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(i) Draw a diagram of a… (Class 12 Biology 2024, Q32a)

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BiologyCBSE Class 12 · Board exam 2024, set 57/5/1 · 5 marks · Long answer

CBSE Class 12 Biology 2024: question 32(a)

Set in the CBSE Class 12 board exam of 2024, paper 57/5/1, section E, question 32(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q32(a) · 5 marks · Long answerHuman Reproduction

(i) Draw a diagram of a human sperm. Label any four parts and write their functions. (4)
(ii) In a human female, probability of an ovum to get fertilized by more than one sperm is impossible. Give reason. (1)

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 57/5/1.

Hints

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

Hint 1

A sperm has a head, a middle piece and a tail. What does each contain?

Hint 2

Which part supplies energy, and which part contains enzymes?

Hint 3

Think about what happens to the zona pellucida once the first sperm touches it.

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) Diagram (described): Draw an elongated sperm with, in order, a head (an oval nucleus capped anteriorly by an acrosome), a neck, a middle piece packed with spiral mitochondria, and a long tail, all enclosed by the plasma membrane.

  2. Acrosome – a cap-like structure filled with enzymes that help the sperm penetrate the ovum during fertilisation.

    1 mark

  3. Head / nucleus – contains the haploid chromosomal (genetic) material.

    1 mark

  4. Middle piece – contains numerous mitochondria, which produce energy for the movement of the tail.

    1 mark

  5. Tail – provides motility, letting the sperm swim towards the ovum. (The plasma membrane, which envelops and protects the sperm, is also acceptable.)

    1 mark

  6. (ii) When a sperm comes in contact with the zona pellucida of the ovum, it induces changes in the membrane.

    ½ mark

  7. These changes block the entry of any additional sperm, so fertilisation by more than one sperm (polyspermy) is prevented.

    ½ mark

Answer: (i) Sperm diagram labelled with acrosome (enzymes for penetration), head/nucleus (genetic material), middle piece (mitochondria for energy) and tail (motility). (ii) Contact of a sperm with the zona pellucida induces membrane changes that block entry of other sperms.

Where the marks are

  • Four correct labels on the diagram (½ mark each)
  • A correct function for each labelled part (½ mark each)
  • Sperm contact with the zona pellucida induces membrane changes (½ mark)
  • These changes block entry of additional sperms (½ mark)

Revise the chapter

  • Chapter: Human Reproduction (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Human Reproduction, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 57/5/1: 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.