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Answer the following. (Science 2025 31/2/1 Q35b)

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ScienceCBSE Class 10 · Board exam 2025, set 31/2/1 · 5 marks · Long answer

CBSE Class 10 Science 2025: question 35(b)

Set in the CBSE Class 10 board exam of 2025, paper 31/2/1, section D, question 35(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q35(b) · 5 marks · Long answerLife Processes

Answer the following.

  1. (i)

    State the role of rings of cartilage present in the throat.

    0 marks
  2. (ii)

    Discuss the role of the ribs and diaphragm when air is taken in during the breathing cycle.

    0 marks
  3. (iii)

    Why do we get muscle cramps during heavy exercise? Explain.

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/2/1.

Hints

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

Hint 1

What would happen to a soft tube if the air inside it were removed?

Hint 2

When the chest gets bigger, what happens to the air pressure inside?

Hint 3

Which type of respiration occurs when oxygen is short, and what product does it form in muscles?

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) The rings of cartilage in the throat (trachea) keep the air passage open. They ensure that it does not collapse when there is little or no air in it.

    1 mark

  2. (ii) When we breathe in, the muscles between the ribs contract and lift the ribs upward and outward. At the same time, the diaphragm contracts and flattens.

    1 mark

  3. (ii) This makes the chest cavity larger and lowers the pressure inside it. As a result, air is sucked into the lungs and fills the expanded alveoli.

    1 mark

  4. (iii) During heavy exercise, the muscle cells need energy faster than oxygen can be supplied. They then switch to anaerobic respiration, in which pyruvate is converted into lactic acid: glucose → pyruvate → lactic acid + energy.

    1 mark

  5. (iii) The build-up of lactic acid in the muscles causes muscle cramps.

    1 mark

Answer: (i) The rings keep the air passage from collapsing. (ii) Ribs are lifted and the diaphragm flattens, so the chest cavity enlarges and air is sucked into the lungs. (iii) Lack of oxygen leads to anaerobic respiration; pyruvate becomes lactic acid, and its build-up causes cramps.

Where the marks are

  • Rings of cartilage prevent collapse of the air passage (1 mark)
  • Ribs lifted and diaphragm flattens (1 mark)
  • Chest cavity enlarges and air is sucked into the lungs (1 mark)
  • Lack of oxygen leads to anaerobic respiration, converting pyruvate to lactic acid (1 mark)
  • Accumulation of lactic acid causes cramps (1 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 paper2025 board paper, set 31/2/1: 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.