Which of the following describes antigens and antibodies correctly?

• A. Antibodies are Y-shaped proteins produced by B-cells
• B. Antigens trigger the production of lipids by B-cells
• C. Antigens are lipid molecules that anchor to membranes
• D. Antigens are foreign molecules triggering an immune response; antibodies are Y-shaped proteins produced by B-cells that bind specifically to antigens

Answer: (D)

Antigen recognition by antibodies centers on two linked ideas: antigens are foreign molecules that trigger an immune response, and antibodies are Y-shaped proteins produced by B cells that bind specifically to those antigens. The best description combines both parts, because it explains not only what starts the immune response, but also how antibodies target the exact invader. Antigens can be proteins, sugars, lipids, or other foreign substances, and when they’re detected, B cells become plasma cells that secrete antibodies tailored to that specific antigen. This binding can neutralize the threat directly or mark it for attack by other immune components. The other statements fall short because one mentions antibodies without the triggering antigen, another wrongly says antigens induce lipid production by B cells, and another incorrectly defines antigens as lipid molecules anchored to membranes. So the description that includes both the triggering foreign molecule and the antibody’s specific binding to that molecule best captures how this system works.