Cellular energy refers to the energy produced and used by cells to perform various functions necessary for life. This energy is primarily generated through a process called cellular respiration, where cells convert nutrients, like glucose, into adenosine triphosphate (ATP), the main energy currency of the cell. In addition to cellular respiration, some cells can also produce energy through photosynthesis, a process used by plants and certain microorganisms to convert sunlight into chemical energy. Both processes are essential for maintaining cellular activities, growth, and overall organism health.