C₄ Plant Productivity and Calvin Pathway — NEET Biology
📚 Practice ConceptEven though a very few cells in a C₄ plant carry out the biosynthetic – Calvin pathway, yet they are highly productive. Can you discuss why?
Which of the following statements correctly describe photorespiration in the context of environmental factors and plant types? S1: Photorespiration is a process that occurs only in the presence of both O₂ and light, leading to the loss of fixed carbon. S2: Under high light intensities and limiting CO₂ conditions, photorespiration can become more pronounced in C₃ plants. S3: The C₄ pathway has evolved as a mechanism to enhance photorespiration in plants adapted to hot, dry climates. S4: Photorespiration directly contributes to the synthesis of ATP and NADPH for the Calvin cycle in C₃ plants. S5: In C₄ plants, the activity of RuBisCO in mesophyll cells is the primary factor in minimizing photorespiration.
View solution & NCERT explanation
Correct answer: A — S1, S2 are correct
Let's evaluate each statement: S1: Photorespiration is a light-dependent process that requires O₂ and results in the release of CO₂ (loss of fixed carbon). This statement is correct. NCERT states: "In C3 plants some O2 does bind to RuBisCO, and hence CO2 fixation is decreased... Rather it results in the release of CO2 with the utilisation of ATP." The term 'photorespiration' itself implies dependence on light. (Page 147, Section 11.9, Paragraph 3). S2: High light intensities lead to increased O₂ production and CO₂ consumption, thus lowering the CO₂:O₂ ratio inside the leaf. This, combined with high temperatures, favors the oxygenase activity of RuBisCO in C₃ plants, increasing photorespiration. This statement is correct. NCERT states: "It is the relative concentration of O2 and CO2 that determines which of the two will bind to the enzyme." and implicitly through C4 adaptation (Page 147, Section 11.9, Paragraph 3). S3: The C₄ pathway is an adaptation to *minimize* photorespiration, not enhance it. It is common in plants adapted to dry tropical regions. This statement is incorrect. NCERT states: "In C4 plants photorespiration does not occur." and C4 plants "tolerate higher temperatures". (Page 145, Section 11.8; Page 147, Section 11.9, Paragraph 4). S4: Photorespiration does not synthesize ATP or NADPH; instead, it consumes ATP. This statement is incorrect. NCERT states: "In the photorespiratory pathway there is no synthesis of ATP or NADPH." (Page 147, Section 11.9, Paragraph 3). S5: In C₄ plants, RuBisCO is located in the bundle sheath cells, not mesophyll cells. PEPcase in mesophyll cells is responsible for initial CO₂ fixation, which helps in minimizing photorespiration by delivering a high concentration of CO₂ to the bundle sheath cells. This statement is incorrect. NCERT states: "It is important to register that the mesophyll cells lack RuBisCO enzyme." and "The bundle sheath cells are rich in an enzyme Ribulose bisphosphate carboxylase-oxygenase (RuBisCO)" (Page 146-147, Section 11.8). Therefore, only statements S1 and S2 are correct.
What does NCERT say about Even though very few?
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Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
176/180MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.