Question

The end product of C3 cycle is :

• A. Oxaloacetic acid
• B. 3,4-bisphosphoglycerate
• C. Ribulose 5-phosphate
• D. 3-phosphoglycerate

Hint:

Keep the key products of both major photosynthetic pathways clear:
- \(\text{C}_3\) Cycle $\rightarrow$ 3-phosphoglycerate (3-PGA, a 3-Carbon compound)
- \(\text{C}_4\) Cycle $\rightarrow$ Oxaloacetic acid (OAA, a 4-Carbon compound)

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The \(\text{C}_3\) cycle (Calvin cycle) is the primary pathway of photosynthetic carbon fixation, where atmospheric carbon dioxide is converted into organic compounds.

Step 3: Detailed Explanation:
During the initial carboxylation phase of the Calvin cycle, carbon dioxide (\(\text{CO}_2\)) is fixed onto a five-carbon acceptor molecule, Ribulose 1,5-bisphosphate (RuBP), catalyzed by the enzyme RuBisCO.
The resulting unstable six-carbon intermediate quickly splits into two molecules of a stable three-carbon compound: 3-phosphoglycerate (3-PGA).
In multiple-choice questions, this initial stable product is frequently referred to as the primary product or end product of the carboxylation stage of the \(\text{C}_3\) cycle.
Evaluating the other options:
- Oxaloacetic acid is a four-carbon compound and is the first stable product of the \(\text{C}_4\) pathway, not the \(\text{C}_3\) cycle.
- 3,4-bisphosphoglycerate is not a standard metabolic intermediate of this cycle.
- Ribulose 5-phosphate is produced during the regeneration phase of the cycle.

Step 4: Final Answer:
The primary stable product of the \(\text{C}_3\) cycle is 3-phosphoglycerate.