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The graph below shows… (Class 12 Biology SQP 2025-26, Q30)

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BiologyCBSE Class 12 · Sample paper, session 2025-26 · 4 marks · Case-based

CBSE Class 12 Biology sample paper 2025-26: question 30

From the official CBSE sample question paper for 2025-26, section D, question 30, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q30 · 4 marks · Case-basedCompetency-basedHuman Health and Disease

The graph below shows the Antibody concentration in young calves. Study the graph and answer the questions that follow:

(For visually impaired students: The antibody concentration in a young calf was studied. It was found that the antibodies derived from colostrum (passive immunity) decreased from day 1 to 14, while the antibodies derived from immune cells (active immunity) increased between day 1 to day 14 and remained steady thereafter.)

  1. A

    What do you think is the difference between passive and active immunity in this case?

    1 mark
  2. B

    What kind of immunity will be observed when a vaccine is administered to the calf and why?

    2 marks
  3. C

    What kind of trend does passive immunity show and why?

    1 mark

  4. OR

    D

    Why does active immunity start after 14 days as per the above graph?

    1 mark

Figure in the paper: Graph of antibody concentration (y-axis) vs time (x-axis, marked 1 d and 14 d). Passive immunity (colostrum) curve rises sharply to a peak at about day 1 then falls steeply to a low level. Active immunity (immune system) curve stays low until ~14 d then rises steadily to a high plateau. The period between 1 d and 14 d where both are low is marked 'High risk period'. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

Where do colostrum antibodies come from – the calf or the mother?

Hint 2

A vaccine introduces an antigen; think about memory cells.

Hint 3

Borrowed antibodies cannot be replenished; the calf's own response has a lag phase.

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. A. Passive immunity comes from ready-made antibodies in colostrum. It is immediate but transient and creates no memory cells. Active immunity comes from antibodies made by the calf's own immune system. It starts after a lag but is long-lasting and memory-based.

    1 mark

  2. B. A vaccine gives active immunity. It contains inactivated or weakened pathogens (or antigenic proteins) that cannot cause disease but are still recognised as foreign.

    1 mark

  3. The calf's B- and T-lymphocytes are activated, and antibodies are produced against the pathogen. Memory B- and T-cells are also formed, so on later exposure the calf mounts a quick, strong response, giving long-term protection.

    1 mark

  4. C. Passive immunity peaks at about day 1 and then falls steeply. The colostrum antibodies are used up or broken down, and no memory cells are made to replace them.

    1 mark

  5. D (alternative to C). Active immunity is slow to develop. The calf's immune system needs time to meet antigens, activate lymphocytes and build up enough antibodies, so the response becomes significant only after about 14 days.

Answer: A. Passive – ready-made colostrum antibodies, quick, short-lived, no memory; active – own antibodies, slow, long-lasting, memory. B. Active immunity – vaccine antigens induce antibodies and memory cells. C. Peaks at day 1 then declines (antibodies used up, no memory). D. Active immunity is slow; it takes time to build up.

Where the marks are

  • Distinguishes passive and active immunity (1 mark)
  • Vaccine gives active immunity (1 mark)
  • Reason – weakened antigen activates lymphocytes, antibodies and memory cells form (1 mark)
  • C: declining trend as antibodies are used up with no memory / D: active immunity is slow to develop (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 paperSample paper 2025-26: 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.