AQA B3 - Complete Summary

This is a complete summary of everything in B3. It is very detailed so you may just want to look at the particular cards that you are stuck on.

This is based on the CGP AQA Biology revision guide. I have just summarised it. You may find some of it is very similar because there is no other way of saying things. They did all the hard work though. 

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Diffusion and Osmosis

Diffusion - The passive movement of particles from an area of high concentration to an area of low concentration. 

Osmosis - Similar to diffusion, but involving water, this is the passive movement of water molecules from a dilute solution to a more concentrated one. 

Passive is just a posh word for "without energy". 

Remember, when there are LOTS of water molecules, this is DILUTE.When there are FEW water molecules, this is CONCENTRATED. It is talking about the number of other particles in the solution e.g. particles of orange squash in your drink. 

We did this in B2 so this should just be a refresher. 

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Active Transport

Active Transport - This is where particles move against the concentration gradient. So they move from an area of low concentration to an area of high concentration. This requires energy from respiration which is called ATP.

This is used in our digestive system when there is a low concentration of nutrients such as glucose in the gut but a high concentration of this glucose in the blood. Glucose is very important in our bodies as it is the key component in respiration and so we want to get as much of it as possible. That is why active transport is used because this way or bodies can get ALL of the glucose into the blood stream.

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Gas Exchange in Plants

The leaves of plants have small holes in the underside of their leaves called stomata. These can be controlled by guard cells which can open and close to change the size of the stomata. 

It is through these stomata that the plant loses water via transpiration. This is where carbon dioxide enters the plant and where water vapour and oxygen diffuse out. 

The water vapour leaves by diffusion because there is a lot of it inside the leaf and less in the air outside. The hotter, drier and windier the conditions, the faster the rate of transpiration. 

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Breathing In

  • The Intercostal muscles and diaphragm contract.
  • The Thorax volume increases.
  • This decreases the pressure in the lungs and air is drawn in.

Breathing Out

  • The Intercostal muscles and diaphragm relax.
  • The Thorax volume decreases.
  • Air is forced out. 


Find a diagram (or draw your own) of the lungs and make sure the can label all of the parts. trachea, bronchiole, bronchus, alveoli, intercostal muscles, diaphragm, thorax.

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Alveoli and Villi

Alveoli - These are found in the lungs. They help to transfer oxygen into the blood and remove waste carbon dioxide out of the lungs. They have 4 main adaptations which are:

  • A large surface area 
  • A moist lining for dissolving gases
  • Very thin walls
  • A very good blood supply

Villi - These are found in the small intestine. They help to increase the surface area to make the absorption of digested food much faster. They have 3 main adaptations which are:

  • Microvilli to increase the surface area even more
  • Very thin walls
  • A very good blood supply
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Our body has a double circulation system. There are a number of key points to note about our circulation system: 

  • Arteries carry oxygenated blood away from the heart at high pressure (apart from the pulmonary artery)
  • Veins carry deoxygenated blood back to the heart at low pressure (except the pulmonary vein)
  • The arteries split into thousands of capillaries in organs which take the blood to every cell.

Arteries - have thicker walls than veins because of the high pressure.

Veins - have small valves to stop back flow.

Capillaries  - they use diffusion to deliver food and oxygen to body tissues and take carbon dioxide and other waste away. Their walls are only once cell thick so that it's easy for substances to pass through.

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Blood is made up of white blood cells, red blood cells, plasma and platelets. 

White Blood Cells - These fight infection. (this was in Core Science and is very unlikely to come up in the Extension exam but make sure you know it - better safe than sorry!)

Red Blood Cells - These carry oxygen. They are biconcave and don't have a  nucleus which allows for a large surface area to carry oxygen. They also contain haemoglobin which combines with oxygen in the lungs to make oxyhaemoglobin. In cells this process is reversed and the oxygen detaches from the haemoglobin.

Plasma - This is the liquid part of the blood. It carries the red blood cells, white blood cells, platelets, nutrients, carbon dioxide, urea, hormones and antinbodies.

