Q50. Which statement accurately describes photosynthesis in green plants?
[RRB NTPC (Graduate), CBT-I — 25 March 2026]
(A) It occurs mainly in mitochondria
(B) It changes light energy into chemical energy
(C) It breaks down glucose to release energy
(D) It occurs mainly at night
Answer: (B) It changes light energy into chemical energy
Explanation: Photosynthesis captures solar energy through chlorophyll and stores it in chemical bonds of carbohydrates. Chloroplasts, not mitochondria, are its principal sites in green plant cells. Glucose breakdown belongs to cellular respiration, whereas photosynthesis mainly synthesises energy-rich organic substances.
Q49. The primary food substance formed by a plant during photosynthesis belongs to which category?
[RRB NTPC (Graduate), CBT-I — 24 March 2026]
(A) Minerals
(B) Proteins
(C) Vitamins
(D) Carbohydrates
Answer: (D) Carbohydrates
Explanation: Green plants combine carbon dioxide and water using light energy to synthesise carbohydrates. Simple sugars may subsequently be converted into starch for storage. Proteins and many other compounds can be manufactured later using these carbon skeletons and additional mineral nutrients.
Q48. Which structures together allow a leaf to take in carbon dioxide and convert sunlight into chemical energy?
[DSSSB MTS — 3 May 2026, Shift 3]
(A) Cuticle and stem
(B) Petals and sepals
(C) Veins and root hairs
(D) Stomata and chloroplasts
Answer: (D) Stomata and chloroplasts
Explanation: Stomata are microscopic pores that allow carbon dioxide to diffuse into a leaf. Chloroplasts contain chlorophyll and perform photosynthesis. Root hairs and veins aid absorption or transport, but neither replaces the gas-exchange function of stomata or the light-capturing machinery.
Q47. Where does photosynthesis chiefly occur in a typical green plant?
[DSSSB MTS — 3 May 2026, Shift 3]
(A) Only in stem tissues
(B) In chloroplasts of leaf cells
(C) Inside the roots
(D) Only in flowers
Answer: (B) In chloroplasts of leaf cells
Explanation: Leaf cells contain many chloroplasts, organelles carrying photosynthetic pigments and enzymes. Their chlorophyll absorbs light that supports carbohydrate synthesis. Green stems can also photosynthesise, but leaves are the main food-producing organs in most ordinary green plants.
Q46. Which adaptation allows many desert plants to photosynthesise while reducing daytime water loss?
[RRB Technician Grade III — 6 March 2026]
(A) Photosynthesis is restricted to darkness
(B) Carbon dioxide is taken in at night and carbohydrates are synthesised in daylight
(C) Light is collected at night and stored as starch
(D) Oxygen is absorbed at night while carbon dioxide is released by day
Answer: (B) Carbon dioxide is taken in at night and carbohydrates are synthesised in daylight
Explanation: Many desert succulents use CAM photosynthesis. Their stomata open at night, allowing carbon dioxide uptake with relatively little water loss. The carbon is temporarily stored in organic acids and later used during daytime carbohydrate synthesis, when the stomata can remain shut.
Q45. Which description best fits autotrophic nutrition?
[RRB Group D — 29 December 2025, Shift 2]
(A) Digesting dead matter outside the body
(B) Feeding only on other living organisms
(C) Making organic food from carbon dioxide and water using sunlight
(D) Taking ready-made organic food from a host
Answer: (C) Making organic food from carbon dioxide and water using sunlight
Explanation: Autotrophs synthesise their own organic food from simpler inorganic materials. In green plants, light and chlorophyll enable this conversion of carbon dioxide and water into carbohydrates. The other descriptions concern saprotrophic, holozoic or parasitic forms of nutrition.
Q44. Food produced by photosynthesis but not immediately used is commonly stored in plants as what?
[RRB Group D — 21 December 2025, Shift 3]
(A) Glucose only
(B) Protein
(C) Starch
(D) Cellulose only
Answer: (C) Starch
Explanation: Plants may convert surplus soluble sugars formed through photosynthesis into insoluble starch. Starch serves as an energy reserve and can later be broken down when required. Iodine solution turning blue-black is a standard school experiment demonstrating starch in a leaf.
