Rate of Photosynthesis

The rate of photosynthesis is not constant — it varies depending on environmental conditions. Understanding the factors that affect the rate of photosynthesis and the concept of limiting factors is a core part of the AQA GCSE Biology Bioenergetics topic. This lesson explores each factor in detail and explains how they interact.

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What Is Meant by the Rate of Photosynthesis?

The rate of photosynthesis is a measure of how quickly a plant converts carbon dioxide and water into glucose and oxygen. It can be measured in several ways:

• The volume of oxygen produced per unit time (e.g. cm3 per minute)
• The volume of carbon dioxide absorbed per unit time
• The increase in biomass (dry mass) over time

A faster rate of photosynthesis means the plant is producing more glucose and oxygen in a given time period.

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Limiting Factors

A limiting factor is the factor that is in shortest supply at any given time, and therefore directly controls the rate of a reaction. Even if other factors are plentiful, the rate cannot increase beyond the point set by the limiting factor.

The three main limiting factors for photosynthesis are: