Biology Module 3

A complete set of revision notes for all of the AQA GCSE Biology - Module 3.

This follows the revision guide and includes - 

  • Exchange of Materials
  • Circulation/Transporting Materials
  • Homeostasis/Keeping Internal Conditions Constant
  • Human Impact on the Environment

All the notes I make are summary notes and may include inside jokes/sarcasm/anecdotes (but no swearing) to keep me entertained whilst I revise. If you are put off by this I apologise but the primary reason for these cards was for my personal revision. However if this doesn't bother you then continue on! Thank you!


Biology Module 3

Exchange of Materials - 1.1 Osmosis

Osmosis - The random diffusion of water from a high to a low concentration through a Partially-                 Permeable Membrane (PPM). The overall moevement in this direction is called the                   'Net Movement' 

If there is a high water concentration then it is a dilute solution.

If there is a low water concentration then it is a concentrated solution.

(Don't be confused by ^ in exams. It may be included to put you off)

Tip - Remember osmosis refers to the movement of water molecules only. 

Osmosis can be used to transfer water in and out of cells. 

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Biology Module 3

Exchange of Materials - 1.2 Active Transport

Active Transport  - This allows cells to take in substances through a Partially-Permeable Membrane against the concentration gradient because they are in short supply. 

To enable 'Active Transport' to work, energy released from respiration is required. 


   Cells are able to absorb ions from dilute solutions such as -

  • Root Cells absorbing mineral ions from the dilute solutions in the soil. These are in a dilute solution but needed for the plants life
  • Glucose can be re-absorbed from the Kidney tubule via Active Transport as the enrgy is needed for the body to function.

Remember Active Transport needs energy. Osmosis and diffusion don't.  

For a diagram of Active Transport look at p 70. 

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Biology Module 3

Exchange of Materials - 1.3 The Sports Drink Dilemma

Exercise causes your body to heat. To counter act this your body produces sweat. Whilst this does work in cooling your overall temperature down it uses a lot of vital water and mineral ions. Over-exertion or an excess of sweating may casue dehydration. 

Exercise also requires energy. The energy used comes from Glucose being broken down in respiration in the muscles.  

Our bodies need to maintain a constant water, sugar and mineral supply and so during exercise these must be replaced. Sounds obvious but apparently loads miss this out. 

Sports drinks are solutions of sugar and mineral ions (and naturall water to rehydrate the cells).The drinks are designed to balance the concentration of body fluids and concentrations inside cells. If the drink concentration matches the body fluids the solution is called isotonic. 

Many debate whether Sports drinks are actually effective. Some think they are good for athletes who exercise a lot, others think that just water will be fine. 

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Biology Module 3

Exchange of Materials - 1.4 Exchanging Materials - The Lungs

Like most complex organs the lungs have a special exchange surface e.g. solutes are absorbed by the intestine, oxygen is absorbed by the lungs and CO(2) removed from them. 

To be an efficient exchange surface you have to have - 

  • a large surface area
  • thin walls (usually one cell thick) or a short diffusion path
  • an efficient transport system - in animals this is the blood circulatory system. 

The lungs contain the 'Gaseous Exchange Surface'. To increase the surfacce area of the lungs it contains alveoli (air sacs). Alveoli have thin walls, a large surface area to volume ration and a good blood supply. Oxygen diffuses into the many capillaries surrounding the alveoli and carbon dioxide diffuses back out into the lungs to be breathed out. 

To keep a steep  diffusion gradient the lungs are ventilated. 

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Biology Module 3

Exchange of Materials - 1.5 Ventilating the Lungs

Breathe In

  • The Intercostal muscles between the ribs and the diaphragm contract.
  • The ribcage moves up and out and the diaphragm flattens
  • The volume of the thorax increases
  • The pressure in the thorax decreases and air is drawn in

Breathe Out

  • The Intercostal Muscles of the ribcage and diaphragm relax
  • The ribcage moves up and down and in and the diaphragm becomes domed.
  • The volume of the thorax decreases
  • The pressure increases and air is drawn out. 

