AQA GCSE Science B3 Revision Cards

Notes if you are going to be doing the B3 exam on the 13th January 2011. Useful if you are going to be starting your revision very soon in preparation.

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  • Created by: Anisah
  • Created on: 05-10-10 21:04

Lungs and gas exchange

Lungs are Situated in the upper part of body , thorax (chest).

Delicate and protected by rib cage.

Thorax is separated from the abdomen (lower part of body) by the diaphragm (sheet of muscle).

Breathing in - Oxygen is absorbed from the air.

Breathing out - Carbon dioxide is removed from your body

Oxygen + Carbon dioxide = Respiratory Gases

Process = Gas exchange


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Aerobic Respiration;

Glucose + Oxygen => Carbon Dioxide + Water (+ energy)

C6H12O6 + 6O2 => 6CO2 + 6H2O + energy

Glucose-Food eaten, Oxygen- breathedin, Carbon Dioxide-breathed out , Water-Lost from body, Energy-We use this to do things.

Anaerobic Respiration;

Glucose => lactic acid + a little energy

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Adaptions For Gas Exchange

The lungs are specialised in many ways..;

Millions of alveoli (tiny air sacs) = large surface area.

Alveoli are moist; lined with a thin layer of water.

Alveoli walls are one cell thick; respiratory gases do not have to diffuse far.

Rich blood supply; millions of capillaries bring blood to lungs.

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Diffusion occurs when particles are spread out and are free to move. Diffusion is the movement of molecules or particles from a region of high concentration to a region of low concentration. Particles diffuse down a concentration gradient.


Oxygen diffuses from air breathed in into the alveoli down a concentration gradient into the red blood cells whilst carbon dioxide is diffusing in the opposite direction from the plasma into the alveoli.

Teabag diffusion - tea leaves diffuse through teabag to give the water its colour and taste of tea.

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Mechanical digestion - which breaks the food down into smaller pieces. Chemical digestion - which further breaks the food down to molecule size

It is a passive process and no energy is used.

Carbohydrates => Glucose (broken down by carbohydrase enzymes)

Proteins => Amino Acids (broken down by protease enzymes)

Fats => Glycerol and Fatty Acids (broken down by lipase enzymes)

Active transport - absorbed against a concentration gradient, as this uses energy from respiration. Enabling cells to absorb ions from very dilute solutions.

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Glucose => absorbed into the blood (diffusion and active transport)

Amino Acids => absorbed into the blood (diffusion and active transport)

Glycerol and fatty acids => cells lining the small intestine (diffusion) => fats reformed and passed into the lymphatic system (active transport)

Lymphatic System - Returns fluids that have leaked out of blood capillaries back into the blood system.

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Adaptations for absorption

Small intestine is adapted to absorb digested food;

It is long (approximately 3 metres)

Milllions of finger like projections on inner surface - villi (increasing surface area vastly)

The villus has an epithelium which allows the passage of digested food stuffs to the blood vessels & lacteal vessel in each villus.

Each villus has a branch of the lymphatic system for transporting absorbed fats.

Each villus has a rich blood capillary system for transporting glucose and amino acids.

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Roots absorb lots of water and mineral ions from the soil. Root hairs are adapted as every plant has millions and these vastly increase the surface area so they can absorb all that is needed.

Transpiration - When plants lose water (as vapour) from the surface of their leaves.Transpiration happens mostly in HOT DRY WINDY conditions.

If a plant loses more water by transpiration than is replaced through its roots then the plant will wilt and then die.

Transpiration happens through the stomata-tiny pores (on the underside of leaves). A stoma is surrounded by two guard cells which can open and close to control the size of the stoma.Stomata close to reduce water loss.

When the stomata are open Carbon dioxide diffuses into the leaf from the air.

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This is super useful!

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