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

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

The optimum light intensity for $C_3$ plants is 50-70% and up to 25% of full sunlight in $C_4$ plants. Beyond this saturation point, rate of photosynthesis begins to decline. The optimum temperature at which rate of photosynthesis is maximum is ${10}^{\circ }C$ - ${25}^{\circ }C$ for $C_3$ plants and ${30}^{\circ }C$-${45}^{\circ }C$ for $C_4$ plants.

So, in given graph the rate of photosynthesis of M plant is decline at near ${20}^{\circ }C$ temperature and 50% of light. So, it is a $C_3$ plants which is affected by high light intensity and temperature.