National League for Nursing (NLN PAX) Practice Exam

The substance that carries energy within cells and is produced during cellular respiration is ATP (adenosine triphosphate). During the process of cellular respiration, glucose is broken down to release energy, and this energy is then used to form ATP. ATP acts as an energy currency within the cell, providing the energy necessary for various cellular processes, including muscle contraction, nerve impulse propagation, and biochemical reactions.

While glucose is the initial fuel source that provides the energy when metabolized, it does not function as an energy carrier within the cell in the same way ATP does. Oxygen acts as an electron acceptor in the electron transport chain, but it is not directly responsible for carrying energy. Carbon dioxide is a byproduct of cellular respiration and does not carry energy, rather it is a waste product that must be expelled from the cell and ultimately the body. Thus, ATP is the correct answer, as it directly holds and transports the energy produced during cellular respiration for immediate use by the cell.