Define metabolism.

Explanation

**Step-by-Step Text Solution:**

1. **Definition of Metabolism**: Metabolism is defined as the sum total of all the biochemical processes that occur within a living organism. It encompasses all the chemical reactions that sustain life.

2. **Types of Metabolism**: Metabolism can be divided into two main categories:
- **Anabolic Processes**: These are the processes that involve the building up or synthesis of complex molecules from simpler ones. Anabolic processes require energy and are essential for growth, repair, and maintenance of cells and tissues.
- **Catabolic Processes**: These processes involve the breakdown of complex molecules into simpler ones, releasing energy in the process. Catabolic reactions are crucial for providing the energy needed for various cellular activities.

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