Regarding the anatomical characteristics of C4 plants (Kranz Anatomy), evaluate these statements:
I. Bundle sheath cells are arranged in layers around vascular bundles. II. Bundle sheath cells contain a large number of chloroplasts. III. Bundle sheath cells possess thin, highly gas-permeable cell walls to promote oxygen diffusion. IV. Bundle sheath cells lack intercellular spaces.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because Kranz anatomy consists of large bundle sheath cells arranged around vascular bundles with abundant chloroplasts, thick cell walls and no intercellular spaces. Statement III is incorrect because the thick bundle sheath cell walls are relatively impermeable to gases, minimizing CO2 leakage and oxygen entry.
Question 42 of 100
📘 CLASS XI
Consider the following statements regarding initial CO2 fixation in the Hatch and Slack pathway:
I. Primary CO2 acceptor in mesophyll cells is Phosphoenolpyruvate (PEP), a 3-carbon compound. II. The enzyme catalysing initial fixation is PEP carboxylase (PEPcase). III. Mesophyll cells of C4 plants lack the enzyme RuBisCO. IV. Initial CO2 fixation yields Oxaloacetic acid (OAA), a 4-carbon acid.
Which of the statement(s) given above is/are correct?
All four statements are correct. In C4 mesophyll cells, PEP accepts CO2 in the presence of PEP carboxylase to form oxaloacetic acid (OAA). Mesophyll cells lack RuBisCO, which is confined to bundle sheath cells.
Question 43 of 100
📘 CLASS XI
Regarding transport and decarboxylation in the C4 cycle, consider the statements below:
I. OAA in mesophyll cells is converted into malic acid or aspartic acid. II. Malic or aspartic acid is transported through plasmodesmata into bundle sheath cells. III. Decarboxylation of C4 acid in bundle sheath cells produces CO2 and a 3-carbon acid. IV. The released 3-carbon acid is transported back to mesophyll cells where it is converted back to PEP.
Which of the statement(s) given above is/are correct?
All four statements are correct. OAA is converted into malate or aspartate, transported to bundle sheath cells, decarboxylated to release CO2 and a 3-carbon compound (pyruvate), which returns to mesophyll cells for regeneration of PEP.
Question 44 of 100
📘 CLASS XI
Consider the following statements regarding enzyme distribution in C4 plants:
I. Mesophyll cells contain PEPcase but lack RuBisCO. II. Bundle sheath cells contain RuBisCO but lack PEPcase. III. Both mesophyll and bundle sheath cells contain high levels of RuBisCO. IV. Calvin cycle in C4 plants operates exclusively inside bundle sheath cells.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because mesophyll cells possess PEP carboxylase whereas bundle sheath cells contain RuBisCO and carry out the Calvin cycle. Statement III is incorrect because RuBisCO is absent from mesophyll cells in C4 plants.
Question 45 of 100
📘 CLASS XI
Regarding the dual enzymatic nature of RuBisCO, evaluate the following statements:
I. RuBisCO is the most abundant enzyme in the world. II. The active site of RuBisCO can bind to both CO₂ and O₂. III. RuBisCO has a higher affinity for O₂ than for CO₂. IV. Relative concentrations of O₂ and CO₂ determine whether carboxylation or oxygenation occurs.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because RuBisCO is the most abundant enzyme and can bind both CO₂ and O₂, with the reaction depending on their relative concentrations. Statement III is incorrect because RuBisCO has a much greater affinity for CO₂ than for O₂.
Question 46 of 100
📘 CLASS XI
Consider the following statements regarding the photorespiratory pathway in C₃ plants:
I. Oxygenation of RuBP by RuBisCO forms one molecule of 3-PGA (3C) and one molecule of phosphoglycolate (2C). II. Photorespiration results in the net synthesis of glucose and ATP. III. Photorespiration releases CO₂ with the consumption of ATP. IV. Photorespiration yields neither ATP nor NADPH.
Which of the statement(s) given above is/are correct?
Statements I, III and IV are correct because photorespiration produces 3-PGA and phosphoglycolate, releases CO₂, consumes ATP and generates neither ATP nor NADPH. Statement II is incorrect because photorespiration is a wasteful process and does not synthesize glucose or ATP.
Question 47 of 100
📘 CLASS XI
Regarding the reasons why C₄ plants lack photorespiration, consider the statements below:
I. Decarboxylation of C₄ acid in bundle sheath cells floods the cellular environment with CO₂. II. High internal CO₂ concentration around RuBisCO maximizes carboxylation and suppresses oxygenation. III. Bundle sheath cells lack oxygen because PS II is absent in their chloroplasts. IV. Absence of photorespiration contributes to superior agricultural yields in C₄ crops.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because decarboxylation raises CO₂ concentration around RuBisCO, suppressing oxygenation and improving productivity. Statement III is incorrect because suppression of photorespiration is mainly due to high CO₂ concentration, not complete absence of oxygen.
Question 48 of 100
📘 CLASS XI
Consider the following statements concerning light intensity as a limiting factor in photosynthesis:
I. At low light intensities, there is a linear relationship between incident light and rate of CO₂ fixation. II. At higher light intensities, the photosynthetic rate plateaus as other factors become limiting. III. Light saturation for most plants occurs at 10% of full sunlight. IV. Beyond light saturation point, further increases in light intensity cause chlorophyll breakdown (photo-oxidation) and rate decline.
Which of the statement(s) given above is/are correct?
All four statements are correct. Photosynthesis increases linearly at low light, reaches saturation around 10% of full sunlight for many plants, and excessive light can lead to photo-oxidation and decline in photosynthetic efficiency.
Question 49 of 100
📘 CLASS XI
Regarding atmospheric CO₂ concentration and photosynthetic response in C₃ and C₄ plants:
I. Current atmospheric CO₂ concentration ranges between 0.03% and 0.04% (300–400 μLL⁻¹). II. C₄ plants reach CO₂ saturation at approximately 360 μLL⁻¹. III. C₃ plants reach CO₂ saturation only beyond 450 μLL⁻¹. IV. Increasing CO₂ level up to 0.05% enhances CO₂ fixation rate in C₃ plants.
Which of the statement(s) given above is/are correct?
All four statements are correct. Atmospheric CO₂ is approximately 0.03–0.04%. C₄ plants saturate near 360 μLL⁻¹, whereas C₃ plants saturate above 450 μLL⁻¹, and increasing CO₂ up to about 0.05% enhances photosynthesis in C₃ plants.
Question 50 of 100
📘 CLASS XI
Consider the following statements regarding the effect of temperature and water on photosynthesis:
I. Light reactions are temperature-controlled to a much greater extent than dark reactions. II. C₄ plants have a higher optimum temperature than C₃ plants because they are adapted to dry tropical regions. III. Tropical plants have higher temperature optima than temperate plants. IV. Water stress reduces photosynthesis primarily through stomatal closure (CO₂ limitation) and leaf wilting (reduced surface area).
Which of the statement(s) given above is/are correct?
Statements II, III and IV are correct because C₄ and tropical plants possess higher temperature optima, while water stress mainly reduces photosynthesis through stomatal closure and wilting. Statement I is incorrect because the dark (enzymatic) reactions are much more temperature-sensitive than the light reactions.
