Ecology, Ecosystem and Functions of Ecosystem: UPSC Previous Year Questions (Environment and Ecology)
24 previous year UPSC Prelims questions on ecology and ecosystems are listed here, from 1996 to 2025. UPSC asks about food chains and trophic levels, biogeochemical cycles, detritivores, symbiosis and plant adaptations. The 2025 paper compared rain forests with other oxygen sources. The explanations show how each organism fits in the ecosystem.
Explanations state facts as of the year each question was asked; words like “recently” refer to that year.
Showing 21–24 of 24 questions
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UPSC 2011Environment and Ecology · Ecology, Ecosystem and Functions of Ecosystem
Q21. If a tropical rainforest is removed, it does not regenerate quickly as compared to a tropical deciduous forest. This is because
Explanation
Tropical rainforests and tropical deciduous forests differ in their nutrient cycles, soil composition, and regeneration capacity. When a tropical rainforest is removed, it does not regenerate quickly because of the nutrient-poor soil. In tropical rainforests, the warm and humid conditions promote rapid decomposition of organic matter by bacteria and fungi. But due to the high density of plant life the nutrients released are immediately absorbed by plants leaving the soil infertile. In contrast the tropical deciduous forests have richer soils be-cause the leaf litter decomposes and replenishes soil nutrients more effectively. Options (b), (c) and (d) are incorrect:
Propagules (seeds, spores, or other reproductive structures) of rainforest trees generally have high viability. However, the regeneration of rainforests is hindered more by soil nutrient deficiencies than by the viability of propagules. Many rainforest species are fast-growing especially pioneer species that colonize disturbed areas. However, the lack of nutrients in the soil limits their growth and the overall regeneration of the forest. In rainforests slow regeneration is due to nutrient loss and not exotic/invasive species. If soils were fertile, native plants would recover quickly but rainforest soils are typically nutrient-poor which limits their regrowth.
UPSC 2010Environment and Ecology · Ecology, Ecosystem and Functions of Ecosystem
Q22. A pesticide which is a chlorinated hydrocarbon is sprayed on a food crop. The food chain is: Food crop - Rat - Snake - Hawk. In this food chain, the highest concentration of the pesticide would accumulate in which one of the following?
Explanation
This increasing concentration of a toxic substance as it moves up the food chain is known as biomagnification. Predators at the highest trophic levels like hawks suffer the most severe effects, including reproductive issues, weakened immune systems, and neurological damage due to the high pesticide load. When a chlorinated hydrocarbon pesticide like DDT enters the food chain, it accumulates in fatty tissues through bioaccumulation. As predators consume contaminated prey, the pesticide concentration increases, peaking in top predators due to biomagnification. Thus in the above food chain--Food crop Rat Snake Hawk--the hawk experiences the highest pesticide concentration.
UPSC 2000Environment and Ecology · Ecology, Ecosystem and Functions of Ecosystem
Q23. Within biological communities, some species are important in determining the ability of a large number of other species to persist in the community. Such species are called:
Explanation
Keystone species play a crucial role in maintaining eco-system structure and function, having a disproportionate impact relative to their abundance. Like the keystone in an arch, they support the stability of the entire system. These species influence population sizes, modify the environment, and affect species diversity and community composition. Removing a keystone species can disrupt the ecosystem, leading to biodiversity loss and instability. Some of the Keystone Species are: Sea Otters(kelp forest ecosystem). Wolves and other top predators(Grassland ecosystem), Elephants(Savannah), Beavers and Starfish. Options (b), (c) and (d) are incorrect:
Allopatric species are species that evolve separately due to geographic isolation, Eg. African and Indian elephants. Sympatric species are species that evolve separately within the same geographic area. Threatened species are species at risk of becoming endangered in the near future due to factors like habitat loss, climate change, and human activities.
UPSC 1996Environment and Ecology · Ecology, Ecosystem and Functions of Ecosystem
Q24. Consider the following programmes: 1. Afforestation and development of wastelands 2. Reforestation and replantation in existing forests 3. Encouraging the wood substitutes and supplying other types of fuel 4. Promotion of wide use of insecticides and pesticides to restrict the loss of forest area from degradation caused by pests and insects. The National Forest Policy of 1988 includes:
Explanation
National forest policy 1988 was introduced with the principal aim of ensuring environmental stability and maintaining ecological balance including atmospheric equilibrium which are vital for sustenance of all life forms, human, animal and plant. Key objectives of National Forest Policy 1988 are:
Increasing substantially the forest/tree cover in the country through massive afforestation, reforestation and social forestry programmes Encouraging efficient utilisation of forest produce and maximising substitution of wood. Checking soil erosion and denudation in the catchment areas of rivers, lakes, reservoirs. However, the National Forest Policy of 1988 does not promote the wide use of insecticides and pesticides. Instead, it emphasizes the importance of maintaining a balanced ecosystem and preserving biodiversity within forests.
Answer key for these questions
Q
UPSC year
Correct answer
21
2011
(a) The soil of rainforest is deficient in nutrients
22
2010
(d) Hawk
23
2000
(a) Keystone species
24
1996
(d) 1, 2 and 3
What UPSC has tested in Ecology, Ecosystem and Functions of Ecosystem
In the phosphorus cycle the weathering of rocks is the main source of the nutrient.
Earthworms, millipedes and sea cucumbers are detritivores; jellyfish are not.
Alfalfa, chickpea and clover are nitrogen-fixing plants.
In grasslands, trees do not replace grasses in ecological succession because of water limits and fire.
An ecosystem is a community of organisms interacting with each other and with their physical environment.
Frequently asked questions
How many previous year UPSC questions are there on Ecology, Ecosystem and Functions of Ecosystem?
This page covers 24 previous year UPSC Prelims GS Paper-I questions on Ecology, Ecosystem and Functions of Ecosystem (Environment and Ecology), asked from 1996 to 2025. Each has the correct answer and an explanation.
Which biogeochemical cycle depends on the weathering of rocks?
The phosphorus cycle. Phosphorus has no significant atmospheric phase, so rocks are its main reservoir, and weathering releases phosphate into soil and water, from where plants take it up.
What are detritivores?
Organisms that feed on dead plant and animal matter, such as earthworms, millipedes and sea cucumbers. They break down detritus into smaller pieces and return nutrients to the soil or sediment.
Why do trees not replace grasses in some grasslands?
Because water is limited and fires are frequent. Grasses recover quickly after fire and tolerate dry spells, so seedlings of trees cannot establish, and the grassland persists as a stable ecosystem.