Memorise the diagram on p72  because this is a better description. 

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Biology Module 3

Exchange of Materials - 1.6 Artificial Breathing Aids

Reasons why people can't get oxygen into their blood - 

  • If alveoli are damaged, the surface area for gas exchange is reduced
  • If the tubes leading to the their muscles will not work to pull the ribcage up and out

Breathing Aids Developed - 

  • Iron Lung. Used for people with Polio. Lay with chest ealed in a large metal container. When air was drawn out of the cylinder the person's chest moved out and they breathed in . The vacuum which was formed inside the cylinder created a negative pressure. When air was pumped back in to the cylinder it created pressure on the chest and forced air out of the person's lungs.
  • We can use bags of air to force air down the trachea. This is an example of Positive Pressure. 
  • Positive Pressure aids are often smaller, easier to manage in the home and can be linked to computers for control. 
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Biology Module 3

Exchange of Materials - 1.7 Exchange in the gut

Food is digested in the gut into small soluble molecules that can be absorbed into the blood in the small intestine.

To help this villi line the small intestines walls and are the exchange surface for food molecules. They - 

  • greatly improve the surface area
  • have very thin walls and there are a number of capillaries
  • soluble products can be absorbed into the villi via active transport or diffusion. 

Tip - always relate the features of an exchange surface e.g. alveoli in the lungs, villi in the small intestine. 

Learn diagram on p74

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Biology Module 3

Exchange of Materials - 1.8 Exchange in Plants

Stomata - 

  • Gases diffuse in and out of these holes on a leaves surfacce
  • The size is controlled by the guard cells surrounding them 
  • Oxygen - needed for respiration and is a waste product of photosynthesis
  • Carbon dioxide - needed for photosynthesis and is a waste product of repsiration.
  • Plants also lose water through the stomata due to evaporation in leaves. 

Due to thin, flat shape of leaves, gases don't need to diffuse very far. There are also internal air spaces. 

Root hair cells increase the surface area of the roots so inreased amounts of water and minerals are absorbed into the plant. If plants lose water faster than it is replaced by the roots then the stomata close up to prevent the plant from withering. 

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Biology Module 3

Exchange of Materials - 1.9 Transpiration

Transpiration Stream - The movement of water through plants. Plants take up water via the roots. This goes through the plants to leaves. In leaves the water evaporates and leaves the plant as a gas through the stomata. 

Evaporation/Transpiration is more rapid in dry, hot, windy or bright conditions. 

Evaporation/Transpiration is less rapid in wet, cold, still or dark conditions. 

To prevent excessive water loss Guard cells close up the stomata. 

Wilting also reduces water loss because the leaves collapse and hang down which reduces surface area. 

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Biology Module 3

Transporting Materials - 2.1 The Circulatory System and The Heart

The Human circulatory System consists of blood vessels, the heart and the blood. 

  • The Heart - a muscular organ which consists of two pumps. These pump blood around the                        body.
  • Right Pump - forces deoxygenated blood to lungs where it gets oxygen and loses CO(2). Blood                     returns to the heart 
  • Left pump - pumps oxygenated blood around the body. This pump is bigger than the other.
  • Aorta - carries oygenated blood around the body. On left hand side of heart. (If its a diagram it may be a mirror image this is hard to explain look at the diagram in your book).
  • Pulmonary vein - brings oxygenated blod from lungs
  • Left pump - consists of left atrium, left ventricle and heart valves. The heart muscle wall is thicker on this side than the right, 
  • Vena Cava - brings deoxygenated blood from body to heart. 
  • Pulmonary Artery - takes deoxygenated blood from heart to lungs to get oxygen
  • Right pump - consists of right atrium, right ventricle and heart valves. 
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Biology Module 3

Transporting Materials - 2.2 Keeping the Blood Flowing

Arteries - 

  • Carry blood away from the heart (Pulmonary Artery, Aorta) 
  • Have thick walls containing muscle and elastic tissue

Veins - 

  • Have thinner walls than arteries
  • Often have valves along their length to prevent blackflow of blood. 

