Define digestion.

Explanation

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

1. **Understanding Digestion**: Digestion is a biological process that involves the breakdown of food substances.

2. **Breaking Down Molecules**: The primary function of digestion is to convert large, insoluble molecules into smaller, soluble molecules. This is essential because large molecules cannot be absorbed directly into the bloodstream.

3. **Role of Water**: The smaller molecules must be water-soluble to be absorbed effectively. This solubility allows them to mix with the watery plasma of blood.

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