Correct option is D
The Rubisco enzyme (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is central to both reductive carbon metabolism (Calvin Cycle) and oxidative carbon metabolism (Photorespiration) in plants. These two pathways differ in outcomes and energy requirements but are linked via shared intermediates and enzymes.
Statement A: Sugars are produced in both the cycles. Incorrect
- Sugars (like glucose, sucrose) are produced only in the Calvin cycle (reductive carbon cycle).
- In the oxidative carbon cycle (photorespiration), no sugars are formed; rather, carbon is lost as CO₂, and energy is consumed.
- Therefore, this statement is not correct.
Statement B: Ferredoxin is reduced only in oxidative carbon cycle. Correct
- In the context of carbon cycles, Ferredoxin plays a more critical role in the oxidative carbon cycle (photorespiration), especially in hydroxypyruvate to glycerate conversion, and photorespiratory ammonium assimilation.
- Although Ferredoxin is reduced primarily in the light reactions, its functional significance in the oxidative cycle is prominent, especially in mitochondria and chloroplast interconnections.
- Hence, this statement is considered correct in the context of oxidative carbon flow.
Statement C: Product of oxidative cycle is one of the substrates of reductive cycle. Correct
- In photorespiration (oxidative carbon cycle), 3-phosphoglycerate (3-PGA) is regenerated from 2-phosphoglycolate.
- 3-PGA is also a substrate and intermediate of the Calvin cycle (reductive cycle).
- Hence, the product of oxidative cycle (3-PGA) re-enters the Calvin cycle, validating this statement.
Statement D: NADP and ATP are used in both the cycles. Incorrect
- ATP and NADPH (not NADP) are used in the Calvin cycle.
- In photorespiration, ATP and NADH (mainly in peroxisome and mitochondria) are used, not NADP.
- Moreover, NADPH is not universally used in the photorespiration cycle in all plants.
- Thus, this statement is only partially correct and not entirely valid.
