Which molecule is primarily responsible for transferring energy within cells?

ATP, or adenosine triphosphate, is the primary energy carrier in all living cells. The structure of ATP consists of three phosphate groups, and when the terminal phosphate group is removed through hydrolysis, energy is released; this energy can then be used to fuel various cellular processes such as muscle contraction, nerve impulse propagation, and biochemical synthesis.

While other molecules like NADH and FADH2 do play important roles in cellular respiration and energy transfer, particularly in relation to the electron transport chain, their function is more about transporting electrons rather than directly providing energy for cellular processes. Glucose is a crucial energy source and is broken down to produce ATP, but it does not function as an immediate energy carrier like ATP does. Therefore, ATP is recognized as the molecule that directly delivers energy for crucial cellular functions.