Oxford AQA International GCSE Biology

Full syllabus for OxfordAQA IGCSE Biology specification 9201

ORGANISATION (Oxford AQA International GCSE Biology)

All organisms are constituted of one or more cells. Multi–cellular organisms have cells that are differentiated according to their function.

All the basic functions of life are the result of what happens inside the cells which make up an organism. Growth is the result of multiple cell divisions.

Cell structure (Oxford AQA International GCSE Biology)
a. Most animal cells (eukaryotic cells) have the following parts:
• a nucleus, which controls the activities of the cell
• cytoplasm, in which most of the chemical reactions take place
• a cell membrane, which controls the passage of substances into and out of the cell
• mitochondria, which is where most energy is released in respiration
• ribosomes, which is where protein synthesis occurs.
b. In addition to the above, plant cells (eukaryotic cells) often have:
• chloroplasts, which absorb light energy to make food
• a permanent vacuole filled with cell sap.
Plant and algal cells also have a cell wall made of cellulose, which strengthens the cell.
c. A bacterial cell (prokaryotic cell) consists of cytoplasm and a membrane surrounded by a cell wall; the genes are not in a distinct nucleus; some of the genes are located in circular structures called plasmids.
d. Cells may be specialised to carry out a particular function.

Students should be able, when provided with appropriate information, to relate the structure of different types of cell to their function in a tissue, an organ, or the whole organism.

Principles of organisation (Oxford AQA International GCSE Biology)

a. Large multicellular organisms develop systems for exchanging materials. During the development of a multicellular organism, cells differentiate so that they can perform different functions.
b. A tissue is a group of cells with similar structure and function.
c. Organs are made of tissues. One organ may contain several tissues.
d. Organ systems are groups of organs that perform a particular function.
Students should develop an understanding of size and scale in relation to cells, tissues, organs and systems

Animal tissues, organs and organ systems (Oxford AQA International GCSE Biology)

a. Examples of animal tissues include:
• muscular tissue, which can contract to bring about movement
• glandular tissue, which can produce substances such as enzymes and hormones
• epithelial tissue, which covers some parts of the body.
b. An example of an animal organ is the stomach, which contains:
• muscular tissue, to allow contents to move through the digestive system
• glandular tissue, to produce digestive juices
• epithelial tissue, to cover the outside and the inside of the stomach.
c. An example of an animal organ system is the digestive system, a system in which humans and other
mammals exchange substances with the environment. The digestive system includes:
• glands, such as the pancreas and salivary glands, which produce digestive juices
• the stomach and small intestine, where digestion occurs
• the liver, which produces bile
• the small intestine, where the absorption of soluble food occurs
• the large intestine, where water is absorbed from the undigested food, producing faeces.

Plant tissues, organs and systems (Oxford AQA International GCSE Biology)

a. Examples of plant tissues include:
• epidermal tissues, which cover the plant
• palisade mesophyll, which carries out photosynthesis
• spongy mesophyll, which has air spaces to facilitate diffusion of gases
• xylem and phloem, which transport substances around the plant.
b. Plant organs include stems, roots and leaves.
Details of the internal structure of these organs are limited to the leaf and to the position of the xylem and phloem in a dicotyledonous primary root and primary stem

Transport in cells (Oxford AQA International GCSE Biology)
The movement of substances into and out of cells.
a. Diffusion is the spreading of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration. The greater the difference in concentration, the faster the rate of diffusion.
b. Dissolved substances can move into and out of cells by diffusion.
c. Oxygen required for respiration passes through cell membranes by diffusion.
d. Osmosis is the diffusion of water from a dilute to a more concentrated solution through a selectively permeable membrane that allows the passage of water molecules.
e. Differences in the concentrations of the solutions inside and outside a cell cause water to diffuse into or out of the cell by osmosis.
Students should be familiar with experiments related to diffusion and osmosis as well as the terms isotonic, hypertonic, turgor and plasmolysis.

Required practical:
Investigate the effect of different concentrations of solutions separated by a partially permeable membrane.
f. Substances are sometimes absorbed against a concentration gradient. This requires the use of energy from respiration. The process is called active transport.
g. Active transport enables plants to absorb ions from very dilute solutions, eg by root hair cells. Similarly,
sugar may be absorbed from low concentrations in the intestine and from low concentrations in the kidney
tubules.
h. A single-celled organism has a relatively large surface area to volume ratio. All the necessary exchanges
occur across its surface membrane.

The increased size and complexity of an organism increases the difficulty of exchanging materials.

i. In multicellular organisms many organ systems are specialised for exchanging materials. The effectiveness of an exchange surface is increased by:
• having a large surface area that is thin, to provide a short diffusion path
• (in animals) having an efficient blood supply
• (in animals, for gaseous exchange) being ventilated.
Students should be able to explain how the small intestine and lungs in mammals, and the roots and leaves in plants, are adapted for exchanging materials.
j. Gas and solute exchange surfaces in humans and other organisms are adapted to maximise effectiveness.

