Factors Affecting the Rate of Photosynthesis

To survive, all plants need to carry out photosynthesis. Four main factors affect the rate of photosynthesis:

  • The amount of chlorophyll
  • Temperature
  • Light intensity
  • Carbon dioxide concentration

Chlorophyll

Chlorophyll is a green pigment in plants that are located in the chloroplasts.

Chlorophyll absorbs light energy, which is needed for photosynthesis. So, plants that have less chlorophyll will not be able to carry out as much photosynthesis. Plants that grow in darker areas synthesise more chlorophyll, so they can absorb more light.

Plant diseases can affect the amount of chlorophyll an individual plant has or can produce. This can affect the rate at which the plant photosynthesises.

Temperature

Temperature affects the kinetic energy of particles. So, in plants, temperature affects the speed at which enzymes and substrate molecules (carbon dioxide and water) move in a plant. When the temperature increases, the number of successful collisions increases, so the rate of photosynthesis increases.

Photosynthesis is controlled by enzymes, so the rate of successful collisions does not increase continuously. At low temperatures, the rate of photosynthesis is limited by the number of collisions between enzymes and substrate molecules. However, at higher temperatures, the enzymes begin to denature. This is when the active site changes shape so much that it is no longer complementary to the substrate. So, the rate of reaction decreases.

AThe rate of photosynthesis increases as the number of collisions between enzymes and substrate increases
BThis is the optimum temperature
CThe enzymes begin to denature, so the rate of photosynthesis decreases

Light Intensity

Plants use light energy for photosynthesis, so it is essential. Increasing the light intensity will increase the rate of photosynthesis. Eventually, the rate of photosynthesis will stop increasing because another factor (limiting factor) such as carbon dioxide or temperature is in short supply.

At a certain point, increasing the light intensity past the optimum does not affect the rate of photosynthesis.

AAt low light intensities, the increase in the rate of photosynthesis is linear
BAt this point, another factor becomes limiting
CThe graph levels off and the rate becomes constant

For example, as you increase the light intensity, plants can absorb more light energy for photosynthesis. This causes the rate of photosynthesis to increase.

However, it may reach a point when the temperature becomes a limiting factor. So, increasing the light intensity will no longer increase the rate of photosynthesis. At this point, the rate of photosynthesis will not increase until the temperature increases.

  • In this case, increasing the temperature will cause the light intensity to plateau at a higher rate

Carbon Dioxide Concentration

Carbon dioxide is required for photosynthesis. So, increasing the concentration of carbon dioxide increases the rate of photosynthesis. Although up until a certain point, at which another factor (limiting factor) required for photosynthesis is in short supply.

AAt lower concentrations, the increase in the rate of photosynthesis is linear
BAt this point, another factor becomes limiting
CThe graph levels off and the rate becomes constant

Increasing the concentration of carbon dioxide above the optimum will not affect the rate of photosynthesis.