CBSE Class 12 Biology 2023: question 32(a)
Set in the CBSE Class 12 board exam of 2023, paper 57/1/1, 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 answerCompetency-basedHuman Health and Disease
A time-bound vaccination programme is followed for the children in our country from their birth up to ten years of age. A graph plotted below shows the effect of the vaccination followed by infection by the same pathogen, and the antibody concentration in the blood of the child.
(i) Explain why the administration of a vaccine causes an increase in the antibody concentration.
(ii) If the child is infected with the same pathogen almost four months later, the antibody concentration in his/her blood increases very fast. Explain why.
(iii) A table given below gives information about different types of immunity and how they are attained. Identify 'P', 'Q', 'R', 'S' and 'T' in the table.
| Type of immunity | Production of antibodies | Presence of memory cells | Mode attained | |
|---|---|---|---|---|
| (1) | Natural, active | Yes | 'P' | 'Q' |
| (2) | Natural, passive | No | 'R' | Across the placenta during pregnancy/breast feeding |
| (3) | Acquired, active | 'S' | Yes | Getting a vaccine during breast feeding |
| (4) | Acquired, passive | 'T' | No | Getting an injection of antibodies |
Figure in the paper: Graph of antibody concentration in blood (y-axis) vs days after administration of vaccine (x-axis, 0 to 500). Vaccine administered at day 0; a small rise (low peak) in antibodies up to about day 100-150, falling; reinfection with same pathogen at about day 130 followed by a very rapid, much higher rise peaking around day 250 and then slowly declining. See it in the official paper.
Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 57/1/1.
Hints
Open one hint at a time and try again before the next.
Hint 1
What does a vaccine contain, and which cells respond by making antibodies?
Hint 2
Why is the second response to the same pathogen faster and stronger than the first?
Hint 3
Active immunity means the body makes its own antibodies and memory; passive means it receives ready-made antibodies.
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.
- ½ mark
(i) A vaccine contains antigenic proteins of the pathogen, or inactivated/weakened pathogens.
- 1 mark
These antigens activate the immune system. B-lymphocytes produce antibodies against them, giving a primary (humoral) immune response, so antibody concentration rises (the first, smaller peak in the graph).
- ½ mark
(ii) The vaccination also produced memory B and T cells.
- ½ mark
On a later infection by the same pathogen, these memory cells recognise it quickly and mount a rapid, intense secondary (anamnestic) response. This is why the antibody level rises very fast and very high.
- ½ mark
(iii) P = Yes (natural active immunity forms memory cells).
- ½ mark
Q = catching the infection (being naturally infected by the pathogen).
- ½ mark
R = No (passively received antibodies leave no memory cells).
- ½ mark
S = Yes (the vaccine makes the body produce its own antibodies).
- ½ mark
T = No (ready-made antibodies are injected; the body makes none).
Answer: (i) Vaccine antigens stimulate B-cells to make antibodies (primary response); (ii) memory cells give a rapid secondary/anamnestic response; (iii) P – Yes, Q – catching an infection, R – No, S – Yes, T – No
Where the marks are
- Vaccine contains antigen (½ mark) that stimulates B-cells to make antibodies, a primary/humoral response (1 mark)
- Memory cells formed (½ mark) give a fast secondary/anamnestic response (½ mark)
- P = Yes, Q = catching infection, R = No, S = Yes, T = No (½ × 5 marks)
Revise the chapter
- Chapter: Human Health and Disease (notes, formulas, where marks are lost and every past question)
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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.