The enzymes remain unchanged at the end of the reaction.

Answer

### Step-by-Step Solution:

1. **Understanding Enzymes**: Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are typically proteins that facilitate reactions without being consumed in the process.

2. **Role of Enzymes in Reactions**: Enzymes work by lowering the activation energy required for a reaction to occur. This means that they allow reactions to happen more quickly and efficiently.

3. **Formation of Enzyme-Substrate Complex**: When an enzyme interacts with its substrate (the substance upon which an enzyme acts), it forms an enzyme-substrate complex. This complex is a temporary structure that allows the reaction to take place.

4. **Catalysis Process**: During the reaction, the enzyme helps to convert the substrate into products. This involves the enzyme changing the substrate's structure, which facilitates the chemical reaction.

5. **Regeneration of the Enzyme**: After the reaction has occurred, the enzyme releases the product and returns to its original state. This is crucial because it means that the enzyme can be used repeatedly for multiple reactions.

6. **Conclusion**: Since enzymes are not consumed in the reaction and return to their original form, they remain unchanged at the end of the reaction. This characteristic is essential for their role in biological systems, allowing them to catalyze numerous reactions without being depleted.