Answer: Histamine.
- A Insulin
- B Thyroxine
- C Adrenaline
- D Histamine
Correct answer: D. Histamine
Explanation: On allergen contact, mast cells release histamine, causing sneezing, itching, swelling and other allergy symptoms.
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.