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Answer the following. (Class 12 Biology 2026, Q33a)

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

CBSE Class 12 Biology 2026: question 33(a)

Set in the CBSE Class 12 board exam of 2026, paper 57/1/1, 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

Answer the following.

  1. (i)

    Name the protozoan species that is responsible for causing the most serious and even fatal malarial disease.

    0 marks
  2. (ii)

    Name the host in which the parasite completes its sexual stages and explain the changes taking place.

    2 marks
  3. (iii)

    How does the parasite damage the human body after entering the blood stream ?

    0 marks
  4. (iv)

    Suggest two effective preventive measures to control the spread of this disease in endemic regions.

    1 mark

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

Hints

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

Hint 1

Recall the life cycle of Plasmodium in two hosts.

Hint 2

Which host takes up gametocytes, and where do the sporozoites end up?

Hint 3

Think of the toxin released when the parasite bursts out of red blood cells.

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) Plasmodium falciparum causes malignant malaria, the most serious and often fatal form.

    ½ mark

  2. (ii) Host. The sexual stages are completed in the female Anopheles mosquito.

    ½ mark

  3. (ii) Changes in the mosquito.

    • When the mosquito bites an infected person, it takes up gametocytes along with the blood.
    • In the mosquito's gut the gametes form and fuse (fertilisation), and the parasite develops further, producing sporozoites.
    • The sporozoites migrate to the mosquito's salivary glands. From there they are injected into a new human host at the next bite.
    1½ marks

  4. (iii) Sporozoites entering the blood first reach the liver cells and multiply there. They then attack red blood cells and multiply asexually inside them. The RBCs rupture and release a toxic substance, haemozoin. Haemozoin causes chills and high fever that recur every 3–4 days.

    1½ marks

  5. (iv) Any two preventive measures:

    • Avoid stagnant water in and around homes, and clean water coolers regularly, so that mosquitoes cannot breed.
    • Use mosquito nets and wire mesh on doors and windows.
    • Introduce larvivorous fish such as Gambusia into ponds.
    • Spray insecticides in ditches and drains.
    1 mark

Answer: (i) Plasmodium falciparum; (ii) female Anopheles mosquito – gametocytes taken up, fertilisation and development in the gut, sporozoites move to the salivary glands; (iii) multiply in liver cells, then in RBCs; RBCs rupture releasing haemozoin, causing chills and recurring high fever; (iv) e.g. remove stagnant water, use mosquito nets / Gambusia fish

Where the marks are

  • Names Plasmodium falciparum (½ mark)
  • Names the female Anopheles mosquito as host (½ mark)
  • Gives three changes in the mosquito: gametocyte uptake, fertilisation and development in the gut, sporozoites to the salivary glands (½ × 3 = 1½ marks)
  • Describes liver and RBC multiplication, RBC rupture and haemozoin causing chills and fever (1½ marks)
  • Gives any two preventive measures (½ + ½ = 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 57/1/1: 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.