Explanation:
Enzymes are biological catalysts. They speed up the rate of reaction (without themselves being chemically changed at the end of reactions) Enzymes only speeds up the rate of reactions they don't break down stuff
in addition, proteins are broken down in chemical reactions. enzymes being proteins of course will get broken down as well but they do not break themselves down since they never will break anything down
enzymes are needed as they lower activation energy (activation energy is often supplied in the form of heat but for some reactions to take place, the heat energy required may be too hot for a body to handle (such as a human body) this will cause negative effects to the reactants and the body. as a result, enzymes are the ones who help to reduce such happenings) and speed up rate of chemical reactions. by lowering activation energy, less heat is needed to be supplied to the reactants for them to react and hence less energy is required (aka in most cases less heat is required)
hope that gives you a better understanding on enzymes :)
