Limiting Factors of Photosynthesis

Building on the previous lessons, this lesson takes a deeper look at how light intensity, carbon dioxide concentration and temperature interact as limiting factors. You will also explore how commercial growers use this knowledge to maximise crop production. This is a frequently tested area in the AQA GCSE Combined Science Trilogy (8464) exam.

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Recap: What Is a Limiting Factor?

A limiting factor is the factor that is in the shortest supply at a given time, and so directly controls the rate of photosynthesis. Increasing this factor will increase the rate — until a different factor becomes limiting instead.

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Light Intensity as a Limiting Factor

At low light intensities, light is the limiting factor. Increasing light intensity increases the rate of photosynthesis proportionally.

At the plateau on a graph of rate vs light intensity, light is no longer limiting. Either CO₂ concentration or temperature is now the factor preventing a further increase.

Graph Description

graph LR
    A["Low light"] -->|"Rate rises linearly"| B["Moderate light"]
    B -->|"Rate increase slows"| C["High light — plateau"]
    C --> D["Another factor is now limiting"]