Ecological Pyramids (Biomass, Energy, Numbers)

Attempt the quiz above first, then review every question with its correct answer and a short explanation below.

1. Q1.Who first developed the concept of ecological pyramids?

   • A.Charles Elton✓ Correct Answer
   • B.Eugene Odum
   • C.Arthur Tansley
   • D.Raymond Lindeman

   Explanation: According to NCERT concepts, the ecological pyramids were first developed by Charles Elton in 1927, which is why they are also sometimes called Eltonian pyramids.

2. Q2.Which of the following ecological pyramids is always upright and can never be inverted?

   • A.Pyramid of Numbers
   • B.Pyramid of Biomass
   • C.Pyramid of Energy✓ Correct Answer
   • D.Both Pyramid of Numbers and Biomass

   Explanation: NCERT Class 12 Biology, Chapter 14, states that the pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.

3. Q3.In an aquatic ecosystem like a sea, the pyramid of biomass is generally:

   • A.Upright
   • B.Inverted✓ Correct Answer
   • C.Spindle-shaped
   • D.Bell-shaped

   Explanation: According to NCERT Class 12 Biology, 'The pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton.' Phytoplankton are the primary producers but have low standing crop biomass at any given time due to rapid turnover.

4. Q4.What does a trophic level in an ecological pyramid represent?

   • A.A specific species
   • B.A functional level, not a species✓ Correct Answer
   • C.An individual organism
   • D.A geographical region

   Explanation: NCERT Class 12 Biology emphasizes that a trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time (e.g., a sparrow eating seeds vs insects).

5. Q5.If a single oak tree supports thousands of herbivorous insects and hundreds of carnivorous birds, the pyramid of numbers will be:

   • A.Upright
   • B.Strictly inverted
   • C.Spindle-shaped✓ Correct Answer
   • D.Horizontal

   Explanation: As per NCERT concepts, a single tree (producer) at the base has a count of 1. It supports many herbivorous insects (primary consumers). These are eaten by fewer carnivorous birds (secondary/tertiary consumers). This results in a spindle-shaped pyramid.

6. Q6.Which of the following is a major limitation of ecological pyramids mentioned in NCERT?

   • A.They do not include primary producers.
   • B.They accommodate food webs easily.
   • C.They do not take into account the same species occupying two or more trophic levels.✓ Correct Answer
   • D.They give too much importance to decomposers.

   Explanation: NCERT Class 12 Biology lists limitations of ecological pyramids: (1) It assumes a simple food chain, which almost never exists; (2) It does not accommodate a food web; (3) It does not take into account the same species occupying more than one trophic level; (4) Saprophytes/decomposers are not given any place.

7. Q7.The mass of living material at a particular trophic level at a particular time is called:

   • A.Standing state
   • B.Standing crop✓ Correct Answer
   • C.Gross primary productivity
   • D.Net primary productivity

   Explanation: NCERT Class 12 Biology Chapter 14 states: 'Each trophic level has a certain mass of living material at a particular time called as the standing crop.' Standing crop is measured as the mass of living organisms (biomass) or the number in a unit area.

8. Q8.Why is biomass measurement in terms of dry weight considered more accurate than fresh weight?

   • A.Fresh weight is too difficult to measure.
   • B.Dry weight is independent of seasonal moisture variations.✓ Correct Answer
   • C.Fresh weight does not include organic compounds.
   • D.Dry weight includes the weight of trapped water.

   Explanation: NCERT Class 12 Biology states that measurement of biomass in terms of dry weight is more accurate because fresh weight contains water content which varies widely depending on environmental conditions and seasonal moisture.

9. Q9.Which trophic level receives the least amount of energy in a standard upright pyramid of energy?

   • A.Primary producers
   • B.Primary consumers
   • C.Secondary consumers
   • D.Tertiary/Top consumers✓ Correct Answer

   Explanation: According to the 10% law of energy transfer (NCERT Chapter 14), only 10% of energy is transferred to each higher trophic level. Therefore, the top/tertiary consumers receive the least amount of energy at the apex of the pyramid.

10. Q10.Which of the following statements about decomposers in relation to ecological pyramids is true?

    • A.They occupy the base of the pyramids.
    • B.They are placed at the top of the pyramids.
    • C.पारिस्थितिक पिरामिडों में उन्हें कोई स्थान नहीं दिया गया है।✓ Correct Answer
    • D.उन्हें प्राथमिक उपभोक्ताओं के साथ शामिल किया गया है।

    Explanation: NCERT Class 12 Biology explicitly notes as a limitation: 'Saproophytes (decomposers) are not given any place in ecological pyramids even though they play a vital role in the ecosystem.'

