Rate of photosynthesis

• Rate of Photosynthesis


  The rate at which photosynthesis occurs
• Factors that affect the rate of photosynthesis

  • Light
  • CO2
  • Temperature
• Experiment to measure the rate of photosynthesis

  1. Set up a source of light at a specific distance from the plant

  2. Measure the volume of gas produced by the plant over a set time

  3. Analyze the proportion of oxygen in the gas produced
• Not enough light slows down the rate of photosynthesis
• As light intensity increases

  The rate of photosynthesis increases steadily up to a point
• Beyond a certain light intensity, further increases won't affect the rate of photosynthesis
• If light is not the limiting factor, it will be either temperature or CO2 level
• In the lab, light intensity can be changed by moving a lamp closer to or further from the plant
• To get a graph showing the relationship between light intensity and rate of photosynthesis, you need to measure light intensity using a light meter or do calculations
• Too little CO2 also slows down the rate of photosynthesis
• As CO2 concentration increases

  The rate of photosynthesis increases up to a point
• After a certain CO2 concentration, the rate of photosynthesis no longer increases
• If light and CO2 are in plentiful supply, then temperature is the limiting factor
• Usually, if temperature is the limiting factor, it's because it's too low
• If the plant gets too hot, the enzymes needed for photosynthesis and other reactions will be destroyed, usually around 45°C
• A graph could show the effect of both light intensity and temperature on the rate of photosynthesis
• The line for the effect of light intensity would level off at a higher point than the line for temperature, indicating that temperature is the limiting factor
• A graph could also show the effect of both light intensity and CO2 concentration on the rate of photosynthesis
• The line for the effect of CO2 concentration would level off at a higher point than the line for light intensity, indicating that CO2 is the limiting factor
• The Canadian pondweed experiment can be used to measure the rate of photosynthesis
• Canadian pondweed experiment


  1. Set up a source of light at a specific distance from the plant

  2. Measure the volume of gas produced by the plant over a set time

  3. Analyze the proportion of oxygen in the gas produced
• The apparatus used in the Canadian pondweed experiment can be altered to measure the effect of factors like CO2 on the rate of photosynthesis
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