Topic Summaries

Rate of photosynthesis

GCSE > Biology > WJEC > GCSE Biology Topic Summaries > Photosynthesis and respiration > Rate of photosynthesis
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Science skills: Measuring results

  • There are various factors that can affect the rate of photosynthesis. These factors interact and the one that limits the reaction rate of photosynthesis is known as the limiting factor, meaning the rate cannot increase without changing that condition.
Factor Effect on photosynthesis rate
Temperature
  • Increases as temperature increases, as molecules have more kinetic energy, so they collide more and react faster.
  • Decreases at temperatures that are too high as the enzymes involved in photosynthesis denature.
Light intensity
  • Increases as light intensity increases, as light energy is needed for the reaction.
  • If the distance between the plant and light is doubled, the rate is quartered (inverse square law): \(\text{light intensity}\propto\frac{1}{\text{distance}^2} \)
Carbon dioxide concentration
  • Increases as concentration increases, as carbon dioxide is needed for reaction
Amount of chlorophyl
  • Increases as chlorophyll amount increases, as chlorophyll absorbs light energy needed for reaction.
  • Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining a profit (e.g. if photosynthesis rate is only limited by the current light intensity, increasing the temperature in the greenhouse will not have a big effect).
  • The glucose produced in photosynthesis may be used in:
    • Respiration to provide energy for the plant.
    • Converted into insoluble starch for storage for later use.
    • Producing fat or oil for storage.
    • Producing cellulose, which strengthens the cell wall.
    • Producing amino acids for protein synthesis and growth, which also requires nitrate ions from the soil.

Graphs of photosynthesis (HT only)

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