1. What is a limiting factor?
What is the ideal combination of factors for the maximum rate of photosynthesis?
enough light
enough carbon dioxide
ideal temperature (not too hot or cold)
How is the rate affected if one of these factors is restricted?
If one of the factors is restricted, the rate of photosynthesis will be below the maximum possible rate.
The restricted factor controls how quickly photosynthesis occurs and so limits the rate. It is called the limiting factor.

2. Photosynthesis and light – limiting factors
How does the amount of light affect the rate of photosynthesis on this labelled graph?
As the amount of light increases, so does the rate. The limiting factor is light. 1 2 2
Here, increasing the amount of light has no affect on the rate. The limiting factor is now carbon dioxide or temperature.
What must be increased for the rate to increase?
rate of photosynthesis 1
light intensity

3. Photosynthesis and carbon dioxide – limiting factors
How does the amount of carbon dioxide affect the rate of photosynthesis on this labelled graph? 1
As the amount of carbon dioxide goes up, so does the rate. The limiting factor is carbon dioxide. 2 2
Here, increasing the amount of carbon dioxide has no affect on the rate. Light or warmth is now the limiting factor.
What must be increased for the rate to increase?
rate of photosynthesis 1
concentration of
carbon dioxide

4. Photosynthesis and temperature – limiting factors
How does temperature affect the rate of photosynthesis on this labelled graph? 1
As temperature increases, so does the rate because photosynthetic enzymes work best in the warmth. Here, the limiting factor is temperature.
rate of photosynthesis 2
Most plant enzymes are destroyed at about 45°C. Here, photosynthesis stops and the rate falls to zero.
What is the limiting factor? 2 1
0oC
temperature
45oC

5. Limiting factors activity