Enzymes are biological catalysts that increase the rate of chemical reactions within cells. Enzymes are mostly proteins that catalyze chemical reactions by lowering the activation energy required for the reaction to occur.

Explanation:

Enzymes lower activation energy:
Activation energy is the energy required to initiate a chemical reaction. In a chemical reaction, the reactant molecules need to collide with each other with sufficient energy to overcome the energy barrier and form the product. Enzymes lower the activation energy by providing an alternate pathway for the reaction to occur. This alternate pathway requires less energy, and hence the reaction proceeds at a faster rate.

Example:
The breakdown of sucrose into glucose and fructose requires an input of energy. In the presence of the enzyme sucrase, the activation energy required for the reaction is lowered, and the reaction occurs spontaneously.

Enzymes are specific:
Enzymes are specific to the reaction they catalyze, and they bind to the reactants at a specific site called the active site. The shape of the active site is complementary to the shape of the reactant molecule, and this specificity ensures that only the correct reactants bind to the enzyme.

Example:
The enzyme lactase catalyzes the breakdown of lactose into glucose and galactose. Lactase specifically binds to the lactose molecule, and the reaction occurs at a faster rate.

Enzymes are not consumed in the reaction:
Enzymes are not consumed in the reaction, and they can be used to catalyze the same reaction repeatedly. Enzymes are not changed by the reaction, and they can be reused multiple times.

Example:
The enzyme catalase catalyzes the breakdown of hydrogen peroxide into water and oxygen. Catalase is not consumed in the reaction, and it can be used to catalyze the same reaction repeatedly.

In conclusion, enzymes increase the rate of reaction by lowering the activation energy required for the reaction to occur. This allows the reaction to occur at a faster rate.