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. Pant M is a $C_4$ plant for which the optimum temperature is around ${20}^{o}C$
• C. Pant 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 plant and cannot function at light intensities above the saturation point

Answer 1

The correct option is C Pant M is a $C_3$ plant which is more affected at higher temperature and higher light intensity as compared to plant L

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 20% 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 ${10}^{0}C-{25}^{0}Cfor{C}_3$ plants and $30-{45}^{0}Cfor{C}_4$ 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. So, the correct answer is 'Pant M is a C3 plant which is more affected at higher temperature and higher light intensity as compared to plant L'.