Consider the following statements regarding Photorespiration in C3 plants:
I. RuBisCO active site can competitively bind both CO2 and O2. II. When O2 binds to RuBisCO, RuBP is converted into one molecule of 3-phosphoglycerate (3C) and one molecule of phosphoglycolate (2C). III. Photorespiration is a highly efficient process that synthesizes additional ATP and NADPH. IV. Photorespiration results in the release of CO2 with the utilization of ATP.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because RuBisCO has both carboxylase and oxygenase activities, and photorespiration releases CO2 while consuming ATP. Statement III is incorrect because photorespiration does not produce ATP, NADPH or sugars.
Question 22 of 100
📘 CLASS XI
Regarding the mechanism of photorespiration suppression in C4 plants:
I. Photorespiration is absent in C4 plants because they increase CO2 concentration at the enzyme site. II. Decarboxylation of C4 acids in bundle sheath cells elevates intracellular CO2 concentration around RuBisCO. III. High local CO2 levels ensure RuBisCO functions as a carboxylase, minimizing oxygenase activity. IV. Lack of photorespiration contributes to higher biomass productivity and yield in C4 plants.
Which of the statement(s) given above is/are correct?
Statements I, II, III and IV are all correct. In C4 plants, decarboxylation of C4 acids in bundle sheath cells increases CO2 concentration around RuBisCO, suppressing oxygenase activity, preventing photorespiration and improving productivity.
Question 23 of 100
📘 CLASS XI
Consider the following statements concerning Blackman’s Law of Limiting Factors and light intensity:
I. Blackman (1905) stated that if a chemical process is affected by more than one factor, its rate is determined by the factor nearest to its minimal value. II. At low light intensities, there is a linear relationship between incident light and CO2 fixation rate. III. Light saturation for plants occurs at 100% of full sunlight. IV. Except for plants in shade or dense forests, light is rarely a limiting factor in nature.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct. Blackman stated that the limiting factor controls the rate of a process. At low light intensity, photosynthesis increases linearly with light. Light saturation generally occurs at about 10% of full sunlight, making Statement III incorrect.
Question 24 of 100
📘 CLASS XI
Regarding carbon dioxide concentration as a limiting factor in photosynthesis:
I. Carbon dioxide is the major limiting factor, with atmospheric concentrations between 0.03% and 0.04%. II. Increasing CO2 concentration up to 0.05% increases CO2 fixation rates in plants. III. C4 plants show saturation at higher CO2 levels (>450 µL L-1) compared to C3 plants (360 µL L-1). IV. Greenhouse crops like tomatoes and bell peppers are grown in CO2-enriched atmospheres for higher yields.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct. Atmospheric CO2 is a major limiting factor, increasing CO2 enhances photosynthesis up to an optimum level, and greenhouse crops benefit from CO2 enrichment. Statement III is incorrect because C4 plants saturate at lower CO2 concentrations than C3 plants.
Question 25 of 100
📘 CLASS XI
Consider the following statements regarding the effects of temperature and water stress on photosynthesis:
I. Dark reactions, being enzymatic, are controlled by temperature to a much greater extent than light reactions. II. C4 plants respond to higher temperatures and possess a higher temperature optimum than C3 plants. III. Water stress affects photosynthesis directly by altering the physical structure of P680 reaction centres. IV. Water stress causes stomatal closure (reducing CO2 availability) and leaf wilting (reducing surface area and metabolic activity).
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct. Temperature primarily affects the enzyme-mediated dark reactions, C4 plants have higher temperature optima, and water stress reduces photosynthesis indirectly through stomatal closure and wilting. Statement III is incorrect because water stress does not directly alter P680 reaction centres.
Question 26 of 100
📘 CLASS XI
Consider the following statements regarding Mohl’s half-leaf experiment:
I. Mohl’s half-leaf experiment is used to demonstrate that carbon dioxide is required for photosynthesis. II. One half of the leaf is enclosed in a test tube containing cotton soaked in KOH, which absorbs CO2. III. Upon testing with iodine, the portion of the leaf enclosed inside the test tube turns deep blue-black. IV. The portion of the leaf exposed to air tests positive for starch, confirming CO2 is necessary for carbohydrate synthesis.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because KOH absorbs CO2 inside the test tube, preventing starch formation in the enclosed leaf portion. The exposed half forms starch and gives a positive iodine test. Statement III is incorrect because the enclosed portion does not turn blue-black.
Question 27 of 100
📘 CLASS XI
Regarding the spatial alignment of chloroplasts within mesophyll cells in response to light, consider the following statements:
I. Chloroplasts align themselves along the walls of mesophyll cells to receive the optimum quantity of incident light. II. Under low to moderate light intensity, chloroplasts align with their flat surfaces perpendicular to the incident light. III. Under extremely high light intensity (bright sunlight), chloroplasts align parallel to the incident light along lateral walls to avoid photo-damage. IV. Chloroplasts are permanently fixed to the cell wall and cannot change their orientation.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because chloroplasts reorient themselves according to light intensity to optimize light absorption and prevent photodamage. Statement IV is incorrect because chloroplasts are mobile within the cytoplasm.
Question 28 of 100
📘 CLASS XI
Consider the following statements regarding the absorption and action spectra of photosynthesis:
I. An absorption spectrum shows the fraction of light absorbed by a pigment across different wavelengths. II. An action spectrum depicts the relative rate of photosynthesis at different wavelengths of light. III. The action spectrum of photosynthesis shows complete one-to-one overlap with the absorption spectrum of Chlorophyll a. IV. Photosynthesis occurs predominantly in the blue and red regions of the visible spectrum.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct. The action spectrum measures photosynthetic efficiency, whereas the absorption spectrum measures pigment absorption. Statement III is incorrect because accessory pigments contribute to the action spectrum.
Question 29 of 100
📘 CLASS XI
With reference to the Light Harvesting Complex (LHC), consider the following statements:
I. LHC molecules are composed of hundreds of pigment molecules bound to protein matrices. II. Each LHC contains all photosynthetic pigments including multiple reaction centre molecules of Chlorophyll a. III. The pigment molecules surrounding the reaction centre function as an antenna system to harvest photons. IV. The reaction centre is formed by a single molecule of Chlorophyll a.
Which of the statement(s) given above is/are correct?
Statements I, III and IV are correct because the antenna pigments harvest light and transfer energy to a single reaction-centre chlorophyll a molecule. Statement II is incorrect because the reaction centre consists of only one special chlorophyll a molecule.
Question 30 of 100
📘 CLASS XI
Regarding the electron transport chain (ETC) in non-cyclic photophosphorylation, evaluate the following statements:
I. Primary electron acceptor of PS II passes the excited electron to an electron carrier system consisting of cytochromes. II. Movement of electrons through the cytochrome complex is downhill on a redox potential scale. III. Electrons passed down the ETC from PS II are physically returned to PS II to fill the electron hole. IV. Excitation of PS I by 700 nm light impels electrons to an acceptor with a higher redox potential.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct. Electrons move from PS II through cytochromes to PS I, and excited PS I transfers electrons to a higher redox potential acceptor. Statement III is incorrect because PS II receives replacement electrons from water photolysis.
