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REVISION NOTES: BIOLOGY 3
UNIT 1: EXCHANGE OF MATERIALS



Active Transport

Two of the main ways in which diffused substances are transported across cells are osmosis and
diffusion. Diffusion is the movement of a fluid across a concentration gradient useful to the cells
osmosis is the movement of water across…

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REVISION NOTES: BIOLOGY 3
UNIT 1: EXCHANGE OF MATERIALS



lungs (found in the thorax) are protected by the rib cage. The lungs are separated from the
digestive organs, found in the abdomen, by the diaphragm.






The lungs have been adapted especially for making gas exchange more efficient. They are made…

Page 3

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REVISION NOTES: BIOLOGY 3
UNIT 1: EXCHANGE OF MATERIALS



molecules from food enter the bloodstream. This is why food is broken down during the digestion
process. After being broken down, the food molecules are small enough to pass through the walls of
the small intestine and into the blood vessels.…

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REVISION NOTES: BIOLOGY 3
UNIT 1: EXCHANGE OF MATERIALS






Gills do not work in air, and "suffocate" out of water ­ because if they are not kept moist constantly
the gills stick together and there isn't enough surface area for the fish to get enough oxygen from the
air to…

Page 5

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REVISION NOTES: BIOLOGY 3
UNIT 1: EXCHANGE OF MATERIALS






A problem is that water is always being lost by evaporation. So allowing carbon dioxide in will also
lose water vapour. However, the plant does not need carbon dioxide all the time, because at night
there is no sunlight ­ so…

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A clear set of notes with colourful diagrams that can be used with AQA Biology Unit 3 on exchange surfaces.It is important to be able to label diagrams confidently. Try using the revision notes to make a mind map or a set of flash cards to  test your knowledge.

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