Answer: Secondary.
- A Primary
- B Central
- C Secondary
- D Embryonic
Correct answer: C. Secondary
Explanation: Secondary lymphoid organs (spleen, lymph nodes, tonsils, MALT) are sites where mature lymphocytes encounter antigens.
An antibody is Y-shaped, with two identical antigen-binding sites at the tips of the variable regions - each shaped to recognise one specific antigen - while the constant (Fc) region at the base is recognised by immune cells to trigger further responses.
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.