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(i) Name and explain the… (Class 12 Biology 2024, Q33a)

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BiologyCBSE Class 12 · Board exam 2024, set 57/1/1 · 5 marks · Long answer

CBSE Class 12 Biology 2024: question 33(a)

Set in the CBSE Class 12 board exam of 2024, paper 57/1/1, section E, question 33(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

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

(i) Name and explain the property present in normal cells but is lost in cancer cells. (1½)
(ii) All normal human cells have genes that may become cancerous under certain conditions. Name them and explain how. (1)
(iii) State the role of the following techniques in detection and diagnosis of cancer :
(1) Biopsy and Histopathology (1)
(2) Magnetic Resonance Imaging (1½)

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 57/1/1.

Hints

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

Hint 1

Think about what normally happens when a dividing cell touches its neighbours.

Hint 2

The genes in (ii) are the normal cellular counterparts of viral oncogenes.

Hint 3

For MRI, recall what kind of field and radiation it uses, and how that differs from X-rays.

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) The property is contact inhibition.

    ½ mark

  2. (i) In normal cells, contact with neighbouring cells inhibits further uncontrolled growth and division. Cancer cells have lost this property, so they keep dividing and form masses of cells called tumours.

    1 mark

  3. (ii) These genes are cellular oncogenes (c-onc), also called proto-oncogenes.

    ½ mark

  4. (ii) When they are activated under certain conditions, for example by mutation caused by carcinogens or by oncogenic viruses, they cause oncogenic transformation of the cells, which then become cancerous.

    ½ mark

  5. (iii)(1) Biopsy and histopathology: a piece of the suspected tissue is cut into thin sections, stained, and examined under a microscope by a pathologist. Abnormal, increased cell numbers or growth confirm cancer.

    1 mark

  6. (iii)(2) MRI: it detects cancers of internal organs. It uses strong magnetic fields and non-ionising radiations to accurately detect pathological and physiological changes in living tissue.

    1½ marks

Answer: (i) Contact inhibition, which is lost in cancer cells, so they divide uncontrollably and form tumours.
(ii) Proto-oncogenes (cellular oncogenes); when activated (for example by mutation or carcinogens) they cause oncogenic transformation.
(iii)(1) Biopsy and histopathology: stained thin sections of the suspected tissue are examined microscopically for abnormal cell growth.
(iii)(2) MRI: uses strong magnetic fields and non-ionising radiation to detect changes in internal organs and tissues.

Where the marks are

  • (i) Names contact inhibition (½ mark)
  • (i) Explains that cell contact stops uncontrolled growth in normal cells and that this is lost in cancer cells (1 mark)
  • (ii) Names proto-oncogenes / cellular oncogenes (½ mark)
  • (ii) States that activation under certain conditions causes oncogenic transformation (½ mark)
  • (iii)(1) Thin, stained tissue sections examined under a microscope by a pathologist (1 mark)
  • (iii)(2) Detects cancer of internal organs (½ mark) using strong magnetic fields and non-ionising radiation to detect pathological and physiological changes (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 paper2024 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.