UPSC Environment and Ecology – Chapter 2: Ecosystem Functions – Energy Flow, Food Chains and Nutrient Cycles (32 MCQs)

← Back

UPSC Environment and Ecology – Chapter 2: Ecosystem Functions – Energy Flow, Food Chains and Nutrient Cycles (32 MCQs) – 32 questions, subject: Environment. Every question has the correct answer with a one-line explanation; tap "Show Answer". Free practice for TNPSC, UPSC, SSC, Bank and RRB exams – Shanmugam IAS Academy, Coimbatore.

Get daily current affairs & exam alerts – follow us YouTube WhatsApp Channel Telegram Channel Facebook Page Instagram
Share with friends & study groups
Link to this page from your website / blog (HTML code)
1.  

Net primary productivity is:

Correct Answer: C [gross primary productivity minus respiration by producers]

Explanation:

NPP is the energy left after producers use part of GPP in respiration; it is the food available to consumers.

2.  

The ten per cent law of energy transfer is associated with:

Correct Answer: A [Lindeman]

Explanation:

R. L. Lindeman's 1942 trophic-dynamic study of energy flow is credited with the ten per cent law.

3.  

Which pyramid is never inverted?

Correct Answer: C [Pyramid of energy]

Explanation:

Energy is lost as heat at every trophic level, so each level always holds less energy than the one below.

4.  

A pyramid of biomass is often inverted in:

Correct Answer: D [the sea]

Explanation:

In many seas a small standing crop of fast-growing phytoplankton supports a larger biomass of zooplankton and fish.

5.  

A food chain that begins with dead organic matter is called a:

Correct Answer: C [detritus food chain]

Explanation:

A detritus food chain begins with dead organic matter such as leaf litter, eaten by detritivores like earthworms.

6.  

Which of the following is a primary producer in ocean food chains?

Correct Answer: B [Diatoms]

Explanation:

Diatoms are photosynthetic algae, so they fix sunlight and form the base of ocean food chains.

7.  

Which one of the following gives the steps of decomposition in the order in which they are generally described?

Correct Answer: A [Fragmentation, leaching, catabolism, humification, mineralisation]

Explanation:

detritus is first broken up, then leached, acted on by enzymes, turned into humus and finally mineralised (Section 2.5).

8.  

Decomposition is fastest in:

Correct Answer: C [warm and moist conditions]

Explanation:

Warmth and moisture speed up the activity of bacteria and fungi, as in tropical rainforests.

9.  

Which of the following is a sedimentary cycle?

Correct Answer: B [Phosphorus cycle]

Explanation:

Phosphorus has its reservoir in rocks and enters the cycle through weathering, so its cycle is sedimentary.

10.  

The bacterium that fixes nitrogen in the root nodules of legumes is:

Correct Answer: B [Rhizobium]

Explanation:

Rhizobium lives in the root nodules of legumes and fixes atmospheric nitrogen in symbiosis with the plant.

11.  

Assertion (A): Food chains rarely have more than four or five links.

Reason (R): Only about ten per cent of energy passes from one trophic level to the next.

Correct Answer: A [Both A and R are true, and R is the correct explanation of A]

Explanation:

With only about ten per cent of energy passed on at each step, too little remains to support many more levels.

12.  

Which of the following removes carbon dioxide from the atmosphere?

Correct Answer: D [Photosynthesis]

Explanation:

Photosynthesis takes in carbon dioxide and fixes it into sugars, removing it from the atmosphere.

13.  

Which of the following groups of services did the Millennium Ecosystem Assessment (2005) identify?

Correct Answer: A [Provisioning, regulating, cultural and supporting]

Explanation:

The 2005 Millennium Ecosystem Assessment grouped ecosystem services as provisioning, regulating, cultural and supporting.

14.  

Consider the following statements:

1. IPBES was established in 2012.
2. TEEB was launched in 2007.
3. The Dasgupta Review was published by the World Bank.

Which of the statements given above are correct?

Correct Answer: D [1 and 2 only]

Explanation:

the Dasgupta Review was commissioned by the UK Treasury.

15.  

Arrange the following in chronological order:

1. IPBES established
2. Millennium Ecosystem Assessment
3. Lindeman's trophic-dynamic concept
4. Dasgupta Review

Select the correct answer:

Correct Answer: C [3-2-1-4]

Explanation:

1942, 2005, 2012, 2021.

16.  

In the sea-grass beds of the Gulf of Mannar, the dugong feeds mainly on sea-grass. At which trophic level does the dugong feed there?

Correct Answer: B [Second trophic level – primary consumer]

Explanation:

the dugong is a herbivorous grazer of sea-grass, so it is a primary consumer at the second trophic level (Table 2.1).

17.  

Which of the following is an example of a detritus food chain?

Correct Answer: B [Leaf litter → earthworm → bird]

Explanation:

It starts with dead organic matter, leaf litter, eaten by the detritivore earthworm, which a bird then eats.

18.  

Azolla used in paddy fields adds nitrogen because it:

Correct Answer: B [houses nitrogen-fixing cyanobacteria]

Explanation:

Azolla's leaves house the cyanobacterium Anabaena azollae, which fixes atmospheric nitrogen and enriches paddy fields.

19.  

