With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct ?
With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct ?
(1) Increasing atmospheric CO2 concentration up to 0.05% can enhance CO2 fixation rate
(2) C3 plants respond to higher temperatures with enhanced photosynthesis while C4 plants have much lower temperature optimum
(3) Tomato is a greenhouse crop which can be grown in CO2 enriched atmosphere for higher yield
(4) Light saturation for CO2 fixation occurs at 10% of full sunligh
2 Answers
The correct answer is (2)
In C3 plants photosynthesis decreases at higher temperature due to increased photorespiration. C4 plants have higher temperature optimum because of the presence of enzyme called pyruvate phosphate dikinase, which is sensitive to low temperature.
Correct option (c) C3-plants respond to higher temperature with enhanced photosynthesis, while C4-plants have much lower- temperature optimum
Explanation :
In C4 -plant, the initial fixation of CO2 occurs in mesophyll cell. The primary acceptor of CO2 is phosphoenol pyruvate (PEP). It combines with CO2 in the presence of enzyme PEP carboxylase to form the first stable product, i.e. Oxalo Acetic Acid(OAA). Where as C3 -plants lack PEP enzymes. They possess RuBisCO enzyme. This enzyme can work as both carboxylase (fixation of CO2) and oxygenase (fixation of O2). RuBisCO has a much greater affinity for CO2 than for O2 and the binding is competive. At higher temperature, its affinity for CO2 decrease and it works as oxygenase.
Therefore, at higher temperature photosynthesis decrease in C3 -plants, while in C4 -plants it increases.