Interpreting graphs about limiting factors of photosynthesis
Results of investigations into limiting factors of photosynthesis can be presented as a graph. Typically, these will have the following profiles.
Light intensity
The rate of photosynthesis will increase as light intensity increases. The graph will level out at the point when another limiting factor prevents any further increase in the rate of photosynthesis.
Carbon dioxide concentration
The rate of photosynthesis will increase as carbon dioxide concentration increases. The graph will level out at the point when another limiting factor prevents any further increase in the rate of photosynthesis.
Temperature
The rate of photosynthesis will increase as temperature increases until the optimum temperature is reached. The rate will then decrease as the temperature increases further. This is because the enzymes involved will become denatured.
It is useful to be able to interpret a graph like the example below.
This graph shows the effect of light intensity on the rate of photosynthesis at two different carbon dioxide concentrations.
Light intensity is limiting the rate of photosynthesis at light intensities of 0 to 3.75 units. As light intensity is increased the rate of photosynthesis increases.
At light intensities of 3.75 to 5.5, a carbon dioxide concentration of 0.03 per cent is insufficient and limits the rate of photosynthesis. A carbon dioxide concentration of 0.1 per cent is sufficient and the rate of photosynthesis continues to increase as light intensity increases.
At light intensities of 5.5 units and above, a carbon dioxide concentration of 0.1 per cent is limiting and the rate of photosynthesis does not increase even when light intensity is increased.
Light intensity is not limiting the rate of photosynthesis at light intensities of five to eight units. As light intensity is increased the rate of photosynthesis remains the same.
At light intensities of five to eight units carbon dioxide concentration is limiting the rate of photosynthesis. If the light intensity is kept the same, and the carbon dioxide concentration is increased from 0.03 per cent to 0.10 per cent then the rate of photosynthesis increases.
