Photosynthesis in Higher PlantsNEET Botany · Class 11 · NCERT Chapter 13

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Anoxygenic photosynthesis, which does not produce oxygen, is characteristic of bacteria like $\text{Rhodospirillum}$. This process uses electron donors other than water, unlike the oxygenic photosynthesis in algae and plants, so option (a) is correct.

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Manganese, chlorine and calcium help in photolysis of water during light reaction of photosynthesis.

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Light-independent reactions or Dark reactions occur in stroma/ stromal matrix. During these reactions carbon dioxide is reduced to carbohydrates.

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Red drop occurs due decreased functioning of PS-II beyond 680 nm and when both PS-I and PS-II are functioning together there is enhancement in quantum yield.

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Photolysis of water occurs in the lumen of thylakoids which has the highest number of protons.

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Anthocyanin is stored in vacuoles.

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𝐶4 plants have high rate of photosynthesis at higher temperature.

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Water vapour comes out and 𝐶𝑂2 diffuses simultaneously through stomatal opening because diffusion coefficient of water and 𝐶𝑂2 is different and it moves along its concentration gradient.

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In C3 plants photosynthesis is decreased at higher temperature due to increased photorespiration. C4 plants have higher temperature optimum because of the presence of pyruvate phosphate dikinase enzyme, which is sensitive to low temperature.

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PEP is 3C compound which serves as primary CO2 acceptor in the mesophyll cell cytoplasm of C 4 plants like maize, sugarcane, Sorghum etc.

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Green sulphur bacteria do not produce oxygen during photosynthesis, as they use hydrogen sulfide as an electron donor instead of water. NCERT XI chapter Photosynthesis in Higher Plants explains that oxygenic photosynthesis, which produces oxygen, is characteristic of plants and cyanobacteria, while anoxygenic photosynthesis, which does not produce oxygen, is found in green sulphur bacteria, so option (c) is correct.

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NADH is not a product of the light reaction of photosynthesis. The light reaction produces NADPH, ATP, and oxygen, as described in NCERT XI chapter Photosynthesis in Higher Plants, making option (b) the correct answer.

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Plastoquinone facilitates the transfer of electrons from PS-II to the cytochrome b${}_6$f complex during the light reactions of photosynthesis. This is part of the electron transport chain in the thylakoid membrane, as described in NCERT XI chapter Photosynthesis in Higher Plants, so option (a) is correct.

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During photorespiration, the oxygenation activity of RuBisCo leads to the formation of one molecule of 3-phosphoglycerate (3-C) and one molecule of phosphoglycolate (2-C). NCERT XI chapter Photosynthesis in Higher Plants describes this process, so option (d) is correct.

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Sorghum, a C4 plant, fixes CO2 into oxaloacetic acid as the first stable product in the mesophyll cells. This is a key feature of the C4 pathway, as described in NCERT XI chapter Photosynthesis in Higher Plants, so option (b) is correct.

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The primary CO2 acceptor is a 3-carbon molecule, phosphoenol pyruvate (PEP) and is present in the mesophyll cells. Mesophyll cells of C4 plants lack RuBisCO enzyme.

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The large cells around the vascular bundles of C 4 plants form bundle sheath. These cells have large number of chloroplasts to perform calvin cycle.

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Manganese is required for the splitting of water molecules during the light-dependent reactions of photosynthesis. NCERT XI chapter Photosynthesis in Higher Plants states that manganese is a component of the oxygen-evolving complex, so option (b) is correct.

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The reaction center in Photosystem II (PS II) has an absorption maximum at 680 nm, corresponding to the chlorophyll a molecule P680. NCERT XI chapter Photosynthesis in Higher Plants describes this as the primary pigment responsible for light absorption in PS II, so option (b) is correct.

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For the synthesis of one molecule of glucose, the Calvin cycle requires 18 ATP and 12 NADPH₂. This is derived from the fact that 6 CO₂ molecules are fixed to produce one glucose, and each CO₂ fixation requires 3 ATP and 2 NADPH₂, so option (c) is correct.

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In the equation GPP - R = NPP, R represents respiratory loss, which is the amount of energy used by the plant for its metabolic processes. NCERT XI chapter Photosynthesis in Higher Plants defines these terms, so option (d) is correct.

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For dark reaction of photosynthesis there are the requirement of 2CO ATP NADPH ⎤ ⎥ ⎥ ⎥⎦ - 54 - NEET (UG)-2024 (Code-Q1)

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For fixation of 1 molecule of CO2 in Calvin cycle 3 ATP molecules and 2 NADPH molecules are required. SECTION-B

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In C3 plant, some O2 bind to RuBisCO, and hence CO2 fixation is decreased. Statement II is incorrect, photorespiration does not occur in C 4 plants as they lack RuBisCO in mesophyll. Hence statement I is the only correct option. - 60 - NEET (UG)-2024 (Code-Q1)

Solution

The pigments and their colours are:

• Chlorophyll a — Blue-green (most common, principal photosynthetic pigment)
• Chlorophyll b — Yellow-green (accessory pigment)
• Xanthophylls — Yellow (carotenoid family)
• Carotenoids — Yellow to Yellow-orange (β-carotene is the most abundant carotenoid in higher plants)

Hence the correct match is A-III, B-I, C-II, D-IV.

Solution

Carboxylation is the most crucial step of the Calvin cycle where $C{O}_2$ is utilised for the carboxylation of RuBP.
This reaction is catalysed by enzyme RuBP carboxylase. Since this enzyme also has an oxygenase activity, RuBisCO has higher affinity for carbon dioxide than oxygen.