Limiting Factors of Photosynthesis

Learning Outcomes

Discuss light intensity, carbon dioxide concentration and temperature as limiting factors on the rate of photosynthesis.

🕜Estimated Time: 45 mins

What is a Limiting Factor?

Determining the limiting factor

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What is a Limiting Factor?

A limiting factor (e.g. temperature) directly affects the rate of a chemical reaction.
The rate of the reaction can only be increased if the value of the limiting factor is increased.
Examples of limiting factors that may affect the rate of photosynthesis are
- - Light intensity
  - Concentration of carbon dioxide
  - Temperature

Determining the limiting factor

The graphs below illustrate the effect of the different factors on the rate of photosynthesis, and how we decide which is the limiting factor at any one time.

The limiting factor may be different at various intervals - for example, it is not always the case that temperature is a limiting factor, as you will see below.

1. Increase in light intensity

As light intensity increases from 0 to A, rate of photosynthesis increases
- - Light intensity is the limiting factor.
As light intensity increases beyond A, light is no longer the limiting factor since rate of photosynthesis remains constant
- - Other factors are limiting

2. Increase in temperature

If we try to increase the temperature from 20oC to 30oC (graph 2), there is no large increase in the rate of photosynthesis.
- - Temperature is not an important limiting factor.

3. Increase in concentration of carbon dioxide

If we try to increase the concentration of carbon dioxide from 0.03% to 0.13% (graph 3), there is a large increase in the rate of photosynthesis.
- - Carbon dioxide concentration is the limiting factor in region AB of graph 1.

4. Increase in temperature

At 0.13% of carbon dioxide concentration and further increasing the temperature to 30oC (graph 4) causes a large increase in the rate of photosynthesis.
- - Temperature is the limiting factor in region EF of graph 3.

Note!

Under normal atmospheric condition, carbon dioxide is usually the limiting factor since atmospheric carbon dioxide concentration remains constant at about 0.03%.

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