Final answer:
Muscle cells have a high concentration of mitochondria due to their significant need for ATP, which mitochondria produce through the process of cellular respiration.
Step-by-step explanation:
Muscle cells contain numerous mitochondria because of their high metabolism of ATP. This is especially true in cells that require significant amounts of energy, such as the leg muscles of a marathon runner. Mitochondria, referred to as the "powerhouses" or "energy factories" of the cell, are responsible for producing adenosine triphosphate (ATP), which is vital for cellular processes such as muscle contraction.
In the context of high energy requirements, such as in muscle cells, the number of mitochondria correspond to the energy demands of the cell. Consequently, muscle cells will have a high concentration of mitochondria to meet these energy requirements efficiently through the process known as cellular respiration.