UPSC CSE Prelims
Fundamentals of Ecology Previous Year Questions (PYQs)
Showing solved Previous Year Questions for Chapter: Fundamentals of Ecology
Topic Breakdown: Scroll →
Which of the following adds/add nitrogen to the soil?
- Excretion of urea by animals
- Burning of coal by man
- Death of vegetation
Select the correct answer using the codes given below.
Detailed Explanation:
✅ Statement 1 – Correct: Urea (CO(NH₂)₂) excreted by animals is decomposed by soil microbes into ammonia, which is further converted into nitrates and nitrites, adding nitrogen to soil.
❌ Statement 2 – Incorrect: Burning of coal releases nitrogen oxides (NOₓ) into the atmosphere, not directly into soil; these contribute to air pollution and acid rain.
✅ Statement 3 – Correct: Death of vegetation leads to decomposition by bacteria and fungi, which breaks down organic matter and releases nitrogen compounds back into soil.
With reference to the food chains in ecosystems, which of the following kinds of an organism is/are known as decomposer organism/organisms?
- Virus
- Fungi
- Bacteria
Select the correct answer using the codes given below.
Detailed Explanation:
Fungi and Bacteria are the primary decomposers in ecosystems that break down dead organic matter into simpler inorganic substances, recycling nutrients back into the environment.
Viruses are not decomposers—they are metabolically inactive outside host cells and function as obligate intracellular parasites that require living cells to replicate, playing no role in decomposition.
In the grasslands, trees do not replace the grasses as a part of an ecological succession because of
Detailed Explanation:
Grasslands maintain themselves as climax communities due to two primary limiting factors: water scarcity and periodic fires.
Grasses have meristematic tissue at the base (not tips), allowing rapid regrowth after fire, while tree seedlings die in fires. Additionally, low annual precipitation (25-75 cm) and thin, dry soil prevent tree establishment, maintaining grasslands in a sub-climax stage.
🧐 Not Sure What to Study Next?
Get a personalised study plan based on your goals, time and revision needs.
With reference to food chains in ecosystems, consider the following statements :
- A food chain illustrates the order in which a chain of organisms feeds upon each other.
- Food chains are found within the populations of a species.
- A food chain illustrates the numbers of each organism which are eaten by others.
Which of the statements given above is/are correct?
Detailed Explanation:
✅ Statement 1 – Correct: A food chain illustrates the linear sequence in which organisms feed upon each other, showing the order of energy flow from producers → primary consumers → secondary consumers → tertiary consumers.
❌ Statement 2 – Incorrect: Food chains operate between different species, not within populations of a single species; they represent inter-species feeding relationships across different trophic levels.
❌ Statement 3 – Incorrect: A food chain shows only the feeding relationship and direction of energy flow, not the numbers or biomass of organisms; ecological pyramids illustrate numerical or biomass relationships.
The Millennium Ecosystem Assessment describes the following major categories of ecosystem services: provisioning, supporting, regulating, preserving, and cultural. Which one of the following is a supporting service?
Detailed Explanation:
Millennium Ecosystem Assessment (2005) classifies ecosystem services into four categories: Provisioning, Regulating, Supporting, and Cultural.
Supporting Services are foundational services necessary for production of all other ecosystem services, including nutrient cycling, soil formation, primary production, and photosynthesis.
Provisioning Services include food, water, timber, and fiber production (Option 1).
Regulating Services include climate regulation, disease control, water purification, and crop pollination (Options 2 and part of 3).
Cultural Services include spiritual, recreational, aesthetic, and educational benefits (Option 4's diversity maintenance also overlaps with supporting).
Option 3 is correct because nutrient cycling is the definitive supporting service listed, even though pollination is technically classified as a regulating service in the original MA framework.
What would happen if phytoplankton of an ocean is completely destroyed for some reason?
- The ocean as a carbon sink would be adversely affected.
- The food chains in the ocean would be adversely affected.
- The density of ocean water would drastically decrease.
Detailed Explanation:
✅ Statement 1 – Correct: Phytoplankton perform photosynthesis and absorb atmospheric CO₂, converting it into organic carbon through carbon sequestration. Their destruction would severely impair the ocean's role as a carbon sink.
✅ Statement 2 – Correct: Phytoplankton form the base of marine food chains, being the primary producers consumed by zooplankton and small fish, which support larger marine organisms. Their complete destruction would collapse oceanic food webs.
❌ Statement 3 – Incorrect: Ocean water density is determined by temperature and salinity, not by the presence of microscopic phytoplankton. Their removal would have negligible impact on water density.
Showing 16 to 21 of 21 questions