Question

When the intensity of light is gradually increased from low to high the rate of photosynthesis ________________________.

• A. increases
• B. decreases
• C. increases and then decreases
• D. decreases and then increases

Answer 1

The correct option is C increases and then decreases

The rate of photosynthesis increases linearly as the intensity of light is gradually increased from low to high. When the intensity of light is high, the rate of photosynthesis does not increase further as other factors become limiting. An increase in incident light beyond a particular point causes the breakdown of chlorophyll and hence decreases the rate of photosynthesis. The graph given below shows the variation of the rate of photosynthesis with respect to the intensity of light. In region-A light intensity is the limiting factor. In region B some factor other than light intensity is becoming a limiting factor. In region-C denotes that light intensity is no longer a limiting factor. Point-D represents the saturation point for light intensity and Point-E represents the maximum rate of photosynthesis. So the rate of photosynthesis slowly increases and then decreases.