Students should be able to explain how gas and solute exchange surfaces are adapted to maximise effectiveness

BIOENERGETICS AND ECOLOGY (Oxford AQA International GCSE Biology)

Food provides materials and energy for organisms to carry out the basic functions of life and to grow. Some plants and bacteria are able to use energy from the Sun to generate complex food molecules. Animals obtain energy by breaking down complex food molecules and are ultimately dependent on green plants for energy. In any ecosystem there is competition among species for the energy and materials they need to live and reproduce.

BIOENERGETICS (Oxford AQA International GCSE Biology)

Photosynthesis (Oxford AQA International GCSE Biology)

a. Photosynthesis is summarised by the equations:
carbon dioxide + water == light ==> glucose + oxygen
6CO₂ + 6H₂O == light ==> C₆H₁₂O₆ + 6O₂
b. During photosynthesis:
• light is absorbed by a green substance called chlorophyll, which is found in chloroplasts in some plant cells and in algae
• light is used to convert carbon dioxide (from the air) and water (from the soil) into sugar (glucose)
• oxygen is released as a by-product.
c. The rate of photosynthesis may be limited by:
• low temperature
• shortage of carbon dioxide
• shortage of light.
These factors interact and any one of them may be the factor that limits photosynthesis.

Students should be able to relate the principle of limiting factors to the economics of enhancing the following conditions in greenhouses

including temperature,  carbon dioxide concentration  and  light intensity.

Required practical:
Investigate how variables affect the rate of photosynthesis.
d. The glucose produced in photosynthesis may be used as a source of chemical energy or converted to larger molecules for storage and use later. The glucose can be:
• used for respiration
• converted into insoluble starch for storage
• used to produce fat or oil for storage
• used to produce cellulose, which strengthens the cell wall
• used to produce proteins.
e. To produce proteins, plants also use nitrate ions that are absorbed from the soil

EXCHANGE AND TRANSPORT IN PLANTS (Oxford AQA International GCSE Biology)
a. In flowering plants:
• carbon dioxide enters leaves by diffusion through the stomata
• most of the water and mineral ions are absorbed by roots.
b. The surface area of roots is increased by root hairs, and the surface area to volume ratio of leaves is increased by the flattened shape and internal air spaces.
c. Plants have stomata to obtain carbon dioxide from the atmosphere and to remove oxygen produced in photosynthesis. Stomata also help to control the rate of water loss.
d. Plants mainly lose water vapour from their leaves. Most of the loss of water vapour takes place through the stomata.
• Evaporation is more rapid in hot, dry and windy conditions.
• If plants lose water faster than it is replaced by the roots, the stomata can close to prevent wilting.
e. The size of stomata is controlled by guard cells, which surround them.
f. Flowering plants have separate transport systems:
• xylem tissue transports water and mineral ions from the roots to the stem and leaves
• the movement of water from the roots through the xylem and out of the leaves is called the transpiration stream
• phloem tissue carries dissolved sugars from the leaves to the rest of the plant, including the growing regions and the storage organs. This process is called translocation
• the structure of the xylem and the phloem is related to its function.

Circulation in humans (Oxford AQA International GCSE Biology)

a. Substances are transported from where they enter the body to the cells, or from the cells to where they are removed from the body, by the circulatory system (the heart, the blood vessels and the blood).
b. The heart is an organ that pumps blood around the body in a double circulatory system. Much of the wall of
the heart is made from muscle tissue.
c. The heart has four main chambers (right and left atria and right and left ventricles).
d. The natural resting heart rate is controlled by a group of cells that act as a pacemaker, located in the right atrium. Artificial pacemakers are electrical devices used to correct irregularities in the heart rate.
e. In coronary heart disease, layers of fatty material build up inside the coronary arteries and narrow them. This reduces the flow of blood through the coronary arteries, resulting in a lack of oxygen for the heart muscle. Stents are used to keep the coronary arteries open.
f. In some people heart valves may become faulty. There are two main faults – the heart valve tissue might stiffen, preventing the valve from opening fully, or the heart valve might develop a leak. Faulty heart valves can be replaced using:
• biological valves – valves from humans or other mammals
• mechanical valves.

g. Artificial hearts are occasionally used to keep patients alive whilst waiting for a heart transplant, or to allow the heart to rest as an aid to recovery.

h. Blood enters the atria of the heart. The atria contract and force blood into the ventricles. The ventricles contract and force blood out of the heart. Valves in the heart ensure that blood flows in the correct direction.
Knowledge of the names of the heart valves is not required.
i. Blood flows from the heart to the organs through arteries and returns through veins. There are two
separate circulation systems, one for the lungs and one for all other organs of the body.
Knowledge of the blood vessels associated with the heart is limited to aorta, vena cava, pulmonary artery, pulmonary vein and coronary arteries.
j. Arteries have thick walls containing muscle and elastic fibres. Veins have thinner walls and often have valves to prevent back-flow of blood.
k. In the organs, blood flows through very narrow, thin-walled blood vessels called capillaries. Substances needed by the cells in body tissues pass out of the blood and substances produced by the cells pass into the blood, through the walls of the capillaries.
l. Blood is a tissue consisting of a fluid called plasma, in which the white blood cells, platelets and red blood cells are suspended.
m. Blood plasma transports:
• carbon dioxide from the organs to the lungs
• soluble products of digestion from the small intestine to other organs
• urea from the liver to the kidneys.
n. Red blood cells have no nucleus. They are packed with a red pigment called haemoglobin. Red blood cells transport oxygen from the lungs to the organs. In the lungs haemoglobin combines with oxygen to form oxyhaemoglobin. In other organs oxyhaemoglobin splits up into haemoglobin and oxygen.
o. White blood cells have a nucleus. They form part of the body’s defence system against microorganisms.
p. Platelets are small fragments of cells. They have no nucleus. Platelets help blood to clot at the site of a wound.
q. Blood clotting is a series of enzyme-controlled reactions, resulting in the change of fibrinogen to fibrin, which forms a network of fibers (fibres) trapping blood cells and forming a clot.
r. Antigens are proteins on the surface of cells