Q43. Which process is NOT a direct part of photosynthesis in green plants?
[RRB Group D — 19 December 2025, Shift 3]
(A) Reducing carbon dioxide to carbohydrates
(B) Converting light into chemical energy
(C) Absorbing light with chlorophyll
(D) Breaking down carbohydrates to release energy
Answer: (D) Breaking down carbohydrates to release energy
Explanation: Photosynthesis stores incoming light energy in manufactured carbohydrates, while cellular respiration releases usable energy by breaking down those organic compounds. Although both processes occur in plants, glucose breakdown for energy belongs to respiration, not the photosynthetic food-making process.
Q42. Green plants occupy which basic ecological role in an ecosystem?
[CGPSC Preliminary Examination — 9 February 2025]
(A) Primary producers
(B) Primary consumers
(C) Secondary consumers
(D) Decomposers
Answer: (A) Primary producers
Explanation: Most green plants are primary producers because they create organic food using sunlight, water and carbon dioxide. Herbivores obtain this stored energy by eating plants, while other consumers depend on it indirectly. Decomposers recycle materials from dead organisms instead of producing food photosynthetically.
Q41. Which organism can use both autotrophic and heterotrophic modes of nutrition?
[RRB NTPC (Graduate), CBT-I — 13 June 2025]
(A) Amoeba
(B) Euglena
(C) Plasmodium
(D) Paramecium
Answer: (B) Euglena
Explanation: Euglena is capable of photosynthesis in adequate light because it has chloroplasts. Under certain conditions it can also obtain organic nutrients from its surroundings. This nutritional flexibility is called mixotrophy and contrasts with the predominantly heterotrophic feeding of Amoeba and Paramecium.
Q40. Which is the main pigment responsible for capturing light for photosynthesis in algae?
[SSC CGL 2024 Tier-II — held 18 January 2025]
(A) Chlorophyll
(B) Melanin
(C) Xanthophyll alone
(D) Carotenoid alone
Answer: (A) Chlorophyll
Explanation: Many algae contain chlorophyll, which captures light energy required for photosynthesis. Accessory pigments, including carotenoids and xanthophylls, can broaden light absorption. Melanin is not the principal photosynthetic pigment. Algae, like green plants, can prepare food through this process.
Q39. Consider these statements:
(1) Stomata absorb sunlight.
(2) Photosynthesis reduces carbon dioxide to carbohydrates.
Which is correct?
[RPF Constable 2024 examination — held 7 March 2025]
(A) Statement 1 only
(B) Both statements
(C) Statement 2 only
(D) Neither statement
Answer: (C) Statement 2 only
Explanation: Stomata mainly regulate entry of carbon dioxide and exit of gases and water vapour. Chlorophyll pigments absorb sunlight, not stomatal pores. Carbon dioxide is fixed and reduced during photosynthesis, eventually contributing carbon to carbohydrates, making only the second statement correct.
Q38. Which partners commonly live together to form a lichen?
[Maharashtra TET Paper II — 23 November 2025]
(A) Bacteria and fungi only
(B) Algae and bacteria only
(C) Fungi and algae
(D) Fungi and viruses
Answer: (C) Fungi and algae
Explanation: A lichen is generally a partnership between a fungus and a photosynthetic alga, or sometimes a cyanobacterium. The photosynthetic partner supplies organic food, and the fungus offers support, water and minerals. NCERT uses lichens to illustrate symbiotic relationships.
Q37. How can a red or purple leaf carry out photosynthesis despite not appearing green?
[WBCS Preliminary Examination — 2024]
(A) Other pigments replace photosynthesis entirely
(B) Chlorophyll remains present but is masked by other pigments
(C) The leaf obtains glucose through airborne spores
(D) All coloured leaves are permanently non-photosynthetic
Answer: (B) Chlorophyll remains present but is masked by other pigments
Explanation: Red, purple or brown pigments can conceal the green colour of chlorophyll without eliminating it. If chlorophyll and suitable conditions are present, the leaf still absorbs light and makes carbohydrates. Leaf colour alone therefore does not determine photosynthetic capability.
