Consider the following statements regarding the proton gradient across the thylakoid membrane:
I. Proton accumulation in the thylakoid lumen creates a high concentration of H⁺ inside the lumen relative to the stroma. II. High proton concentration in the lumen causes a decrease in lumen pH. III. Breakdown of the proton gradient occurs via proton diffusion through the CF₀ channel into the stroma. IV. Synthesis of ATP takes place on the inner surface of the thylakoid membrane inside the lumen.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because protons accumulate in the lumen, lowering its pH, and diffuse through CF₀ into the stroma to drive ATP synthesis. Statement IV is incorrect because ATP synthesis occurs on the stromal side of the thylakoid membrane by the CF₁ headpiece.
Question 62 of 100
📘 CLASS XI
With reference to the requirements for chemiosmotic synthesis of ATP in chloroplasts, evaluate these statements:
I. Chemiosmosis requires an intact membrane. II. It requires a proton pump to transport protons across the membrane. III. It requires a proton gradient across the thylakoid membrane. IV. It requires the enzyme RuBisCO to directly pump protons into the lumen.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because chemiosmosis depends on an intact membrane, proton pump, proton gradient, and ATP synthase. Statement IV is incorrect because RuBisCO functions in carbon fixation and has no role in proton pumping.
Question 63 of 100
📘 CLASS XI
Consider the following statements regarding Melvin Calvin and the discovery of the C₃ pathway:
I. Calvin used radioactive ¹⁴C in green algal photosynthesis studies. II. He identified 3-phosphoglyceric acid (3-PGA) as the first carbon fixation product in C₃ plants. III. Calvin established that 3-PGA is the universal first product of carbon fixation in all photosynthetic plants. IV. Melvin Calvin was awarded the Nobel Prize in 1961 for mapping the complete photosynthetic carbon reduction cycle.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because Calvin used radioactive ¹⁴C, identified 3-PGA as the first stable product in C₃ plants, and received the Nobel Prize in 1961. Statement III is incorrect because OAA is the first stable product in C₄ plants.
Question 64 of 100
📘 CLASS XI
Regarding the primary CO₂ acceptor in C₃ plants, consider the statements below:
I. The primary CO₂ acceptor in C₃ plants is a 5-carbon ketose sugar. II. The acceptor molecule is Ribulose-1,5-bisphosphate (RuBP). III. The carboxylation reaction is catalysed by the enzyme RuBP carboxylase-oxygenase (RuBisCO). IV. One molecule of RuBP combines with one molecule of CO₂ to form one molecule of 3-PGA.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because RuBP is a 5-carbon ketose sugar that accepts CO₂ in a RuBisCO-catalysed reaction. Statement IV is incorrect because one RuBP molecule produces two molecules of 3-PGA.
Question 65 of 100
📘 CLASS XI
Consider the following statements regarding the energy requirements of the Calvin Cycle:
I. Carboxylation of RuBP consumes 2 ATP per CO₂ fixed. II. Reduction of 3-PGA consumes 2 ATP and 2 NADPH per CO₂ fixed. III. Regeneration of RuBP consumes 1 ATP per CO₂ fixed. IV. The total energetic cost to fix one molecule of CO₂ in the Calvin cycle is 3 ATP and 2 NADPH.
Which of the statement(s) given above is/are correct?
Statements II, III and IV are correct because reduction requires 2 ATP and 2 NADPH, regeneration requires 1 ATP, giving a total cost of 3 ATP and 2 NADPH per CO₂ fixed. Statement I is incorrect because carboxylation itself does not consume ATP.
Question 66 of 100
📘 CLASS XI
Regarding C₄ plants and their adaptations, evaluate the following statements:
I. C₄ plants are evolutionary adaptations suited to dry tropical regions. II. C₄ leaves exhibit a specialized internal anatomy known as Kranz anatomy. III. C₄ plants tolerate higher temperatures and higher light intensities than C₃ plants. IV. C₄ plants undergo high rates of photorespiration under warm sunny conditions.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because C₄ plants are adapted to dry tropical conditions, possess Kranz anatomy, and tolerate higher temperature and light intensity. Statement IV is incorrect because photorespiration is absent in C₄ plants.
Question 67 of 100
📘 CLASS XI
Consider the following statements regarding Kranz anatomy in C₄ leaves:
I. Large cells clustered around vascular bundles are called bundle sheath cells. II. Bundle sheath cells may be arranged in several concentric layers around vascular bundles. III. Chloroplasts of bundle sheath cells feature extensive grana stacks and high rates of water splitting. IV. Cell walls of bundle sheath cells are thick and impervious to gaseous exchange.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because bundle sheath cells surround vascular bundles, occur in concentric layers, possess thick walls, and lack intercellular spaces. Statement III is incorrect because bundle sheath chloroplasts are typically agranal and do not perform photolysis of water.
Question 68 of 100
📘 CLASS XI
Regarding primary carbon fixation in C₄ mesophyll cells, consider the statements below:
I. The primary CO₂ acceptor in mesophyll cells is Phosphoenolpyruvate (PEP). II. PEP is a 3-carbon compound. III. Fixation of CO₂ in mesophyll cells is catalysed by PEP carboxylase (PEPcase). IV. Mesophyll cells of C₄ plants contain abundant RuBisCO enzyme.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because PEP (3C) accepts CO₂ through PEP carboxylase to produce oxaloacetic acid. Statement IV is incorrect because mesophyll cells of C₄ plants lack RuBisCO.
Question 69 of 100
📘 CLASS XI
Consider the following statements regarding the transport and decarboxylation steps in the Hatch and Slack pathway:
I. Oxaloacetic acid (OAA) formed in mesophyll cells is converted to malic acid or aspartic acid. II. Malic acid or aspartic acid is transported from mesophyll cells into bundle sheath cells via plasmodesmata. III. Decarboxylation of C₄ acids in bundle sheath cells yields CO₂ and a 3-carbon acid. IV. Decarboxylation in bundle sheath cells directly absorbs CO₂ to regenerate PEP on site.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because OAA is converted into malate or aspartate, transported to bundle sheath cells, and decarboxylated to release CO₂ and a 3-carbon acid. Statement IV is incorrect because decarboxylation releases CO₂, and PEP regeneration occurs back in mesophyll cells.
Question 70 of 100
📘 CLASS XI
Regarding the dual affinity and binding behaviour of RuBisCO, evaluate these statements:
I. RuBisCO has active binding sites capable of interacting with both CO₂ and O₂. II. RuBisCO has a significantly higher affinity for CO₂ than for O₂. III. Binding of CO₂ or O₂ is competitive and depends on their relative concentrations. IV. When CO₂ and O₂ concentrations are equal, RuBisCO exclusively binds O₂.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because RuBisCO binds both CO₂ and O₂ competitively but has a greater affinity for CO₂. Statement IV is incorrect because RuBisCO preferentially binds CO₂ when concentrations are equal.
