Answer:
With the help of cellular respiration, the mitochondria produced energy-rich compound ATP (adenosine triphosphate).
The ATP molecule holds the energy in the form of its phosphate bonds.
This energy is released by hydrolysis of ATP which results in the formation of ADP (adenosine diphosphate).
Sometimes, the ADP is further hydrolyzed to produce more energy. It results in the production of AMP (adenosine monophosphate).
The energy released from ATP hydrolysis is in the form of heat which is coupled with all the cellular activities like cellular transportation, repair, replication, apoptosis et cetera.