4.1.2 Rate of photosynthesis

• What does a limiting factor do?

  Restrict rate of photosynthesis (stop from increasing) if in low levels.
• Describe and explain how temperature affects rate of photosynthesis

  1. As temperature increases, rate increases (so temperature =limiting factor)

  ● As enzymes controlling photosynthesis gain kinetic energy

  2. Above an optimum temperature, rate decreases

  ● As enzymes denature (active site changes shape)
• Describe and explain how light intensity affects rate of photosynthesis

  1. As light intensity increases, rate increases (so light intensity = limiting factor)

  ● As light provides energy needed for photosynthesis

  2. Above a certain light intensity, rate stops increasing

  ● Another factor is limiting eg. temperature / CO2
• Describe and explain how CO2 concentration affects rate of photosynthesis

  1. As CO2 conc. increases, rate increases (so CO2 conc. = limiting factor)

  ● As CO2

  is a reactant / raw material needed for photosynthesis

  2. Above a certain CO2 conc., rate stops increasing

  ● Another factor is limiting eg. temperature / light intensity
• How does chlorophyll affect the rate of photosynthesis?

  Affects how much light energy can be absorbed
• What law describes the relationship between distance of a light source

  from a plant and light intensity? (HT only)

  Inverse square law
• How can farmers use their

  knowledge of limiting factors to increase their profits? (HT only)

  ● Remove limiting factors → gain maximum rate of photosynthesis → increase plant yield

  ● Profit from extra yield must be greater than the costs of providing conditions
• Why is this statement wrong?

  “Water is a limiting factor

  in photosynthesis.”

  It is not considered a limiting factor as the volume needed is very small and water

  shortages affect other processes in the plant before affecting photosynthesis.
• What factor is most likely to limit the rate of

  photosynthesis in plants in a greenhouse on a

  hot summer’s day? Explain why. (4)

  ● Carbon dioxide concentration

  ● As atmospheric carbon dioxide conc. is very low

  ● Temperature is high

  ● Light intensity is high