Calvin Cycle and CO₂ Fixation — NEET Biology
📚 Practice ConceptLet us now see how the ATP and NADPH are used in the biosynthetic phase. We saw earlier that CO₂ is combined with H₂O to produce (CH₂O)n or sugars. It was of interest to scientists to find out how this reaction proceeded, or rather what was the first product formed when CO₂ is taken into a reaction or fixed. Just after world war II, among the several efforts to put radioisotopes to beneficial use, the work of Melvin Calvin is exemplary. The use of radioactive ¹⁴C by him in algal photosynthesis studies led to the discovery that the first CO₂ fixation product was a 3-carbon organic acid. He also contributed to working out the complete biosynthetic pathway; hence it was called Calvin cycle after him. The first product identified was 3-phosphoglyceric acid or in short PGA. How many carbon atoms does it have?
Match the following (Column I with Column II): COLUMN I a) Biosynthetic phase (Dark reactions) b) C₃ pathway c) C₄ pathway d) Primary CO₂ acceptor in C₄ plants e) First stable product in C₃ plants COLUMN II (Feature / Product) 1. ATP and NADPH from light reactions are used for CO₂ fixation 2. First stable product is 3-phosphoglyceric acid (3-PGA) 3. First stable product is oxaloacetic acid (OAA) 4. Ribulose-1,5-bisphosphate (RuBP) is the primary CO₂ acceptor 5. Phosphoenolpyruvate (PEP) is the primary CO₂ acceptor
View solution & NCERT explanation
Correct answer: C — a–1, b–4, c–3, d–5, e–2
(a) Biosynthetic phase → Uses ATP & NADPH from light reactions (1). (b) C₃ pathway → RuBP is the primary CO₂ acceptor (4). (c) C₄ pathway → First stable product is OAA (3). (d) Primary CO₂ acceptor in C₄ plants → PEP (5). (e) First stable product in C₃ plants → 3-PGA (2).
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