AQA Biology GCSE   

Modules 11.1 - 12.7


Module 11.4 (Infections) - What causes infectious

  • microorganisms that cause infectious diseases are called pathogens.
  • bacteria and viruses may reproduce rapidly inside the body and may produce toxins which make us feel ill.
  • viruses damage cells in which they reproduce.
  • white blood cells help to defend the body against pathogens.
  • white blood cells ingest pathogens.
  • white blood cells produce antibodies which destroy paticular bacteria and viruses.
  • they produce antitoxins which counteract with the toxins released by pathogens.
  • some medicines help to relieve the symptoms of disease but do not kill the pathogens.
  • antibiotics kill bacteria inside the body.
  • antibiotics can not kill viral pathogens as they live and reproduce inside body cells.
  • viral drugs are difficult to develop without damaging body tissue.
  • some strains of bacteria are resistant to antibiotics. This has happened due to natural selection.
  • an example of a resistant strain is MRSA.
  • reducing overuse of antibiotics can reduce antibiotic resistance.
  • people can be immunised by introducing small quantites of dead or inactive forms of the pathogen.
  • vaccines stimulate white blood cells to produce antibodies. This makes the person immune to future infection.
  • if the pathogen is met again, the correct antibody can be rapidly produced.
  • MMR is a vaccine used to protect against measles, mumps and rubella.
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Module 11.5 (Survival) - What determines where pat

  • to survive, organisms require a supply of material from their surroundings and from the other living organisms there.
  • plants compete with each other for light, water and nutrients.
  • animals compete with each other for food, mates and territory.
  • organisms have features which help them survive in the conditions which they normally live.
  • animals and plants may be adapted to cope with specific features of their environment e.g. thorns, poisons and warning colours.
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Module 11.3 (Drugs and Alcohol) - How do we use/ab

  • drugs can be beneficial but can harm the body.
  • many drugs are made from natural substances and have been known about by indigenous people for many years.
  • scientists need to test new drugs thoroughly/
  • drugs are tested in the lab to see if they are toxic. They are trialed on human volounteers to find any side effects.
  • thalidomide is a drug that was developed as a sleeping pill but also proved to relieve morning sickness in pregnant women.
  • it had not been tested and the babies born had severe limb abnormalities.
  • thalidomide was banned but can be used to treat leprosy.
  • some people use drugs recreationally. Some more harmful than others, some are legal others are not.
  • the impact of legal drugs is greater than illegal drugs because more people use them.
  • drugs change the chemical processes in people's bodies.
  • people can become dependent or addicted to drugs and can suffer withdrawal symptoms without them.
  • heroine and cocaine are very addictive.
  • nicotine is the addictive substance in tobacco smoke.
  • tobacco smoke contains carcinogens.
  • the smoke also contains monoxide which reduces the oxygen carrying capacity of the blood. In pregnant women this can deprive the foetus of oxygen and lead to a low birth rate.
  • alcohol affects the nervous system by slowing down reactions and it helps people to relax.
  • Alcohol can lead to a lack of self control unconsciousness or coma. It can damage the liver and brain (when consumed in excess).
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Module 12.1 (Cells) - What are animals and plants

  • a nucleus controls the activity of the cell.
  • cytoplasm is where chemical reactions take place.
  • a cell membrane controls the passage of substances in and out of the cell.
  • the mitochondria are where the most energy is released in respiration.
  • protein synthesis occurs in ribosomes.
  • plants have cell walls to strengthen the cell.
  • plant cells have chloroplasts to absorb light energy to make food.
  • plant cells have a permanent vacuole filled with cell sap.
  • chemical reactions inside cells are controlled by enzymes.
  • cells can be specialised to carry out a paticular function.
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Module 12.2 (Cells) - How do dissolved substances

  • dissolved substances can move into and out of cells by diffusion and osmosis.
  • diffusion is the spreading of the particles of a gas, or a substance in a soloution, resulting in a net movement from a region where they are of a higher concentration (to a region of lower concentration).
  • the greater the difference in concentration, the faster the rate of diffusion.
  • oxygen for respiration passes through the cell membranes by diffusion.
  • water often moves across boundaries by osmosis.
  • osmosis is the diffusion of water from a dilute to a more concentrated soloution through a partially permeable membrane that allows the passage of water molecules.
  • differences in the concentrations of the soloutions inside and outside of a cell causes water to move into or out of the cell by osmosis.
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Module 12.4 (Food Chains) - What happens to energy

  • radiation from the sun is the source of energy for most communities of living organsims.
  • green plants capture a small part of the solar energy that reaches them. this energy is stored in the substances which make up the cells of the plants.
  • the living mass (biomass) at each stage can be drawn as a pyramid of biomass.
  • at each stage in a food chain, less material and less energy are contained in the biomass of the organsims.
  • the efficiency of food production can be increased by reducing the number of stages in the food chains.
  • the efficiency of food production can be improved by restricting energy loss production from food animals by limiting their movement and controlling the temperature of their surroundings.
  • the amount of energy is reduced at each stage in the food chain.
  • some materials  and energy are lost in waste materials.
  • respiration supplies all the energy needed for the living processes, including movement.
  • energy is lost to the environment as heat to the surroundings.
  • the losses are large in mammals and birds whose bodies must be kept at a constant temperature which is higher than that of their surroundings.
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Module 12.5 (The Carbon Cycle) - What happens to t

