Skip to content

Some plant and animal… (Class 12 Biology SQP 2025-26, Q32A)

questionbuddy.in/q/cbse-12-biology-2025-26-sqp-q32a-some-plant-animal-pathogens-serve

BiologyCBSE Class 12 · Sample paper, session 2025-26 · 5 marks · Long answer

CBSE Class 12 Biology sample paper 2025-26: question 32(A)

From the official CBSE sample question paper for 2025-26, section E, question 32(A), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q32(A) · 5 marks · Long answerBiotechnology: Principles and Processes

Some plant and animal pathogens serve as one of the tools of recombinant DNA (rDNA) technology.'
A. Name one animal and one plant pathogen and discuss the pathogenic nature of both. State how they serve as a tool in rDNA technology.
B. What are the enzymes needed for rDNA technology?
C. A farmer owns a cotton farm land which is getting infested with coleopteran pests. He is not willing to use the microbes to protect his farm.
i. Name an alternate method to introduce the gene of interest the pathogen would have otherwise delivered and discuss how the alternate method would deliver the gene.
ii. State how this gene would control the pest.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

Which bacterium causes crown gall and which viruses can cause cancer in animals?

Hint 2

Think of 'molecular scissors' and 'molecular glue'.

Hint 3

Without a microbe, DNA can be shot into plant cells; the Bt protoxin becomes active only at a particular gut pH.

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. Animal pathogen – retroviruses: They can transform normal animal cells into cancerous cells. Plant pathogen – Agrobacterium tumefaciens: It causes crown gall disease by transferring a piece of DNA called T-DNA (from its Ti plasmid) into plant cells, turning normal cells into tumour cells.

    1 mark

  2. Use in rDNA technology: The pathogenic genes are removed, so 'disarmed' retroviruses and the disarmed Ti plasmid can no longer cause disease. They are used as cloning vectors to deliver desirable genes into animal and plant cells.

    1 mark

  3. B. The key enzymes are restriction endonucleases (molecular scissors that cut DNA at specific sites) and DNA ligase (joins the cut DNA fragments). DNA polymerase, used in PCR, is also needed.

    1 mark

  4. C(i) Biolistics (gene gun): Plant cells are bombarded with high-velocity micro-particles of gold or tungsten coated with DNA carrying the cry gene. The DNA enters the cells and integrates into the plant genome, so no microbial vector is needed.

    1 mark

  5. C(ii) The cry gene codes for the Bt toxin, made as an inactive protoxin in the plant. When the pest eats the plant, the alkaline pH of its gut converts the protoxin into the active toxin. The active toxin binds the midgut epithelial cells and creates pores, so the cells swell and lyse and the pest dies.

    1 mark

Answer: A. Retrovirus (cancer-causing) and Agrobacterium tumefaciens (crown gall via T-DNA); disarmed forms used as vectors. B. Restriction endonuclease and DNA ligase. C(i) Biolistics/gene gun – DNA-coated gold/tungsten particles; (ii) cry gene → Bt protoxin activated in alkaline gut, pores in gut epithelium, pest dies.

Where the marks are

  • Names retrovirus and Agrobacterium with their pathogenic nature (1 mark)
  • States their use as disarmed cloning vectors (1 mark)
  • Restriction enzyme and ligase (1 mark)
  • Biolistics/gene gun with gold/tungsten micro-particles (1 mark)
  • Bt toxin activated in alkaline gut, damages gut epithelium (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 2025-26: 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.