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Explain the process by which… (Class 12 Biology 2023, Q19b)

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BiologyCBSE Class 12 · Board exam 2023, set 57/1/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2023: question 19(b)

Set in the CBSE Class 12 board exam of 2023, paper 57/1/1, section B, question 19(b), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19(b) · 2 marks · Very short answerBiotechnology: Principles and Processes

Explain the process by which a bacterial cell can be made 'competent' to take up foreign DNA from its surroundings, using divalent cations and temperature treatment.

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

Hints

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

Hint 1

Which divalent cation is commonly used to treat bacteria?

Hint 2

Think of a cold–hot–cold temperature sequence.

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. DNA is hydrophilic and cannot pass through the cell membrane on its own, so bacterial cells must first be made competent.

  2. The bacterial cells are treated with a specific concentration of a divalent cation such as **calcium ()**.

    ½ mark

  3. This treatment increases the efficiency with which DNA enters the bacterium through pores in its cell wall.

    ½ mark

  4. The recombinant DNA is then forced into the cells by incubating the cells with the DNA on ice.

    ½ mark

  5. The cells are then given a brief **heat shock at ** and placed back on ice, which allows the cells to take up the DNA.

    ½ mark

Answer: Treat cells with Ca²⁺ (raises DNA entry through wall pores) → incubate with rDNA on ice → heat shock at 42 °C → back on ice

Where the marks are

  • Treatment with a specific concentration of Ca²⁺ (½ mark)
  • Increases DNA entry through cell wall pores (½ mark)
  • Incubation with rDNA on ice (½ mark)
  • Heat shock at 42 °C, then back on ice (½ 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 paper2023 board paper, set 57/1/1: 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.