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Given below is the… (Class 12 Biology SQP 2024-25, Q30)

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BiologyCBSE Class 12 · Sample paper, session 2024-25 · 4 marks · Case-based

CBSE Class 12 Biology sample paper 2024-25: question 30

From the official CBSE sample question paper for 2024-25, 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

Given below is the pattern of temperature in a person suffering from a non-viral disease transmitted by mosquitoes. Study the graph and answer the questions that follow:

  1. A.

    Explain the factor(s) responsible for this pattern of temperature.

    1 mark
  2. B.

    How does this pathogen multiply in the human body?

    2 marks
  3. C.

    How is this infection transmitted to humans?

    1 mark

  4. OR

    D.

    Which stages of the life cycle of this pathogen are completed in the mosquito’s gut?

    1 mark

Figure in the paper: Line graph of temperature (°C, 35 to 41) vs time (days, 0 to 13). Temperature fluctuates repeatedly in peaks and troughs, with peaks rising over time: about 38.7 at day 3, 38.8 at day 5, 40 at day 6.7, 40.3 at day 8.2, 40.8 at day 10.2, falling to about 36-37 between peaks, ending near 36.8 at day 12. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

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

Hint 1

A recurring fever with chills every few days suggests malaria.

Hint 2

Think of the toxin released when infected RBCs burst.

Hint 3

The parasite multiplies first in one organ and then in blood cells; sexual stages begin in humans but are completed in the mosquito.

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. The disease is malaria, caused by the protozoan Plasmodium and spread by mosquitoes.

    A. The repeated fever spikes come from the rupture of RBCs, which releases a toxic substance called haemozoin. This causes chills and high fever that recur every 3–4 days, matching each cycle of RBC bursting.

    1 mark

  2. B. Sporozoites injected by the mosquito reach the liver. There the parasite multiplies asexually, the liver cells burst, and the parasites are released into the blood.

    1 mark

  3. B. The parasites then attack red blood cells and multiply asexually again. The RBCs rupture and the released parasites infect new RBCs. Some parasites in the RBCs develop into the sexual stages (gametocytes).

    1 mark

  4. C. Infection is transmitted by the bite of an infected female Anopheles mosquito, which injects sporozoites (the infectious stage) into the human body.

    1 mark

  5. D. In the mosquito's gut, fertilisation of the gametes and further development take place. The sporozoites formed then move to the salivary glands.

Answer: A. RBC rupture releasing haemozoin causes chills and fever every 3–4 days; B. Asexual multiplication in liver cells, then in RBCs, with gametocytes forming in RBCs; C. Bite of female Anopheles injecting sporozoites; D. Fertilisation and development.

Where the marks are

  • Links fever pattern to RBC rupture and haemozoin release (1 mark)
  • Asexual multiplication in liver cells with release into blood (1 mark)
  • Asexual multiplication in RBCs and formation of gametocytes (1 mark)
  • C: bite of female Anopheles introducing sporozoites (1 mark) OR D: fertilisation and development in the mosquito gut (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 2024-25: 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.