Limiting Factors

Biology: Cambridge International A Level, topic 13.1.4

The Rate of Photosynthesis

The four key factors affecting the rate of photosynthesis are:

Rate of photosynthesis increases up to the optimum temperature (about 45°C). Above this temperature, the rate starts to fall.
Enzymes such as rubisco play an important role in photosynthesis.
At low temperatures enzymes have less kinetic energy and are less likely to successfully collide with the substrate. This means fewer enzyme substrate complexes are formed.
Above the optimum temperature, enzymes will denature and the rate of photosynthesis will fall.

Increasing light intensity increases the rate of photosynthesis because more energy is provided.
In low light intensities the light-dependent reaction cannot take place. This causes levels of reduced NADP and ATP to fall.
Reduced NADP and ATP are necessary to convert GP to TP and to regenerate RuBP.
Without reduced NADP and ATP the Calvin cycle cannot take place and rate of photosynthesis declines.

Increasing the CO₂ concentration increases the rate of photosynthesis.
At high CO₂ concentrations, there is more carbon available for fixation in the Calvin cycle.
If the rate of the Calvin cycle increases, more GP and TP is produced and more RuBP is regenerated.
Very high CO₂ concentrations can cause stomata to open wider causing more water to be lost.
Too much water loss will then cause the stomata to close and the rate of photosynthesis to slow again.

High chlorophyll concentration gives a high rate of photosynthesis.
If there is more chlorophyll, light can be absorbed at a faster rate. This will cause the light-dependent reaction rate to increase.