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On spraying Bacillus… (Class 12 Biology 2023, Q27)

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

CBSE Class 12 Biology 2023: question 27

Set in the CBSE Class 12 board exam of 2023, paper 57/5/1, 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 and its Applications

On spraying Bacillus thuringiensis on an infected cotton crop field the pests are killed by the toxin, however the toxin although produced by the bacteria does not affect it. Explain giving reason.

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

Think about the form in which the toxin is stored inside the bacterium.

Hint 2

Ask what condition inside the insect's gut changes the toxin into its active form.

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. Bacillus thuringiensis produces the Bt toxin as an inactive protoxin, in crystal form. So the toxin does not harm the bacterium itself.

    ½ mark

  2. The insect pest ingests the inactive protoxin while feeding on the sprayed crop.

    ½ mark

  3. The alkaline pH of the insect's gut solubilises the crystals and converts the protoxin into the active toxin.

    ½ mark

  4. The active toxin binds to the surface of the midgut epithelial cells.

    ½ mark

  5. It creates pores in these cells.

    ½ mark

  6. The cells swell and lyse, and the insect dies.

    ½ mark

Answer: The toxin is made as an inactive protoxin, so the bacterium is safe. The alkaline insect gut activates it, and the active toxin binds midgut epithelial cells, forms pores, and causes swelling, lysis and death of the pest.

Where the marks are

  • Toxin produced as an inactive protoxin, so the bacterium is unaffected (½ mark)
  • Protoxin ingested by the insect (½ mark)
  • Activated by the alkaline pH of the gut (½ mark)
  • Binds to midgut epithelial cells (½ mark)
  • Creates pores (½ mark)
  • Swelling, lysis and death of the insect (½ 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 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.