B3 exchange of materials.

Active transport.

Substances get in and out of cells through:

  • diffusion
  • osmosis
  • active transport.

osmosis and diffusion : involve movement of substances from a higher concentration to a lower concentration.

A cell may need to take up a substance against the concentration gradient. This is called active transport.

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Exchange of materials in the lungs.

The lungs are in the thorax and are protected by the rib cage.

Lungs exchange carbon dioxide and oxygen with the atmosphere.

Alveoli - the site of gas exchange, have a

  • large surface area,
  • a high blood supply
  • thin walls, and
  • are moist so that ...

diffusion can take place quickly.

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Exchange in the gut.

Digested food is absorbed by the capilaries along side the small intestine (gut).

Villi -

fingerlike prjections. greatly increase the surace area of the small intestine.

small intestine has a rich blood supply.

absorbtion in the gut it by ...

  • diffusion
  • active transport.
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exchange of materials in other organsisms

Fish: exhange oxygen through gills.

Frogs: exchange oxygen through their skin.

Insects: exchange oxygen through holes in their sides leading to a series of tubes.

Common features in all living organsisms:

  • Large surface area
  • moist
  • gases are transported away quickly to maintain concentration gradient.
  • mebranes (where gases diffuse) are thin.
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Exchange in plants.

Gases diffuse in and out of leaves through tiny holes called 'stomarta'.

photosynthesis: carbon dioxide + water + (sunlight) = oxygen + glucose.

respiration = opposite.

Plants take up water and minerals through their roots.

Leaves are flat and thin so gases have less distance to diffuse across.

Leaves ans roots have adaptions for efficent exchange of materials.

- root hair cells to increase surface area.

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They take and loose water through the stomarta and exchange gases.


Plants take up water through the roots, water passes through the plant, it evapourates through the leaves.

Speed up transpiration ?

  • dry days - air can hold more water
  • hot days - more energy causing water to evapourate
  • windy days - and water built up around the plant if blown awa


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