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In the given diagram: (Class 10 Science 2023, Q29b)

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ScienceCBSE Class 10 · Board exam 2023, set 31/6/1 · 3 marks · Short answer

CBSE Class 10 Science 2023: question 29(b)

Set in the CBSE Class 10 board exam of 2023, paper 31/6/1, section C, question 29(b), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q29(b) · 3 marks · Short answerControl and Coordination

In the given diagram:

  1. (i)

    Name the parts labelled A, B, and C.

    0 marks
  2. (ii)

    Write the functions of A and C.

    0 marks
  3. (iii)

    Reflex arcs have evolved in animals? Why?

    0 marks

Figure in the paper: Reflex arc diagram: a hand touching a hot pan at the lower left. Nerve pathway runs from the hand up the arm to the spinal cord, which is shown in a vertebral column cross-section at the right. Label A points to the sensory nerve fibre on the arm pathway (upward arrow); label B points to a grey region in the spinal cord (spinal cord/grey matter inter-neuron area); label C points to a muscle in the upper arm (biceps). See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/6/1.

Hints

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

Hint 1

Follow the impulse: hand → spinal cord → muscle. Each label is one stage of this path.

Hint 2

For (iii), compare how long it takes to think with how fast you must react to a hot object.

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) A – sensory neuron

    ½ mark

  2. B – relay neuron (in the spinal cord)

    ½ mark

  3. C – effector, i.e. the muscle of the arm

    ½ mark

  4. (ii) A carries the impulse from the receptor (skin of the hand) to the spinal cord.

    ½ mark

  5. C responds to the stimulus by contracting, so the hand is pulled away from the hot pan.

    ½ mark

  6. (iii) Reflex arcs have evolved because the thinking process of the brain is not fast enough. A reflex arc gives a quick response without conscious thought, which protects the body from danger.

    ½ mark

Answer: (i) A sensory neuron, B relay neuron, C effector (muscle); (ii) A carries impulse from receptor to spinal cord, C responds by contracting; (iii) the brain's thinking is too slow, so reflex arcs give quick protective responses.

Where the marks are

  • Names A, B, C correctly (½ mark each)
  • Function of A (½ mark)
  • Function of C (½ mark)
  • Reason for evolution of reflex arcs (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Control and Coordination, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 31/6/1: 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.