Metabolism is

Options

A. Release of energy
B. Gain of energy
C. Relase or gain of energy
D. Catabolism of a reaction

Answer

### Step-by-Step Solution:

1. **Understanding Metabolism**: Metabolism refers to all the biochemical reactions that occur within a living organism to maintain life. It encompasses two main processes: catabolism and anabolism.

2. **Defining Catabolism**: Catabolism is the process where complex molecules are broken down into simpler ones. This process typically releases energy, which can be used by the organism for various functions.

3. **Defining Anabolism**: Anabolism, on the other hand, is the process of building complex molecules from simpler ones. This process requires energy input, meaning that energy is gained during this phase.

4. **Energy Dynamics**: In metabolism, you have both the release of energy during catabolic reactions and the gain of energy during anabolic reactions. This dual nature of metabolism is essential for maintaining the energy balance within an organism.

5. **Evaluating the Options**:
- Option A (Release of energy) only covers catabolism.
- Option B (Gain of energy) only covers anabolism.
- Option C (Release or gain of energy) encompasses both catabolism and anabolism, making it the most comprehensive choice.
- Option D (Catabolism of a reaction) is too narrow as it only focuses on one aspect of metabolism.

6. **Conclusion**: Based on the definitions and the evaluation of the options, the correct answer is **Option C: Release or gain of energy**.