s. In organ transplants a diseased organ is replaced with a healthy one from a donor. The recipient’s antibodies may attack the antigens on the donor organ as they do not recognise them as part of the recipient’s body.
To prevent rejection of the transplanted organ:
• a donor organ with a ‘tissue-type’ similar to that of the recipient is used
• the recipient is treated with drugs that suppress their immune system.
Students should be able to evaluate the advantages and disadvantages of treating organ failure by mechanical devices or transplant.

t. There are four main types of human blood: O, A, B and AB. Blood group O is the universal donor.
Students should understand:
• the need for blood typing
• the ABO compatibility table.

Digestion (Oxford AQA International GCSE Biology)

a. Starch (a carbohydrate), proteins and fats are insoluble. They are broken down into soluble substances so that they can be absorbed into the bloodstream in the wall of the small intestine. In the large intestine much of the water mixed with the food is absorbed into the bloodstream. The indigestible food which remains makes up the bulk of the faeces. Faeces leave the body via the anus.
Students should be able to recognise the following on a diagram of the digestive system: salivary glands, oesophagus, stomach, liver, gall bladder, pancreas, duodenum, small intestine, large intestine, anus.
b. Enzymes help the breakdown of food in the digestive system.
• Enzymes are large proteins that act as biological catalysts. Catalysts increase the rate of chemical reactions and are utilized in the digestive process to speed up the breakdown of large molecules to small molecules for absorption into the bloodstream.
• The shape of an enzyme is vital for the enzyme’s function. High temperatures denature the enzyme, changing the shape of the active site.
• Different enzymes work best at different pH values.
• Some enzymes work outside the body cells. The digestive enzymes are produced by specialised cells in glands and in the lining of the gut. The enzymes then pass out of the cells into the gut, where they come into contact with food molecules. They catalyse the breakdown of large molecules into smaller molecules.

Required practical:
Investigate how different temperatures, and pH affect the rate of digestion.
c. Digestive enzymes.
• The enzyme amylase is produced in the salivary glands, the pancreas and the small intestine. Amylase catalyses the breakdown of starch into sugars in the mouth and small intestine.
• Protease enzymes are produced by the stomach, the pancreas and the small intestine. These enzymes catalyse the breakdown of proteins into amino acids in the stomach and the small intestine.
• Lipase enzymes are produced by the pancreas and small intestine. These enzymes catalyse the breakdown of lipids into fatty acids and glycerol in the small intestine.
• The stomach also produces hydrochloric acid. The enzymes in the stomach work most effectively in acid conditions.
• The liver produces bile, which is stored in the gall bladder before being released into the small intestine. Bile neutralises the acid that was added to food in the stomach. This provides alkaline conditions in which enzymes in the small intestine work most effectively.
• Bile also emulsifies fats (breaks large drops of fats into smaller droplets). This increases the surface area of fats for lipase enzymes to act upon.

Some microorganisms produce enzymes that pass out of the cells. These enzymes have many uses in the home and in industry.
Students should be able to give examples of some enzymes used in the home and industry and relate data to
the properties of enzymes.

Breathing (Oxford AQA International GCSE Biology)

a. The respiratory (breathing) system takes air into and out of the body so that oxygen from the air can diffuse into the bloodstream and carbon dioxide can diffuse out of the bloodstream into the air. The lungs are in the upper part of the body (thorax), protected by the ribcage and separated from the lower part of the body (abdomen) by the diaphragm.
Students should be able to recognise the following on a diagram of the respiratory system: ribs, intercostal muscles, diaphragm, lungs, trachea, bronchi, bronchioles, alveoli.
b. To inhale:
• the intercostal muscles contract, pulling the ribcage upwards
• at the same time the diaphragm muscles contract, causing the diaphragm to flatten
• these two movements cause an increase in the volume of the thorax
• the consequent decrease in pressure to below that of the air surrounding the body results in
atmospheric air entering the lungs.
To exhale:
• the intercostal muscles relax, allowing the rib cage to move downwards
• at the same time the diaphragm muscles relax, allowing the diaphragm to resume its domed shape
• these two movements cause a reduction in the volume of the thorax
• the consequent increase in pressure results in air leaving the lungs.
c. The alveoli provide a very large surface area, richly supplied with blood capillaries, so that gases can readily
diffuse into and out of the blood.

d. A healthy person constantly breathes automatically. However, spontaneous breathing may stop due to disease or injury. If this happens the patient can be helped to breathe by using a mechanical ventilator.
There are two main types of mechanical ventilator:
• negative pressure ventilators, which cause air to be ‘drawn’ into the lungs
• positive pressure ventilators, which force air into the lungs.