Q36. Which enzyme is considered the most abundant in the living world?
[WBCS Preliminary Examination — 2024]
(A) Lipase
(B) DNase
(C) Zymase
(D) RuBisCO
Answer: (D) RuBisCO
Explanation: RuBisCO catalyses carbon dioxide fixation in the Calvin cycle, a major pathway by which photosynthetic organisms make organic molecules. Its extraordinary abundance reflects the enormous scale of photosynthesis across plants and algae. This extends the basic NCERT treatment of carbohydrate production.
Q35. In a typical green leaf cell, which structure contains chlorophyll?
[UPSC CDS-II General Knowledge — 1 September 2024]
(A) Nucleus
(B) Ribosome
(C) Chloroplast
(D) Chromosome
Answer: (C) Chloroplast
Explanation: Chloroplasts are specialised plant-cell organelles containing chlorophyll pigments and photosynthetic membranes. Light is absorbed there and converted into chemical energy. Ribosomes synthesise proteins, chromosomes carry genetic information, and the nucleus coordinates many cellular activities rather than housing most leaf chlorophyll.
Q34. Microorganisms such as Rhizobium, Nitrosomonas and Nitrobacter are most directly linked to which natural cycle?
[SSC CGL Tier-I — 12 September 2024]
(A) Nitrogen cycle
(B) Carbon cycle
(C) Water cycle
(D) Sulphur cycle
Answer: (A) Nitrogen cycle
Explanation: Rhizobium fixes atmospheric nitrogen in association with legumes. Nitrosomonas and Nitrobacter participate in nitrification by converting reduced nitrogen compounds into more oxidised forms. Together they illustrate microbial transformations that maintain nitrogen availability for plants and replenish nutrients in ecosystems.
Q33. Which substance is NOT required as an input for photosynthesis?
[UPSC NDA-II General Ability — 3 September 2023]
(A) Chlorophyll
(B) Carbon dioxide
(C) Water
(D) Oxygen
Answer: (D) Oxygen
Explanation: Carbon dioxide and water are raw materials, while chlorophyll absorbs light energy needed to synthesise carbohydrates. Oxygen is generally released as a product of oxygenic photosynthesis, rather than required as an input. This distinction is central to the school-level photosynthesis equation.
Q32. Approximately what percentage of incident sunlight is captured by green plants as food energy in a typical terrestrial ecosystem?
[UPSC NDA-II General Ability — 3 September 2023]
(A) 1%
(B) 5%
(C) 8%
(D) 10%
Answer: (A) 1%
Explanation: Only a small fraction of incoming solar radiation becomes stored chemical energy through primary production. A commonly used ecological approximation is around one percent for terrestrial ecosystems. Actual capture efficiency varies with vegetation, climate, season and the definition of incident radiation.
Q31. What usually happens to a stomatal pore when water enters its guard cells?
[SSC CGL Tier-I — 27 July 2023, Shift 3]
(A) Guard cells shut permanently
(B) The pore opens
(C) The pore disappears
(D) The pore always closes
Answer: (B) The pore opens
Explanation: Water entering guard cells increases their turgor pressure. Because their walls stretch unevenly, the cells curve and the opening generally widens. Stomatal opening enables carbon dioxide uptake for photosynthesis, although the same pores also permit water vapour to escape.
Q30. What is the name of the green leaf pigment that captures sunlight?
[SSC MTS — 2 May 2023, Evening]
(A) Cladophyll
(B) Chlorophyll
(C) Xanthophyll
(D) Cytoplasm
Answer: (B) Chlorophyll
Explanation: Chlorophyll absorbs light that fuels photosynthetic reactions in green plant cells. It is located mainly in chloroplast membranes. Xanthophyll is an accessory yellow pigment, cytoplasm is the cellular matrix, and cladophyll describes a modified stem rather than the green pigment.
Q29. Which conducting tissue carries water and dissolved minerals from roots towards leaves?
[SSC MTS — 3 May 2023, Afternoon]
(A) Xylem
(B) Parenchyma
(C) Collenchyma
(D) Phloem
Answer: (A) Xylem
Explanation: Xylem vessels conduct water and dissolved mineral nutrients upward from roots to stems and leaves. This supplies water for photosynthesis and other metabolic functions. Phloem principally distributes organic food made by photosynthesis, while parenchyma and collenchyma have different major roles.
