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The rate of photosynthesis is not constant — it changes depending on the environmental conditions around the plant. Understanding the factors that affect the rate of photosynthesis and how to interpret graphs showing these effects is a key part of the Edexcel GCSE Biology (1BI0) specification.
A limiting factor is the factor that is in shortest supply and therefore restricts the rate of a process. For photosynthesis, there are three main limiting factors:
At any given time, only one factor can be the limiting factor. Increasing the supply of the limiting factor will increase the rate of photosynthesis — but only up to a point, when a different factor becomes limiting.
Exam Tip: A common 6-mark question asks you to explain how limiting factors affect the rate of photosynthesis. Structure your answer by discussing each factor separately and explain what happens when it is no longer limiting.
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