Question

Study the given graph showing the effect of light intensity on the rate of photosynthesis. Which of the following statements regarding this is correct?

• A. Light is a limiting factor in the region A
• B. Region C represents that rate of photosynthesis is not increased further by increasing light intensity because some other factor became limiting
• C. Point D represents the intensity of light at which some other factor became limiting
• D. All of these

Answer 1

Answer: (D)

A limiting factor is defined as a factor which is deficient to such an extent that increase in its magnitude directly increases the rate of the process. In the given graph, rate of photosynthesis initially increases with an increase in light intensity (region $A$) but soon it levelled off. Thus, initially light intensity was limiting the rate of photosynthesis. However, when light intensity was present in sufficient amounts (region $C$), rate of photosynthesis did not increase further. This is due to the fact that in region $C$, some other factor (e.g. $CO_{2}$ concentration) became the limiting factor. At this region, the rate of photosynthesis could be further enhanced only by the increase in availability of other limiting factor (e.g. $CO_{2}$).