Q28. What is the ultimate energy source for most living organisms?
[SSC MTS — 11 May 2023, Morning]
(A) Soil
(B) The Sun
(C) Water
(D) Air
Answer: (B) The Sun
Explanation: Sunlight drives photosynthesis in plants, algae and many bacteria. These producers transform solar energy into chemical energy stored in organic food. Food chains pass this energy to consumers, so most ecosystems depend ultimately on the Sun even when individual organisms never receive sunlight.
Q27. When organisms produce their own food from simple inorganic substances, their nutrition is called what?
[SSC MTS — 11 May 2023, Evening]
(A) Heterotrophic
(B) Autotrophic
(C) Saprotrophic
(D) Holozoic
Answer: (B) Autotrophic
Explanation: In autotrophic nutrition, organisms synthesise organic compounds from simple inorganic materials. Green plants normally use light energy for this process. Saprotrophs absorb nutrients from decaying matter, whereas heterotrophs generally rely on food manufactured by other organisms.
Q26. Which water-soluble plant pigments commonly cause red, blue and purple colours in many fruits and leaves?
[SSC CHSL — 10 August 2023, Shift 1]
(A) Coumarins
(B) Anthocyanins
(C) Quercetin alone
(D) Naringenin alone
Answer: (B) Anthocyanins
Explanation: Anthocyanins are flavonoid pigments that commonly give plant tissues red, purple or blue shades. Their visible colour can mask chlorophyll in some leaves. A coloured leaf may therefore remain photosynthetically active even when its green pigment is not obvious.
Q25. Which of these is an insectivorous plant?
[CTET Paper I — 18 January 2023]
(A) Cuscuta
(B) Lichen
(C) Pitcher plant
(D) Cactus
Answer: (C) Pitcher plant
Explanation: Pitcher plants possess modified leaves that trap insects and digest them to obtain scarce mineral nutrients, especially nitrogen. They still carry out photosynthesis to make carbohydrates. Cuscuta is parasitic, lichens represent symbiosis, and cactus is a xerophytic plant.
Q24. Which plants in this list commonly fix atmospheric nitrogen through a legume–bacterium association:
1 Alfalfa,
2 Amaranth,
3 Chickpea,
4 Clover,
5 Purslane,
6 Spinach?
[UPSC CSE Preliminary Examination — 2022]
(A) 1, 3 and 4 only
(B) 1, 3, 5 and 6 only
(C) 2, 4, 5 and 6 only
(D) 1, 2, 4, 5 and 6
Answer: (A) 1, 3 and 4 only
Explanation: Alfalfa, chickpea and clover belong to the legume family and commonly develop root nodules containing nitrogen-fixing bacteria. Amaranth, purslane and spinach are not such legumes. This association converts atmospheric nitrogen into compounds useful for plant nutrition and soil fertility.
Q23. Which statement correctly describes the light-driven events of photosynthesis?
[UPSC CDS-II General Knowledge — 4 September 2022]
(A) Light becomes kinetic energy that oxidises carbon dioxide
(B) Light directly reduces water into sugar
(C) Chlorophyll uses chemical energy to oxidise carbon dioxide
(D) Chlorophyll absorbs light, enabling water splitting and carbon-dioxide reduction
Answer: (D) Chlorophyll absorbs light, enabling water splitting and carbon-dioxide reduction
Explanation: Chlorophyll captures radiant energy during the light-dependent reactions, helping drive the splitting of water. The resulting energy carriers support carbon dioxide reduction and carbohydrate synthesis. Photosynthesis is fundamentally energy storage and carbon fixation, not glucose breakdown or direct conversion into kinetic energy.
Q22. Which statement about plant mineral nutrition is incorrect?