Capillaries - 

  • Are narrow thin-walled vessels
  • Carry the blood through the organs and allow the exchange of substances with all tthe living cells in the body.

Stents - Can be inserted to keep blood vessels open. Metal framework. Lack of blood flow will                    cause organs to be deprived of the necessary oxygen. 

Artificial/Animal valves can be inserted in the heart to cure leaky/damaged valves. Otherwise blood could flow in the wrong direction 

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Biology Module 3

Transporting Materials - 2.3 Transport in the Blood

Blood is made of  - 

  • Plasma - The clear fluid that transports the other cells. It also transports Carbon Dioxide from organs to the lungs, Soluble digestion products from small intestine to other organs and urea from the liver to the kidneys where urea is made. 
  • White Blood Cells - These have a nucleus and are part of the bodies immune system. 
  • Platelets - Are small fragments of cells. THey do not have a nucleus. They hep blood to clot at wound sites so that scabs can be formed. 
  • Red Blood Cells - Biconcave discs which have no nucleus. Contain the red pigment haemoglobin which combines with oxygen to form Oxyhaemoglobin in the lungs. Carries Oxyhaemoglobin to the organs and muscles where the oxyhaemoglobin splits into haemoglobin and oxygen. 

Learn the diagrams on p79

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Biology Module 3

Transporting Materials - 2.4 Artificial or Real?

Artificial Blood

  • Most patients just need a blood tranfusion which is just extra plasma.
  • Blood from blood donors can be separated into cells and plasma. Any donated blood must be refrigerated.
  • Perfluorocarbons (PFC's) or artificial  blood can be used. It does not need refrigeration. It doesn't contain cells. 
  • Artificial blood is expensive and does not carry as much oxygen. Some types don't mix well with blood because they are insoluble in water. 
  • Can cause side-effects

Artificial Hearts

  • For patients who suffer heart failure. A lack of donors means artificial ones are being developed. 
  • Do not need to match person's tissue. No need for immunosuppressant drugs. 
  • Problems with blood clotting, long stays in hospital and expense. 
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Biology Module 3

Transporting Materials - 2.5 Transport Materials in Plants

Plants have separate transport systems. 

Xylem - 

  • Transports water and mineral ions from the roots to the stem, leaves and flowers. 
  • That water that moves through the Xylem forms 'The Transpiration Stream'
  • It is mono-directional (water only goes in one direction - upwards)

Phloem Tissue - 

  • Carries dissolved sugars from the leaves to the rest of the plant, including the growing regions and the storage organs. 
  • Bi-directional. 

Look and learn the diagram in your Biology folder. 

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Biology Module 3

Keeping Internal Conditions Constant - 3.1 Controlling Internal Conditions

Homeostasis - The act of keeping conditions controlled within in a narrow range. In the body                                temperature, blood glucose, water, ion content and levels of waste product are all                          controlled via Homeostasis. 

Waste Products Removed include - 

  • Carbon dioxide - produced in respiration and removed via the lungs when we breathe out.
  • Urea - produced in the liver from the breakdown of amino acids and removed by the kidneys in the urine (temporarily stored in bladder). 

Water and ions enter the body when we eat and drink. If the water or ion content in the body is wrong, too much water may move in or out of cells - this could damage or destroy cells. 

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Biology Module 3

Keeping Internal Conditions Constant - 3.2 The Human Kidney

Kidneys - Filter the blood removing excess products and waste products and leaving out the products your blood needs.

The Production of Urine -

  • 1. Filter the blood
  • 2. Reabsorb all the sugar back into the blood
  • 3. Reabsorb all the dissolved ions the body needs back into the blood 
  • 4. Reabsorb as much water as the body needs
  • 5. Release urea, excess ions and water in the urine.

Learn the diagram on p82 like the back of your hand. 

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Biology Module 3

Keeping Internal Conditions Constant - 3.3 Dialysis - an artificial Kidney

If a person suffers from Kidney failure, dialysis can keep them alive. 

