13.1.4

Limiting Factors

Test yourself

The Rate of Photosynthesis

The four key factors affecting the rate of photosynthesis are:

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Temperature

  • Rate of photosynthesis increases up to the optimum temperature (about 45°C). Above this temperature, the rate starts to fall.
  • Enzymes such as rubisco play an important role in photosynthesis.
  • At low temperatures enzymes have less kinetic energy and are less likely to successfully collide with the substrate. This means fewer enzyme substrate complexes are formed.
  • Above the optimum temperature, enzymes will denature and the rate of photosynthesis will fall.
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Light intensity

  • Increasing light intensity increases the rate of photosynthesis because more energy is provided.
  • In low light intensities the light-dependent reaction cannot take place. This causes levels of reduced NADP and ATP to fall.
  • Reduced NADP and ATP are necessary to convert GP to TP and to regenerate RuBP.
  • Without reduced NADP and ATP the Calvin cycle cannot take place and rate of photosynthesis declines.
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Carbon dioxide (CO2) concentration

  • Increasing the CO2 concentration increases the rate of photosynthesis.
  • At high CO2 concentrations, there is more carbon available for fixation in the Calvin cycle.
  • If the rate of the Calvin cycle increases, more GP and TP is produced and more RuBP is regenerated.
  • Very high CO2 concentrations can cause stomata to open wider causing more water to be lost.
  • Too much water loss will then cause the stomata to close and the rate of photosynthesis to slow again.
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Chlorophyll concentration

  • High chlorophyll concentration gives a high rate of photosynthesis.
  • If there is more chlorophyll, light can be absorbed at a faster rate. This will cause the light-dependent reaction rate to increase.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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