linkage.

Syllabus 17.4.18: You must be able to use

genetic diagrams to predict the results of
18.2. Adaptive Features
monohybrid crosses involving codominance or
Adaptive feature: an inherited feature that helps an organism
sex linkage and calculate phenotypic ratios.
to survive and reproduce in its environment

18. Variation & Selection Xerophytes live in deserts where water is scarce and
evaporation is rapid or in windy habitats. Their features
are:
18.1. Variation Deep roots reach the water far underground
Leaves reduced spines with minimum surface area for
Variation: differences between individuals of the same transpiration
species Shallow spreading roots to collect occasional rain
Both genetic and environmental factors cause phenotypic Rolled leaves, leaf hairs and stomata sunk in pits to
variation trap moist air
Continuous variation: results in a range of phenotypes Waxy leaf cuticle, impermeable water
between two extremes; examples include body length and Stomata open at night and close at midday when
body mass evaporation is highest
Discontinuous variation: results in a limited number of E.g. cactus and marram grass
phenotypes with no intermediates (e.g. ABO blood groups,
seed shape in peas and seed colour in peas) Hydrophytes: live wholly or partly submerged in water.
It is usually caused by genes only, and both genes and the Their features are:
environment cause continuous variation. Leaves are highly divided to create a large surface
area for absorption and photosynthesis
Syllabus 18.1.5: You must be able to investigate and describe Minimal cuticle formation
examples of continuous and discontinuous variation 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

18.3. Selection
Natural Selection
Mutation
The greater chance of passing on genes by the best-
Mutation: A genetic change. adapted organisms.
The development of strains of antibiotic-resistant bacteria
Gene mutation: a change in the base sequence of DNA is an example of natural selection.
Mutation is the way in which new alleles are formed The surviving organisms reproduce since they don’t get
Mutation, meiosis, random mating and random eaten up, so variation has caused the species to evolve.
fertilisation are sources of genetic variation in populations
Ionising radiation and some chemicals increase the rate Process of Natural Selection:
of mutation

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1. genetic variation within populations Food Web: showing a network of interconnected food chains.
2. production of many offspring
3. struggle for survival, including competition for
resources
4. There is a greater chance of reproduction by
individuals who are better adapted to the environment
than others; these individuals pass on their alleles to
the next generation.

Adaptation: the process of natural selection by which

populations become more suited to their environment over
many generations.
Energy is transferred between organisms in a food chain
Artificial Selection by ingestion
Producer: an organism that makes its organic nutrients,
Artificial Selection: breeds organisms with valued
usually using energy from sunlight through
characteristics together to produce offspring that share those
photosynthesis
valuable characteristics.
Consumer: an organism that gets its energy by feeding on
It can be used to produce organisms that are more other organisms.
economically valued Consumers may be classed as primary, secondary,
For example, cows that produce more milk, wheat that is tertiary and quaternary according to their position in a
easier to separate from grain, dogs that have a better food chain
Herbivore: an animal that gets its energy by eating plants
appearance
Carnivore: an animal that gets its energy by eating other
Process of Selective Breeding: animals
Decomposer: an organism that gets its energy from dead
Selecting by individuals with desirable features or waste organic matter (i.e. a saprotroph)
Crossing three individuals to produce the next generation Trophic level: the position of an organism in a food chain,
Selection of offspring showing the desirable features food web or ecological pyramid.
Primary consumer: eat vegetables
Selective breeding by artificial selection is carried out over
Secondary consumer: eat meat/drink milk
many generations to improve crop plants and domesticated
Tertiary consumer: eat a predatory fish, salmon
animals.
Food chains usually have fewer than five trophic levels

19. Organisms and their because energy transfer is inefficient:

Sun produces light, and less than 1% of the energy falls

Environment onto leaves.
Producers ‘fix’ only about 5-8% of that energy because of
transmission, reflection and incorrect wavelength.
19.1. Energy Flow
Primary consumers only get between 5-10% because
The sun is the principal source of energy input to some parts are indigestible (e.g., cellulose) and do not eat
biological systems. the whole plant.
Energy flow is NOT a cycle; it starts from the sun, and then The secondary consumer gets between 10-20% because
that energy is harnessed by plants, which are eaten by the animal matter is more digestible & has a higher
energy value.
animals, which other animals eat.
At each step, energy is lost to the environment. At each level, heat is lost by respiration.