About half of the world's oxygen is produced by:

Correct Answer: A [marine phytoplankton and photosynthetic bacteria]

Explanation:

Marine phytoplankton and photosynthetic bacteria produce about half of the world's oxygen, more than any land ecosystem.

20.  

In which ecosystem is the pyramid of number usually inverted?

Correct Answer: D [A single large tree with many insects]

Explanation:

One large tree supports a great number of insects, so the producer level has fewer individuals than the level above.

21.  
UPSC Prelims 2025

With reference to the planet Earth, consider the following statements:

I. Rain forests produce more oxygen than that produced by oceans.

II. Marine phytoplankton and photosynthetic bacteria produce about 50% of the world's oxygen.

III. Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air.

Which of the statements given above is/are correct?

Correct Answer: B [II only]

Explanation:

Marine phytoplankton and bacteria make about half of Earth's oxygen; statement I reverses the truth and water holds far less oxygen than air.

22.  
UPSC Prelims 2022

Which of the following are nitrogen-fixing plants?

1. Alfalfa
2. Amaranth
3. Chickpea
4. Clover
5. Purslane (Kulfa)
6. Spinach

Select the correct answer using the code given below:

Correct Answer: A [1, 3 and 4 only]

Explanation:

legumes.

23.  
UPSC Prelims 2021

In case of which one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrients to enter the cycle?

Correct Answer: C [Phosphorus cycle]

Explanation:

Phosphorus has no significant gaseous phase; it is released into the cycle mainly by weathering of phosphate rocks.

24.  
UPSC Prelims 2021

Consider the following kinds of organisms:

1. Copepods
2. Cyanobacteria
3. Diatoms
4. Foraminifera

Which of the above are primary producers in the food chains of oceans?

Correct Answer: B [2 and 3]

Explanation:

Cyanobacteria and diatoms photosynthesise, so they are primary producers; copepods and foraminifera are mostly consumers.

25.  
UPSC Prelims 2021

Which of the following are detritivores?

1. Earthworms
2. Jellyfish
3. Millipedes
4. Seahorses
5. Woodlice

Select the correct answer using the code given below.

Correct Answer: C [1, 3 and 5 only]

Explanation:

Earthworms, millipedes and woodlice feed on dead organic matter; jellyfish and seahorses are predators.

26.  
UPSC Prelims 2014

Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth?

1. Volcanic action
2. Respiration
3. Photosynthesis
4. Decay of organic matter

Select the correct answer using the code given below:

Correct Answer: C [1, 2 and 4 only]

Explanation:

Volcanic action, respiration and decay of organic matter all release carbon dioxide; photosynthesis removes it.

27.  
UPSC Prelims 2014

Which one of the following is the correct sequence of a food chain?

Correct Answer: A [Diatoms-Crustaceans-Herrings]

Explanation:

Diatoms are producers, crustaceans such as copepods eat them, and herrings feed on the crustaceans.

28.  
UPSC Prelims 2014

Which one of the following is the process involved in photosynthesis?

Correct Answer: B [Free energy is converted into potential energy and stored.]

Explanation:

Photosynthesis traps light (free) energy and stores it as potential chemical energy in food.

29.  
UPSC Prelims 2013

With reference to the food chains in ecosystems, which of the following kinds of organism is/are known as decomposer organism/organisms?

1. Virus
2. Fungi
3. Bacteria

Select the correct answer using the code given below:

Correct Answer: B [2 and 3 only]

Explanation:

Fungi and bacteria break down dead organic matter and release nutrients; viruses multiply only inside living host cells.

30.  
UPSC Prelims 2013

Which one of the following is the correct sequence of ecosystems in the order of decreasing productivity?

Correct Answer: C [Mangroves, grasslands, lakes, oceans]

Explanation:

Mangroves are among the most productive ecosystems and open oceans among the least per unit area, as in the official key.

31.  
UPSC Prelims 2013

With reference to food chains in ecosystems, consider the following statements:

1. A food chain illustrates the order in which a chain of organisms feeds upon each other.
2. Food chains are found within the populations of a species.
3. A food chain illustrates the numbers of each organism that are eaten by others.

Which of the statements given above is/are correct?

Correct Answer: A [1 only]

Explanation:

A food chain shows only the order of feeding; it links different species and does not show numbers eaten.

32.  
UPSC Prelims 2013

Which of the following adds/add nitrogen to the soil?

1. Excretion of urea by animals
2. Burning of coal by man
3. Death of vegetation

Select the correct answer using the code given below:

Correct Answer: C [1 and 3 only]

Explanation:

Urea excreted by animals and decomposing dead vegetation both return nitrogen compounds to the soil.

➤ Full notes, maps, tables, a reason for every option and Mains PYQs – U18 · Environment and Ecology (UPSC book, ₹249): www.shanmugamiasacademy.in/study-materials/upsc-environment-ecology

📘 U18 · Environment, Ecology, Biodiversity and Climate Change – UPSC Civil Services (Prelims & Mains)
Here you get the answer with a one-line explanation. 24 chapters · 701 MCQs incl. UPSC Prelims PYQs with a reason for every option · 120 Mains questions + Mains PYQs · maps, tables, revision cards
Get the book – ₹249 ₹499 →
Score: 0 Answered: 0 / 0