20. Approximately what percentage of sunlight falling on leaves is captured as food energy by green plants in a terrestrial ecosystem, according to the standard school-level estimate?
[SSC CHSL 2022 cycle, held 17 Mar 2023 (Shift 4)]
- (A) 20%
- (B) 10%
- (C) 1%
- (D) 5%
Answer: (C) 1%
Explanation: The conventional ecology textbook approximation is that green plants convert about one percent of incident sunlight into stored food energy at ecosystem scale. Actual conversion efficiency varies greatly with vegetation, climate and measurement method; this is an approximate examination figure, not a universal constant.
19. Which gas is required as a raw material for photosynthesis?
[RRB NTPC CBT-I, 8 Jan 2021 (Shift 2)]
- (A) Carbon dioxide
- (B) Oxygen
- (C) Hydrogen gas
- (D) Carbon monoxide
Answer: (A) Carbon dioxide
Explanation: Plants take carbon dioxide through stomata and incorporate its carbon into sugars via the Calvin cycle. Water is the source of electrons in oxygenic photosynthesis. Oxygen is released during water splitting, while carbon monoxide and hydrogen gas are not ordinary raw materials.
18. Which organelle uses light energy to support photosynthesis?
[RRB NTPC CBT-I, 7 Apr 2021 (Shift 1)]
- (A) Golgi apparatus
- (B) Mitochondrion
- (C) Ribosome
- (D) Chloroplast
Answer: (D) Chloroplast
Explanation: Chloroplasts contain thylakoids with photosystems that convert light energy into ATP and NADPH. The stroma then uses those molecules to support carbon fixation. Mitochondria mainly mediate aerobic respiration, ribosomes make proteins, and the Golgi apparatus modifies and sorts cellular products.
17. How many ATP molecules does the Calvin cycle require for the net synthesis of one glucose from six COâ‚‚ molecules?
[CGPSC (Chhattisgarh PCS), Prelims 2020]
- (A) 16
- (B) 18
- (C) 20
- (D) 24
Answer: (B) 18
Explanation: For six carbon dioxide molecules, the Calvin cycle requires 18 ATP and 12 NADPH to produce two net molecules of glyceraldehyde-3-phosphate, sufficient to make one glucose. This ATP expenditure covers both reduction reactions and regeneration of RuBP.
16. Which element is NOT a constituent of the chlorophyll molecule?
[66th BPSC Preliminary Re-examination 2020]
- (A) Calcium
- (B) Carbon
- (C) Magnesium
- (D) Hydrogen
Answer: (A) Calcium
Explanation: Chlorophyll contains carbon, hydrogen, oxygen, nitrogen and a central magnesium ion. Calcium is important to plant physiology but is not part of the basic chlorophyll molecular structure. Magnesium deficiency commonly causes leaf yellowing, called chlorosis, because chlorophyll production is impaired.
15. Which gas is released as a by-product of oxygenic photosynthesis?
[65th BPSC Preliminary Examination 2019]
- (A) Carbon dioxide
- (B) Oxygen
- (C) Nitrogen
- (D) Sulphur dioxide
Answer: (B) Oxygen
Explanation: Oxygen is formed when water molecules are oxidised by the oxygen-evolving complex attached to Photosystem II. Carbon dioxide is used to build carbohydrates. This photosynthetic oxygen release underpins much of atmospheric oxygen available for aerobic organisms.
14. In which cell organelle is solar energy converted into ATP during photosynthesis?
[65th BPSC Preliminary Examination 2019]
- (A) Mitochondrion
- (B) Chloroplast
- (C) Ribosome
- (D) Peroxisome
Answer: (B) Chloroplast
Explanation: Photophosphorylation takes place across thylakoid membranes of chloroplasts. Light-powered electron transport establishes a proton gradient that drives ATP synthase, producing ATP. The mitochondrion also makes ATP, but principally by oxidative phosphorylation rather than by using captured sunlight.
13. Succulent plants that fix COâ‚‚ at night as malic acid and use it during daytime follow which pathway?
[RPSC Biology Paper-II 2018]
- (A) Cyclic plants
- (B) CAM pathway
- (C) Pitcher-plant pathway
- (D) Photorespiratory pathway
Answer: (B) CAM pathway
Explanation: Crassulacean acid metabolism allows CAM plants to capture carbon dioxide at night and store it temporarily as organic acids such as malate. Releasing carbon dioxide during the day permits carbon fixation while stomata stay relatively closed, conserving water in arid habitats.
12. Which enzymes catalyse primary carbon dioxide fixation in C₃ and C₄ plants, respectively?
[RPSC Biology Paper-II 2018]
- (A) RuBisCO in C₃; PEP carboxylase in C₄
- (B) PEP carboxylase in C₃; RuBisCO in C₄
- (C) RuBisCO exclusively in both initial fixation steps
- (D) PEP carboxylase exclusively in both initial fixation steps
Answer: (A) RuBisCO in C₃; PEP carboxylase in C₄
Explanation: C₃ plants initially fix carbon dioxide by RuBisCO in the Calvin cycle. C₄ plants first fix bicarbonate by PEP carboxylase in mesophyll cells, producing oxaloacetate; RuBisCO subsequently operates in bundle-sheath cells. Therefore both enzymes occur in C₄ metabolism, but their roles differ.
11. During photosynthesis, sunlight energy is transformed chiefly into which form?
[MPPSC (Madhya Pradesh PCS), Prelims 2018]
- (A) Chemical energy
- (B) Mechanical energy
- (C) Sound energy
- (D) Gravitational energy
Answer: (A) Chemical energy
Explanation: Photosynthesis converts absorbed light energy into chemical energy, temporarily held in ATP and NADPH and ultimately stored in organic compounds. This energy supplies plant metabolism and food chains. Light is not primarily converted to sound or mechanical energy during this process.
