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Metabolism is the term used for all the chemical reactions that go on inside an organism's body.

These reactions build up molecules, and break them down. They are controlled by enzymes.

In plants, here's a summary of the reactions that build up substances following photosynthesis:

In plants, here's a summary of the reactions that break down compounds:

In animals, here's a summary of the reactions that build up substances following the absorption of the products of digestion:

In animals, here's a summary of the reactions that break down compounds:

Glycogen is broken down to meet short-term demands for energy.

Longer term, lipids are broken down. Proteins may be broken down during starvation.