Answer: IgG.
- A IgA
- B IgM
- C IgE
- D IgG
Correct answer: D. IgG
Explanation: IgG is the most abundant antibody in blood serum (~80%). It provides long-term immunity, can cross the placenta to protect the fetus, and is the main antibody of secondary immune responses.
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.