The main energy source for cellular processes is adenosine triphosphate (ATP). ATP serves as the primary energy carrier in living organisms, facilitating various biochemical reactions necessary for life. When cells need energy, ATP can be broken down into adenosine diphosphate (ADP) and inorganic phosphate, releasing energy that powers cellular activities such as muscle contraction, nerve impulse propagation, and metabolic processes. Cells constantly regenerate ATP from nutrients through cellular respiration, allowing them to maintain the energy balance required for growth, reproduction, and overall functioning.