The mode of action of an enzyme is:

Options

A. Decreasing potential energy
B. Increasing activation energy
C. Increasing kinetic energy
D. Decreasing activation energy

Answer

To solve the question regarding the mode of action of an enzyme, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Enzymes**: Enzymes are biological catalysts that speed up chemical reactions in living organisms. They lower the energy barrier for reactions, allowing them to occur more easily and quickly.

2. **Activation Energy Concept**: Activation energy is the minimum energy required for a reaction to occur. It is a crucial concept in understanding how enzymes function.

3. **Graphical Representation**: To visualize the effect of enzymes, we can plot a graph with the x-axis representing the progress of the reaction and the y-axis representing energy levels.

4. **Without Enzyme**: In the absence of an enzyme, the activation energy required for the reaction is relatively high, as indicated by a higher peak on the graph.

5. **With Enzyme**: When an enzyme is present, it lowers the activation energy required for the reaction. This is represented by a lower peak on the graph, indicating that less energy is needed for the reaction to proceed.

6. **Conclusion**: Since enzymes decrease the activation energy required for reactions, they increase the rate of reaction. Therefore, the correct answer to the question is that the mode of action of an enzyme is to **decrease activation energy**.

### Final Answer:
The mode of action of an enzyme is **decreasing activation energy**.