Respiration (Oxford AQA International GCSE Biology)

a. Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen), to transfer energy.
b. During aerobic respiration chemical reactions occur that use glucose (a sugar) and oxygen and transfer
energy.
c. Aerobic respiration is summarised by the equations:
glucose + oxygen ==> carbon dioxide + water (+ energy)
C₆H₁₂O₆ + 6O₂==> 6CO₂ + 6H₂O (+ energy)
d. Aerobic respiration takes place continuously in both plants and animals.
e. Most of the reactions in aerobic respiration take place inside mitochondria.
f. The energy that is transferred during respiration may be used by the organism in a variety of ways:
• to build larger molecules from smaller ones
• in animals, to enable muscles to contract
• in mammals and birds, to maintain a steady body temperature in colder surroundings
• in plants, to build up sugars, nitrates and other nutrients into amino acids, which are then built up into
proteins.
g. During exercise the human body needs to react to the increased demand for energy. A number of changes take place:
• the heart rate increases, increasing blood flow to the muscles
• the rate and depth of breathing increase
• glycogen stored in the muscles is converted back to glucose.
h. These changes increase the supply of glucose and oxygen to, and increase the rate of removal of carbon
dioxide from, the muscles.
i. If insufficient oxygen is reaching the muscles, energy is transferred by anaerobic respiration.
glucose ==> lactic acid
C₆H₁₂O₆ ==> 2C₃H₆O₃
j. Anaerobic respiration in muscles is the incomplete breakdown of glucose, which causes a build-up of lactic acid. An oxygen debt needs to be repaid to oxidise the lactic acid to carbon dioxide and water.
k. As the breakdown of glucose is incomplete, much less energy is transferred in anaerobic respiration than during aerobic respiration.
l. During long periods of vigorous activity muscles become fatigued and stop contracting efficiently. One cause of muscle fatigue is the build-up of lactic acid in the muscles. Blood flowing through the muscles eventually removes the lactic acid.
Required practical:
Investigate the effects of exercise on the human body.
m. Anaerobic respiration in plant cells and in some microorganisms results in the production of ethanol and
carbon dioxide.

ECOLOGY (Oxford AQA International GCSE Biology)

Materials including carbon and water are continually recycled by the living world, being released through respiration of animals, plants and decomposing microorganisms and taken up by plants in photosynthesis. All species live in ecosystems composed of complex communities of animals and plants dependent on each other and that are adapted to particular conditions, both abiotic and biotic.

Energy transferred in ecosystems (Oxford AQA International GCSE Biology)

a. Radiation from the Sun is the source of energy for most communities of living organisms. Plants and algae transfer about 1 % of the incident energy from light for photosynthesis. This energy is stored in the substances that make up the cells of the plants.
b. Only approximately 10 % of the biomass from each trophic level is transferred to the level above it because:
• some materials and energy are always lost in the organisms’ waste materials
• respiration supplies all the energy needs for living processes, including movement. Much of this energy is eventually transferred to the surroundings.
Construction of food webs and chains, and of pyramids of numbers, is not required. An understanding of pyramids of numbers is not required.
c. The biomass at each stage can be drawn to scale and shown as a pyramid of biomass.
Students should be able to interpret pyramids of biomass and construct them from appropriate information.

d. The efficiency of food production can be improved by reducing the number of stages in a food chain.

Adaptations, interdependence and competition (Oxford AQA International GCSE Biology)

a. To survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there.
b. Plants often compete with each other for light and space, and for water and nutrients from the soil.
c. Animals often compete with each other for food, mates and territory.
d. Organisms, including microorganisms, have features (adaptations) that enable them to survive in the conditions in which they normally live.
e. Some organisms live in environments that are very extreme, containing high levels of salt, high temperatures or high pressures. These organisms are called extremophiles.
f. Adaptations include:
• structural adaptations, eg the ways in which organisms are shaped, or coloured
• behavioural adaptations, eg migration, huddling together
• functional adaptations, related to processes such as reproduction and metabolism.
Students given appropriate information should be able to suggest how animals and plants are adapted to their environment.

