NDA General Studies · Biology · 24 questions · 2017 to 2026
NDA Ecology, environment and applied biology previous year questions with solutions
Ecology and applied biology close the Biology section of the General Studies paper: about one question in two hundred and fifty, and fading. Each question is one fact: a trophic level, a greenhouse gas, a protected area, a crop. Every question UPSC has set on it since 2017, solved. Grouped by the method each needs, newest first; open a question for its answer and worked solution.
19.1 Ecosystems, food chains and the flow of energy (4)19.2 Air, water and soil: pollution and the depletion of resources (4)19.3 Biodiversity, its loss and threatened species (4)19.4 Protected areas and international conventions (5)19.5 Agriculture and crop improvement (4)19.6 Microbes in human welfare (3)
19.1 Ecosystems, food chains and the flow of energy
1. NDA 2023 (II)
The green plants in a terrestrial ecosystem absorbs sunlight that falls on their leaves and convert it into food energy. The percentage of solar radiation absorbed by all green plants for the process of photosynthesis is about
Answer and solution
Answer: (a) 1%
Method. Energy captured by plants
NCERT Class 10 Science (Our Environment, C13-A15): green plants in a terrestrial ecosystem capture only about 1% of the energy of sunlight falling on their leaves and convert it into food energy.
2. NDA 2019 (I)
Which one of the following organisms represents the primary consumer category in an ecosystem?
Answer and solution
Answer: (a) Caterpillar
Method. Primary consumer = herbivore
A caterpillar eats leaves, so it is a primary consumer (herbivore); the crabapple tree is a producer, the frog a secondary consumer and the sparrowhawk a higher consumer (Class 10 Science, C13-A13).
3. NDA 2018 (II)
Statement I:
Phytoplankton produce most of the organic carbon in the ocean.
Statement II:
Algae are produced in the cold water biome.
Phytoplankton produce most of the organic carbon in the ocean.
Statement II:
Algae are produced in the cold water biome.
Answer and solution
Answer: (b) Both the statements are individually true but Statement II is not the correct explanation of Statement I
Method. Statement I/II item on ocean productivity
Statement I is true: phytoplankton (microscopic algae, diatoms) do most of the photosynthesis in the ocean and so produce most of its organic carbon. Statement II is also true as a fact: algae grow abundantly in nutrient-rich cold water. But the reason phytoplankton produce the carbon is photosynthesis, not cold water, so II does not explain I. Code (b).
The truth of Statement II is loosely worded; I take it as true but not the explanation. The alternative reading (II false, option c) is the risk.
4. NDA 2018 (I)
Which one of the following group of organisms forms a food chain?
Answer and solution
Answer: (b) Grass, goat and human
Method. Food chain = linked feeding relation, producer to consumer
A food chain begins with a producer: grass, eaten by goat (herbivore), eaten by human (Class 10 Science, Our Environment, C13-A11, C13-A13). In (a) humans do not feed on grass in a chain with fish; (c) a tree cutter does not feed the tiger; (d) goat and cow are both herbivores with no producer.
19.2 Air, water and soil: pollution and the depletion of resources
5. NDA 2023 (I)
Which one of the following is not a main greenhouse gas?
Answer and solution
Answer: (b) Oxygen
Method. Negative stem: greenhouse gases
Water vapour, CO2 and methane trap infrared radiation; oxygen (O2) does not, so it is not a main greenhouse gas (Class 9 Science, NS13-A13).
6. NDA 2020 (I)
Which one of the following is NOT a cause of depletion in groundwater?
Answer and solution
Answer: (a) Afforestation
Method. Negative stem: groundwater depletion
Afforestation helps rain water seep into the ground and so recharges groundwater. Loss of forests, over-pumping and concrete cover (which stops infiltration) all deplete it. So (a) is NOT a cause.
7. NDA 2018 (II)
Which one of the following greenhouse gases is in largest concentration in the atmosphere?
Answer and solution
Answer: (c) Carbon dioxide
Method. Greenhouse gas abundance
Among the greenhouse gases CO2 is the most abundant (about 0.04 per cent of air, or 400+ ppm), whereas methane, nitrous oxide and CFCs are present in ppm-to-ppt amounts (Class 9 Science, NS13-A13, A38; standard reference). Water vapour is more abundant still but is not listed.
8. NDA 2017 (II)
Which one of the following is a cause of acid rains?
Answer and solution
Answer: (c) Sulphur dioxide
Method. Acid rain: oxides of sulphur and nitrogen
Sulphur dioxide from burning coal and oil forms sulphurous and sulphuric acids in rain water (Class 10 Science, environment chapter; standard reference). Ozone, ammonia and carbon monoxide are not the cause of acid rain.
