AQA Biology Unit 3

These revision cars are what I wrote myself to help me learn the Biology 3 Unit. I used the AQA Biology Revision Guide to help me with them as that is where I got my initial knowledge from. I found them useful when doing a quick recap of the whole unit.

They cover the complete unit.

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  • Created by: antonia
  • Created on: 19-05-09 17:17

Gas and Solute Exchange

Respiration Equation:


  • Disolved substances move by DIFFUSION.
  • Diffusion is from an area of HIGH concentration to one of LOW concentration.
  • OSMOSIS is the "diffusion" of water across a partially permeable membrane from high water concentration to low water concentration.
  • When substances are dissolved against a concentration gradient it is called ACTIVE TRANSPORT.

The VILLI and ALVEOLI are specialised for material exchange. They have a LARGE SURFACE AREA, MOIST SURFACE, THIN WALLS and a GOOD BLOOD SUPPLY.

The alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide. The villi are specialised so that digested food is absorbed into the blood much more quickly.

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  • CO2 diffuses into air spaces within the leaf and then into the cells where PHOTOSYNTHESIS happens.
  • The underneath of a leaf is it's EXCHANGE SURFACE. It is covered in tiny holes called STOMATA.
  • Oxygen and water vapour diffuse out through the stomata.
  • Guard cells close the stomata when the plant is losing water fast than it can be replaced.

TRANSPIRATION - when water diffuses out through the stomata as their is more of it inside than in the air outside. Transpiration happens quicker when the air is hot, dry and windy. THE LOSS OF WATER VAPOUR FROM THE SURFACE OF THE PLANT.

The leaf of a plant is specialised to make the exchange surface more effective. The flattened shape increases the area of the exchange surface. The walls of the cells inside form another surface and the air spaces inside these increase the area of this surface so there is more chance for CO2 to get into the cells.

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Active Transport

Active Transport: when substances are absorbed AGAINST a concentration gradient - from an area of HIGH to LOW concentration.

  • ROOT HAIRS take in minerals using active transport.
  • If they followed the rules of diffusion they should go the opposite way.
  • Active transport allows the plant to absorb minerals against a concentrastion gradient.

Root hair cells are specialised for absorbing water and minerals. They have long 'hairs' protruding into the soil giving the cell a larger surface area. Most of the water and minerals which get into a plant are absorbed by the root hair cells.

Active transport in humans: Active transport is used in the gut when the concentration of nutrients in the gut is lower than the concentration in the blood. When theres a higher concentration of glucose in the gut it diffuses naturally into the blood. But when it is not ACTIVE TRANSPORT allows the glucose and amino acids to be taken into the blood.

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The Breathing System

  • The lungs are in the THORAX - the upper part of your 'body'.
  • It is separated by the diaphragm from the lower part of the body.
  • The ribcage protects the lungers.

Breathing In: The air goes through the trachea -> splits into two tubes called bronchi -> the bronchi split into smaller tubes called bronchioles -> the bronchioles end at small bags called the alveoli where gas exchange takes place.

When breathing IN intercostal muscles and diaphragm CONTRACT. Thorax volume INCREASES. Pressure decreases and air is drawn IN.

When breating OUT intercostal muscles and diaphragm RELAX. Thorax volume DECREASES. Pressure increases and air is forced OUT.

The lungs transfer oxygen to the blood and remove waste CO2 from it. This happens in the alveoli.

Red Blood - has carbon dioxide Blue Blood - has oxygen

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The Circulation System

The heart is TWO pumps. The right side pumps DEOXYGENATED BLOOD to the lungs to collect oxygen and remove CO2. The left side pumps oxygenated blood around the body.

Arteries carry blood AWAY from the heart at a high pressure.

Arteries carry oxygenated blood and veins carry deoxygenated blood. HOWEVER, the exceptions to this rule are the pulmonary artery and pulmonary vein. The pulmonary artery carries deoxygenated blood to the lungs. The pulmonary vein carries oxygenated blood away from the lungs.

The arteries split off into tiny capillaries which take blood to every cell in the body.

