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 subtraction point is 100% of full sunlight.
B- Plant M is a $C_4$ plant for which the optimum temperature is around 20°C
C- Plant M is a $C_3$ plant which is more affected by higher temperature and higher light intensity as compared to plant L.
D- Plant L is a plant and can not function at light intensities above the saturation point.

Answer 1

Hint: Rate of photosynthesis is greater in intense light than diffuse light . But a higher light intensity the process of photooxidation occurs and photosynthesis apparatus may get destroyed.

Complete answer:
When a plant can achieve maximum rate of photosynthesis at light intensity that is known as light saturation point. In $C_3$ sun plants its value is 50-70% of full sunlight and in $C_4$ sun plants it is up to 20% of full sunlight. The rate of photosynthesis starts to decline beyond the saturation point. When the rate of photosynthesis is maximum is 100C−250C for $C_3$ ​ plants and 30−450C for $C_4$ plants is called optimum temperature. So from the given statement , it is clear that in the given graph, plant L is a C $C_4$ plant and plant M is a $C_3$ plant. So, the option c is the correct answer that plant M is a $C_3$ plant which is more affected at higher temperature and higher light intensity as compared to plant L.

Additional information:
Factors affecting photosynthesis:
1.Light quality and wavelength: maximum photosynthesis takes place in red light than in blue light.
2.Light intensity: rate of photosynthesis is greater in intense light than diffuse light
3.Temperature: Optimum temperature for photosynthesis is 20-35°C
4.Water : The rate of photosynthesis reduces due to lack of water
5.Inhibitors: All the chemicals are used as herbicides which mostly block electron transport system
6.Minerals:For the structure of chlorophyll and enzymes magnesium and nitrogen are essential.

Note: Compensation point is very low in $C_4$ plants while in $C_3$ plants it is very high. $C_3$ plants are common in dicots and monocots both while $C_4$ plants are very rare in dicots. Enzymes of the Calvin cycle are found in all green plants. Enzymes of the calvin cycle are found in all green cells. In $C_4$ plants enzymes of the calvin cycle are absent in mesophyll cells while present in a bundle of sheath.