Students should be able to explain how some parasites are adapted for living on or inside their hosts. For
example:
• fleas live amongst the hair of mammals
• tapeworms live inside the intestines of mammals

Decay and the carbon cycle (Oxford AQA International GCSE Biology)

a. Living organisms remove materials from the environment for growth and other processes. These materials are returned to the environment either in waste materials or when living things die and decay.
b. Materials decay because they are broken down (digested) by microorganisms. Microorganisms are more active and digest materials faster in warm, moist, aerobic conditions.
c. The decay process releases substances that plants need to grow.
d. In a stable community, the processes that remove materials are balanced by processes that return materials. The materials are part of a constant cycle.
e. The constant cycling of carbon is called the carbon cycle.
In the carbon cycle:
• carbon dioxide is removed from the environment by green plants and algae during photosynthesis
• the carbon from the carbon dioxide is used to make carbohydrates, fats and proteins, which make up the body of plants and algae
• when green plants and algae respire, some of this carbon becomes carbon dioxide and is released into the atmosphere
• when green plants and algae are eaten by animals and these animals are eaten by other animals, some of the carbon becomes part of the fats and proteins that make up the bodies of the consumers
• when animals respire, some of this carbon becomes carbon dioxide and is released into the atmosphere
• when plants, algae and animals die, some animals and microorganisms feed on their bodies
• carbon is released into the atmosphere as carbon dioxide when microorganisms respire
• by the time the microorganisms and detritus feeders have broken down the waste products and dead
bodies of organisms in ecosystems and cycled the materials as plant nutrients, all the energy originally absorbed by green plants and algae has been transferred
• combustion of wood and fossil fuels releases carbon dioxide into the atmosphere.
Students should be able to apply the principles of the carbon cycle.

HUMANS AND THEIR EFFECTS ON THE ENVIRONMENT (Oxford AQA International GCSE Biology)
a. Rapid growth in the human population and an increase in the standard of living mean that increasingly more waste is produced. Unless waste and chemical materials are properly handled, more pollution will be
caused.
b. Waste may pollute:
• water, with sewage, fertiliser or toxic chemicals
• air, with smoke and gases such as sulfur dioxide, which contributes to acid rain
• land, with toxic chemicals such as pesticides and herbicides, which may be washed from land into water
• sewage and fertilisers may cause eutrophication:
• an increase in the concentration of mineral ions in the water stimulates the growth of algae and/or plants
• eventually the growth of the algae and/or plants results in some of these being unable to receive sufficient light for photosynthesis and these organisms die
• there is a large increase in the population of microorganisms that feed on these dead organisms
• the respiration of the microorganisms depletes the oxygen concentration in the water, leading to the death of aerobic organisms.
c. Large-scale deforestation in tropical areas has led to reduction in biodiversity.
Students should be able to describe the effects of deforestation.
d. Levels of carbon dioxide and methane in the atmosphere are increasing, and contribute to ‘global warming’.
An increase in the Earth’s temperature of only a few degrees Celsius may:
• cause big changes in the Earth’s climate
• cause a rise in sea level
• cause changes in migration patterns, eg in birds
• result in changes in the distribution of species.
Throughout this section, students should be able, when provided with appropriate information

• to analyse and interpret scientific data concerning environmental issues
• to evaluate methods used to collect environmental data and consider their validity and reliability as evidence for environmental change.

ORGANISMS’ INTERACTION WITH THE ENVIRONMENT (Oxford AQA International GCSE Biology)

Changes in environmental conditions may be biotic or abiotic and can result in responses from an organism which protect the organism from harm and support maintenance of the species. Such responses may impact on the internal stability of the organism or promote certain behaviours to protect it.

The human nervous system (Oxford AQA International GCSE Biology)

a. The nervous system enables humans to react to their surroundings and to coordinate their behaviour.
b. Information from receptors passes along cells (neurones) as impulses to the central nervous system (CNS). The CNS is the brain and spinal cord. The brain coordinates the response.
c. Reflex actions are automatic and rapid. They often involve sensory, relay and motor neurones.
d. In a simple reflex action such as a pain-withdrawal reflex:
• impulses from a receptor pass along a sensory neurone to the CNS
• at a junction (synapse) between a sensory neurone and a relay neurone in the CNS, a chemical is released that causes an impulse to be sent along a relay neurone
• a chemical is then released at the synapse between a relay neurone and motor neurone in the CNS, causing impulses to be sent along a motor neurone to the effector
• the effector is either a muscle or a gland: a muscle responds by contracting and a gland responds by releasing (secreting) chemical substances.
e. Effectors include muscles and glands.
Students should be able, when provided with appropriate information, to analyse a particular given
example of behaviour in terms of:
stimulus → receptor → coordinator → effector → response

Homeostasis (Oxford AQA International GCSE Biology)

a. Automatic control systems in the body keep conditions inside the body relatively constant.
b. Control systems include:
• cells called receptors, which detect stimuli (changes in the environment)
• coordination centres that receive and process information from receptors
• effectors, which bring about responses.
c. Receptors are found in many organs, including:
• the eyes – sensitive to light
• the ears – sensitive to sound, and to changes in position (which enables us to keep our balance)
• the tongue and in the nose – sensitive to chemicals (enable us to taste and to smell)
• the skin – sensitive to touch, pressure, pain and to temperature changes
• the brain – sensitive to blood temperature and the concentration of water in the blood
• the pancreas – sensitive to the concentration of glucose in the blood.
Knowledge and understanding of the structure and functions of sense organs such as the eye and the ear is not required.
d. Coordination centres include the brain and spinal cord and the pancreas.
e. Internal conditions that are controlled include

• temperature
• the water content of the body
• the ion content of the body
• blood glucose levels.

