What does it mean when an ecosystem is recolonized?

To colonize is when is the process in biology by which a species spreads to new areas so if something is recolonized it would be live if birds migrate and then return and re take over where they lived before  

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.