Describe what an enzyme is and how it works according to the lock and key model

The Lock and Key Analogy of Enzymes and Substrates: Enzymes act as a catalyst in a given chemical reaction (for example, lactase allows lactose to break down into Glucose and Galactose); enzymes lower the amount of energy required to make a reaction occur. There is a key concept to this theory: Enzymes are designed work for only one reaction; there is only one key that fits the lock perfectly. Without enzymes, our bodies wouldn't be able to handle the amount of heat the reactions that occur inside if there weren't any enzymes (or the reactions just wouldn't occur! In the Lock and Key Analogy, the substrate (Lactose in the example) is the "key".