The main currency of energy in biological systems is ATP, or adenosine triphosphate. ATP is a high-energy molecule that stores and transports energy within cells, fueling various biochemical reactions essential for life. It is produced mainly through cellular respiration and photosynthesis, allowing organisms to harness energy from nutrients and sunlight. ATP consists of adenine, ribose, and three phosphate groups; the energy is released when one of the phosphate bonds is broken. This energy powers cellular processes like muscle contraction, active transport, and biosynthesis, making ATP crucial for life.