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The graph given below… (Class 12 Biology SQP 2023-24, Q19)

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BiologyCBSE Class 12 · Sample paper, session 2023-24 · 2 marks · Very short answer

CBSE Class 12 Biology sample paper 2023-24: question 19

From the official CBSE sample question paper for 2023-24, section B, question 19, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19 · 2 marks · Very short answerCompetency-basedHuman Health and Disease

The graph given below indicates the administration of the first (L) and second dose (M) of a vaccine. The corresponding response of the body is indicated by X and Y. Interpret the graph and explain the reason for such a response shown by the body.

Figure in the paper: Graph of concentration of antibody (y) vs time (x). First dose L is followed by a small peak X; second dose M is followed by a much higher, steeper peak Y. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

Compare the heights of the two peaks. Which one is larger?

Hint 2

Think about what the immune system 'remembers' after its first encounter with an antigen.

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. After the first dose (L), the body meets the antigen of the weakened or inactivated pathogen for the first time. It gives a slow, low-intensity primary immune response (X) with little antibody.

    1 mark

  2. After the second dose (M), the memory B and T cells formed during the first contact recognise the same antigen. They produce a rapid, highly intensified secondary (anamnestic) response (Y). This response is faster and stronger, with far more antibody, so the pathogen is removed more effectively. This is why booster doses are given.

    1 mark

Answer: X = weak primary immune response to the first exposure; Y = fast, strong secondary response due to immunological memory formed after the first dose.

Where the marks are

  • Interprets X as low-intensity primary response on first contact with antigen (1 mark)
  • Interprets Y as rapid, intensified secondary response due to 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 paperSample paper 2023-24: 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.