Biology B3 Revision

Revision for AQA B3 exam, all topics.

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Substances get in and out of cells through Diffusion, Osmosis and Active Transport.

Diffusion and Osmosis involve substances moving from an area of high concentration, to low concentration. BUT, a cell may need to take a substance AGAINST a concentration gradient- this is called ACTIVE TRANSPORT.

 Active transport uses energy from respiration to carry substances over a cell membrane using a protein.

Active transport is found in:

-Glucose moving from kidney to blood

- Mineral Ions in soil moving into plants.

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The lungs exchange oxygen (needed for AEROBIC respiration), and carbon dioxide (a product of respiration).

Aerobic respiration=

Oxygen + Glucose > Carbon Dioxide + Water + Energy

The lungs have millions of tiny air sacs named ALVEOLI, which increase the surface area of the lungs greatly.

They also have a rich blood supply, a steep concentration gradient with movement of gases, they are moist to aid diffusion, and the cells around the alveoli are very thin, so gases do not have to travel far.

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Victoria Beadie


This is really helpful, thankyou. It is funny though when it skips words, or when the tone of voice suddenly jumps right up.

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