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Give reasons for the… (Class 10 Science 2024, Q29a)

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ScienceCBSE Class 10 · Board exam 2024, set 31/2/1 · 3 marks · Short answer

CBSE Class 10 Science 2024: question 29(a)

Set in the CBSE Class 10 board exam of 2024, paper 31/2/1, section C, question 29(a), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q29(a) · 3 marks · Short answerLife Processes

Give reasons for the following :

  1. (i)

    Alveoli in lungs are richly supplied with blood capillaries.

    0 marks
  2. (ii)

    Respiratory pigment in the blood takes up oxygen and not carbon dioxide.

    0 marks
  3. (iii)

    During anaerobic respiration, a 3-carbon molecule is formed as an end product instead of in human beings.

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/2/1.

Hints

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

Hint 1

Think of what the blood has to pick up and give out in the alveoli.

Hint 2

For (iii), what is missing in muscle cells during heavy exercise?

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) Alveoli are surrounded by a dense network of blood capillaries so that oxygen and carbon dioxide can be exchanged efficiently between the air in the alveoli and the blood. Oxygen diffuses into the blood and diffuses out over a very large area.

    1 mark

  2. (ii) The respiratory pigment haemoglobin has a very high affinity for oxygen. So it picks up oxygen in the lungs. Carbon dioxide is more soluble in water and is carried mostly dissolved in plasma.

    1 mark

  3. (iii) In human muscles, when oxygen is in short supply (for example during vigorous exercise), glucose is not oxidised completely. Pyruvate (a 3-carbon molecule) is converted into lactic acid, another 3-carbon molecule, instead of being broken down to and water.

    1 mark

Answer: (i) For efficient exchange of gases; (ii) haemoglobin has a high affinity for oxygen; (iii) lack of oxygen means incomplete oxidation of glucose, forming 3-carbon lactic acid.

Where the marks are

  • (i) Efficient gas exchange (1 mark)
  • (ii) High affinity of haemoglobin for oxygen (1 mark)
  • (iii) Lack of oxygen leads to incomplete oxidation of glucose, forming lactic acid, a 3-carbon molecule (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 paper2024 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.