Anabolism is the building up aspect of metabolism. During anabolism, biochemical pathways assemble complex organic molecules from simpler ones. The breaking down aspect of metabolism, catabolism, involves processes by which living things extract energy from food. Reactions in metabolic pathways involve energy. All energy utilized by living things originates with sunlight. Green plants convert the sun's radiant energy into chemical energy during the process of photosynthesis, and store it initially in the bonds of glucose. When the cells of living things need energy, the process of cellular respiration transfers energy from the bonds of glucose to the bonds of adenosine triphosphate (ATP). The energy in ATP is then available for work by the cell. Photosynthesis is an anabolic process that builds up glucose from carbon dioxide and water and gives off oxygen. Cellular respiration is a catabolic process that breaks down glucose and gives off carbon dioxide and...