Humans eating plants is more efficient than humans eating

Food Chains and Food Webs animals because:

Food Chain: a chart showing the flow of energy (food) from We need only a couple of vegetables to have one meal but
one organism to the next, beginning with a producer, for to have the meat, we must feed the animal a lot of plant
example: 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.

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Ecological Pyramids happen because of lightning or microorganisms providing

them through decomposition.
Pyramid of Numbers Pyramid of Biomass 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
Shows the number of each Pyramid, which shows the
nitrogen-containing substances into atmospheric nitrogen
organism in a food chain biomass
When moving up the pyramid,
the number of individuals
(number of individuals × their 19.3. Population
individual mass)
decreases
Population: a group of organisms of one species living in
the same area at the same time.
The pyramids of biomass are ALWAYS pyramid-shaped.
Community: all of the populations of different species in
an ecosystem.
19.2. Nutrient Cycles Ecosystem: a unit containing the community of organisms
and their environment interacting together.
Carbon Cycle
Factors Affecting the Rate of Population Growth

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.
Carbon is taken from the atmosphere by photosynthesis
(plants)
It is passed on to animals and decomposers by feeding.
19.4. Sigmoid Population Growth Curve
It is returned by respiration in plants and animals and
decomposed by microorganisms.

Fossilisation is NOT needed anymore - from

2023 onwards

Nitrogen Cycle
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.

Nitrogen-fixing bacteria provide usable nitrogen for

20. Human Influences on
plants; these may exist in the root nodules where they live
in symbiosis with the plants (nitrogen fixation), or this can
Ecosystems

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Insecticides (kill insects): meant to kill insects which eat

20.1. Food Supply
crops, but can kill other useful insects such as bees, which
are pollinators, or by bioaccumulation (the increase in the
Humans have increased food production because:
dose of toxin from one level of the food chain to the next)
Agricultural machinery to use larger areas of land and Herbicides (kill weeds): can be harmful to animals which
improve efficiency eat the plants
Chemical fertilisers help crops grow better
Insecticides: a type of pesticide that kills insects Non-biodegradable plastics:
Herbicides: a type of pesticide that kills weeds Choke birds, fish and other animals
Selective breeding to improve production by crop plants Fill up the animals’ stomachs so that they can’t eat food
and livestock Collect in rivers and get in the way of fish
Large-scale monoculture: the continuous production of one Global Warming:
type of genetically identical crop.
Increase in the average temperature of the Earth
Negative Impacts of Large-scale Monoculture
Methane from the burping of cows
If a natural disaster occurs, the whole crop could be It started at the same time as humans began burning
wiped out. fossil fuels
If pests & diseases attack crops, they could harm them Scientists believe fossil fuels are causing this – not proven
easily yet
Using large fields and pesticides reduces the variety It increased carbon dioxide and methane concentrations
of species. This hinders biodiversity. in the atmosphere, causing an enhanced greenhouse
When insecticides are used persistently, the pests effect that leads to climate change.
may eventually become resistant to them, reducing
their effectiveness Eutrophication: when water plants receive too many
nutrients.
Negative Impacts of Intensive Livestock Production
Welfare issues for the livestock Fertilisers are put in soil by farmers.
Diseases can spread easily among them Fertilisers with nitrates/detergents with phosphates leach
Waste can pollute land and waterways nearby into rivers and lakes after rain
Water plants grow more than usual
20.2. Habitat Destruction They block sunlight and kill plants underneath
They die and sink to the bottom
Biodiversity: the number of different species that live in an Bacteria/fungi decompose remains using the O2 and
area. decreasing the O2 concentration
Fish and other creatures die from oxygen starvation
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 harm
habitats.
Effects of deforestation
20.4. Conservation
Reduced biodiversity/destroys habitats/extinction
Sustainable resource: one which is produced as rapidly as it is
Loss of CO2 fixation, thus increase in CO2, thus global
removed from the environment so that it does not run out
warming
Soil erosion: tree roots cannot retain soil and go into Some resources can be conserved and managed
rivers, making the water dirty & causing blockages, sustainably, limited to forests and fish stocks.
and the soil becomes less fertile
Flooding: 75% of water is usually absorbed by foliage, 1. Forests can be conserved using education, protected
root systems or evaporates. After deforestation, water areas, quotas and replanting.
accumulates in valleys. 2. Fish stocks can be conserved using education, closed
seasons, protected areas, controlled net types and
mesh size, quotas and monitoring.
20.3. Pollution
Natural resources:
Pollution due to pesticides:

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Water: used to grow food, keep it clean, provide power, complex molecules.
control fires, and drink. We get water constantly through
rainfall, but we use the planet’s freshwater faster than it
can be replenished.
Fossil fuels need to be conserved as they will soon run
out; therefore, they should be replaced with green energy
forms.