CONTROL OF WATER AND ION CONTENT OF THE BODY (Oxford AQA International GCSE Biology)
a. Water leaves the body via the lungs when we breathe out and the skin when we sweat. Excess water is removed via the kidneys in the urine.
b. Urea and ions are lost via the skin when we sweat. Excess ions are removed via the kidneys in the urine.
c. In the liver:
• excess amino acids are deaminated to form ammonia, which is converted into urea for excretion
• poisonous substances are detoxified, and the breakdown products are excreted in the urine via the kidneys
• old blood cells are broken down and the iron is stored.
d. In a healthy kidney:
• the blood is filtered
• all the glucose is reabsorbed
• the dissolved ions needed by the body are reabsorbed
• as much water as the body needs is reabsorbed
• urea, excess ions and excess water are released as urine.
e. If the water content of the blood is too low, the pituitary gland releases a hormone called ADH into the blood. This causes the kidneys to reabsorb more water and results in a more concentrated urine.
f. If the water content of the blood is too high, less ADH is released into the blood. Less water is reabsorbed in the kidneys, resulting in a more dilute urine.
g. The production of ADH is controlled by a negative feedback mechanism.

Temperature control (Oxford AQA International GCSE Biology)

a. Body temperature is monitored and controlled by the thermoregulatory centre in the brain. The thermoregulatory centre has receptors sensitive to the temperature of the blood flowing through the brain. The name of the centre in the brain (hypothalamus) is not required.
b. Temperature receptors in the skin send impulses to the thermoregulatory centre, giving information about skin temperature.
c. If the core body temperature is too high:
• blood vessels supplying the skin capillaries dilate so that more blood flows through the capillaries and more energy is transferred from the skin to the environment
• sweat glands release more sweat, which cools the body as it evaporates.
Core Tier students are not expected to describe details of changes in the blood vessels when the core body temperature is too high, but should understand that the skin looks red when we are hot due to increased blood flow.
d. Sweating helps to cool the body. More water is lost when it is hot, and more fluid has to be taken through drink or food to balance this loss.
If the core body temperature is too low:
• blood vessels supplying the skin capillaries constrict to reduce the flow of blood through the capillaries
• muscles may ‘shiver’ – their contraction needs respiration, which transfers energy to warm the body.
Core Tier students are not expected to describe details of changes in the blood vessels when the core body temperature is too low.

Control of blood glucose (Oxford AQA International GCSE Biology)

a. The blood glucose concentration is monitored and controlled by the pancreas. Much of the glucose is stored as glycogen in the liver and muscles. When these stores are full, excess glucose is stored as lipid.
b. If blood glucose levels are too high, the pancreas produces the hormone insulin, which allows the glucose to move from the blood into the cells.
c. When blood glucose levels fall, the pancreas produces a second hormone, glucagon. This causes glycogen to be converted into glucose and released into the blood.
d. In Type 1 diabetes a person’s blood glucose level may be too high because the pancreas does not produce enough of the hormone insulin. Type 1 diabetes may be controlled by careful diet, exercise, and by injecting insulin.
e. Type 2 diabetes develops when the body does not respond to its own insulin. Obesity is a significant factor in the development of Type 2 diabetes. Type 2 diabetes can be controlled by careful diet, exercise and by drugs that help the cells to respond to insulin

Behaviour (Oxford AQA International GCSE Biology)

a. Sexual reproduction requires the finding and selection of a suitable mate, and can involve courtship behaviours that advertise an individual’s quality. Animals have different mating strategies, including:
• a mate for life
• several mates over a life time
• a mate for a breeding season
• several mates over one breeding season.
b. Some animals have developed special behaviours for rearing their young. Parental care can be a successful evolutionary strategy, including:
• increased chance of survival of offspring
• increased chance of parental genes being passed on by the offspring.
Students should be able to explain how, within the animal kingdom, parental care may involve risks to the parents

c. The different behaviours displayed by animals include:
• innate behaviour
• imprinting
• habituation
• classic conditioning
• operant conditioning.
d. Humans can make use of conditioning when training captive animals for specific purposes, including:
• sniffer dogs
• police horses.
e. Methods of communication within the animal kingdom. Animals use a variety of types of signals to communicate.
Students should be able to describe the types of signals animals use to communicate eg sound, chemical, visual.

Infection and response (Oxford AQA International GCSE Biology)

a. Microorganisms that cause infectious disease are called pathogens.
b. Bacteria and viruses may reproduce rapidly inside the body. Bacteria may produce poisons (toxins) that make us feel ill. Viruses live and reproduce inside cells, causing damage.
Knowledge of the structure of viruses is not required

