Final answer:
The immunoglobulin that binds to antigens on food, bacteria, or incompatible blood cells is IgG. It is the main antibody in blood during late primary and early secondary responses and it has the ability to clear pathogens, activate complement proteins, and cross the placenta.
Step-by-step explanation:
The immunoglobulin that primarily binds to antigens on food, bacteria, or incompatible blood cells is IgG. IgG is the main antibody found in blood and is significant for its ability to clear pathogens. It can activate complement proteins, aiding in antibacterial activities, and it is also the immunoglobulin that crosses the placenta to protect the fetus. It operates during both the late primary immune response and the early secondary immune response, thanks to class switching. Unlike IgE, which is associated with allergic responses, or IgA, which protects against respiratory and digestive pathogens primarily at mucosal sites, IgG circulates in the blood and interstitial fluids, thus making it effective against a wide range of pathogens, including those on food, bacteria, and incompatible blood cells.