Immunity NEET 2026: Secondary Lymphoid Organs Explained

Which organs are secondary lymphoid organs in the immunity NEET 2026 question?

The immunity NEET 2026 answer is B: (b) tonsils and (c) spleen only. Select the pair consisting entirely of secondary lymphoid organs from the four structures listed below.

The answer choices are:

Source: NEET 2026, held on 21 June 2026, Code-50. The question bank classifies its difficulty as medium; this is not an official NEET difficulty rating. All four organs participate in immunity, but the classification depends on lymphocyte development versus antigen-driven response.

What NCERT rule gives answer B?

B: tonsils and spleen. The supplied official solution follows the Immunity section of NCERT Class 12 Biology, Human Health and Disease, identified there as Chapter 8. It separates organs where lymphocytes develop from organs where mature lymphocytes encounter antigens and mount responses.

Step 1: classify by function before checking the choices.

• Primary lymphoid organs: immature lymphocytes differentiate into antigen-sensitive lymphocytes here. Bone marrow and thymus belong to this group.
• Secondary lymphoid organs: mature lymphocytes interact with antigens, proliferate and mount immune responses here. The supplied examples are spleen, lymph nodes, tonsils and Peyer’s patches.

“Antigen-sensitive” does not mean that an antigen-driven immune response has already occurred. It describes the ability acquired during lymphocyte development.

“Helps in immunity” is too broad a test. Classify by the organ’s role in lymphocyte development or antigen-driven response, not merely by whether it participates in immunity.

How do all four organs and answer choices classify?

Bone marrow and thymus are primary; tonsils and spleen are secondary. Classify every listed organ first, rather than accepting a pair because one member is correct.

Step 2: assign each organ its category and functional reason.

Step 3: collect only the secondary entries. These are (b) and (c). Exclude bone marrow and thymus because their defining roles here concern lymphocyte development and maturation.

Step 4: test every answer choice.

• A, (a) and (b): primary plus secondary. Reject.
• B, (b) and (c): secondary plus secondary. Accept.
• C, (b) and (d): secondary plus primary. Reject.
• D, (a) and (d): primary plus primary. Reject.

Both members must satisfy the classification, not just one. Only B contains two secondary lymphoid organs.

Why is option A wrong if bone marrow produces immune cells?

Option A fails because production is not the same as antigen-driven response. The faulty inference is: “Bone marrow produces immune cells, so it must be a secondary lymphoid organ.” Both categories participate in immunity, so participation alone cannot distinguish them.

This mistake creates A by correctly retaining tonsils but incorrectly admitting bone marrow to the secondary group. Instead, ask where lymphocytes develop versus where mature lymphocytes encounter antigens and mount responses.

Under the supplied marking scheme, A earns minus one mark and B earns four marks. Correcting A to B changes the score by:

That is a five-mark improvement, not a five-mark question. For revision, pair each organ name with its function, as in NEET Biology Preparation: NCERT, Recall and Revision.

Can you apply the same rule to three related immunity questions?

Apply the development-versus-response rule to each organ, including names not listed in the original question. These are original NCERT-based practice questions, not additional verified NEET PYQs.

Question 1: Which pair contains only primary lymphoid organs?

Worked answer: A. Bone marrow supports lymphocyte formation and B-cell maturation; thymus supports T-cell maturation. Both therefore belong to the primary group.

Question 2: Which listed structure is not a secondary lymphoid organ?

Worked answer: C. The word “not” asks for the organ outside the secondary group.

• Peyer’s patches: secondary, supporting antigen interaction and immune responses.
• Lymph nodes: secondary, where mature lymphocytes interact with antigens.
• Thymus: primary, supporting T-cell maturation.
• Spleen: secondary, supporting antigen interaction and immune responses.

Question 3: Mature lymphocytes encounter an antigen, proliferate and initiate an immune response. Does this describe primary or secondary lymphoid organs?

Worked answer: secondary. The lymphocytes have already matured before the stated events begin. Antigen interaction, proliferation and response identify the secondary-organ role, not primary-organ maturation.

Now cover the answers and classify all six names: bone marrow, thymus, tonsils, spleen, lymph nodes and Peyer’s patches. Give a functional reason for each before checking your classification.

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