In the beginning of of platelet plug formation, the chemical produced by endothelial cells at the site of injury is called .

Ahypothesis that has been tested again and again , with similar results each time may become a law , true or false

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.

Adigestive system that is a series of tubes beginning at the mouth and ending at the anus is a digestive system.