Question

which of the following best defines an antigen?
a protein that destroys pathogens
an antibody receptor
a cell that engulfs microbes
a molecule that triggers an immune response
question 4 (1 point)
which immunoglobulin is typically the first to appear during a primary immune response?
igm
igd
iga
igg

Explanation:

• For the first question: An antigen is a molecule that triggers an immune response. Antibodies (not antigens) are proteins that can act against pathogens. An antigen is not a cell that engulfs microbes (that would be a phagocyte like a macrophage). And while antibodies bind to antigens, an antigen is not an "antibody receptor" in the typical sense of the definition.
• For the second question: During a primary immune response, IgM (immunoglobulin M) is typically the first immunoglobulin to appear. IgD has a less - well - defined role in the primary immune response. IgA is more involved in mucosal immunity (e.g., in the gut and respiratory tract secretions). IgG is more prominent in secondary immune responses.

Answer:

• First question: A molecule that triggers an immune response
• Second question: IgM