Question

With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct ?

(a) Light saturation for CO₂ -fixation occurs at 10% of full sunlight

(b) Increasing atmospheric CO₂ concentraion upto 0.05%  can enhance CO_{2 -}fixation rate

(c) C₃-plants respond to higher temperature with enhanced photosynthesis, while C₄-plants have much lower- temperature optimum

(d) Tomato is a greenhouse crop, which can be grown in CO₂ enriched atmosphere for higher yield

Answer 1

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.