Question

With reference to factors affecting the rate of photosynthesis , which of the following statements is not correct?
A. Tomato is a greenhouse crop which can be grown in a $C{O_2}$ - enriched atmosphere for higher yield.
B. Light saturation for $C{O_2}$ fixation occurs at $10\%$ of full sunlight.
C. Increasing atmospheric $C{O_2}$ concentration up to $0.05\%$ can enhance $C{O_2}$ fixation rate.
D. ${C_3}$ plants respond to higher temperature with enhanced photosynthesis while ${C_4}$ plants have much lower temperature optimum.

Answer 1

Greenhouse crops are the crops grown under suitable and controlled environments. ${C_4}$ plants are very adapted to tropical climates and can tolerate a wide range of temperature in comparison to ${C_3}$ plants.

Complete answer:
When we talk about photorespiration, it is the process occuring by which plants perform metabolism with the help of enzyme RUBISCO(ribulose ) which leads to the wastage of energy produced at the time of photosynthesis. This process of photorespiration interferes with the working and functioning of ${C_3}$ cycle. The oxygen available in these plants binds with the enzyme RuBiSCO, due to which carbon dioxide fixation decreases. There is neither synthesis of any kind of sugar nor any $ATP$ is synthesized. Instead, it only ends up by the release of carbon dioxide by utilising the $ATP$ formed during phosphorylation. Hence, photorespiration does not occur in ${C_4}$ plants but comes in action in ${C_3}$ plants. Therefore in ${C_3}$ plants photosynthesis decreases at higher temperatures due to involvement of photorespiration. Whereas, ${C_4}$ plants' higher temperature is favourable to them due to the presence of enzymes known as pyruvate phosphate dikinase that remain sensitive to low temperature.
Hence the correct option is option D i.e ${C_3}$ plants respond to higher temperature with enhanced photosynthesis while ${C_4}$ plants have much lower temperature optimum.

Hence, the correct answer is option (D).

Additional information: The rate of photosynthesis is controlled by various factors like duration of light, temperature, water, oxygen, and some internal factors are also counted like chlorophyll content.

Note: If we increase the carbon dioxide amount under controlled conditions and light and temperature are not regarded as limiting factors then the rate of photosynthesis increases upto $1\%$ of carbon dioxide concentrations.