The products of animal and human digestion are required for the synthesis of new biomolecules, the replacement of excreted essential nutrients, and the energy (calories) for all cellular and organ functions. This chapter provides a representation of a general mammalian metabolic cell, such as a hepatocyte, which would contain the major cellular organelles and metabolic pathways. Plants generally possess much of the same metabolism that many animal cells perform and do so with an architectural array of similar organelles. Structurally, the plant cell is different from mammalian cells in possessing a rigid cell wall, glyoxysomes, vacuoles, and chloroplasts. The sum of all chemical events within a living animal or plant cell is what is referred to as metabolism. Metabolism can generally be subdivided into anabolic and catabolic metabolism. Anabolic and catabolic metabolic pathways are generally determined by their biosynthetic or degradative activity and whether ATP is consumed or generated in the process.