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(i) Identify and name the… (Class 12 Biology 2023, Q19a)

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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(a)

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

Q19(a) · 2 marks · Very short answerCompetency-basedBiotechnology: Principles and Processes

(i) Identify and name the structures 'A' and 'B' marked in the image given below :
(ii) State their importance in various biotechnology experiments.

Figure in the paper: (A) a circular double-stranded DNA (plasmid); (B) a bacteriophage with polyhedral head containing DNA, tail sheath and tail fibres. See it in the official paper.

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

One structure is a small ring of DNA; the other is a virus with a head and tail.

Hint 2

What do we call the vehicles that carry a gene of interest into a host and multiply it?

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. (i) 'A' is a plasmid, an extrachromosomal, circular, double-stranded DNA found in bacteria.

    ½ mark

  2. 'B' is a bacteriophage, a virus that infects bacteria.

    ½ mark

  3. (ii) Plasmids are used as cloning vectors. They carry a foreign gene into the host cell and replicate independently of chromosomal DNA, often in high copy number. They can also carry selectable markers such as antibiotic-resistance genes.

    ½ mark

  4. Bacteriophages are also used as cloning vectors. They can replicate inside bacterial cells independently of the chromosomal DNA and reach a high copy number per cell, so the linked foreign DNA is multiplied.

    ½ mark

Answer: A – plasmid; B – bacteriophage; both act as cloning vectors that carry and multiply foreign DNA in a host

Where the marks are

  • Identifies A as plasmid (½ mark)
  • Identifies B as bacteriophage (½ mark)
  • Importance of plasmid as vector (½ mark)
  • Importance of bacteriophage as vector (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.