<span>A scientific theory is NOT a wild guess. It must be consistent with known experimental results and it must have predictive power. As new knowledge is gained, theories are refined to better explain the data. A law is a mathematical relationship that is consistently found to be true.</span>
Enzymes will make chemical reactions go faster.
Enzymes are a type of catalyst that will cause the activation energy of a chemical reaction to go lower.
Activation energy is the key substance that is needed to get a reaction going. By lowering the amount of energy needed to start a reaction, the reaction can go more quickly.
I would say the the circulatory system because blood flows throught your body