What is an antigen?

An antigen is a substance that stimulates an immune response in the body. When an antigen is recognized by the immune system, it triggers the production of antibodies, which are proteins specifically designed to bind to that antigen. This process is crucial for the immune system to identify and neutralize foreign invaders, such as bacteria, viruses, and other pathogens. The response generated by antigens forms the basis of immunity, allowing the body to remember past infections and respond more effectively if the same antigens are encountered again in the future.

The other options do not accurately describe what an antigen is. Antibodies are different molecules that are generated in response to antigens and serve to identify and eliminate them, while minerals and hormones serve distinct roles in maintaining health and regulating bodily functions, but they are not classified as antigens. Thus, the definition of an antigen as a substance that stimulates an immune response correctly encapsulates its role in immunology.