  • living things remove materials from the environment for growth and other processes.
  • there materials are returned to the environment in waste materials or when living things die and decay.
  • materials decay because they are broken down (digested) by microorganisms.
  • microorganisms digest materials faster in warm moist conditions.
  • many microorganisms are more active when there is plenty of oxygen.
  • the decay process releases substances which plants need to grow.
  • in a stable community, the processes which remove materials are balanced by processes that return materials. The material are cycled.
  • the cycling of carbon is called the carbon cycle.
  • carbon dioxide is removed from the environment by photosynthesis.
  • the carbon from the carbon dioxide is used to make carbohydrates, fats and proteins which make up the body of plants.
  • some carbon dioxide is returned to the atmosphere when green plants respire.
  • plants are eaten by animals, some of this carbon becomes part of the fats and proteins which make up their bodies.
  • when animals respire some carbon becomes carbon dioxide and it is released into the atmosphere.
  • when plants and animals die, some animals and microorgansims feed on their bodies. carbon is released into the atmosphere as carbon dioxide when these organisms respire.
  • by the time the microorgansims and detritus feeders have broken down the waste products and dead bodies of organisms in ecosystems and cycled the materials as plant nutirients, all the energy originally capture by green plants has been transferred.
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Module 12.6 (Enzymes) - What are enzymes and what

  • catalysts increase the rate of chemical reactions.
  • biological catalysts are called enzymes.
  • enzymes are protein molecules made up of long chains of amino acids.
  • these long chains are folded to produce a special shape which enables other molecules to into the enzymes. The special shape enables other molecules to fit into the enzyme - known as a lock and key design.
  • high temperatures destroy this special shape, the enzyme becomes denatured (usually ~ 40 degrees celcius).
  • different enzymes work best at different pH values.
  • enzymes inside living cells catalyse processes such as respiration, protein synthesis.
  • during aerobic respiration chemical reactions occur that uses glucose and oxygen and releases energy.
  • aerobic respiration is summarised by the equation

                   glucose + oxygen -----> carbon dioxide + water (and light energy)

  • energy from respiration is used to build up larger molecules using smaller ones.
  • energy is used to contract muscles.
  • energy is used to maintain a steady body temperature.
  • in plants energy is used to build up sugars, nitrates and other nutrients into amino acids which are then built up into proteins.
  • energy inside living cells catalyse the reactions that build up amino acids and proteins.
  • some enzymes work outside body cells.
  • the digestive enzymes are produced in specialised cells in glands in the lining of the gut.
  • these enzymes catalyse the breakdown of large to small molecules.


  • this enzyme is produced in the salivary glands, the pancreas and the small intestine.
  • it catalyses the breakdown of starch into sugars in the mouth and small intestine.


  • this enzyme is prioduced in the stomach, the pancreas and the small intestine.
  • it catalyses the breakdown of proteins to amino acids molecules in the stomach and small intestine.


  • this enzyme is produced by the pancreas and small intestine.
  • they breakdown lipids into fatty acids and glycerol in the small intestine.


  • the stomach produces hydrochloric acid. The enzymes in the stomach work most effectively in these acidic conditions.
  • the liver produces bile.
  • bile is stored in the gall bladder and released into the small intestine.
  • bile neutralises the acid that was added in the stomach.
  • bile provides alkaline conditions in which the enzymes in the small intestine work most effectively.
  • some microorganisms produce enzymes which pass out of the cells.
  • these enzymes have many uses in the home and industry.
  • in the home, biological detergents may contain protein digesting and fat digesting enzymes.
  • in industry proteases are used to pre-digest the proteins in some baby foods.
  • in industry, carbohydrases are used to convert glucose syrup into fructose syrup.
  • fructose is sweeter and therefore can be used in smaller quantities in slimming foods.
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Module 11.1 (Humans) - How do human bodies respond

  • the nervous system enable humans to react to their environment.
  • receptors detect stimuli.
  • information passes from nerves to brain and the brain stimulates responses.
  • reflex actions are fast and automatic.
  • receptors  -  are proteins that allow signal molecules to attach to it, it detects the presence of chemicals and this will be sent on as a message to the brain. They are found clustered in special sense oragans such as your eyes and skin.
  • sensory neurones  -  these are cells which carry impulses from your sense organs to your central nervous system.
  • relay neurones  -  these connect a sensory neurone and a motor neurone. They are found in the CNS, often in the spinal cord.
  • effector organ  -  muscles and glands which respond to impulses from the nervous system.
  • synapses  -  the gaps between neurones where the transmission of information is chemical. When an impulse arrives at the junction between two neurones, chemicals are released which cross the synapse.
  • hormones are chemicals that are secreted by glands and are transported by target organs in the bloodstream.
  • internal conditions in the body are controlled. This includes water, ions, temperature and blood sugar.
  • water leaves via the lungs, sweating and urine from the kidney.
  • ions are lost by sweating and from the kidney.
  • temperature is controlled so enzymes work best.
  • blood sugar controlled so energy supply is constant.
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Module 11.2 (Diet) - What can we do keep our bodie