[RRB Group D — 9 September 2022, Shift 2]
(A) Green plants obtain carbon from atmospheric carbon dioxide
(B) Minerals are poorly absorbed by water
(C) Iron and manganese are micronutrients
(D) Roots usually take up water from soil
Answer: (B) Minerals are poorly absorbed by water
Explanation: Roots generally absorb essential mineral nutrients as dissolved ions in soil water, so the claim about poor absorption through water is incorrect. Carbon enters mainly as carbon dioxide, while iron and manganese are required in relatively small amounts as micronutrients.
Q21. Regarding lichens, which combination is correct:
(i) lichens are algae;
(ii) lichens can photosynthesise;
(iii) lichens are fungi alone;
(iv) lichens are symbiotic associations;
(v) lichens are saprotrophs?
[HPSC Haryana Civil Services Preliminary Examination — July 2022]
(A) i and v
(B) ii and iv
(C) i, iii and v
(D) ii, iv and v
Answer: (B) ii and iv
Explanation: Lichens consist of a photosynthetic partner and a fungus living in close association. The photosynthetic partner supplies organic food, while the fungus provides physical support and access to water and minerals. A lichen is not simply an alga or a fungus alone.
Q20. Match each mode of nutrition with its example: autotrophic, holozoic, parasitic and saprotrophic. Which sequence is correct?
[CTET Paper II, Mathematics & Science — 11 January 2022]
(A) Algae, Amoeba, Cuscuta, Mushroom
(B) Mushroom, Amoeba, Algae, Cuscuta
(C) Cuscuta, Mushroom, Amoeba, Algae
(D) Amoeba, Algae, Mushroom, Cuscuta
Answer: (A) Algae, Amoeba, Cuscuta, Mushroom
Explanation: Algae generally make their own food by photosynthesis; Amoeba engulfs food through holozoic nutrition. Cuscuta withdraws food from a living host, and mushroom fungi absorb nutrients from decaying organic matter. These four examples distinguish major nutritional modes.
Q19. Which organisms can most readily survive on a surface without soil: 1 Fern, 2 Lichen, 3 Moss, 4 Mushroom?
[UPSC CSE Preliminary Examination — 2021]
(A) 1 and 4 only
(B) 2 only
(C) 2 and 3
(D) 1, 3 and 4
Answer: (C) 2 and 3
Explanation: Lichens can colonise bare rock because their partners obtain water and nutrients from the environment, while mosses can occupy moist surfaces with little or no soil. Ferns generally need more developed substrates; mushrooms require suitable organic material as their food source.
Q18. Which description correctly identifies a light-driven reaction during photosynthesis?
[UPSC NDA-II General Ability — 14 November 2021]
(A) Chemical energy is transformed into light energy
(B) Carbon dioxide is oxidised to make carbohydrate
(C) Water is converted directly into hydrogen gas for storage
(D) Absorbed light energy drives the splitting of water
Answer: (D) Absorbed light energy drives the splitting of water
Explanation: The light-dependent reactions use absorbed sunlight to drive photolysis of water, producing oxygen, protons and electrons. The electrons contribute to energy-rich intermediates used for carbon fixation. Carbon dioxide is reduced into carbohydrates rather than oxidised; hydrogen gas is not a normal product.
Q17. Which bacterium helps form nitrogen-fixing root nodules in leguminous plants?
[RRB NTPC CBT-I — 24 July 2021, Shift 2]
(A) Clostridium
(B) Escherichia
(C) Rhizobium
(D) Salmonella
Answer: (C) Rhizobium
Explanation: Rhizobium bacteria live in nodules on the roots of many leguminous plants. They convert atmospheric nitrogen into a biologically usable form, while plants supply them with carbohydrates and shelter. This mutually beneficial association can lower the need for added nitrogen fertilisers.
Q16. Which set names the key inputs needed for photosynthesis in green plants?
[RRB NTPC CBT-I — 27 February 2021, Shift 1]
(A) Carbon dioxide, water and sunlight
(B) Sunlight, chloroflexi and water
(C) Water, oxygen and sunlight
(D) Oxygen, water and light only
Answer: (A) Carbon dioxide, water and sunlight
Explanation: Plants absorb carbon dioxide from air and water from soil. Using light captured by chlorophyll, they produce carbohydrates and release oxygen. Oxygen is ordinarily an output of the process, whereas light, water and carbon dioxide are essential requirements.
