Define metabolism.

Explanation

**Step-by-Step Solution:**

1. **Definition of Metabolism**: Metabolism refers to all the chemical reactions that occur within an organism to maintain its living state. It encompasses processes that convert food into energy and the building blocks necessary for growth and repair.

2. **Categories of Metabolism**: Metabolism can be divided into two main categories:
- **Catabolism**: This is the process of breaking down complex molecules into simpler ones. It releases energy that the organism can use. An example of a catabolic process is glycolysis, where glucose is broken down to produce energy.
- **Anabolism**: This involves the synthesis of complex molecules from simpler ones. It requires energy, which is often derived from catabolic processes. Examples include the synthesis of carbohydrates and nucleic acids.

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