Final answer:
Immunoglobulins have antigen-binding sites on their Fab regions, with the number and arrangement varying between antibody classes. IgM has ten binding sites due to its pentameric structure, while IgG has two. Affinities for antigen binding can also differ among antibody classes.
Step-by-step explanation:
Immunoglobulins, also known as antibodies, have antigen-binding sites on their Fab regions. The number and arrangement of these binding sites differ depending on the antibody class. For example, IgM has ten identical antigen-binding sites due to its pentameric structure, making it efficient for binding to many bacterial surfaces and promoting complement activation, opsonization, and cell lysis. IgG, on the other hand, has two Fab sites for binding to antigens. Additionally, affinities for antigen binding can also vary between different classes of antibodies.