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A farmer grew 2… (Class 12 Biology SQP 2023-24, Q27a)

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BiologyCBSE Class 12 · Sample paper, session 2023-24 · 3 marks · Short answer

CBSE Class 12 Biology sample paper 2023-24: question 27(a)

From the official CBSE sample question paper for 2023-24, section C, question 27(a), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27(a) · 3 marks · Short answerCompetency-basedBiotechnology and its Applications

A farmer grew 2 varieties of corn crop in field A and B. He grew normal corn crops in field A and GM corn crops in field B. He observed corn borers attacked only in field A. To control it, spores of Bt were sprayed in field A.
a) Name the gene in the spores responsible for the control of this pest.
b) What effect will the spores of Bt have on the insect pest?
c) How has field B developed resistance against this pest?

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

Which cry gene protects corn against the corn borer?

Hint 2

Why is the toxin harmless in the bacterium but deadly in the insect?

Hint 3

How does the GM plant obtain the ability to make the toxin?

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. a) The gene is *cry*IAb, whose toxin controls the corn borer.

    ½ mark

  2. b) Bt spores contain the toxin as an inactive crystalline protoxin.

    ½ mark

  3. When the insect eats it, the alkaline pH of the insect gut solubilises the crystals and activates the toxin.

    ½ mark

  4. The active toxin binds to the midgut epithelial cells, creating pores. The cells swell and lyse, and the insect dies.

    ½ mark

  5. c) Field B has Bt corn (GM crop). The Bt toxin gene was isolated, cloned and inserted into the corn genome by recombinant DNA technology. The plant makes the toxin itself, so it is resistant to corn borers.

    1 mark

Answer: a) cryIAb. b) The inactive crystal toxin is activated by alkaline gut pH and lyses midgut epithelial cells, killing the insect. c) The Bt cry gene was inserted by rDNA technology, so the GM corn expresses the toxin and resists the pest.

Where the marks are

  • Names cryIAb (0.5 mark)
  • Toxin present as inactive crystals (0.5 mark)
  • Activated by alkaline pH of insect gut (0.5 mark)
  • Midgut epithelial cells become porous, swell and lyse (0.5 mark)
  • Bt gene inserted by rDNA technology, plant expresses toxin (1 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 2023-24: 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.