Answer: Antigens.
- A Antigens
- B Antibodies
- C Hormones
- D Enzymes
Correct answer: A. Antigens
Explanation: Vaccines present antigens (from weakened/killed pathogens or their parts) so the body makes memory cells without disease.
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.