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With the help of a… (Class 12 Biology SQP 2023-24, Q33b)

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BiologyCBSE Class 12 · Sample paper, session 2023-24 · 5 marks · Long answer

CBSE Class 12 Biology sample paper 2023-24: question 33(b)

From the official CBSE sample question paper for 2023-24, section E, question 33(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q33(b) · 5 marks · Long answerHuman Health and Disease

With the help of a flow chart illustrate how an infected animal cell can survive while viruses are being replicated or released.

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

Think of a virus that has RNA as its genetic material and lives inside human macrophages.

Hint 2

Which enzyme lets this virus convert its RNA into DNA, and where does that DNA go?

Hint 3

Follow the chain from entry to integration to new virus formation to release, noting what happens to the host cell.

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. The example is a retrovirus (HIV) infecting an animal cell such as a macrophage.

    Step 1: The virus enters the animal cell, and its RNA genome is released into the cytoplasm.

    1 mark

  2. ↓

    Step 2: The viral enzyme reverse transcriptase uses the viral RNA as a template to make viral DNA.

    1 mark

  3. ↓

    Step 3: The viral DNA is incorporated into the host cell's genome.

    1 mark

  4. ↓

    Step 4: The host cell's machinery now transcribes the integrated DNA, producing new viral RNA and viral proteins. These assemble into new virus particles.

    1 mark

  5. ↓

    Step 5: New viruses are released and can infect other cells, such as helper T-lymphocytes. The infected cell itself survives while viruses are being replicated and released. A macrophage therefore acts as an 'HIV factory' that keeps producing virus.

    1 mark

Answer: Flow chart: Virus enters cell → viral RNA released → reverse transcriptase makes viral DNA → viral DNA integrates into host genome → new viral RNA and proteins form new viruses → new viruses released to infect other cells, while the infected cell (e.g. macrophage, an 'HIV factory') survives.

Where the marks are

  • Entry of retrovirus and release of viral RNA (1 mark)
  • Reverse transcriptase forms viral DNA (1 mark)
  • Viral DNA integrates into host genome (1 mark)
  • New viral RNA and particles produced (1 mark)
  • New viruses released to infect other cells while the infected cell survives, e.g. macrophage as HIV factory (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Human Health and Disease, 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.