Dialysis Machines

  • Performs the same job as the kidneys. Blood flows between PPM's. 
  • Dialysis fluid contains the same concentration of useful substances that the patients blood does e.g. glucose and mineral ions. This means that these substances do not diffuse out of the blood so they do not need to be reabsorbed. Urea diffuses out from the blood into the dialysis fluid. 
  • Dialysis restores the concentration of subsnaces in the blood back to normal but needs to be carried out at regular intervals.

If a kidney becomes available the patient may have a kidney tranpslnt. If the transplant is succesful the person will not need furthr dialysis. 

Learn by heart (see what I did their ;)) the two diagrams. 

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Biology Module 3

Keeping Internal Conditions Constant - 3.4 Kidney Transplants

Kidney Tranplant - a better option for most patients. Replaces the damaged kidney with a                                         healthy one. Can come from a victim of a fatal accident or a living donor. 

To prevent 'rejection' the donor must be of a strong 'tissue match' to the patient.

If it is not a good tissue match there are proteins on the surface of cells called antigens. The recipients antibodies may attack these antigens because it see's them as foreign. This is rejection.

To prevent rejection the patient must take drugs afterwards to suppress the immune response. These are called 'Immunosuppressants' Drugs. 

There is a high risk before the operation because the immune system must be repressed leaving them highly susceptible to common infections. 

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Biology Module 3

Keeping Internal Conditions Constant - 3.5 Controlling Body Temperature

The core body temperature must be kept stable. It is monitored by the Thermoregulatory Centre in the brain - receptors detect the temp of blood flowing through the brain. Temperature receptors in the skin also send signals to the brain about skin temperatures. 

To cool the body down - 

  • Blood vessels near the skin dilate to allow more blood to flow through the capillaries their. Energy is transferred by radiation and the skin cools. Vasaldilation. 
  • Sweat glands produce sweat. The water evaporates from the skin surface. The energy required for the water to evaporate comes from the skins surface - so we cool down

To heat the body up - 

  • Blood vessels constrict so there is a lack of blood flow near skin. Less energy is radiated. Vasalconstriction
  • We 'shiver'. Muscles quickly contract. this requires respiration and some of the energy released warms the blood.  
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Biology Module 3

Keeping internal Conditions Constant - 3.6 Treatment and Temperature Issues

Things Doctors need to consider when discussing Kidney transplant or dialysis with patients - 

  • The health of a patient
  • how long the patient has been on dialysis
  • The total cost of treatment 
  • The risks of a transplant operation e.g. infection, anaesthetics
  • The availability of donor kidneys
  • Should everyone be on a transplant list automatically or shuld they choose
  • Should people paid to be donors?
  • Should people pay for a new kidney to jump the queue.

Extreme Environments

  • Elderly people are more likely to suffer from hypothermia because they don't move around as much.
  • Explorers have to learn to recognise the symptoms of dehydration and hypothermia. 
  • Children have a large s.a to volume ratio. This means they dehydrate quickly in hot conditions and transfer energy to surroundings quickly in cold conditions. If body temp alters drastically then the enzymes denature and the body cannot function. Read more on this. 
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Biology Module 3

Keeping Internal Conditions Constant - 3.7 Controlling the blood glucose

The pancreas monitors and controls the level of blood sugar in our blood. 

Too much and the pancrease makes insulin - this causes the Glucose to move from the blood into the cells.

In the liver excess glucose is converted to Glycogen for storage. 

Type 1 Diabetes - When no (or little) Insulin is produced by the Pancreas and the blood sugar level                           becomes to high. It can be controlled by injections of Insulin and careful                                       monitering of diet and exercise.

If however there is too much Insulin and the blood levels fall to much the pancreas detects this and releases Glucagon, another hormone. This causes the Glycogen in the liver to convert back into Glucose and is released back into the blood. 

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Biology Module 3

Keeping Internal Conditions Constant - 3.8 Treating Diabetes

Type 1 Diabetes is treated with human Insulin made by genetically engineered bacteria. Before every meal, the diabetic must inject Insulin. 

Some use pumps and can adjust the level of insulin injected by the pump. 

