They make energy

Mitochondria are often referred to as the powerhouses of the cells. They generate the energy that our cells need to do their jobs. For example, brain cells need a lot of energy to be able to communicate with each other and also to communicate with parts of the body that may be far away, to do this substances need to be transported along the cells, which needs lots of energy. Muscle fibres also need a lot of energy to help us to move, maintain our posture and lift objects.