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(i) Draw the structure of an… (Class 12 Biology 2026, Q33a)

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BiologyCBSE Class 12 · Board exam 2026, set 57/5/1 · 5 marks · Long answer

CBSE Class 12 Biology 2026: question 33(a)

Set in the CBSE Class 12 board exam of 2026, paper 57/5/1, section E, question 33(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q33(a) · 5 marks · Long answerHuman Health and Disease

(i) Draw the structure of an antibody molecule and label any four of its parts.
(ii) Differentiate between active and passive immunity. Write any three differences. 2+3=5

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 57/5/1.

Hints

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

Hint 1

An antibody is a Y-shaped protein made of four polypeptide chains. Think about what holds them together.

Hint 2

For the differences, ask who makes the antibodies: the body itself, or are they supplied ready-made?

Hint 3

Compare the two on how fast they act, how long they last and whether memory cells form.

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 a Y-shaped molecule made of four polypeptide chains. There are two long heavy (H) chains forming the stem and both arms. There are two short light (L) chains, one along the outer side of each arm. The chains are held together by disulphide (S–S) bonds. The tips of the two arms form the antigen-binding sites. Label any four of: (1) heavy chain, (2) light chain, (3) antigen-binding site, (4) disulphide bonds; also variable region / constant region (H₂L₂ structure).

    2 marks

  2. (ii) Difference 1 (origin): In active immunity, the body's own B-lymphocytes produce antibodies in response to an antigen, through infection or vaccination. In passive immunity, ready-made antibodies are given to the body, e.g. anti-tetanus serum, or IgA in colostrum and antibodies crossing the placenta.

    1 mark

  3. Difference 2 (speed): Active immunity is slow and takes time to give its full response. Passive immunity gives immediate/quick protection.

    1 mark

  4. Difference 3 (duration and memory): Active immunity is long-lasting because memory cells are formed. Passive immunity is short-lived and no memory cells are formed.

    1 mark

Answer: (i) Y-shaped H₂L₂ antibody: two heavy chains, two light chains, disulphide bonds, antigen-binding sites. (ii) Active: own antibodies, slow, long-lasting, memory cells formed. Passive: ready-made antibodies, quick, short-lived, no memory cells.

Where the marks are

  • Correct Y-shaped antibody diagram with any four correct labels (heavy chain, light chain, antigen-binding site, disulphide bond, variable/constant region) (½ × 4 = 2 marks)
  • Active immunity uses antibodies made by the body itself; passive immunity uses pre-formed antibodies given from outside (1 mark)
  • Active is slow; passive is quick (1 mark)
  • Active is long-lasting with memory cells; passive is short-lived with no memory cells (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Human Health and Disease, one at a time, marked against the answer key and marking points.Back to the full paper2026 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.