19.3 Biodiversity, its loss and threatened species
9. NDA 2022 (I)
The International Union for Conservation of Nature (IUCN) has recently categorized the Red Sanders (Red Sandalwood) into
Answer and solution
Answer: (c) near-threatened category
Method. IUCN status of Red Sanders
In December 2021 IUCN moved red sanders (Pterocarpus santalinus) from Endangered to Near Threatened, which is the 'recent' change at the 2022 sitting.
Status at the sitting; IUCN may revise it.
10. NDA 2021 (II)
Which one of the following statements about biodiversity is not correct?
Answer and solution
Answer: (d) More than 100 hotspots of biodiversity are identified in the world.
Method. Negative stem: biodiversity facts
Only 36 hotspots have been identified worldwide, not more than 100, so (d) is not correct. (b) Norman Myers coined 'hotspots' in 1988; (a) Walter G. Rosen coined 'biodiversity' for the 1986 forum (1985 proposal); (c) is the loose usage that hotspots hold rich biodiversity.
Option (a) is borderline (1985 or 1986) but (d) is plainly wrong.
11. NDA 2021 (I)
Keppel Island is completely bleached mainly due to the expansion of
Answer and solution
No correct option. This question is defective as printed in UPSC's paper.
Method. Coral bleaching, Keppel Islands
No answer is printed. Coral bleaching is caused by stress, chiefly elevated sea temperature: the Keppel Islands (southern Great Barrier Reef) bleached in 2006 and 2020 during marine heatwaves, with seaweed overgrowth hindering recovery. None of the four organisms causes bleaching; the only one that damages coral at all is the (crown-of-thorns) starfish, by eating it, which is presumably what the setter had in mind with (a), but the question as set has no correct option.
No answer is printed. Coral bleaching is caused by stress, chiefly elevated sea temperature: the Keppel Islands (southern Great Barrier Reef) bleached in 2006 and 2020 during marine heatwaves, with seaweed overgrowth hindering recovery. None of the four organisms causes bleaching; the only one that damages coral at all is the (crown-of-thorns) starfish, by eating it, which is presumably what the setter had in mind with (a), but the question as set has no correct option.
12. NDA 2020 (I)
Which one of the following is NOT a reason of decrease in biodiversity?
Answer and solution
Answer: (c) Maintaining sacred groves
Method. Negative stem: causes of biodiversity loss
Sacred groves protect biodiversity; deforestation, over-exploitation of forest produce and encroachment all destroy habitat (Class 12 Biology, Biodiversity and Conservation). So (c) is NOT a cause.
19.4 Protected areas and international conventions
13. NDA 2020 (I)
Which one of the following cities is associated with Biosafety Protocol to the Convention on Biological Diversity (2000)?
Answer and solution
Answer: (c) Cartagena
Method. Biosafety Protocol to the CBD
The Cartagena Protocol on Biosafety was adopted in 2000 (Montreal) and is named after Cartagena, Colombia, where talks were held (Class 12 Biology, Biotechnology: Principles). Nairobi = Nagoya-Kuala Lumpur supplementary protocol is not related; Rio de Janeiro = the Earth Summit 1992.
14. NDA 2020 (I)
Which of the following statements with regard to Biosphere Reserve is/are correct?
1. The idea of Biosphere Reserve was initiated by UNESCO in 1973-74
2. There are 18 designated Biosphere Reserves in India
3. All Biosphere Reserves in India have been included in world network of Biosphere Reserves of UNESCO
Select the correct answer using the code given below:
1. The idea of Biosphere Reserve was initiated by UNESCO in 1973-74
2. There are 18 designated Biosphere Reserves in India
3. All Biosphere Reserves in India have been included in world network of Biosphere Reserves of UNESCO
Select the correct answer using the code given below:
Answer and solution
Answer: (c) 1 and 2 only
Method. Biosphere reserves: MAB programme
1 is correct: UNESCO launched the Man and Biosphere programme in 1971 and the biosphere reserve concept was formalised by its task force in 1973-74. 2 is correct for 2020: India had 18 designated biosphere reserves. 3 is wrong: not all are in the UNESCO World Network (e.g. Manas, Dibru-Saikhowa, Dihang-Dibang, Cold Desert and others are not). Hence 1 and 2 only.
Statement 1 depends on the date given by the reference (some say 1971); I follow the 1973-74 task-force date. The 2020 figure 18 held then; it may differ later.
15. NDA 2019 (II)
How many Ramsar conservation sites have been enlisted from India so far?
Answer and solution
Answer: (c) 27
Method. Ramsar sites of India, count at the sitting
India had 27 Ramsar sites when the paper was set in 2019 (26 since 2012; Sundarban Wetland added on 30 January 2019 as the 27th). The count rose to 37 with the ten sites announced in January 2020, 75 by 2022 and over 80 later.
Count as of the 2019 sitting; it has since risen to far more than 27. Answer kept.
