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Explain the role of… (Class 12 Biology SQP 2023-24, Q33a)

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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(a)

From the official CBSE sample question paper for 2023-24, 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

Explain the role of Primary and Secondary Lymphoid organs with the help of suitable examples.

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

Sort the organs into two groups: those where lymphocytes are made or mature, and those where they meet antigens.

Hint 2

The primary group has two members, one in bones and one near the heart.

Hint 3

For the secondary group, recall the spleen, lymph nodes, Peyer's patches and the tissue lining the body's tracts.

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. Lymphoid organs are organs in which lymphocytes originate and/or mature and proliferate.

    ½ mark

  2. Primary lymphoid organs are the bone marrow and the thymus. In these organs, immature lymphocytes differentiate into antigen-sensitive lymphocytes.

    ½ mark

  3. The bone marrow is the main lymphoid organ. All blood cells, including lymphocytes, are produced here, and B-lymphocytes mature here.

    ½ mark

  4. The thymus is a lobed organ lying near the heart, beneath the breastbone. It provides the micro-environment for maturation of T-lymphocytes. It is large at birth and shrinks with age.

    ½ mark

  5. After maturation, lymphocytes migrate to the secondary lymphoid organs. Examples are the spleen, lymph nodes, tonsils, Peyer's patches of the small intestine and the appendix.

    ½ mark

  6. Secondary lymphoid organs are the sites where lymphocytes interact with antigens. The lymphocytes then proliferate to become effector cells.

    ½ mark

  7. The spleen is a large bean-shaped organ containing mainly lymphocytes and phagocytes. It filters the blood by trapping blood-borne microorganisms, and it also stores a large reservoir of erythrocytes.

    ½ mark

  8. Lymph nodes are small solid structures found at intervals along the lymphatic system. They trap microorganisms and other antigens that enter the lymph and tissue fluid.

    ½ mark

  9. Antigens trapped in lymph nodes activate the lymphocytes present there, which triggers the immune response.

    ½ mark

  10. MALT (mucosa-associated lymphoid tissue) lines the respiratory, digestive and urogenital tracts. It makes up about 50% of the body's lymphoid tissue.

    ½ mark

Answer: Primary lymphoid organs (bone marrow, thymus) are where lymphocytes are formed and mature into antigen-sensitive cells. Secondary lymphoid organs (spleen, lymph nodes, tonsils, Peyer's patches, appendix, MALT) are where lymphocytes meet antigens and proliferate into effector cells.

Where the marks are

  • Definition of lymphoid organs (0.5 mark)
  • Primary organs named with their role in differentiation (0.5 mark)
  • Bone marrow role (0.5 mark)
  • Thymus location and role (0.5 mark)
  • Secondary organs named (0.5 mark)
  • Role of secondary organs: antigen interaction and proliferation (0.5 mark)
  • Spleen structure and function (0.5 mark)
  • Lymph nodes trap antigens (0.5 mark)
  • Activation of lymphocytes in lymph nodes (0.5 mark)
  • MALT, about 50% of lymphoid tissue (0.5 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.