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Pathogens are often… (Class 12 Biology SQP 2026-27, Q27)

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BiologyCBSE Class 12 · Sample paper, session 2026-27 · 3 marks · Short answer

CBSE Class 12 Biology sample paper 2026-27: question 27

From the official CBSE sample question paper for 2026-27, section C, question 27, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27 · 3 marks · Short answerBiotechnology: Principles and Processes

Pathogens are often considered harmful, yet they have been adapted as powerful tools in genetic engineering. Explain how pathogens have been modified into useful vectors. Describe the role of a similarly modified plant vector and animal vector.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

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

Hint 1

What natural ability of some pathogens is useful to a genetic engineer?

Hint 2

Recall the tumour-inducing plasmid in plants and the cancer-causing viruses in animals.

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. Modification of pathogens: some pathogens naturally transfer their DNA into host cells. Scientists remove their disease-causing genes but keep this ability to deliver DNA, so the disarmed pathogen becomes a useful vector.

    1 mark

  2. Plant vector: the Ti plasmid of Agrobacterium tumefaciens normally causes tumours in dicots. It has been disarmed into a cloning vector that is no longer pathogenic but still delivers desired genes into plants. For example, nematode-specific genes introduced through it produce dsRNA. This triggers RNA interference, which silences the mRNA of Meloidogyne incognita and protects tobacco plants.

    1 mark

  3. Animal vector: retroviruses normally transform normal cells into cancerous cells. They have been engineered by removing the cancer-causing genes while keeping their ability to integrate DNA into the host genome. This makes them effective vectors for delivering genes into animal cells.

    1 mark

Answer: Pathogens are disarmed by removing their disease genes but keeping DNA transfer. Plant vector: the Ti plasmid of Agrobacterium (e.g. for RNAi-based nematode resistance). Animal vector: disarmed retroviruses.

Where the marks are

  • Pathogens disarmed: disease genes removed, DNA-transfer ability retained (1 mark)
  • Ti plasmid of Agrobacterium as a plant vector, with its role (1 mark)
  • Disarmed retroviruses as animal vectors (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biotechnology: Principles and Processes, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: 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.