16. NDA 2018 (I)
Which one among the following is the largest tiger reserve of India in terms of area of the core/critical tiger habitat?
Answer and solution
Answer: (c) Nagarjunasagar Srisailam
Method. Largest core/critical tiger habitat
Nagarjunsagar-Srisailam Tiger Reserve (Andhra Pradesh and Telangana) has the largest core area, about 3,728 sq km (NTCA list). Manas, Pakke and Periyar have much smaller cores.
Based on the NTCA data at the 2018 sitting.
17. NDA 2017 (II)
Which set of the following biosphere reserves in India is included in the World Network of Biosphere Reserves?
Answer and solution
Answer: (a) Gulf of Mannar, Nokrek, Panchmarhi and Simlipal
Method. UNESCO World Network of Biosphere Reserves (as of 2017)
As of 2017 the Indian reserves in the World Network were Nilgiri, Gulf of Mannar, Sundarbans, Nanda Devi, Nokrek, Pachmarhi, Simlipal, Achanakmar-Amarkantak, Great Nicobar and Agasthyamala. Option (a) has all four in that list. Kanchenjunga (listed 2018), Panna (2020) and Seshachalam (never listed) rule out (b), (c) and (d).
The World Network list changes; this is the position at the 2017 sitting.
19.5 Agriculture and crop improvement
18. NDA 2023 (II)
How many of the following pairs of specialized agriculture and its products are correctly matched?
1. Apiculture: Honey
2. Sericulture: Silk
3. Silviculture: Forestry
4. Viticulture: Grapes
Select the correct answer using the code given below:
1. Apiculture: Honey
2. Sericulture: Silk
3. Silviculture: Forestry
4. Viticulture: Grapes
Select the correct answer using the code given below:
Answer and solution
Answer: (a) 4
Method. Matching of agricultural terms
Apiculture is bee-keeping for honey, sericulture is rearing silkworms for silk, viticulture is grape growing, and silviculture is the growing and care of trees for forestry. All four pairs are correctly matched.
19. NDA 2020 (I)
Which one of the following terms describes the practice of growing two or more crops simultaneously on the same piece of land?
Answer and solution
Answer: (b) Mixed cropping
Method. Mixed cropping vs intercropping
NCERT Class 9 Science (Improvement in Food Resources) defines mixed cropping as growing two or more crops simultaneously on the same piece of land. Intercropping is also two or more crops together, but in definite row patterns, and crop rotation is sequential, not simultaneous. The wording given matches mixed cropping.
Intercropping (c) is the nearest rival; the question gives no row pattern, so mixed cropping fits.
20. NDA 2017 (II)
Golden rice is a genetically-modified crop plant where the incorporated gene is meant for biosynthesis of
Answer and solution
Answer: (b) Vitamin A
Method. Golden rice: provitamin A
Golden rice is transgenic rice carrying genes (e.g. for phytoene synthase from daffodil) that make beta-carotene, the precursor of vitamin A (Class 12 Biology, Biotechnology and its Applications).
21. NDA 2017 (I)
Sugarcane is one of the important cash crops in India. It is grown to obtain
Answer and solution
Answer: (d) Sucrose
Method. Sugarcane stores sucrose
Sugarcane stems store sugar as sucrose, which is crystallised to make table sugar (standard crop reference). Starch is the store of potato and cereals; glucose and fructose are monosaccharides that are only minor constituents of cane juice.
19.6 Microbes in human welfare
22. NDA 2017 (II)
Which one of the following statements about microbes is not correct?
Answer and solution
Answer: (c) No antibiotic has been obtained from any microbe.
Method. Negative stem: microbes and antibiotics
The statement that is NOT correct is (c). Penicillin (from Penicillium) and streptomycin (from Streptomyces) are antibiotics obtained from microbes (Class 12 Biology, Microbes in Human Welfare). (a) sewage treatment uses microbes, (b) fermenters make beverages (yeast), (d) bioactive molecules such as cyclosporin A and statins come from microbes.
23. NDA 2017 (II)
The term 'Probiotic' is applied to
Answer and solution
Answer: (d) Live microbial food supplement
Method. Definition of probiotic
Probiotics are live microbial food supplements (e.g. Lactobacillus in curd) that benefit the gut (Class 12 Biology, Microbes in Human Welfare). An antibiotic kills microbes; an antacid neutralises acid.
24. NDA 2017 (II)
Which one of the following microbes causes acidification and curding of milk?
Answer and solution
Answer: (a) Lactic Acid Bacillus
Method. Lactic acid bacteria set milk into curd
Lactic acid bacteria (LAB, e.g. Lactobacillus) convert lactose to lactic acid, which coagulates milk protein and curdles it (Class 12 Biology, Microbes in Human Welfare). Clostridium botulinum causes botulism, Vibrio cholerae cholera, and Saccharomyces cerevisiae is baker's yeast.