30. What ecological role do photosynthetic cyanobacteria usually occupy?
[SSC MTS, 30 Oct 2024 (Shift 2)]
- (A) Primary consumers
- (B) Producers
- (C) Decomposers only
- (D) Tertiary consumers
Answer: (B) Producers
Explanation: Cyanobacteria are prokaryotes that perform oxygenic photosynthesis using chlorophyll a. They convert inorganic carbon into organic material, supporting aquatic and terrestrial food webs. Some also fix atmospheric nitrogen, but their producer status arises from making food using light.
29. Which structure within a plant leaf contains the chlorophyll used in photosynthesis?
[UPSC CDS-II, General Knowledge (1 Sep 2024)]
- (A) Nucleus
- (B) Ribosome
- (C) Chloroplast
- (D) Chromosome
Answer: (C) Chloroplast
Explanation: In higher plants, chlorophyll occurs in the thylakoid membranes of chloroplasts. These organelles house both the light reactions and the Calvin cycle. Nuclei and chromosomes store genetic information, while ribosomes synthesise proteins rather than absorb photosynthetic light.
28. Which of the following is NOT required as a reactant or essential condition for photosynthesis?
[UPSC NDA-II, General Ability (3 Sep 2023)]
- (A) Chlorophyll
- (B) Carbon dioxide
- (C) Water
- (D) Oxygen
Answer: (D) Oxygen
Explanation: Oxygen is released as a by-product when water is split during the light reactions. Photosynthesis needs water, carbon dioxide, light and the relevant photosynthetic machinery, including chlorophyll. Oxygen is used in respiration and can compete with carbon dioxide at RuBisCO.
27. After boiling a sunlit leaf in water and alcohol, what colour develops on adding iodine if starch is present?
[UPSC CDS-I, General Knowledge (16 Apr 2023)]
- (A) Colourless
- (B) Green
- (C) Blue-black
- (D) White
Answer: (C) Blue-black
Explanation: Alcohol removes chlorophyll so the iodine result can be observed clearly. Iodine forms a blue-black complex with starch accumulated in a photosynthesising leaf. Boiling in water kills the tissue and makes cell membranes more permeable; chlorophyll removal follows.
26. Which unicellular green alga has a characteristic cup-shaped chloroplast?
[SSC CHSL Tier-I, 10 Aug 2023 (Shift 4)]
- (A) Hydrodictyon
- (B) Ulva
- (C) Chlamydomonas
- (D) Oedogonium
Answer: (C) Chlamydomonas
Explanation: Chlamydomonas is a unicellular green alga with a conspicuous cup-shaped chloroplast that captures light for photosynthesis. Hydrodictyon forms colonies, Ulva is a multicellular sea lettuce, and Oedogonium grows as unbranched filaments, so they do not fit the description.
25. Which regions of visible light are most strongly absorbed by chlorophyll?
[68th BPSC Preliminary Examination 2023]
- (A) Red and blue
- (B) Green and blue
- (C) Green and red
- (D) Green and yellow
Answer: (A) Red and blue
Explanation: Chlorophyll has strong absorption bands in blue and red wavelengths but reflects or transmits much of the green region. This produces the familiar green appearance of leaves. Accessory pigments broaden overall absorption, while chlorophyll a remains the principal reaction-centre pigment.
24. Which microscopic photosynthetic organisms form the main primary-producer base of marine food webs?
[SSC MTS, 6 Sep 2023 (Shift 2)]
- (A) Phytoplankton
- (B) Zooplankton
- (C) Viruses
- (D) Most decomposer fungi
Answer: (A) Phytoplankton
Explanation: Phytoplankton include microscopic algae and cyanobacteria that fix carbon dioxide using sunlight. They produce organic matter eaten by zooplankton and other consumers and contribute substantially to global oxygen production. Zooplankton mostly graze rather than photosynthesise.
23. Which set correctly pairs cell organelles with their main functions?
[UPSC CDS, General Knowledge (3 Sep 2023)]
- (A) Mitochondria—respiration; chloroplast—photosynthesis; ribosome—protein synthesis
- (B) Mitochondria—photosynthesis; chloroplast—respiration; ribosome—protein synthesis
- (C) Mitochondria—respiration; chloroplast—protein synthesis; ribosome—photosynthesis
- (D) Mitochondria—protein synthesis; chloroplast—respiration; ribosome—starch storage
Answer: (A) Mitochondria—respiration; chloroplast—photosynthesis; ribosome—protein synthesis
Explanation: Mitochondria principally perform aerobic energy metabolism, chloroplasts perform photosynthesis, and ribosomes assemble proteins from amino acids. These functions belong to different cellular structures, although chloroplasts and mitochondria also contain their own ribosomes for synthesising some internal proteins.
22. Which statement correctly describes photosynthesis?
[UPSC CDS-II, General Knowledge (4 Sep 2022)]
- (A) Light energy becomes kinetic energy that oxidises carbon dioxide
- (B) Light energy directly reduces water to carbon dioxide
- (C) Chlorophyll absorbs chemical energy to oxidise carbon dioxide
- (D) Chlorophyll captures light; water is split and carbon dioxide is reduced
Answer: (D) Chlorophyll captures light; water is split and carbon dioxide is reduced
Explanation: Photosynthetic pigments capture light and drive electron transfer. Water loses electrons during photolysis, whereas carbon dioxide gains reducing equivalents in the Calvin cycle to form carbohydrate. Thus water is oxidised and carbon dioxide is reduced; the other choices reverse these events.
21. Which natural compound enables green plants to absorb the light needed for photosynthesis?
[SSC MTS, 6 Jul 2022 (Shift 3)]
- (A) Chlorophyll
- (B) Glucose
- (C) Curcumin
- (D) Lectin
Answer: (A) Chlorophyll
Explanation: Chlorophyll is the key light-absorbing pigment in plants. Its porphyrin-like head contains magnesium and is embedded with associated proteins in thylakoid membranes. Glucose is a photosynthetic product, while curcumin and lectins do not form the normal plant photosynthetic antenna.
