This set covers the building blocks of ecology: how energy and matter move through ecosystems, how ecological pyramids are drawn, and how communities change over time. These concepts form the base for most Environment questions in UPSC Prelims.
How to practise: read each question and tap the option you think is correct. You will see right away whether you got it, along with a short explanation, and your score is tracked at the bottom of the screen. This set has 15 questions.
Topics covered in this set
- Food chains and food webs
- Trophic levels and the ten percent law
- Ecological pyramids
- Ecological succession
- Nitrogen, carbon and phosphorus cycles
- Ecotones, niches and biomagnification
UPSC Environment MCQs with answers and explanations
Q1. The term 'ecosystem' was first used by which ecologist?
a) Ernst Haeckel
b) Arthur Tansley
c) Eugene Odum
d) Charles Elton
Q2. Which of the following is a correct sequence of a grazing food chain?
a) Grass, grasshopper, frog, snake
b) Grass, frog, grasshopper, snake
c) Snake, frog, grasshopper, grass
d) Grasshopper, grass, snake, frog
Q3. The 'ten percent law' of energy transfer between trophic levels was given by:
a) Charles Elton
b) Eugene Odum
c) Raymond Lindeman
d) Norman Myers
Q4. Which ecological pyramid is always upright?
a) Pyramid of numbers
b) Pyramid of biomass
c) Pyramid of energy
d) Pyramid of numbers in a tree ecosystem
Q5. In which ecosystem is the pyramid of biomass usually inverted?
a) Grassland
b) Tropical forest
c) Desert
d) Open ocean
Q6. Which organisms are usually the pioneer species in primary succession on bare rock?
a) Lichens
b) Grasses
c) Shrubs
d) Ferns
Q7. Which of the following statements about ecological succession is correct?
a) Secondary succession is generally slower than primary succession
b) Primary succession begins in an area where no soil existed earlier
c) Hydrarch succession begins in very dry areas
d) The climax community is the first community to colonise an area
Q8. Which bacterium fixes atmospheric nitrogen in the root nodules of leguminous plants?
a) Nitrosomonas
b) Nitrobacter
c) Pseudomonas
d) Rhizobium
Q9. The conversion of nitrates in the soil back into free nitrogen gas is called:
a) Denitrification
b) Nitrification
c) Ammonification
d) Nitrogen fixation
Q10. Which biogeochemical cycle does not have a significant gaseous phase in the atmosphere?
a) Carbon cycle
b) Nitrogen cycle
c) Phosphorus cycle
d) Oxygen cycle
Q11. The starting point of a detritus food chain is:
a) Green plants
b) Dead organic matter
c) Herbivorous insects
d) Top carnivores
Q12. The tendency of an ecotone to have more species and higher population density than either adjoining community is called:
a) Niche partitioning
b) Biomagnification
c) Allelopathy
d) Edge effect
Q13. Why is the concentration of DDT usually highest in fish-eating birds in an aquatic ecosystem?
a) DDT is persistent and accumulates at each higher trophic level
b) Birds produce DDT inside their bodies
c) DDT is rapidly broken down in water but not in air
d) DDT is absorbed only by organisms at the top of the food chain
Q14. Which term best describes the functional role of a species in its ecosystem, including what it eats and how it interacts with others?
a) Habitat
b) Biome
c) Ecological niche
d) Ecotone
Q15. Net primary productivity of an ecosystem is equal to:
a) Gross primary productivity plus respiration losses
b) Gross primary productivity minus respiration losses of producers
c) Secondary productivity minus decomposition
d) Total biomass of all consumers
Quick revision notes
- An ecosystem has biotic components (producers, consumers, decomposers) and abiotic components (light, water, soil, nutrients).
- Energy flow in an ecosystem is one-way, while nutrients move in cycles.
- The pyramid of energy is always upright, but pyramids of numbers and biomass can be inverted.
- Primary succession starts on bare surfaces without soil, while secondary succession starts where soil already exists.
- Nitrogen fixation, nitrification, ammonification and denitrification are the main steps of the nitrogen cycle.
- Biomagnification is the rise in concentration of persistent toxins such as DDT and mercury at higher trophic levels.
Frequently asked questions
What is the difference between a food chain and a food web?
A food chain is a single linear path of energy transfer from producers to top consumers. A food web is a network of interlinked food chains and gives a more realistic picture of feeding relationships.
Why are food chains usually limited to four or five trophic levels?
Only about 10 percent of energy passes from one trophic level to the next. After a few levels, too little energy remains to support another population of consumers.
What is a climax community?
A climax community is the relatively stable final stage of ecological succession in an area. It remains in balance with the local climate and soil until a major disturbance occurs.
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