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(i) What does an ecological… (Class 12 Biology 2024, Q23b)

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BiologyCBSE Class 12 · Board exam 2024, set 57/5/1 · 3 marks · Short answer

CBSE Class 12 Biology 2024: question 23(b)

Set in the CBSE Class 12 board exam of 2024, paper 57/5/1, section C, question 23(b), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q23(b) · 3 marks · Short answerEcosystem

(i) What does an ecological pyramid represent ?
(ii) The Ecological pyramids may have an 'upright' or an 'inverted' shape. Justify with the help of suitable examples.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 57/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Think of how the trophic levels are stacked, from producers at the base to top carnivores.

Hint 2

An upright or inverted shape depends on whether the base is larger or smaller than the levels above it.

Hint 3

Consider phytoplankton and zooplankton in the sea, or one tree carrying many insects.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (i) An ecological pyramid is a diagrammatic representation of the relationship between organisms at successive trophic levels, expressed in terms of number, biomass or energy, with producers at the base.

    1 mark

  2. (ii) Upright pyramid: this shape results when the number, biomass or energy is greatest at the producer level and decreases at each higher trophic level.

    ½ mark

  3. Example of an upright pyramid: the pyramid of number in a grassland, where grasses outnumber herbivores, which outnumber carnivores. (A pyramid of energy is always upright.)

    ½ mark

  4. Inverted pyramid: this shape results when the number or biomass at the producer level is less than that of the consumers.

    ½ mark

  5. Examples of an inverted pyramid: the pyramid of biomass in the sea, where a small standing crop of phytoplankton supports a larger standing crop of zooplankton; or the pyramid of number of a single big tree supporting many insects.

    ½ mark

Answer: (i) The relationship between trophic levels in terms of number, biomass or energy. (ii) Upright when producers exceed consumers (e.g. grassland pyramid of number); inverted when producers are fewer or have less biomass (e.g. sea pyramid of biomass, tree–insect pyramid of number).

Where the marks are

  • Definition of an ecological pyramid in terms of number, biomass or energy at trophic levels (1 mark)
  • Reason for the upright shape (½ mark) with a correct example (½ mark)
  • Reason for the inverted shape (½ mark) with a correct example (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Ecosystem, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 57/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.