AQA Biology, B3 - Exchange of Materials

This is the revision notes I made for GCSE Biology Unit 3, Topic 1, Exchange of Materials.

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  • Created on: 21-03-11 12:54
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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 salt from their
Thorax ­ the upper (chest) region of the body. In humans it includes the rib cage, heart and
Abdomen ­ the lower region of the body .In humans it contains the digestive organs,
kidneys, etc.
Diaphragm ­ the sheet of muscle which divides the thorax from the abdomen
Alveoli ­ the tiny air sacs in the lungs which increase the surface area for gaseous exchange
Stomata ­ openings in the leaves of plants (particularly the underside) which hallow gases
to enter and leave the leaf. They are opened and closed by the guard cells
Xylem ­ the non-living transport tissues in plants, which transports water around the plant
Phloem ­ the living transport tissues in plants which carries sugars around the plant
Transpiration ­ the loss of water vapour from the leaves of plants through the stomata
when they are opened to allow gas exchange for photosynthesis
Transpiration stream ­ the movement of water through a plant from the roots to the
leaves as a result of the loss of water by evaporation from the surface of the leaves
Cuticle ­ the waxy covering of a leaf (or an insect) which reduces water loss from the
Wilting ­ the process by which plants droop when they are short of water or too hot. This
reduces further water loss and prevents cell damage

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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 ions from very dilute solutions and move
molecules through cell membranes using active transport.…read more

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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 broken down into a soluble form, and is then small
enough to pass through the walls of the small intestine into the blood vessels by
diffusion, where there is a lower concentration of food molecules.…read more

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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.…read more


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