What is mitochondria

Answer 1

Martin's answer is correct. I would add that the mitochondria have their own DNA which is inherited only maternally. This fact can make testing of mitochondrial DNA a powerful tool for parentage determination.

Answer 2

This is an organelle found in in most cells, in which the biochemical processes of respiration and energy production occur.

It has a double membrane, the inner part being folded inwards to form layers.