Practice MCQs Optional & Subjects

Ecosystem Energy Flow: Food Chains and Ecological Pyramids — MCQs with Answers

Test what you know about Ecosystem Energy Flow: Food Chains and Ecological Pyramids with 10 UPSC Prelims-style questions. Try each one first, then tap “Show answer” for the correct option and its explanation.

Read the full article
  • 10 practice questions
  • ≈ 10 min
  • Answers & explanations

Answers revealed

Try each question yourself first, then check the answer.

  1. Q1. In a conventional food-chain diagram, an arrow from a grasshopper to a frog indicates which of the following?

    1. Energy transfer when the frog eats the grasshopper
    2. Movement of mineral nutrients only from the frog to grass
    3. Production of food by the frog for the grasshopper
    4. The direction in which the grasshopper searches for food
    Show answer

    Correct answer: (A) Energy transfer when the frog eats the grasshopper

    Explanation

    Correct Answer: (A). The arrow follows energy from the food organism to its consumer. Here the grasshopper is food for the frog. It does not represent the direction of foraging, a supply of food made by the frog, or an exclusively mineral transfer from the frog to a plant.

  2. Q2. Consider the following statements: 1. An omnivore can occupy more than one trophic position. 2. Every species has a single permanent trophic position regardless of its diet. Which of the statements given above is/are correct?

    1. 2 only
    2. 1 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Show answer

    Correct answer: (B) 1 only

    Explanation

    Correct Answer: (B). Statement 1 is correct because a consumer feeding on plants and on herbivores follows different trophic pathways. Statement 2 is incorrect: trophic position describes feeding relationships rather than an unchanging species label. A food web can represent these multiple connections better than a single food chain.

  3. Q3. Consider the following pairs: 1. Earthworm — ingestion and fragmentation of detritus 2. Decomposer fungi — enzymatic breakdown of organic compounds 3. Grazing food chain — begins with dead organic matter How many of the above pairs are correctly matched?

    1. Only one
    2. All three
    3. Only two
    4. None
    Show answer

    Correct answer: (C) Only two

    Explanation

    Correct Answer: (C). Pairs 1 and 2 correctly distinguish detritivore activity from microbial decomposition. Pair 3 is incorrect because a grazing chain starts with living producers being eaten. Dead organic matter starts a detrital chain. Both pathways interact within ecosystems and should not be treated as isolated processes.

  4. Q4. Net primary productivity is obtained by subtracting which quantity from gross primary productivity?

    1. Only herbivore consumption
    2. The entire standing biomass of producers
    3. Respiration of all consumers only
    4. Respiratory expenditure of producers
    Show answer

    Correct answer: (D) Respiratory expenditure of producers

    Explanation

    Correct Answer: (D). NPP is GPP after subtracting the producers’ own respiratory expenditure, using a common area and time basis. Herbivore consumption is a different flow, while standing biomass is a stock. Consumer respiration is not the deduction used to define net primary productivity in this relationship.

  5. Q5. Statement-I: An aquatic biomass pyramid may be inverted without violating energy-transfer constraints. Statement-II: Rapidly replenished phytoplankton can maintain a small standing biomass while supporting greater consumer biomass. Which of the following is correct?

    1. Both statements are correct and II explains I
    2. Both statements are correct but II does not explain I
    3. I is correct but II is incorrect
    4. I is incorrect but II is correct
    Show answer

    Correct answer: (A) Both statements are correct and II explains I

    Explanation

    Correct Answer: (A). Both statements are correct. Standing biomass is a snapshot, whereas production continues over time. Rapid growth and consumption can keep phytoplankton biomass low while replenishing the food available to consumers. This directly explains the possible inversion; it does not imply that energy increases at successive trophic levels.

  6. Q6. Consider the following statements about the ten-percent rule: 1. It is a simplified approximation for transfer between successive trophic levels. 2. It means all producers capture exactly ten percent of incoming sunlight. Which of the statements given above is/are correct?

    1. Both 1 and 2
    2. 1 only
    3. 2 only
    4. Neither 1 nor 2
    Show answer

    Correct answer: (B) 1 only

    Explanation

    Correct Answer: (B). Statement 1 is correct: the rule simplifies trophic transfer, whose actual efficiency varies. Statement 2 incorrectly applies it to the capture of incoming sunlight. It also cannot justify treating every ecosystem as having identical transfer efficiency; food quality, organisms and environmental conditions affect actual energy transfer.

  7. Q7. Which set of units is most suitable for comparing energy flow through trophic levels?

    1. Grams of dry mass per square metre
    2. Number of individuals per hectare
    3. Kilojoules per square metre per year
    4. Grams of dry mass per individual
    Show answer

    Correct answer: (C) Kilojoules per square metre per year

    Explanation

    Correct Answer: (C). Energy flow requires an energy unit together with a consistent area and time basis. Kilojoules per square metre per year meets those requirements. Dry mass per area describes biomass, individuals per area describes abundance, and dry mass per individual describes average mass rather than trophic energy flow.

  8. Q8. A study of a pond measures only organic production by plants growing inside its water. Which additional input could support its detrital food web but remain uncounted?

    1. Metabolic heat recycled into plant food
    2. The number of fish counted without their food supply
    3. Mineral nutrients treated as already formed organic food
    4. Fallen leaves entering from surrounding trees
    Show answer

    Correct answer: (D) Fallen leaves entering from surrounding trees

    Explanation

    Correct Answer: (D). Leaves entering from outside the pond carry organic matter and chemical energy into its detrital pathway. A measurement restricted to production inside the water can omit this input. Counts of fish are not an energy supply, minerals are not equivalent to organic food, and metabolic heat is not recycled this way.

  9. Q9. An increase in algal growth after nutrient enrichment is followed by oxygen depletion. Which process best explains this sequence?

    1. Microbial respiration during decomposition consumes dissolved oxygen
    2. Higher algal biomass always guarantees healthier water
    3. Decomposers stop using energy when organic matter increases
    4. Nutrient elements are converted directly into oxygen-free heat
    Show answer

    Correct answer: (A) Microbial respiration during decomposition consumes dissolved oxygen

    Explanation

    Correct Answer: (A). Decomposition of organic material can raise microbial oxygen demand and reduce dissolved oxygen. More algal biomass therefore does not automatically indicate better ecological health. Decomposers continue using energy for metabolism, while conversion of nutrient elements directly into heat is not the mechanism linking enrichment with oxygen depletion.

  10. Q10. Consider the following statements: 1. Sunlight is the immediate energy source for every producer community. 2. Chemosynthetic microorganisms can use chemical reactions to build organic matter. Which of the statements given above is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Show answer

    Correct answer: (B) 2 only

    Explanation

    Correct Answer: (B). Statement 1 is too absolute: some deep-sea vent producer communities use chemical energy as their immediate source. Statement 2 correctly describes chemosynthetic production. This does not change the ecological role of producers, which build organic matter supplying food webs, whether their energy comes from light or chemical reactions.

More practice MCQ sets

All MCQ sets