Q15. Which organism digests food material outside its body and then absorbs simpler nutrients?
[SSC MTS — 27 October 2021, Afternoon]
(A) Tick
(B) Leech
(C) Yeast
(D) Louse
Answer: (C) Yeast
Explanation: Yeast is a fungus and obtains dissolved nutrients from its surroundings; many fungi secrete enzymes outside their cells to digest complex organic matter. This contrasts with blood-feeding parasites such as ticks, leeches and lice, which obtain nutrition from living hosts.
Q14. From where do plants chiefly obtain mineral nutrients such as nitrogen, phosphorus and potassium?
[WBCS Preliminary Examination — 2020]
(A) Atmosphere directly
(B) Chlorophyll
(C) Soil
(D) Sunlight
Answer: (C) Soil
Explanation: Roots typically absorb nitrogen, phosphorus and potassium from soil in soluble ionic forms. These nutrients support growth and metabolic processes. Although atmospheric nitrogen is abundant, most plants cannot use nitrogen gas directly and rely on mineralised forms or nitrogen-fixing partners.
Q13. Which symbiotic bacterium fixes atmospheric nitrogen in leguminous root nodules?
[SSC MTS — 2 August 2019, Shift 2]
(A) Pseudomonas
(B) Azotobacter
(C) Lactobacillus
(D) Rhizobium
Answer: (D) Rhizobium
Explanation: Rhizobium commonly establishes a mutualistic association in nodules on roots of peas, gram and other legumes. The bacteria supply nitrogen compounds useful for synthesising proteins, while the host plant provides carbohydrates and a protected habitat. Azotobacter generally fixes nitrogen independently.
Q12. Sunlight captured by green plants during photosynthesis is transformed mainly into what?
[MPPSC State Service Preliminary Examination — 2018]
(A) Chemical energy
(B) Physical energy as a separate category
(C) Both physical and chemical energy equally
(D) Neither chemical nor physical energy
Answer: (A) Chemical energy
Explanation: Photosynthesis transforms incoming radiant energy into chemical potential energy stored in organic compounds. The energy supports plant growth and later enters food chains. It is not simply retained as sunlight or converted mainly into heat during the food-synthesis process.
Q11. Which transformation takes place during photosynthesis?
[RPSC Assistant Engineer, General Science — 2018]
(A) Carbohydrates are reduced into carbon dioxide
(B) Light energy changes into chemical energy
(C) Chlorophyll emits the absorbed light without chemical change
(D) Hydrogen and oxygen combine merely to form water
Answer: (B) Light energy changes into chemical energy
Explanation: Photosynthesis uses absorbed light to generate chemical energy that powers carbon fixation and carbohydrate production. The organic food retains part of that energy in chemical bonds. Oxidation of carbohydrates mainly characterises respiration, the reverse metabolic role.
Q10. Which of the following needs can photosynthesis meet for autotrophic organisms: I carbon, II water, III energy?
[SSC CHSL — 6 March 2018, Shift 2]
(A) I only
(B) III only
(C) I and III
(D) I, II and III
Answer: (C) I and III
Explanation: Photosynthesis incorporates carbon from carbon dioxide into organic compounds and captures light as usable chemical energy. Water is an input consumed in the overall process, not a requirement manufactured by it. Hence carbon acquisition and energy capture are the relevant outcomes.
Q9. Which energy conversion correctly describes photosynthesis?
[CGPSC State Service Preliminary Examination — 2017]
(A) Solar energy to heat energy
(B) Solar energy to kinetic energy
(C) Solar energy to potential energy in a mechanical sense
(D) Light energy to mechanical energy
(E) None of these
Answer: (E) None of these
Explanation: Photosynthesis converts radiant energy into chemical energy stored in sugars. None of the listed mechanical or thermal conversions accurately identifies this principal transformation. The question therefore requires the final choice. Chemical energy later supports life processes and ecosystem food chains.
Q8. Photosynthesis proceeds in the presence of chlorophyll and which essential environmental factor?
