Plants and animals must take in and transform energy for use by cells. Plants, through photosynthesis, absorb light energy and form organic molecules such as glucose. Glucose has potential energy in the form of chemical energy stored in its bonds. This chapter covers the metabolic pathways of cellular respiration and describes the chemical reactions that use energy in glucose and other organic molecules to form adenosine triphosphate (ATP). ATP is the cell’s “energy currency” fueling virtually all energy requiring processes. The chemical reactions of cellular respiration are a series of oxidation- reduction (redox) reactions that are divided into three stages: glycolysis, the citric acid cycle and oxidative phosphorylation.