Conversation so far:
what term describes the fluid interior of mitochondria
The fluid contained in the mitochondria is called the matrix
how many membranes do mitochondria have
Mitochondria are made of two membranes: The outer membrane and the inner membrane.
what is the purpose of the outer membrane of mitochondria.
The outer membrane covers the mitochondria and contains it like a skin.
how about the purposes of the inner membrane of the mitochondria
The inner membrane folds over many times and creates layered structures called cristae.

Question: what is the function
Self-contained rewrite: what is the function of cristae in mitochondria