c. White blood cells help to defend against pathogens by:
• ingesting pathogens (phagocytosis)
• producing antibodies, which destroy particular bacteria or viruses
• producing antitoxins, which counteract the toxins released by the pathogens.
d. The immune system of the body produces specific antibodies to kill a particular pathogen. This leads to immunity from that pathogen. In some cases, dead or inactivated pathogens stimulate antibody production. If a large proportion of the population is immune to a pathogen, the spread of the pathogen is very much reduced.
e. People can be immunised against a disease by introducing small quantities of dead or inactive forms of the pathogen into the body (vaccination). Vaccines stimulate the white blood cells to produce antibodies that destroy the pathogen. This makes the person immune to future infections by the microorganism, because the body can respond by rapidly making the correct antibody, in the same way as if the person had previously had the disease. The MMR vaccine is used to protect children against measles, mumps and rubella.
Details of vaccination schedules and side effects associated with specific vaccines are not required.
Students should be able to evaluate the advantages and disadvantages of being vaccinated against a particular disease.
f. Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. It is important that specific bacteria should be treated by specific antibiotics. The use of antibiotics has greatly reduced deaths from infectious bacterial diseases.
g. Antibiotics cannot kill viral pathogens.
Students should be aware that it is difficult to develop drugs that kill viruses without also damaging the body’s tissues.
h. Mutations of pathogens produce new strains. Antibiotics kill individual pathogens of the non-resistant strain but individual resistant pathogens survive and reproduce, so the population of the resistant strain rises. Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen. The new strain will then spread rapidly because people are not immune to it and there is no effective treatment.
Knowledge of development of resistance in bacteria is limited to the fact that pathogens mutate, producing resistant strains.
i. Many strains of bacteria, including MRSA, have developed resistance to antibiotics. Overuse and inappropriate use of antibiotics has increased the rate of development of antibiotic-resistant strains of bacteria. Antibiotics are not currently used to treat non-serious infections such as mild throat infections, in order to slow down the rate of development of resistant strains.
j. The development of antibiotic-resistant strains of bacteria necessitates the development of new antibiotics.
Required practical:
Investigate the effect of disinfectants and antibiotics on uncontaminated cultures of microorganisms.

INHERITANCE (Oxford AQA International GCSE Biology)

Genetic information in a cell is held in the chemical DNA in the form of a four letter code. Genes determine the development and structure of organisms. In asexual reproduction all the genes in the offspring come from one parent. In sexual reproduction half of the genes come from each parent.

Reproduction (Oxford AQA International GCSE Biology)

There are two forms of reproduction:
• sexual reproduction – the joining (fusion) of male and female gametes. The mixture of the genetic information from two parents leads to variety in the offspring
• asexual reproduction – no fusion of gametes and only one individual is needed as the parent. There is no mixing of genetic information and so no genetic variation in the offspring. These genetically identical individuals are known as clones

Cell division (Oxford AQA International GCSE Biology)

a. The nucleus of a cell contains chromosomes. Chromosomes carry genes that control the characteristics of
the body. Each chromosome carries a large number of genes.
b. Many genes have different forms called alleles, which may produce different characteristics.
c. In body cells the chromosomes are normally found in pairs.
d. Body cells divide by mitosis to produce additional cells during growth or to produce replacement cells.
e. When a body cell divides by mitosis:
• copies of the genetic material are made
• the cell then divides once to form two genetically identical body cells.
f. Cells in reproductive organs divide to form gametes.
g. A cell divides to form gametes by meiosis.
h. When a cell divides to form gametes:
• copies of the genetic information are made
• the cell then divides twice to form four gametes, each with a single set of chromosomes.
i. Gametes join at fertilisation to form a single body cell with new pairs of chromosomes. This cell repeatedly divides by mitosis to form many cells. As an organism develops, these cells differentiate to form different kinds of cells.
j. Most types of animal cell differentiate at an early stage whereas many plant cells retain the ability to differentiate throughout life. In mature animals, cell division is mainly restricted to repair and replacement.
k. Cells from human embryos and adult bone marrow, called stem cells, can be made to differentiate into many different types of human cell.
l. In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo will not be rejected by the patient’s body so they may be used for medical treatment.

m. Treatment with stem cells may be able to help conditions such as paralysis.
Knowledge and understanding of stem cell techniques is not required.

Students should be able, when provided with appropriate information, to make informed judgements about the social and ethical issues concerning the use of stem cells from adult bone marrow and embryos in medical research and treatments.
n. Tumours result from the abnormal, uncontrolled growth of cells. Benign tumours do not invade other tissues.
Cells from malignant tumours invade healthy tissue. Some malignant cells may enter the bloodstream and circulate to other parts of the body, forming secondary tumours.
o. Tumours can be caused by chemical carcinogens, eg those found in tobacco smoke and in asbestos, and by ionising radiation, eg UV and X-rays. B

Genetic variation (Oxford AQA International GCSE Biology)

