Final answer:
ATP is used by cells to meet unusually high energy demands, functioning as the primary energy currency for a variety of cellular processes. The body keeps energy stores like glycogen that can be converted into ATP in times of need.
Step-by-step explanation:
In the context of biology and specifically bioenergetics, the compound only used when energy demands are unusually high is adenosine triphosphate (ATP). ATP serves as the primary energy currency of the cell and is used for cellular processes requiring immediate energy, such as anabolism, active transport, cell division, and other endergonic processes. When energy requirements are increased, cells will rapidly consume ATP to meet these needs. The body typically stores energy in other forms, such as glycogen, and these reserves can be mobilized to produce ATP when needed, particularly in times of stress or high energy demand. Moreover, while biofuels could theoretically be used to generate electricity, the rarity and value of renewable liquid fuels preclude their use for such applications.