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  • Created by: Lois_<3
  • Created on: 19-05-11 13:48

diffusion

  • cells are living things, they constantly have to replace substances which are used up (e.g. food and oxygen) and remove other substances which would accumulate (e.g. carbon dioxide, waste products)
  • Diffusion takes place automatically without the need for energy.
  • Diffusion is the spreading of the particles of gas which results in a net movement from a higher concentrated area to a lower concentrated area.
  • The greater the difference in concentration, the faster the rate of diffusion.

 for example: diffusion occurs in the gut

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osmosis

  • Osmosis is the movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
  • The membrane allows the water molecules through but not the solute molecules as they are too large.
  • The effect of Osmosis is to gradually dilute the solution. A good example is hair root cells.

for example: osmosis occurs in plants and their roots

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photosynthesis

  • Green plants make their food using sunlight, this is called photosynthesis.
  • Four things needed are:

- light from the sun

- carbon dioxide diffused from the air

- water from the soil

- chlorophyll in the leaves

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continued...

  • Green plants make their food using sunlight, this is called photosynthesis.
  • Four things needed are:

- light from the sun

- carbon dioxide diffused from the air

- water from the soil

- chlorophyll in the leaves

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things that affect PSS

  • Temperature:

- As temperature rises, so does the rate of photosynthesis.

- As the temperature approaches 45C the enzymes are destroyed -rate drops.

  • Carbon dioxide concentration:

- As the carbon dioxide concentration rises, so does the rate of photosynthesis

- Rise in carbon dioxide leads to have no effect.

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continued...

  • Light intensity:

- As the light intensity increases so does the rate of photosynthesis.

- Rise is light intensity leads to have no effect.

All of these, at a particular time, may be the limiting factor.

Photosynthesis (therefore, growth) can be controlled in a greenhouse, where temperatures

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