Platelets - These are small fragments of cells that help blood to clot at the sight of a wound.

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Exercise increases the heart rate. This is for two main reasons. The body needs more energy to carry out the respiration and so needs more oxygen to release energy from glucose. Also, there will be more carbon dioxide (because of more respiration) which needs to be removed from the cells and the body. If the heart is pumping faster then the blood is flowing at a faster rate and so the oxygen and glucose can get the the mitochondria in the muscle cells faster and the carbon dioxide can be removed faster. 

Exercise has 3 main affects on our body: 

  • increases your breathing rate
  • increases your heart rate
  • dilates the arteries to allow more blood through faster

During vigorous exercise, the muscles sometimes have to use their glycogen stores (most is stored in the liver but the muscles have their own store too) to provide more energy. 

Mitochondria are the site of respiration. 

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Anaerobic Respiration

Anaerobic Respiration - This occurs when there is not enough oxygen present. The "an" part means "without" and the "aerobic" part means "oxygen". 

glucose ----> energy + lactic acid

It is not the most efficient way to break down glucose into energy because it does not produce as much energy as aerobic respiration. It also produces lactic acid which can  get very painful when it builds up in the muscles. 

This form of respiration leads to oxygen debt. This is when you have to "repay" the oxygen that didn't get to your muscles in time. It occurs when you stop exercising and is why your breathing and heart rate stay high for a while after you stop. Oxygen reacts with lactic acid to produce carbon dioxide and water.

Oxygen + lactic acid ----> carbon dioxide + water

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Ultrafiltration - a high pressure builds up which squeezes water, urea, ions and sugar out of the glomerulus and into the Bowman's capsule. The membranes between the blood vessels and the Bowman's capsule act like filters so that the larger molecules like proteins and red blood cells are not squeezed out.

Reabsorption - As the liquid flows along the nephron/tubule, some substances are reabsorbed. All the glucose is reabsorbed using active transport, sufficient ions are reabsorbed using active transport and sufficient water is reabsorbed. The remaining substances continue into the bladder as urine

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Kidney Failure

The kidneys remove waste substances from the blood. If they stop working, waste substances build up in the blood which can eventually lead to death. There are two solutions to this problem: dialysis or a kidney transplant. 

Dialysis - This has to be done regularly (normally about 3 times a week) to keep the levels of substances in the blood about normal. The person's blood travels alongside a partially permeable membrane surrounded by dialysis fluid. Large molecules such as proteins cannot get through the membrane but waste substances and ions can.  The fluid has the same concentration of dissolved ions and glucose as healthy blood meaning that useful ions such as glucose won't be lost from the blood but the waste substances (like urea), excess ions and water can diffuse across. 

Transplants - This is the only cure as dialysis is not a permanent solution. The kidney can be rejected by the patient's immune system by being attacked by antibodies so the patient has to take immuno-suppressant drugs, their bone marrow is "zapped" with radiation to stop white blood cell production and a careful tissue match is found. They have to remain in sterile conditions for a long time after the operation because they can't fight infection.

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Dialysis vs Kidney Transplant


Make a list of the advantages and disadvantages of Kidney Transplants and Dialysis. Make sure you learn these as this is could be in the exam.

Here are a few ideas, put them into the correct category and then add your own. 

Waiting list

Organ rejection

No need for regular hospital trips

no surgery

High blood pressure

High cost in the long run  

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Abiogenesis - the theory that living things can just spontaneously generate from non-living matter. (proven to be wrong). 

Biogenesis - the theory that living things are created from other living organisms

Cheese is made using bacteria. A culture of bacteria is added to milk which produces solid curds in the milk. The curds are then separated from the whey. It is then left to ripen for a short while. Blue cheese has mould added to it to give it it's colour and taste.

Yoghurt is also made using bacteria too. The milk is heat treated to kill off any bacteria and then cooled. A starter culture is then added. The bacteria ferments the lactose sugar in the milk and turns it into lactic acid. This causes the milk to clot and turn into yoghurt. Sometimes sterilised flavours are added after this point. 

