Question

When two plants L and M were exposed to different light intensities and temperatures, they showed changes in their rates of photosynthesis, which have been represented in the following graph.

The graph indicates that

• A. plant $L$ is a $C_3$ plant for which the light saturation point is $100\%$ of full sunlight
• B. plant $M$ is a $C_4$ plant for which the optimum temperature is around $20^{\circ }C$
• C. plant $M$ is a $C_3$ plant which is more affected at higher temperature and higher light intensity as compared to plant $L$
• D. plant $L$ is a $C_4$ plant and cannot function at light intensities above the saturation point

Answer 1

Answer: (C)

The light intensity at which a plant can achieve maximum rate of photosynthesis is called as light saturation point. Its value is $50-70\%$ of full sunlight in $C_3$ sun plants and upto $200\%$ of full sunlight in $C_4$ sun plants (e.g., sugarcane), Beyond saturation point (it is seldom realised in nature in $C_4$ sun plants), the rate of photosynthesis begins to decline, Optimum temperature at which the rate of photosynthesis is maximum is $10^{\circ }C-25^{\circ }C$ for$C_3$ plants and $30-45^{\circ }C$ for $C_4$ plants. Thus, it is clear that in the given graph, plant $L$ is a $C_4$ plant and plant $M$ is a $C_3$ plant.