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(i) Why is respiratory… (Class 10 Science 2024, Q29)

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ScienceCBSE Class 10 · Board exam 2024, set 31/1/1 · 3 marks · Short answer

CBSE Class 10 Science 2024: question 29

Set in the CBSE Class 10 board exam of 2024, paper 31/1/1, section C, question 29, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q29 · 3 marks · Short answerLife Processes

(i) Why is respiratory pigment needed in multicellular organisms with large body size?
(ii) Give reasons for the following :
(a) Rings of cartilage are present in the throat.
(b) Lungs always contain a residual volume of air.
(c) The diaphragm flattens and ribs are lifted up when we breathe in.
(d) Walls of alveoli contain an extensive network of blood vessels.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/1/1.

Hints

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

Hint 1

Think about how far oxygen would have to diffuse in a large body.

Hint 2

For each reason, ask what would go wrong without it: a collapsed tube, no time for exchange, no space for air, no blood to carry the gases.

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) In large organisms, diffusion alone is too slow to supply oxygen to all body cells. A respiratory pigment such as haemoglobin, which has high affinity for oxygen, picks up oxygen in the lungs and carries it to the tissues.

    1 mark

  2. (ii)(a) Rings of cartilage support the throat (trachea) so that the air passage does not collapse when there is less air in it.

    ½ mark

  3. (b) A residual volume of air stays in the lungs so that there is enough time for oxygen to be absorbed and carbon dioxide to be released.

    ½ mark

  4. (c) When the diaphragm flattens and the ribs are lifted, the chest cavity becomes larger, so air is sucked into the lungs.

    ½ mark

  5. (d) Exchange of gases takes place in the alveoli. The dense network of blood vessels lets oxygen pass into the blood and carbon dioxide pass out efficiently.

    ½ mark

Answer: (i) Diffusion alone cannot meet O₂ needs, so the pigment carries O₂; (ii)(a) prevents collapse of air passage; (b) time for gas exchange; (c) chest cavity enlarges; (d) gas exchange occurs in alveoli

Where the marks are

  • Diffusion is insufficient to deliver oxygen in large bodies (1 mark)
  • Cartilage rings prevent collapse of the air passage (½ mark)
  • Residual air allows time for gas exchange (½ mark)
  • Chest cavity enlarges during inhalation (½ mark)
  • Blood vessels at alveoli for exchange of gases (½ mark)

Revise the chapter

  • Chapter: Life Processes (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Life Processes, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 31/1/1: 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.