a. Differences in the characteristics of individuals of the same kind may be due to differences in:
• the genes they have inherited (genetic causes)
• the conditions in which they have developed (environmental causes)
• a combination of genetic and environmental causes.
b. The information that results in plants and animals having similar characteristics to their parents is carried by genes, which are passed on in the sex cells (gametes) from which the offspring develop.
c. The nucleus of a cell contains chromosomes. Chromosomes carry genes that control the characteristics of the body. Chromosomes are normally found in pairs.
d. In human body cells, one of the 23 pairs of chromosomes carries the genes that determine sex. In females the sex chromosomes are the same (XX); in males the sex chromosomes are different (XY).
e. Different genes control the development of different characteristics of an organism. Some characteristics are controlled by a single gene. Each gene may have different forms called alleles.
Students should understand that genes operate at a molecular level to develop characteristics that can be seen.
f. If both chromosomes in a pair contain the same allele of a gene, the individual is homozygous for that gene. If the chromosomes in a pair contain different alleles of a gene, the individual is heterozygous for that gene.
g. An allele that controls the development of a characteristic when it is present on only one of the chromosomes is called a dominant allele. An allele that controls the development of a characteristic only if the dominant allele is not present is called a recessive allele.
Students should be familiar with principles used by Mendel in investigating monohybrid inheritance in peas.
They should understand that Mendel’s work preceded the work by other scientists which linked Mendel’s ‘inherited factors’ with chromosomes.
Extension Tier students should be able to construct genetic diagrams of monohybrid crosses and to predict the outcomes of monohybrid crosses. They should be able to use the terms homozygous, heterozygous, phenotype and genotype.
Core Tier students should be able to interpret genetic diagrams of monohybrid inheritance and sex inheritance, but will not be expected to construct genetic diagrams or use the terms homozygous, heterozygous, phenotype of genotype.
Students should understand that genetic diagrams are biological models which can be used to predict the outcomes of crosses.
Students should be able to interpret genetic diagrams, including family trees.

h. Chromosomes are made up of large molecules of DNA. DNA contains the coded information that determines inherited characteristics.
i. A gene is a small section of DNA. Each gene codes for a particular combination of amino acids, to make a specific protein.
j. DNA is made of very long strands, twisted to form a double helix, which contain four different compounds, called bases.
Students are not expected to know the names of the four bases or how complementary pairs of bases enable DNA replication to take place.
k. A sequence of three bases is the code for a particular amino acid. The order of bases controls the order in which amino acids are assembled to produce a particular protein.

Genetic disorders (Oxford AQA International GCSE Biology)

Attention is drawn to the potential sensitivity needed in teaching about inherited disorders.
a. Some disorders are inherited.
Students should be able to interpret data relating to genetic disorders such as polydactyly, cystic fibrosis and sickle cell anaemia.
b. Some inherited conditions are caused by inheritance of abnormal numbers of chromosomes, eg Down’s Syndrome is caused by the presence of an extra chromosome

Genetic manipulation (Oxford AQA International GCSE Biology)

a. Modern cloning techniques include:
• tissue culture – using small groups of cells from part of a plant.

• 'cuttings’ – an older, but simple, method used by gardeners to produce many identical new plants from a parent plant
• embryo transplants – splitting cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers
• adult cell cloning – the nucleus is removed from an unfertilised egg cell and the nucleus from an adult body cell, eg a skin cell, is inserted into the egg cell. An electric shock then acts as the catalyst for the egg cell to begin to divide to form embryo cells. These embryo cells contain the same genetic information as the adult skin cell. When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development.
b. In genetic engineering, genes from the chromosomes of humans and other organisms can be ‘cut out’ and transferred to cells of other organisms:
• enzymes are used to isolate the required gene
• this gene is inserted into a vector, usually a bacterial plasmid or a virus
• the vector is used to insert the gene into the required cells.
c. Genes can also be transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics.
d. Crops that have had their genes modified in this way are called genetically modified (GM) crops. GM crops include ones that are resistant to insect attack or to herbicides.
e. GM crops generally show increased yields.
f. Concerns about GM crops include the effect on populations of wild flowers and insects, and uncertainty about the effects of eating GM crops on human health.
Students should be able, when provided with appropriate information, to interpret information about cloning techniques and genetic engineering techniques and to make informed judgements about issues concerning cloning and genetic engineering, including GM crops.

VARIATION AND EVOLUTION (Oxford AQA International GCSE Biology)

All life today is directly descended from a universal common ancestor that was a simple one-celled organism. Over countless generations changes resulted from natural diversity within a species which makes possible the selection of those individuals best suited to survive under certain conditions. Organisms not able to respond sufficiently to changes in their environment are at risk of becoming extinct.

Continuous and Discontinuous Variation (Oxford AQA International GCSE Biology)

The causes of variation include:
• genetic variation – different characteristics as a result of mutation or reproduction
• environmental variation – different characteristics caused by an organism’s environmental (acquired characteristics).

Natural selection (Oxford AQA International GCSE Biology)

a. Theories of how organisms have evolved include:
• the theory of evolution by natural selection
• other theories, including that of Lamarck, are based mainly on the idea that changes that occur in an organism during its lifetime can be inherited. We now know that in the vast majority of cases this type of inheritance cannot occur.
b. Evolution occurs via natural selection.
• Individual organisms within a particular species may show a wide range of variation because of differences in their genes.
• Individuals with characteristics most suited to the environment are more likely to survive to breed successfully.
• The genes that have enabled these individuals to survive are then passed on to the next generation.
Students should develop an understanding of the time scales involved in evolution.
c. New species arise as a result of:
• isolation: two populations of a species become separated, eg geographically
• genetic variation: each population has a wide range of alleles that control their characteristics
• natural selection: in each population, the alleles that control the characteristics which help the organism to survive are selected
• speciation: the populations become so different that successful interbreeding leading to fertile offspring, is no longer possible