Enzymes are protein-like compounds that, in small amounts, speed the rate of biological reactions. Unstable, fragile, and easily inactivated, enzymes are produced within living cells to perform specific biochemical reactions. Enzymes exist in plants as well as animals. Without them, life as we know it would not exist. Enzymes cause seeds to sprout, flowers to blossom, plants to grow, autumn leaves to change color, and fruits to ripen.