Answer: Primary.
- A Secondary
- B Primary
- C Tertiary
- D Accessory
Correct answer: B. Primary
Explanation: The primary (central) lymphoid organs - bone marrow and thymus - are where lymphocytes are produced and mature.
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.