Mitochondria is a rod-shaped cell organelle with a double membrane covering.
Mitochondria are considered the 'powerhouse of the cell' as they provide the site for cellular respiration and thereby release energy.
Mitochondria synthesize respiratory enzymes that help in the generation of energy in the form of ATP along with other substances in the cell.
Adenosine triphosphate (ATP) is the energy-carrying molecule in all organisms.
Functions of ATP include transportation of different molecules across the cell membrane, supplying the energy required for muscle contraction, circulation of blood, locomotion, etc.
ATP releases energy by a process called phosphorylation, in which transferring a phosphate group into another molecule by special enzymes.
Final Answer: Energy stored in mitochondria is in the form of adenosine triphosphate.