B2(i) - Life Processes 6.

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The Rate of Photosynthesis.

The rate of photosynthesis is affected by the amount of light, the amount of CO2 and the temperature. Plants also need water for photosynthesis, but when a plant is short of water it becomes a limiting factor in  photosynthesis.

The Limiting Factor Depends on the Conditions. 

1) The amount of water and CO2 and the temperature can all become limiting factors. This just means that it's stopping photosynthesis from happening faster.

2) Which factor is limiting at a particular time depends on the environmental conditions:

  • At night, light is a limiting factor.
  • In winter, the temperature is often a limiting factor.
  • If it is warm and bright enough, CO2 is usually limiting.

Three Important Graphs for The Rate of Photosynthesis.

1) Not Enough Light Slows Down the Rate of Photosynthesis.


1) Light provides the energy needed for photosynthesis.

2) As the light level is raised, the rate of photosynthesis increases steadily - but only up to a certain point.

3) Beyond that, it won't make any difference because then it will either be the temperature or CO2


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