The veins collect deoxygenated blood and carry back to the heart at a low pressure.

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The Blood

Capillaries: Use diffusion to deliver food and oxygen to body tissues and take carbon dioxide and other waste materials away. Their was are only one cell thick making it easier for things to diffuse in and out. They cannot be seen without a microscrope.

Red blood cells carry oxygen. They carry oxygen from the lungs to all the cells in the body. They have a doughnut shape for a large surface area for absorbing more oxygen. They don't have a nucleus to create more room. They contain haemoglobin. When this combines with oxygen it becomes oxyhaemoglobin which is reversed to release oxygen into the cells when the body tissue is reached.

Plasma is the liquid within the blood which carries red and white blood cells as well as platelets. It also carries nutrients such as glucose and amino acids, carbon dioxide from the organs to the lungs, urea from the liver to the kidneys, hormones, as well as antibodies and antitoxins produced by the white blood cells.

Platelets are small fragments of cells that help blood clot at a wound.

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  • Exercise increases your breathing rate meaning to breate much more deeply to meet your bodies demand for extra oxygen.
  • The speed at which your heart pumps blood is increased.
  • The arteries which supply blood to muscles are dilated - made wider.

Muscles are made up of cells which use oxygen to release the energy from glucose which contracts muscles. Exercise requires more oxygen and glucose to be supplied to the cells. This means extra CO2 needs to be removed. Therefore BLOOD HAS TO FLOW AT A FASTER RATE.

GLYCOGEN - some of the stored glucose from food. Mainly stored in the liver but each muscle has its own store. During exercise glucose is used up rapidly and the muscle uses is glycogen store. When this runs low the muscle doesn't get energy and gets tired.

ANAEROBIC RESPIRATION - used if theres not enough oxygen. Anaerobic is WITHOUT oxygen. Lactic acid builds up in the muscles which is painful and tires the muscles. Glucose -> energy + lactic acid

Heavy breathing afterwards oxidises the lactic acid.

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The Kidneys

The kidneys get rid of toxicating waste (e.g urea) and adjust the amount of disolved ions and water in the blood.

If the kidneys fail to remove the waste substances they build up in the blood meaning the levels of ions and water cannot be controlled. Kidney failure leads to death if not treated.

  • Dialysis machines are used to filter the blood. This process has to be done on a regular basis to keep concentrations of ions and water at normal levels and to remove waste.
  • In a dialysis machine the persons blood flows along a SELECTIVELY PERMEABLE BARRIER surrounded by dialysis fluid.
  • Like the kidneys, the barrier is permeable to the ions and waste substances but not large molecules.
  • The fluid has the same concentration as dissolved ions and glucose as that of healthy blood.
  • The onmly substances which diffuse accross the barrier are waste substances and excess water and ions.
  • Dialysis often has to take place three times a week, in 3-4 hour sessions.
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Currently the only way kidney disease can be cured is via a transplant. Kidneys can either be transplanted from a healthy person who has recently died and who is an organ donor or by someone who is still alive, as each person has 2.

However the kidney can be REJECTED just like any other organ. It can be attacked by the antibodies produced by white blood cells. Precautions are taken to prevent this happening:

  • Donors are of a similar tissue type.
  • The immune system is suppressed. The bone marrow recieves radiation treatment to stop white blood cells from being produced. This means they won't attack the new kidney.
  • Drugs can also suppress the immune system. These have to be taken for life.
  • This also means that the person cannot fight disease, and therefore they have to be kept in sterile conditions.
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Yeast is a microorganism, and like many cells has a nucleus, vacuole, cytoplasm, cell membrane and a cell wall.

Yeast can respire anaerobically (without oxygen). This is called FERMENTATION. glucose -> ethanol + C02 + energy


Yeast can respire aerobically (with oxygen). This produces more energy which is need for it to reproduce and grow. glucose + oxygen -> C02 + water + energy

In bread yeast converts the sugars to C02 which makes the bread rise. As it gets trapped in the dough it expands and gets trapped, making the bread fluffy.

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