What is antigen? what does it include? what is its function?

Antigens are proteins that are found on the surface of the pathogen and are viruses, fungi, or bacteria. Nonliving substances such as toxins, chemicals, drugs, and foreign particles.  Antigens are usually carried by proteins and polysaccharides, and less frequently, lipids but it also needs to be attached to a large carrier molecule which is usually a protein.  When an antigen enters the body, the immune system produces antibodies against it. The Antigen stimulates the immune system to produce antibodies. YOUR WELCOME ;)

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.

this would be a math