What are cristae? Give their function.

Explanation

**Step-by-Step Solution:**

1. **Definition of Cristae**: Cristae are the infoldings of the inner membrane of mitochondria. Mitochondria are double membrane-bound organelles found in eukaryotic cells.

2. **Structure of Mitochondria**: Mitochondria consist of two membranes:
- The outer membrane, which is smooth and encloses the organelle.
- The inner membrane, which is highly folded into structures known as cristae.

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