Mitochondria are the major site of ATP and energy production in plants and animals. Mitochondria are double-membraned organelles (like the nucleus) so are said to be surrounded by an envelope. The out...Mitochondria are the major site of ATP and energy production in plants and animals. Mitochondria are double-membraned organelles (like the nucleus) so are said to be surrounded by an envelope. The outer membrane (matrix) is very elastic, the inner is folded many times (christae) and protrudes into the internal cavity. Diagram and transmission electron micrograph of mitochondria. (Diagram by Kelvinsong, public domain; TEM Louisa Howard, Dartmouth College public domain).