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Find out what Lazzaro Spallanzani, Theodor Schwann and Louis Pasteur did to help with the theory of abiogenesis and biogenesis.

Here are some key words to get you thinking:







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Saccharomyces cerevisiae (yeast) is a single-celled fungus. It can respire aerobically (glucose + oxygen ----> carbon dioxide + water + energy) or anaerobically (glucose ----> ethanol + carbon dioxide +energy)

Yeast can be used to make bread. It converts the sugar in the bread to carbon dioxide and some ethanol. The carbon dioxide gets trapped in the crust and makes the bread rise. 

It can also be used to make alcoholic drinks. Barley grains are allowed to germinate (during which starch is broken into sugar by enzymes) and then dried. They are then mashed up with water to form a sugary solution and hops are added to give flavour. The sugary solution is then fermented by the yeast which turns the sugar into alcohol. 

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Microorganisms in Industry

Microorganisms are grown in fermenters on a large scale. These fermenters contain a liquid culture medium which is the source of food and nutrients for the microbes and air is pumped in the provide oxtgen. The temperature must be controlled to keep it as close to the optimum as possible. The microbes produce heat when they respire so a water jacket is wrapped around the outside to cool the mixture. The pH must also be monitored and a motorised stirrer stops the microorganisms falling to the bottom as well as maintaining an even temperature. Sterile conditions are crucial because they prevent contamination. 

Mycoprotein - Mycoprotein is a single-celled protein that is often used as a meat substitute for vegetarians (Quorn). A fungus called Fusarium venenatum is grown in fermenters using similar conditions to above.

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Fuel can be made by fermentation of natural products. Ethanol is made from yeast breaking down either sugar cane juices of maize starch (glucose ----> ethanol + carbon dioxide +energy) They are now starting to adapt cars to run on "gasohol", a mixture of ethanol and petrol. 

Biogas is made by anaerobic fermentation of plant and animal wast. It's made in a simple generator that must be kept at a constant temperature. It can be used on small scales by villages or single families to heating and lighting etc. and the by-products can be used as fertilisers. However, it must be used immediately because it can't be stored as a liquid. 

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Biogas (2)

Biogas generators need the following things:

  • an inlet for waste material
  • an outlet for the digested material
  • an outlet for the biogas

There are 4 things to consider:

  • cost - continuous generators are more expensive than batch generators 
  • convenience - batch generators have to be loaded, emptied and cleaned
  • efficiency - 35C is the optimum temperature and heaters may be needed
  • position - waste will smell during delivery
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Economic and Environmental Effects of Biogas

  • It is "carbon neutral"
  • Doesn't produce significant amounts of sulfur dioxide or nitrogen oxides which cause acid rain
  • Methane is given off from untreated waste and biogas stops it being released into the atmosphere
  • The raw material is cheap and readily available
  • The digested material is a better fertiliser than undigested dung
  • It acts as a waste disposal system


Can you think of any more to add to this list?

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Aseptic Technique

Microorganisms are grown in a petri dish on a small scale. They get their nutrients from agar jelly which can hold the carbohydrates, mineral ions, proteins and vitamins that they may need. 

Aseptic Technique - This is the idea that everything is done under sterile conditions to limit cross contamination.

The key points of aseptic technique:

  • pass innoculating loop(or something similar) through a flame 
  • work near an open flame
  • don't open the lid very much
  • use an autoclave to sterilise the flask/petri dish etc.


Can you think of any more? 

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Jacob Moulton-jones


These are fantastic:D



Jacob Moulton-jones wrote:

These are fantastic:D

Thank you! It took me all afternoon so I really appreciate this!

Muhammad Devraj


amazing summary, thanks :D this will be very useful for the b3 exam on Monday :D 



Muhammad Devraj wrote:

amazing summary, thanks :D this will be very useful for the b3 exam on Monday :D 

You're welcome! Good luck! I'll be there too. 

Laura Gill


thanks for these really helping me with my last minute revision for tomorrow!



are these notes made from the 2011 new spec?

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