What is a limiting factor?
Limiting factor: an environmental factor that restricts the rate of photosynthesis when it is not at a suitable level.
For photosynthesis to proceed rapidly, plants need suitable environmental conditions as well as a supply of the required reactants.
The three main limiting factors considered here are:
| Factor | Why it can affect photosynthesis |
|---|---|
| Light intensity | Light provides the energy that drives the light-dependent reaction. |
| Carbon dioxide concentration | Carbon dioxide is required during carbon fixation in the Calvin cycle. |
| Temperature | Photosynthesis includes enzyme-controlled reactions whose rates depend on temperature. |
If one factor restricts the rate, improving a different factor may have little or no effect. Once the original factor is no longer limiting, another factor may become the one that restricts photosynthesis.
Exam Tip: In data questions, distinguish between describe and explain. A description states the pattern in the data; an explanation gives the biological reason for that pattern.