Enzymes are biological catalysts that are greatly affected by temperature. At too high a temperature, enzymes can be denatured and stop working. At a temperature that's too low, enzymes can freeze no longer work.
Each individual enzyme has its own range of temperatures in which it reacts best. If the temperature of the entire system is raised slightly but is still in the enzyme’s optimal temperature range, then the reaction will speed up. If the temperature is lowered slightly but is still in the optimal range, the reaction will slow down. This phenomenon occurs because enzymes are comprised of amino acids. Temperature causes the bonds between the amino acids either to get stronger or to break. In turn, the enzyme’s activity will be affected.