Consider the following statements regarding the Photorespiratory pathway (C₂ Cycle):
I. Photorespiration is initiated when O₂ binds to RuBisCO instead of CO₂ in C₃ plants. II. Oxygenation of RuBP forms one molecule of 3-PGA (3C) and one molecule of phosphoglycolate (2C). III. The photorespiratory pathway results in the net synthesis of sugars and ATP. IV. Photorespiration releases CO₂ with the consumption of ATP.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because oxygenation of RuBP initiates photorespiration, producing 3-PGA and phosphoglycolate while releasing CO₂ and consuming ATP. Statement III is incorrect because photorespiration synthesizes neither sugars nor ATP.
Question 72 of 100
📘 CLASS XI
Regarding the mechanism that prevents photorespiration in C₄ plants, consider the statements below:
I. Photorespiration is absent in C₄ plants because CO₂ concentration at the RuBisCO site is maintained at high levels. II. Decarboxylation of C₄ acids in bundle sheath cells releases CO₂, raising its intracellular level. III. Elevated CO₂ level ensures RuBisCO functions predominantly as a carboxylase. IV. C₄ plants show lower photosynthetic productivity than C₃ plants due to energy spent in the C₄ cycle.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because decarboxylation of C₄ acids raises CO₂ concentration around RuBisCO, suppressing oxygenation and eliminating photorespiration. Statement IV is incorrect because C₄ plants generally show higher photosynthetic productivity than C₃ plants.
Question 73 of 100
📘 CLASS XI
Consider the following statements regarding Blackman’s Law of Limiting Factors (1905):
I. Blackman formulated the Law of Limiting Factors in 1905. II. When a physiological process is governed by multiple factors, its rate is limited by the factor nearest to its minimal value. III. If a plant leaf receives optimal light and CO₂, temperature can never act as a limiting factor. IV. A limiting factor directly determines the rate of the process if its quantity is altered.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because Blackman’s Law states that the factor nearest its minimum determines the rate of a physiological process. Statement III is incorrect because temperature can become the limiting factor even when light and CO₂ are optimal.
Question 74 of 100
📘 CLASS XI
Regarding light as a factor affecting photosynthesis, evaluate the following statements:
I. Light quality, light intensity, and duration of exposure influence the rate of photosynthesis. II. At low light intensities, there is a linear relationship between incident light and CO₂ fixation rate. III. Light saturation occurs at approximately 10% of full sunlight for most plants. IV. Increasing light intensity beyond saturation point continuously increases photosynthesis without damaging leaf pigments.
Which of the statement(s) given above is/are correct?
Statements I, II and III are correct because light quality, intensity and duration influence photosynthesis, with a linear response at low light and saturation around 10% of full sunlight. Statement IV is incorrect because excessive light causes photo-oxidation (solarization) of chlorophyll, reducing photosynthesis.
Question 75 of 100
📘 CLASS XI
Consider the following statements concerning environmental factor responses in C₃ versus C₄ plants:
I. Dark reactions are enzymatic and are affected by temperature to a greater extent than light reactions. II. C₄ plants have a lower temperature optimum than C₃ plants. III. C₃ plants respond to higher CO₂ levels by showing increased photosynthetic rates. IV. Tomatoes and bell peppers are grown in CO₂-enriched greenhouse environments for higher crop yield.
Which of the statement(s) given above is/are correct?
Statements I, III and IV are correct because dark reactions are enzyme-mediated and temperature sensitive, C₃ plants respond positively to elevated CO₂, and greenhouse cultivation of tomato and bell pepper uses CO₂ enrichment to improve yield. Statement II is incorrect because C₄ plants have a higher temperature optimum than C₃ plants.
Question 76 of 100
📘 CLASS XI
Consider the following statements regarding the role of light in Priestley’s and Ingenhousz’s historical experiments:
I. Priestley’s bell jar experiment succeeded in keeping the mouse alive only when the setup was placed in continuous darkness. II. Jan Ingenhousz showed that sunlight is essential for plants to purify air fouled by burning candles or breathing animals. III. Ingenhousz observed that oxygen bubbles were released by the non-green stems of land plants in direct sunlight. IV. Ingenhousz confirmed that only the green parts of plants in the presence of light could evolve oxygen.
Which of the statement(s) given above is/are correct?
Statements II and IV are correct because Ingenhousz demonstrated that sunlight is essential for air purification and that only green parts of plants evolve oxygen in the presence of light. Statement I is incorrect because light was essential for the mint plant to photosynthesize. Statement III is incorrect because oxygen bubbles were released by green parts of aquatic plants, not non-green stems.
Question 77 of 100
📘 CLASS XI
Regarding the discovery of photosynthetic sites and storage products by Julius von Sachs:
I. Sachs demonstrated in 1854 that glucose is synthesized in green plant cells. II. He identified that glucose is stored immediately as free fructose in chloroplasts. III. Sachs showed that chlorophyll is housed inside discrete bodies within plant cells, later called chloroplasts. IV. He proved that green parts are the exclusive sites where glucose is manufactured in plants.
Which of the statement(s) given above is/are correct?
Statements I, III and IV are correct because Sachs showed that green cells manufacture glucose (stored as starch) and that chlorophyll is localized within chloroplasts. Statement II is incorrect because glucose is stored mainly as starch, not as free fructose.
Question 78 of 100
📘 CLASS XI
Consider the following statements regarding T.W. Engelmann's experiment on the action spectrum of photosynthesis:
I. Engelmann illuminated a multicellular filamentous green alga (Cladophora) using light split by a prism. II. He used obligate anaerobic bacteria to pinpoint the sites of highest photosynthetic activity. III. Bacteria accumulated heavily in the blue and red regions of the illuminated alga. IV. The bacterial accumulation map closely resembled the absorption spectra of chlorophyll a and b.
Which of the statement(s) given above is/are correct?
Statements I, III and IV are correct because Engelmann used Cladophora and aerobic bacteria to produce the first action spectrum showing peaks in blue and red light. Statement II is incorrect because aerobic, not anaerobic, bacteria were used.
Question 79 of 100
📘 CLASS XI
Regarding the general equation of photosynthesis established by Cornelius van Niel:
I. Van Niel formulated the expression: 2H₂A + CO₂ → 2A + CH₂O + H₂O (Light). II. In green plants, H₂O acts as the hydrogen donor and is oxidized to O₂. III. In purple and green sulphur bacteria, H₂O acts as the hydrogen donor and releases O₂. IV. Van Niel's hypothesis proved that oxygen evolved during green plant photosynthesis comes from water, not carbon dioxide.
Which of the statement(s) given above is/are correct?
Statements I, II and IV are correct because Van Niel concluded that water is the hydrogen donor in green plants. Statement III is incorrect because sulphur bacteria use H₂S as the hydrogen donor and produce sulphur or sulphate rather than oxygen.
Question 80 of 100
📘 CLASS XI
Consider the following statements regarding leaf photosynthetic pigments:
I. Chlorophyll a is the primary pigment responsible for trapping light in the reaction centre. II. Chlorophyll b, xanthophylls, and carotenoids are called accessory pigments. III. Accessory pigments absorb light energy at wavelengths where Chlorophyll a does not absorb efficiently and transfer it to Chlorophyll a. IV. Carotenoids prevent photo-oxidation of Chlorophyll a.
Which of the statement(s) given above is/are correct?
All four statements are correct. Chlorophyll a is the reaction-centre pigment, while accessory pigments broaden light absorption and protect chlorophyll a from photo-oxidative damage.
