Exchange of materials


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Active transport

Osmosis and Diffusion is from an are of higher concentration to a lower concentration. 

Active transport is from a lower concentration to a higher concentration. This is 'against the concentration gradient'.

Active transport requires energy as it is not the natural movement of substances.

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Exchange of gases in the lungs

The lungs exchange oxygen for aerobic respiration, and carbon dioxide, which is the waste rpoduct of respiration. 

They have a large surface are with millions of alveoli.

The surfaces are moist and thin to speed up diffusion.

Oxygen diffueses back into the cappilaries surrounding the alveoli.

Carbon dioxide diffuses back out of the lungs.

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Exchange in the gut

Food we eat is digested into small soluble molecules. In the small intestine these are absorbes by the blood.

Villi greatly increase the surface area for absorbtion to take place.

Food can be absorbed against the concentration gradient with active transport.

Villi have a rich blood supply, thin wall, and a large surface area, all to aid diffusion.

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Exchange of materials in other organisms.

All living organisms need oxygen for respiration and to remove carbon dioxide.

All of these organisms have the following features in common - 

Large surface area


Gases are transported away quickly to mnaintain high concentration gradient

Thin membranes for which diffusion takes place

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Exchange in plants

Gases diffuse in plants through the 'stomata'.

Oxygen is needed for respiration and is a waste product of photosynthesis.

Carbon dioxide is the waste product of respiration and needed for photosynthesis.

Leaves are flat and thin so that gases do not need to diffuse far.

Water and mineral ions are taken up through the roots and root hairs increase the surface area.

Although water can evaporate from the leaves, and this is a problem, this can happen on windy humid days.

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Plants take up water thorugh the roots, up the stem, and then evaporates through the leaves. This is Transpiration.

Stomata allow the exchange of gas. 

The plant will wilt if there is too much water loss, althugh guard cells close hte stomata.

Transpiration takes place more quickly on hot, dry, and windy days, because;

Hot days = more energy causing evaporation

Dry days = the air holds up more water 

Windy days = And humidity build up by the plant is blown away.

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