Question

Which of the following is incorrect regarding $C_4$ pathway?

• A. It requires more energy than the $C_3$ pathway for production of glucose.
• B. It overcomes loss due to photorespiration.
• C. The first formed stable compound is a 3 carbon compound, i.e., oxaloacetic acid.
  
• D. It is inhibited by high $C{O}_2$ concentration.

Answer 1

Answer: (C)

The first formed stable compound is a 3 carbon compound, i.e., oxaloacetic acid.

C${}_4$ is the alternative pathway of Calvin cycle (C${}_3$ cycle) taking place during the dark phase of photosynthesis. In the C${}_4$ cycle the first stable compound is 4 C compound called as oxaloacetic acid. So, it is called as C${}_4$ cycle. The primary CO${}_2$acceptor is PEP, a 3 carbon compound. Two CO${}_2$ fixation occur. CO${}_2$ fixation is fast and more efficient. Fixation of 1 molecule of CO${}_2$ requires 5 ATP and 3 NADH. This cycle can operate in low CO${}_2$ concentrations. Also, O${}_2$ has no inhibitory effect on photosynthesis.