NEET Biology: Photorespiration C3 and C4 pathways Practice Questions
13 free multiple-choice questions on Photorespiration C3 and C4 pathways (Photosynthesis and Respiration) for NEET Biology, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.
Practice thousands more NEET questions in the app →Q1. Photorespiration is an energy-wasting process that occurs when the enzyme Rubisco binds to which molecule in the presence of low CO₂ concentrations?
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Correct answer: C — O₂
Photorespiration occurs when Rubisco, instead of binding CO₂, binds O₂ on the same active site, leading to the emission of O₂ instead of CO₂.
Q2. The C₄ pathway effectively concentrates CO₂ around which specific enzyme to maintain efficient carbon assimilation?
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Correct answer: C — RuBisCO
In C₄ plants, CO₂ is initially fixed by PEP carboxylase and then transported to the bundle sheath cells where CO₂ is concentrated around RuBisCO, reducing photorespiration.
Q3. The C4 pathway involves the initial fixation of CO₂ by which initial enzyme in the mesophyll cells?
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Correct answer: A — Phosphoenolpyruvate carboxylase
In C4 plants, PEP carboxylase fixes CO₂ into a four-carbon compound (oxaloacetate), which is then transported to the bundle sheath cells for the Calvin cycle.
Q4. In C4 plants, the initial CO₂ fixation occurs in the mesophyll cells. The resulting four-carbon compound is transported to the bundle sheath cells where it is released. Which compound is typically used for transport in the C4 cycle?
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Correct answer: C — Malate
Malate (or aspartate) is the primary organic acid used for the transport of the fixed carbon from the mesophyll cells to the bundle sheath cells in C4 plants.
Q5. Which of the following is a primary consequence (loss) of photorespiration in photosynthetic organisms?
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Correct answer: C — Release of CO₂
Photorespiration results in the wasteful consumption of energy and the release of previously fixed carbon as CO₂, reducing the net production of sugars.
Q6. Which group of plants utilizes the C4 pathway?
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Correct answer: C — Maize (Corn) and Sugarcane
C4 plants are commonly found in crops like maize and sugarcane, which utilize the C4 mechanism for efficient CO₂ assimilation.
Q7. The enzyme RuBisCO primarily catalyzes which reaction in photosynthesis?
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Correct answer: C — Fixation of CO₂
RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is responsible for the initial fixation of atmospheric carbon dioxide into organic molecules.
Q8. In C4 plants, the initial fixation of CO₂ occurs in which specific cell type?
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Correct answer: C — Mesophyll cells
C4 plants utilize a spatial separation mechanism. Initial CO₂ fixation occurs in the mesophyll cells by PEP carboxylase, fixing CO₂ into a C4 acid. This acid is then transported to the bundle sheath cells where the CO₂ is released and fed into the Calvin cycle.
Q9. The primary drawback of the C₃ pathway compared to the C₄ pathway under standard conditions is:
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Correct answer: B — Higher occurrence of photorespiration.
C₃ plants suffer significantly from photorespiration because RuBisCO can bind O₂ instead of CO₂, leading to the wasteful process of photorespiration.
Q10. In C₃ plants, what is the main biochemical limitation that occurs when the oxygenase activity of RuBisCO is favored over carboxylase activity?
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Correct answer: D — Photorespiration
When O₂ binds to RuBisCO instead of CO₂, it leads to photorespiration, a wasteful process where fixed carbon is released, reducing photosynthetic efficiency.
Q11. In the C3 pathway of photosynthesis, the primary initial fixation step involves the reaction between CO₂ and which organic molecule?
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Correct answer: C — RuBP
The initial fixation step in C3 photosynthesis is the carboxylation reaction where CO₂ is fixed onto Ribulose-1,5-bisphosphate (RuBP), catalyzed by Rubisco.
Q12. What is the function of the CO₂-concentrating mechanism employed by C4 plants?
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Correct answer: C — To reduce the photorespiration by concentrating CO₂ around Rubisco
The CO₂-concentrating mechanism ensures a high local concentration of CO₂ within the bundle sheath cells, minimizing the opportunity for Rubisco to react with O₂ and thus suppressing photorespiration.
Q13. What is the primary biochemical disadvantage of photorespiration in C3 plants?
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Correct answer: A — Increased O₂ fixation in the Calvin cycle
Photorespiration results in the wasteful consumption of ATP and the release of previously fixed carbon, making it an energy-loss process for the plant.
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