Limiting factors of photosynthesis

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  • Created by: J.E.C.
  • Created on: 13-10-13 16:34

Light intensity and rate of photosynthesis

The rate of photosynthesis is commonly measured in one of two ways:

> Volume of oxygen released by plant

> Volume of carbon dioxide taken up by plant

When light is the limitng factor, the rate of photosynthesis is directly proportional to light intensity. As light intensity increases so does the volume of oxygen produced/carbon dioxide taken up to a point at which it is exactly balanced by the carbon dioxide produced/oxygen absorbed by cellular respiration. At this point = no net exchange of gases into/out of the plant = COMPENSATION POINT.

Further increases in light intensity will cause a proportional increase in rate of photosynthesis. However, a point will be reached where further increases in light intensity will have no effect on photosynthesis. .At this point some other factor is limiting the reaction.

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CO2 concentration and rate of photosynthesis

The optimum concentration of carbon dioxide for a consistently high rate of photosynthesis is 0.1%.

CO2 concentration affects enzyme activity, particularly the enzyme that catalyses the combination of RuBP with CO2 in the LIR.

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Temperature and the rate of photosynthesis

Providing other factors are not limited, the rate of photosynthesis increases directly proportional to the temperature. Between 0˚C and 25˚C, the rateof photosynthesis is doubled for every 10˚C rise in temperature. 

For many plants the optimum temperature is 25˚C and after which the rate levels off and rapidly decreases due to enzyme denaturation

Photochemical reactions are not usually affected by temperature so the fact that photosynthesis was temperature-sensitive suggested there was also a chemical process > the LIR.

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