11. Q11.In a grassland ecosystem, the pyramid of numbers is typically:

    • A.Upright✓ Correct Answer
    • B.Inverted
    • C.Spindle-shaped
    • D.T-shaped

    Explanation: In a grassland ecosystem, millions of grass plants (producers) support a smaller number of herbivores (like rabbits, grasshoppers), which in turn support an even smaller number of carnivores. Thus, the pyramid of numbers is upright (NCERT Class 12 Biology).

12. Q12.According to Lindeman's efficiency rule, what percentage of energy is typically transferred to the next trophic level?

    • A.1%
    • B.5%
    • C.10%✓ Correct Answer
    • D.50%

    Explanation: NCERT Class 12 Biology, Chapter 14 states: 'Only 10 per cent of the energy is transferred to each trophic level from the lower trophic level.' This is called the 10% law.

13. Q13.A bird eating a caterpillar that feeds on leaves belongs to which trophic level?

    • A.First trophic level
    • B.Second trophic level
    • C.Third trophic level✓ Correct Answer
    • D.Fourth trophic level

    Explanation: Leaves are producers (T1). The caterpillar is a herbivore/primary consumer feeding on producers (T2). The bird eats the caterpillar, making it a carnivore/secondary consumer, which belongs to the third trophic level (T3) as per NCERT definitions.

14. Q14.Which of the following ecosystems can have an inverted pyramid of numbers?

    • A.Grassland ecosystem
    • B.Pond ecosystem
    • C.Parasitic food chain on a single tree✓ Correct Answer
    • D.Desert ecosystem

    Explanation: In a parasitic food chain, a single tree (producer) supports numerous herbivorous birds (primary consumers), which in turn support many more parasites like lice and bugs (secondary consumers). This creates an inverted pyramid of numbers.

15. Q15.Standing state differs from standing crop because standing state refers to:

    • A.The total biomass of living organisms.
    • B.The amount of inorganic nutrients present in the soil at any given time.✓ Correct Answer
    • C.The rate of energy flow between trophic levels.
    • D.The total productivity of producers.

    Explanation: NCERT Class 12 Biology distinguishes them: Standing crop is the living biomass, whereas standing state is the amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc., present in the soil at any given time.

16. Q16.The number of trophic levels in a food chain is restricted because:

    • A.Decomposers destroy the energy at higher levels.
    • B.Organisms at higher levels reproduce slowly.
    • C.Energy loss at each step is very high, leaving very little energy for higher levels.✓ Correct Answer
    • D.Prey species become extinct quickly.

    Explanation: Based on the 10% law in NCERT, energy decreases exponentially at higher trophic levels. After 4 to 5 trophic levels, the amount of energy remaining is too small to support another trophic level.

17. Q17.Which of the following occupying the same area is at the first trophic level?

    • A.Zooplankton
    • B.Phytoplankton✓ Correct Answer
    • C.Small fish
    • D.Water beetles

    Explanation: NCERT Class 12 Biology states that in aquatic ecosystems, phytoplankton are the primary producers and thus occupy the first trophic level (T1), whereas zooplankton are primary consumers (T2).

18. Q18.When a sparrow eats seeds, fruits, and peas, it is a primary consumer. But when it eats insects and worms, it is a:

    • A.Primary producer
    • B.Secondary consumer✓ Correct Answer
    • C.Tertiary consumer
    • D.Decomposer

    Explanation: As explained in NCERT Class 12 Biology Chapter 14, insects eat plants (insects are T2/primary consumers). The sparrow eating those insects becomes a secondary consumer (T3). This shows a species can occupy multiple trophic levels.

19. Q19.Which of the following represents the correct sequence of trophic levels from base to apex?

    • A.Herbivores -> Carnivores -> Producers -> Top Carnivores
    • B.Producers -> Herbivores -> Carnivores -> Top Carnivores✓ Correct Answer
    • C.Producers -> Carnivores -> Herbivores -> Top Carnivores
    • D.Herbivores -> Producers -> Carnivores -> Top Carnivores

    Explanation: NCERT Class 12 Biology illustrates that the food chain or pyramid flows upwards from producers (1st trophic level) to herbivores (2nd level), then carnivores (3rd level), and finally top carnivores (4th level).

20. Q20.The rate at which radiant energy is stored by photosynthetic activity in producers is called:

    • A.Net Primary Productivity
    • B.Gross Primary Productivity✓ Correct Answer
    • C.Secondary Productivity
    • D.Net Community Productivity

    Explanation: NCERT Class 12 Biology Chapter 14 defines Gross Primary Productivity (GPP) of an ecosystem as the rate of production of organic matter during photosynthesis. Net Primary Productivity (NPP) is GPP minus respiration losses (R).