Factors Affecting Photosynthesis

This lesson covers the factors that affect the rate of photosynthesis — light intensity, carbon dioxide concentration and temperature — as required by the Edexcel GCSE Combined Science specification (1SC0). You also need to understand limiting factors and the inverse square law for light intensity.

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What Is a Limiting Factor?

A limiting factor is the factor that is in shortest supply and therefore restricts the rate of a reaction. Even if other conditions are ideal, the rate of photosynthesis cannot increase beyond the limit set by the factor in shortest supply.

At any given moment, one factor will be the limiting factor. Increasing that factor will increase the rate of photosynthesis — but only up to a point, at which a different factor becomes limiting.

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Factor 1: Light Intensity

Light provides the energy for photosynthesis. As light intensity increases:

• The rate of photosynthesis increases (more energy available).
• Eventually the rate plateaus — light is no longer the limiting factor; another factor (such as CO₂ concentration or temperature) takes over.

The Inverse Square Law

Light intensity follows the inverse square law when you move a lamp further from a plant: