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(i) Define a reflex arc. Why… (Class 10 Science 2024, Q35a)

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ScienceCBSE Class 10 · Board exam 2024, set 31/4/1 · 5 marks · Long answer

CBSE Class 10 Science 2024: question 35(a)

Set in the CBSE Class 10 board exam of 2024, paper 31/4/1, section D, question 35(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q35(a) · 5 marks · Long answerControl and Coordination

(i) Define a reflex arc. Why have reflex arcs evolved in animals ? Trace the sequence of events which occur, when you suddenly touch a hot object.
(ii) Name the part of nervous system which helps in communication between the central nervous system and other parts of the body. What are the two components of this system ?

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/4/1.

Hints

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

Hint 1

Reflexes are handled by the spinal cord without waiting for the brain to think.

Hint 2

List the parts in order, starting from the skin receptor and ending at the muscle.

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 reflex arc is the pathway along which nerve impulses travel during a reflex action, from the receptor through the spinal cord to the effector.

    1 mark

  2. Reflex arcs have evolved because the thinking process of the brain is not fast enough. A reflex arc gives a quick, automatic response that protects the body from injury.

    ½ mark

  3. Sequence on touching a hot object: receptors in the skin detect the heat → sensory neuron carries the impulse to the spinal cord → relay neuron in the spinal cord passes it on → motor neuron carries the impulse to the effector (arm muscle) → the muscle contracts and the hand is withdrawn.

    1½ marks

  4. (ii) The peripheral nervous system carries communication between the central nervous system and other parts of the body.

    1 mark

  5. Its two components are the cranial nerves (arising from the brain) and the spinal nerves (arising from the spinal cord).

    1 mark

Answer: (i) A reflex arc is the pathway of impulses in a reflex action; it evolved for a quick response because the brain is slow. Sequence: receptor → sensory neuron → spinal cord (relay neuron) → motor neuron → muscle (effector). (ii) Peripheral nervous system: cranial nerves and spinal nerves.

Where the marks are

  • Definition of reflex arc (1 mark)
  • Reason: quick response, since thinking is slow (½ mark)
  • Correct sequence receptor → sensory neuron → spinal cord → motor neuron → effector (1½ marks)
  • Peripheral nervous system (1 mark)
  • Cranial nerves and spinal nerves (½ + 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 paper2024 board paper, set 31/4/1: 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.