In the human body, for example, most cells contain mitochondria because they allow for the synthesis of ATP (energy) fueled by the breaking down of sugars (glucose).
Some cells, such as red blood cells, contain zero mitochondria because it is not necessarily beneficial or efficient for them to have any.
In contrast, muscle cells contain more mitochondria than other body cells because more energy is needed for muscles to function, especially during vigorous aerobic and anaerobic activities.
