Question

The $C_3$ cycle is called so because

• A. 3 molecules of $C{O}_2$ are required for the formation of 1 glucose
• B. 3 ATP and 3 NADPH are utilized in this cycle
• C. the cycle has to be repeated 3 times to generate 1 glucose molecule
• D. the first stable product of $C{O}_2$ fixation is a 3 carbon compound

Answer 1

The correct option is D the first stable product of $C{O}_2$ fixation is a 3 carbon compound

Calvin cycle is also called $C_3$ cycle as the first stable product formed is a 3 carbon compound. During the Calvin cycle, there is carbon dioxide fixation and synthesis of glucose. In $C_3$ plants, the primary acceptor of carbon dioxide is a 5 carbon compound, RuBP (ribulose-1,5-bisphosphate). RuBP combines with carbon dioxide and forms into an unstable 6 carbon compound which splits into two molecules of 3-PGA (3-phosphoglycerate). The first stable product formed in $C_3$ plants is 3-PGA, which is a 3 carbon compound. Hence, these plants are called $C_3$ plants and the pathway is called $C_3$ cycle.

6 molecules of $C{O}_2$ are required for the formation of 1 glucose. 3 ATP and 2 NADPH are utilized in one cycle. The cycle has to be repeated 6 times to generate 1 glucose molecule.