Doctors and other scientists are trying to develop new methods of treating and possibly curing Type 1 diabetes. These include - 

  • Pancreas transplants
  • Transplanting Pancreas cells
  • Using embryonic stem cells to produce insulin secreting cells
  • Using adult stem cells from dabetic patients
  • Genetically engineering pancreas cells to make them work properly
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Biology Module 3

How Humans Can Affect the Environment - 4.1 The Effects of the Population Explosion

  • Current size of the world's population is approximately 7 billion. All of these want a better standard of living
  • Humans use raw materials and those that are non-renewable cannot be replaced.
  • Industrial waste occurs when goods are produced
  • When we build, quarry, farm or just dump waste we use up land that available for animals and plants
  • The rise in the human population is affecting the ecology of Earth. 
  • Some problems occur miles away from the source e.g. Sulfur Dioxide gas can be blown to another area before making acid rain there.

We pollute - 

  • Waterways - sewage, fertiliser and toxic chemicals
  • Air - Smoke, gases (Sulfur Dioxie = acid rain)
  • Land - toxic chemicals (Pesticides and Herbicides which are then washed into the water. 
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Biology Module 3

How Humans Can Affect the Environment - 4.2 Land and Water Pollution

Water Pollution - 

  • Herbicides, pesticides and chemical fertilisers all get washed into rivers and streams by rain.
  • Fertilisers and untreated sewage can cause a high level of nitrates in the water. 
  • Toxic chemicals from landfill also leak into the waterways and pollute the water killing organisms such as fish.

Land Pollution - 

  • Sewage - it must be treated properly to remove gut parasites and toxic chemicals or these can get onto the land. Contains human body waste and waste water. 
  • Landfill waste (household and industrial waste) can let toxic chemicals leak out. Radioactive waste in particular is very hazardous.
  • Farming methods pollute the land
  • Herbicides and Pesticides are poisons. They easily get into the food chain harming animal life. Lots are also washed into rivers
  • To keep soil fertile, farmers use chemical fertilisers which gets washed into rivers
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Biology Module 3

How Humans Can Affect the Environment - 4.3 Air Pollution 

  • Anything  burns fuels will produce an acidic gas ( often Sulfur Dioxide) e.g. factories and cars. 
  • This Sulfur Dioxide then dissolves in the wwater vapour in the atmosphere forming an acidic solution
  • This then falls as Acid Rain. Often acid rain occurs a long way away from the gas was produced simply because of winds. 
  • Acid rain kills organisms e.g. trees.
  • Acid rain ca nchange the soil pH which can damage roots and release toxic materials e.g. aluminium ions are released which also damages organisms in the soil and in waterways. 
  • Enzymes which control reactions are very sensitive pH (acidity or alkalinity) 
  • When trees are damaged, food and habitats for many other organisms are lost. 
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Biology Module 3

How Humans Can Affect the Environment - 4.4 Deforestation and Peat Destruction

Deforestation - Multiple trees are cut down. In tropical regions large scale deforestation occurs because of the need for timber and agricultural land.

It has - 

  • Increased the release of CO(2) due to burning and decay of trees.
  • Reduced the rate of CO(2) being extracted from the air via photosynthesis. 
  • Reduced biodiversity due to a loss of habitat/food.

It occured so that - 

  • Crops can be grown to produce ethanol-based biofuels.
  • There can be increases in cattle and rice fields for food.

Problems - 

  • Cattle and rice produce excessive methane (in the agricultural land).
  • Destruction of peat/peat bogs results in CO(2) being released into the atmosphere. Happens because the peat is removed from the bogs and used as compost. The compost is decayed by micro-organisms. Using  peat-free composts saves peat bogs. 
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Biology Module 3

How Humans Can Affect the Environment - 4.5 Global Warming

Carbon Dioxide is sequestered by plants and water. This means that it is taken in and stored by them. Normal balance in the environment means that CO(2) is taken in by plants and released by respiration and decay. 

Levels of CO(2) and Methane are increasing in the atmosphere. They are greenhouse gases and cause the greenhouse effect. 

