In which part of animals does glycogen primarily store energy?

Glycogen primarily stores energy in the liver, making it a central site for energy regulation in animals. The liver acts as a key player in maintaining blood glucose levels, especially during fasting or intense exercise. When the body's glucose levels drop, the liver can break down glycogen into glucose and release it into the bloodstream, ensuring a continuous supply of energy for cells.

While muscles also store glycogen, they do so primarily for local energy use during physical activity. Muscle glycogen is utilized during exercise and is not as readily released into the bloodstream as liver glycogen. The heart, although it requires energy, mainly relies on fatty acids and does not serve as a significant storage site for glycogen. The brain, while highly active and requiring glucose, does not store glycogen; instead, it uses glucose from the blood as its primary energy source.

Overall, the liver is essential for storing and regulating glycogen, making it the primary tissue for energy storage in animals.