  • a healthy diet contains the right balance of different foods to give you the right amount of energy.
  • a person is malnourished if their diet is not balanced.
  • this can lead to the person becoming too fat or too thin.
  • it can also lead to deficiency diseases.
  • the rate at which chemical reactions happen in the body is called the metabolic rate.
  • the metabolic rate varies with the amount of activity, inherited factors and the proportion of muscle to fat in the body.
  • the amount of food you need is affected by how warm it is and how much exercise is taken.
  • people that exercise are fitter than those that do not.
  • metabolic rate remains high for some time after exercise.
  • in the developed world too much food is eaten and too little exercise is taken. This leads to obesity.
  • obesity can lead to arthiritis (worn joints), diabetes (high blood sugar), high blood pressure and heart disease.
  • people in the developing world can suffer from a lack of food.
  • this can lead to a lower resistance to infection and irregular periods.
  • cholesterol is made by the liver and foung in the blood.
  • the amount of cholesterol depends on diet and inherited factors.
  • high levels of cholesterol can lead to an increased chance of heart and vessel disease.
  • there are two types of cholesterol  -  low density lipoproteins (LDL) and high density lipoproteins (HDL).
  • LDL are considered to be bad and HDL are considered to be good. The balance between the two are important.
  • saturated fats increase the blood cholesterol levels.
  • mono-unsaturated and poly-unsaturated fats can reduce blood cholesterol levels. It improves the balance between LDLs and HDLs.
  • too much salt in the diet can lead to increased blood pressure for 30% of the population.
  • processed food contains a high proportion of fat and/or salt.
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Module 11.8 (Humans) - How do humans affect the en

  • rapid growth in the human poulation and an increase in the standard of living means that raw materials are rapidly being used (including non - renewable sources).
  • rapid growth in the human population and an increase in the standard of living means that more waste is produced.
  • rapid growth in the human population and an increase in the standard of living means that unless waste is properly handled more polloution will be caused.
  • humans reduce the amount of land available for other animals and plants by building, quarrying , farming and dumping waste.
  • more waste is being produced which may pollute water with sewage, fertiliser or toxic chemicals.
  • more waste is being produced which may pollute air with smoke and gases.
  • sulphur dioxide contributes to acid rain.
  • more waste is being produced which may pollute land with toxic chemicals such as pesticides and herbicides, which may be washed from land to water.
  • living organisms can be used as polloution indicators.
  • invertebrate animals can be used as water polloution indicators.
  • lichens can be used as air polloution indicators.
  • deforestation in tropical areas occurs for timber and agriculture.
  • deforestation causes an increase in carbon dioxide in the atmosphere (because of burning and the activities of microorgansims).
  • deforestation reduces the rate at which carbon dioxide is removed from the atmosphere and locked up for many years as wood.
  • deforestation leads to reduction in biodiversity. Some of these organisms are now lost for future use.
  • increase in the numbers of cattle and rice fields had led to an increase in methane.
  • carbon dioxide and methane in the atmosphere absorb most of the energy radiated by the earth.
  • some of this energy is radiated back to earth and it keeps the earth warmer than it would be.
  •  a rise in only a few degrees will cause changes to the Earth's climate and cause a rise in the sea levels.
  • improving the quality of life without compromising future generations is called sustainable development.
  • planning at local, regional and global level is needed to manage sustainability.
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Module 12.7 (Humans) - How do we keep our internal

  • carbon dioxide is a waste product from respiration. It leaves the body via the lungs when we breathe out.
  • urea is a waste product of the liver created by the breakdown of excess amino acids.
  • urea is removed by the kidney in the urine which is temporarily stored in the bladder.
  • internal conditions which are controlled include the water content of the body, the ion content of the body, temperature and blood sugar levels.
  • if the water or ion content of the body is wrong too much water may move into or out of the cells and damage them.
  • water and ions enter the body when we eat and drink.
  • sweating helps to cool the body.
  • more water is lost when we are hot, and more water has to be taken as drink or in food to this loss.
  • body temperature is monitored and controlled by the thermoregulatory centre in the brain.
  • temperature receptors in the skin send impulses to the centre giving information about the skin temperature.
  • if the core body temperature is too high blood vessels supplying the skin capillaries dilate so that more blood flows close to the surface and more heat is lost.
  • if the core body temperature is too high, sweat gland release more sweat which cools the body down as it evaporates.
  • If the core body temperature is too low blood capillaries supplying the surface of the skin constrict to reduce the blood flow through the capillaries.
  • if the core body temperature is too low, muscles may shiver. their contractions needs respiration which releases some energy as heat.
  • the blood glucose concentration of the body is monitored and controlled by the pancreas.
  • the pancreas produces the hormone insulin.
  • insulin allows glucose to move from the blood into the cells.
  • diabetes is a disease in which a person's blood glucose concentration may rise to a fatally high level.
  • the pancreas does not produce enough insulin.
  • diabetes can be treated by careful attemtopm to diet and by injecting insulin into the blood.
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