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“Plasmodium protozoan needs… (Class 12 Biology 2023, Q26a)

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BiologyCBSE Class 12 · Board exam 2023, set 57/5/1 · 3 marks · Short answer

CBSE Class 12 Biology 2023: question 26(a)

Set in the CBSE Class 12 board exam of 2023, paper 57/5/1, section C, question 26(a), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q26(a) · 3 marks · Short answerHuman Health and Disease

“Plasmodium protozoan needs both a mosquito and a human host for its continuity.” Explain.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 57/5/1.

Hints

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

Hint 1

Divide the life cycle into an asexual part and a sexual part.

Hint 2

Ask where gametocytes are formed and where fertilisation happens.

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. When an infected female Anopheles mosquito bites a person, the infectious stage, sporozoites, enters the human blood.

    ½ mark

  2. The sporozoites reach the liver cells and multiply there asexually.

    ½ mark

  3. The parasites then attack RBCs, multiply asexually and rupture them, releasing haemozoin, which causes chills and high fever. This is the asexual phase in humans.

    ½ mark

  4. Some parasites in the RBCs develop into gametocytes, which are taken up by a female Anopheles when it bites an infected person.

    ½ mark

  5. Fertilisation of gametes and further development (the sexual phase) take place in the mosquito's gut and produce sporozoites.

    ½ mark

  6. The sporozoites are stored in the mosquito's salivary glands and passed to a new human at the next bite. Since the asexual phase occurs in humans and the sexual phase in the mosquito, Plasmodium needs both hosts to complete its life cycle.

    ½ mark

Answer: Asexual multiplication (liver, RBCs) and gametocyte formation occur in humans; fertilisation and sporozoite formation occur in the mosquito, which also transmits the sporozoites. So both hosts are needed.

Where the marks are

  • Sporozoites enter humans through the bite of a female Anopheles (½ mark)
  • Asexual multiplication in liver cells (½ mark)
  • Asexual multiplication in and rupture of RBCs (½ mark)
  • Gametocytes formed in RBCs and taken up by the mosquito (½ mark)
  • Fertilisation and development into sporozoites in the mosquito gut (sexual phase) (½ mark)
  • Sporozoites stored in salivary glands and transmitted, so both hosts are needed (½ 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 paper2023 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.