Recycling:

Water: water from sewage can be returned to the

environment for human use by sanitation and sewage Why are bacteria useful in biotechnology and genetic
treatment modification?
Paper: sent to special centres where it is pulped to make
raw materials for industry 1. few ethical concerns over their manipulation and
Plastic: fossil fuels, bottles → fleece clothing growth
Metal: mining takes a lot of energy, so recycling saves 2. the presence of plasmids
energy
21.2. Biotechnology
Species and habitats need to be conserved because:

Organisms have value in themselves (ethical value) Biofuel

Value to medicine (new molecules from exotic plants =
new drugs) Use plants to make sugars, which yeast then breaks down
Genetic resources are helpful to humans as well and are to make ethanol.
This process also uses anaerobic respiration.
lost when species disappear (DNA for genetic
engineering)
Each species has its role in its ecosystem; if it is removed, Bread-Making
then the whole ecosystem could collapse
Flour, sugar, water and salt are mixed with yeast to make
The use of artificial insemination (AI) and in vitro
the dough.
fertilisation (IVF) in captive breeding programmes
Amylase breaks down some starch to make maltose and
Endangered species: glucose. This is used by yeast in respiration.
The dough is kept warm and moist (28°C). Yeast ferments
How they become endangered: climate change, habitat sugar, making carbon dioxide, which creates bubbles, so
destruction, hunting, pollution and introduced species bread rises.
If the population size drops, variation decreases Cooking (at 180°C) – kills yeast, evaporates alcohol and
Endangered species can be conserved by monitoring and hardens the outer surface.
protecting species and habitats, education, captive
breeding programmes, and seed banks Use of Enzymes in Biotechnology
Reasons for Conservation Programmes include:
reducing extinction Pectinase:
protecting vulnerable environments
maintaining ecosystem functions by nutrient cycling Fruit juices are extracted using pectinase (breaks down
pectin)
and resource provision, e.g. food, drugs, fuel and
genes Pectin helps plant walls stick together
increase biodiversity If pectin is broke down, it’s easier to squeeze juice from
the fruit
Extraction of juice from fruit, making juice clear, not
21. Biotechnology & Genetic cloudy

Modification Biological Washing powders:

Biological washing powders and liquids contain enzymes

21.1. Biotechnology & Genetic that help remove the stain
The enzymes are coated with a special wax that melts in
Modification the wash, releasing the enzyme
Once the stains have been broken down, they are easier
Bacteria are useful in biotechnology and genetic engineering for detergents to remove
due to their rapid reproduction rate and their ability to make

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Proteases: break down proteins in stains, e.g., grass, Penicillium is added to produce penicillin. They use sugar
blood for respiration and ammonium salts to make protein and
Lipases: break down stains containing fats and oil nucleic acids
Amylases: break down carbohydrate-based stains, such The fermentation vessel consists of ‘PAWS’
as starch Probes monitor temperature and pH
Cellulases: break down cellulose fibres Air provides oxygen for aerobic respiration in fungus
A water-cooled jacket removes heat to maintain a
Lactase: temperature of 24°C.
Stirrer keeps the microorganism suspended (allowing
The enzyme that breaks down lactose (the sugar found in
access to nutrients and oxygen) while maintaining an
milk), people can stop making lactase naturally and,
even temperature.
therefore, can’t digest lactose.
Filtered to remove fungus and then can be crystallized to
make capsules.

21.4. Genetic Modification

Genetic Modification: changing the genetic material of an
organism by removing, altering, 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

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

21.3. Fermenters

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
Penicillin: an antibiotic produced by a fungus called
Penicillium.
They require proper temperature, pH, oxygen, nutrient 21.5. Genetically Modified Crops
supply and waste products.
The stainless steel fermentation vessel contains a Advantages Disadvantages
medium containing sugars and ammonium salts.

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Advantages Disadvantages Advantages Disadvantages

Uniform in shape – easy to Led to the development of
transport/appeal to Natural species may die Drought resistant – less water superweeds – stronger than
consumers GM
Decrease biodiversity/genetic No one knows the long-term
Growing season shorter Higher yields
diversity effects on humans
Solve global hunger Expensive seeds

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Biology

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