[SSC CGL Tier-I — 10 August 2017, Shift 2]
(A) Water alone
(B) Mineral nutrients alone
(C) Carbon dioxide alone
(D) Sunlight
Answer: (D) Sunlight
Explanation: Chlorophyll is the pigment that absorbs light and enables photosynthesis to proceed. Green plants also require carbon dioxide and water as raw materials, but the missing condition in this question is sunlight. Captured radiant energy supports formation of carbohydrates.
Q7. Cuscuta growing over trees and shrubs is an example of which nutritional association?
[MP Police Constable — 23 July 2016, Shift 2]
(A) Autotrophic nutrition
(B) Parasitic nutrition
(C) Saprotrophic nutrition
(D) Insectivorous nutrition
Answer: (B) Parasitic nutrition
Explanation: Cuscuta, commonly called amarbel, is a stem parasite that obtains water and nutrients from a host plant through specialised absorbing structures. Since it depends on living host tissues, its mode is parasitic rather than saprotrophic or insectivorous.
Q6. Which event does NOT occur in the light-dependent stage of photosynthesis?
[RPSC Second Grade Science Teacher — 2015]
(A) Photolysis of water
(B) Reduction of carbon dioxide
(C) Photophosphorylation
(D) Reduction of NADP+
Answer: (B) Reduction of carbon dioxide
Explanation: Water splitting, ATP production and formation of NADPH are associated with the light reactions in chloroplast thylakoid membranes. Carbon dioxide reduction belongs to the Calvin cycle, which uses ATP and NADPH produced by the light-dependent reactions.
Q5. The lichen community that can begin succession on bare rock is a symbiotic association between which organisms?
[UPSC CSE Preliminary Examination — 24 August 2014]
(A) Algae and bacteria
(B) Algae and fungi
(C) Bacteria and fungi
(D) Fungi and mosses
Answer: (B) Algae and fungi
Explanation: A lichen generally consists of a photosynthetic alga associated with a fungus. The alga provides carbohydrates; the fungus helps secure water, minerals and protection. Their ability to grow on exposed rock makes many lichens important pioneer organisms in ecological succession.
Q4. Some organisms can photosynthesise using parts of solar radiation invisible to humans. Which group includes such organisms?
[UPPSC Civil Services Preliminary Examination — 2013]
(A) Trees
(B) Ordinary green algae only
(C) Certain bacteria
(D) Fungi
Answer: (C) Certain bacteria
Explanation: Certain photosynthetic bacteria possess pigments that can capture wavelengths beyond the visible range, including near-infrared radiation. Most green plants primarily use visible light through chlorophyll. Fungi lack chlorophyll and obtain organic food heterotrophically rather than performing photosynthesis.
Q3. What is the principal function of xylem tissue in plants?
[WBCS Preliminary Examination — 2012]
(A) Carrying out photosynthesis
(B) Transporting water and mineral nutrients
(C) Storing every food reserve
(D) Carrying only enzymes
Answer: (B) Transporting water and mineral nutrients
Explanation: Xylem moves water and dissolved mineral ions through the root, stem and leaf system. These substances are essential for photosynthesis and growth. The prepared food is predominantly transported by phloem, not by xylem, making transport of water and minerals correct.
Q2. Which plant commonly opens its stomata during the night and closes them during the day?
[WBCS Preliminary Examination — 2005]
(A) Water lily
(B) Cactus
(C) Sunflower
(D) Fern
Answer: (B) Cactus
Explanation: Many cacti use crassulacean acid metabolism, opening stomata at night to acquire carbon dioxide while limiting daytime water loss. The carbon dioxide can then be used in daytime photosynthesis. This adaptation supports survival in hot, dry environments.
Q1. What happens to energy during photosynthesis?
[WBCS Preliminary Examination — 2002]
(A) Oxygen must be supplied as an essential input
(B) A catabolic breakdown reaction predominates
(C) Light energy is stored as chemical potential energy in food
(D) Stored food energy is released as heat
Answer: (C) Light energy is stored as chemical potential energy in food
Explanation: Photosynthesis is an anabolic food-making process. Sunlight captured by chlorophyll is ultimately stored as chemical potential energy in carbohydrates such as glucose. Releasing this stored energy through breakdown of food is characteristic of respiration, not photosynthesis.