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Explain how advent of… (Class 12 Biology SQP 2024-25, Q32A)

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BiologyCBSE Class 12 · Sample paper, session 2024-25 · 5 marks · Long answer

CBSE Class 12 Biology sample paper 2024-25: question 32(A)

From the official CBSE sample question paper for 2024-25, 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-basedBiotechnology and its Applications

Explain how advent of biotechnology has helped in preventing infestation by nematodes and thereby increasing crop yield.

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

Name the nematode and the crop it attacks.

Hint 2

The technique silences a gene of the parasite using RNA.

Hint 3

Think about how a double-stranded RNA is made inside the transgenic plant and what it does to the nematode's mRNA.

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. Many nematodes parasitise plants and animals. The nematode Meloidogyne incognita infects the roots of tobacco plants and greatly reduces yield.

    ½ mark

  2. A biotechnological strategy based on RNA interference (RNAi) was used to prevent this infestation.

    ½ mark

  3. RNAi occurs in all eukaryotic organisms as a method of cellular defence.

    ½ mark

  4. In RNAi, a specific mRNA is silenced when a complementary dsRNA molecule binds to it and prevents its translation.

    ½ mark

  5. In nature, this complementary RNA may come from viruses with RNA genomes or from transposons that replicate via an RNA intermediate.

    ½ mark

  6. Using Agrobacterium vectors, nematode-specific genes were introduced into the host (tobacco) plant.

    ½ mark

  7. The DNA was introduced so that it produced both sense and anti-sense RNA in the host cells.

    ½ mark

  8. These two complementary RNAs joined to form double-stranded RNA (dsRNA), which started RNAi.

    ½ mark

  9. The dsRNA silenced the specific mRNA of the nematode after it fed on the plant.

    ½ mark

  10. As a result, the parasite could not survive in the transgenic host expressing the interfering RNA. The plant was protected from infestation and crop yield increased.

    ½ mark

Answer: RNAi: Agrobacterium-mediated transfer of nematode-specific genes into tobacco produces sense and antisense RNA, which form dsRNA. This silences the mRNA of Meloidogyne incognita, so the nematode cannot survive and yield is protected.

Where the marks are

  • Names Meloidogyne incognita infecting tobacco roots and reducing yield (0.5 mark)
  • Names RNA interference (RNAi) as the strategy (0.5 mark)
  • RNAi as a cellular defence in eukaryotes (0.5 mark)
  • Silencing of a specific mRNA by complementary dsRNA (0.5 mark)
  • Source of complementary RNA: RNA viruses or transposons (0.5 mark)
  • Agrobacterium vectors used to introduce nematode-specific genes (0.5 mark)
  • Production of sense and antisense RNA (0.5 mark)
  • Formation of dsRNA that initiates RNAi (0.5 mark)
  • Silencing of nematode mRNA (0.5 mark)
  • Parasite cannot survive, so the plant is protected (0.5 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biotechnology and its Applications, 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.