immunity provides general defense against a variety of pathogens, whereas immunity provides defense against specific pathogens.

Animal bodies (and even plant bodies for that matter) are complex enough that life couldn't exist without enzymes. enzymes are usually large, complex biological catalysts that are expensive to make. enzymes speed up the rate of chemical reactions without being used up during the reaction (they can be reused many times). they are highly specific in the reactions they regulate. knowing what enzymes are and how they function, why does this explain why complex life forms could not exist if there were no enzymes.

The influenza virus cause the flu, but not other diseases. why?

Many animals cannot sweat to maintain a stable body temperature. what is one other way animals can cool down?