You would expect to find more mitochondria in a heart cell than in a skin cell. Heart cells, or cardiomyocytes, have a high demand for energy because they are continuously contracting to pump blood throughout the body. This high energy requirement necessitates a greater number of mitochondria to produce ATP, the primary energy currency of the cell, through aerobic respiration.
In contrast, skin cells generally have a lower energy demand compared to heart cells. Although they do contain mitochondria to support their metabolic needs, the quantity is significantly less than that found in heart cells.
Therefore, the density of mitochondria in heart cells reflects their role in sustaining high levels of activity and energy output, whereas skin cells do not require the same level of energy and, consequently, have fewer mitochondria.