Question

Enlist various factors affecting photosynthesis

Answer 1

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The various factors that affect rate of photosynthesis are:

Light

Incident light ∝ CO 2  fixation rate; but at higher light intensities, the rate does not increase further as other factors become limiting

Light is rarely a limiting factor (with exception of the shade plants or plants of dense forest) because light saturation occurs at 10% of the full sunlight.

Beyond a point, if incident light is increased, then it leads to decrease in photosynthesis due to breakdown of chlorophyll.

CO 2  Concentration

Major limiting factor

Usually low in atmosphere (0.03 − 0.04%)

Up to 0.05% − increases rate of CO 2  fixation

> 0.05% − damaging effect

Though both C 3  and C 4  show increase in rate of photosynthesis at high light intensity accompanied by high CO 2   concentration,   the saturation point for C 3  is obtained at higher concentrations as compared to C 4 . Therefore, CO 2  concentration is more of a limiting factor for C 3  plants.

Increased CO 2  concentration is beneficial for greenhouse crops such as tomatoes and bell paper.

Temperature

Dark reactions are more sensitive to an increase in temperature.

C 4  plants respond more to an increase in temperature as compared to C 3  plants.

Adaptations according to habitat also effect temperature optima. Tropical plants have higher temperature optima compared to temperate.

Water

Water stress causes stomata to close and hence, less CO 2  is available.

Water stress causes the leaves to wilt, thereby reducing their surface area and metabolic activity as well.



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