An increase in Earth's temperatures (by only a few degrees) will -

  • Cause big changes in the Earth's climate.
  • Cause a rise in sea level due to melting of ice caps and glaciers
  • Reduce biodiversity
  • Cause changes in migration patterns e.g. birds
  • Result in the distribution of species. 
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Biology Module 3

How Humans Can Affect the Environment - 4.6 Biofuels

Biofuels are made from natural products. Two types are ethanol-based Biofuels and Biogas. 

  • Ethanol-based fuels are made via fermentation
  • Micro-organisms respire anaerobically to produce Ethanol using sugars from crops as energy source.
  • Glucose is produced from maize stach by the action of a carbohydrase.
  • The glucose and sugar cane juices can be fermented by yeast to produce ethanol.
  • The ethanol is exctracted by the process of distillation and can then be used as a fuel in motor vehicles
  • Using ethanol as a fuel could replace fossil fiels in the future. In terms of the 'greenhouse effect' using ethanol as a fuel is much more 'carbon friendly'.
  • Ethanol is described as carbon neutral because only the carbon dioxide used for photosynthesis by the crops is returned to the atmosphere when the ethanol is burned. 
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Biology Module 3

How Humans Can Affect the Environment - 4.7 Biogas

Biogas can be produced during anaerobic fermentation by bacteria. 

Biogas Generators

Plants and any waste material containing Carbohydrates e.g. cattle dung can be broken down in Biogas Generators. 

The generators are maintained at the perfect conditions for decomposition by bacteria. Thye are kept at a suitable temperature in an oxygen-free environment. Many are underground for insulation or have insulating jackets. 

Large scale commercial generators use waste from sugar factories or sewage works. On a small scale generators can be used by a home or farm. 

The gas produced is a fuel and provides energy for heating etc. The more methane in the gas mixture the better the quality of the biogas. 

Learn diagram on p 94 just so you're familiar with the concept. 

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Biology Module 3

How Humans Can Affect the Environment - 4.8 Making Food Production Efficient

Short Food chain = less energy wasted. - This means it is more efficient for us to eat plants than to eat animals. 

We can produce meat efficiently by - 

  • Preventing the animal from moving so it doesn't use energy. This however is cruel and many people view it as controversial. 
  • Keeping the animal in warm shed so it doesn't use as much energy keeping warm. 

This is aboout it. 

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Biology Module 3

How Humans Can Affect the Environment - 4.9 Sustainable Food Production

Sustainable Food Production - Involves managing resources and finding new types of food such as mycoprotein. This ensures there's enough food for the population and the future. 


  • Fish stocks in the ocean are monitored
  • Fishermen can only remove a strict allocation of fish per year (a quota) and must use certain sized nets to avoid catching small, young fish. 


  • The fungus, Fusarium, is grown to produce mycoprotein - a protein-rich food suitable for veggies. Grown aerobically on cheap sugar syrup made from waste starch and the mycoprotein harvested.
  • Micro-organisms can be grown on a large scale in industrial fermenters
  • The conditions in a fermenter must be controlled to ensure maximum growth of the Fusarium.
  • Industrial fermenters are large vessels which have - an oxygen supply for resp., strirrers or gas bubbles to evenly distribute microbes, a water-cooled jacket around the outside (because microbes release energy which heats the mixture up), sensors to monitor pH and temp. 
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Biology Module 3

How Humans Can Affect the Environment - 4.10 Environmental Issues

Human activities that can affect the global environment include - 

  • Deforestation - increased levels of CO(2)
  • Increase in rice growth and cattle cultivation causing an increase in methane. 
  • Building dams - loss of habitat, drying out of rivers, reduction in fertile soil for crops.

The issue of Global Warming divides opinion. Some think the greenhouse effect has caused the increase in temperature, others think it is part of a natural cycle. 

There is a lot of data to support both arguments made in different countries, it can also be noted that ensuring the validity of this data is difficult. Scientists also come to different conclusions based on the same data. These explanations can be biased and opinionated. 


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