NEET 2024 Botany Question 130 Solution

The Calvin cycle proceeds in three stages: 1. Carboxylation: RuBP ($5C$) binds $CO_2$ via RuBisCO to form two molecules of 3-PGA ($3C$). No ATP or NADPH is consumed.

2. Reduction: Two molecules of ATP for phosphorylation and two of NADPH for reduction are consumed per $CO_2$ molecule fixed. 3. Regeneration: Regeneration of the $CO_2$ acceptor molecule RuBP requires one phosphorylation step using one ATP. Total Energy Consumed per $CO_2$: $$\text{Total ATP} = 2 + 1 = 3\;\text{molecules}$$ $$\text{Total NADPH} = 2\;\text{molecules}$$

To produce 1 molecule of hexose glucose ($C_6H_{12}O_6$), six turns of the cycle are required, consuming $6 \times 3 = 18\;ATP$ and $6 \times 2 = 12\;NADPH$, perfectly matching NCERT Table 13.1.