 Metabolic Pathways The term metabolism refers to all of the chemical reactions that are carried out by a cell. Catabolic reactions break large, complex molecules into simpler ones and usually release energy. Antibolic reactions assemble complex molecules from simpler ones and usually require the input of energy. The energy for anabolic reactions is provided by catabolic reactions. This energy can be stored in cells as ATP. Which of these processes are catabolic and which are anabolic? Nearly all organisms rely on the breakdown of glucose to provide energy to their cells. An aerobic organism uses glycosis and aerobic respiration to accomplish this. Let's drag the glucose molecule to the first metabolic pathway that is used in aerobic organisms. Now let's drag the pyruvic acid to the metabolic pathway where it will be processed in an aerob. Let's drag the NADH and FADH2 to the metabolic pathway where they will be processed in an aerob. In the presence of oxygen, aerobic metabolism includes glycosis, the Krebs cycle and the electron transport chain, resulting in an energy gain of 38 ATP per glucose. When oxygen or other electron acceptors are not available, an organism cannot do respiration. Let's click on the glucose molecule and drag it to the first pathway used by an organism that survives by fermentation. Now we'll click on the pyruvic acid and NADH and drag them to the fermentation pathway. The result is lactic acid, alcohol or other end products depending on the fermentation pathway used. Fermentation only results in a gain of 2 ATP per glucose. It does not require oxygen. You have completed this learning activity on metabolic pathways.