Reasoning:

* Energy Demand: Cardiac cells are responsible for continuous, rhythmic contractions of the heart, which require a massive amount of energy. Mitochondria are the powerhouses of the cell, producing ATP (adenosine triphosphate), the primary energy currency.

* Oxygen Consumption: Cardiac cells have a high oxygen consumption rate to fuel their energy production. Mitochondria are the sites of oxidative phosphorylation, the process that utilizes oxygen to generate ATP.

* Metabolic Activity: Cardiac cells have a high metabolic rate, requiring a large number of mitochondria to support their energy demands.

Skin cells, on the other hand, have relatively lower energy demands compared to cardiac cells. Their primary functions include protection, barrier formation, and regeneration. While they still require mitochondria for basic cellular processes, their energy needs are not as high as those of cardiac cells.

Therefore, the presence of a large number of mitochondria in cardiac cells is a direct reflection of their high energy demands and continuous activity.