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(i) (I) Write the scientific… (Class 12 Biology 2026, Q33b)

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

CBSE Class 12 Biology 2026: question 33(b)

Set in the CBSE Class 12 board exam of 2026, paper 57/5/1, section E, question 33(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q33(b) · 5 marks · Long answerHuman Health and Disease

(i) (I) Write the scientific names of the two species of filarial worms causing filariasis.
(II) How do they affect the body of infected persons ?
(III) How does the disease spread ?
(ii) Mention the source and the role of the following in providing defence against infection in the human body :
(I) Histamine
(II) Interferons 1+1+1+2=5

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 57/5/1.

Hints

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

Hint 1

Both filarial worms belong to the same genus, named after the scientist Wucherer.

Hint 2

Filariasis is also called elephantiasis. Think which body parts swell and which insect carries the worm.

Hint 3

Histamine comes from cells involved in allergy, and interferons come from cells already attacked by a virus.

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)(I) The two filarial worms are Wuchereria bancrofti and Wuchereria malayi.

    1 mark

  2. (II) The worms live in the lymphatic vessels for many years. They cause slowly developing chronic inflammation of the organs in which they live, usually those of the lower limbs. This leads to swelling of the legs (elephantiasis), and the genital organs may also become grossly deformed.

    1 mark

  3. (III) The disease spreads from an infected person to a healthy person through the bite of a female mosquito vector (e.g. Culex).

    1 mark

  4. (ii)(I) Histamine: Source: released by mast cells (and basophils). Role: it dilates blood vessels and increases their permeability. This produces the inflammatory response and brings defence cells to the site. When released excessively against harmless allergens, it causes the symptoms of allergy (sneezing, watery eyes, running nose).

    1 mark

  5. (II) Interferons: Source: secreted by virus-infected cells. Role: they protect the neighbouring non-infected cells from further viral infection. This is part of the cytokine barrier of innate immunity.

    1 mark

Answer: (i)(I) Wuchereria bancrofti and W. malayi. (II) Chronic inflammation of lymphatic organs, leading to elephantiasis of the lower limbs and deformity of the genitals. (III) Bite of a female mosquito vector. (ii)(I) Histamine: from mast cells; causes inflammation/allergic response. (II) Interferons: from virus-infected cells; protect non-infected cells from viral infection.

Where the marks are

  • Names both Wuchereria bancrofti and W. malayi (½ + ½ = 1 mark)
  • Effect: chronic inflammation of the organs, swelling of the lower limbs (elephantiasis), deformed genital organs (1 mark)
  • Spread by the bite of a female mosquito vector (1 mark)
  • Histamine: source is mast cells (½) and role is the inflammatory/allergic response (½) (1 mark)
  • Interferons: source is virus-infected cells (½) and role is protecting non-infected cells from viral infection (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 57/5/1: 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.