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Biology Revision
B3.1 ­ Exchange of Materials
Key Words
Active transport ­ the movement of substances against a concentration gradient and/or
across a cell membrane, using energy
Mitochondria ­ the site of aerobic cellular respiration in a cell
Salt glands ­ special glands which enable some animals to remove excess…

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Active Transport

Osmosis depends on a concentration gradient of water and a partially permeable
membrane. Only water moves in osmosis.
Active transport allows cells to move substances from an area of low
concentration into an area of high concentration ­ so they move against the
concentration gradient. Cells can absorb…

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Exchange in the Gut
The molecules from food are very important as they provide fuel for respiration and
the building blocks of the tissues.
They must move from the inside of the small intestine into the
bloodstream by a combination of diffusion and active transport.
During digesting the food is…

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The leaf cells do not need carbon dioxide all the time. When it is dark, they don't
need carbon dioxide because they are not photosynthesising. When light is a
limiting factor on the rate of photosynthesis, the carbon dioxide produced by
respiration can be used for photosynthesis. But on sunny…


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