Final answer:
Heart cells have more mitochondria than sperm cells because they have higher energy demands and metabolic rates to support continuous blood pumping, unlike sperm cells that rely more on glycolysis for energy.
Step-by-step explanation:
Heart cells, also known as cardiac muscle cells, have more mitochondria when compared to sperm cells because they require significantly more energy to support their functions. The heart is essentially a muscle that must work continuously to pump blood throughout the body, necessitating a high metabolic rate and robust energy production. This energy is largely supplied in the form of adenosine triphosphate (ATP), which is synthesized within the mitochondria through a process called cellular respiration. In contrast, while sperm cells also need energy to propel themselves, they rely heavily on glycolysis, which occurs in the cytosol and does not require as many mitochondria for ATP production.