16. Synthesis is the process when atoms or molecules combine to form a larger, more complex molecule. This reaction can be seen as A+B->AB. Synthesis reactions are the basis of constructive, or anabolic activities in body cells. A decomposition reaction occurs when a molecule is broken down into smaller molecules or its constituent aoms, AB-> A+B. These reactions are reverse synthesis reactions and bonds are broken. They underlie all degradative, or catabolic, processes that occur in body cells. Exchange reactions involve both synthesis and decomposition; bonds are both made and broken. In these reactions, part of the reactant molecules change partners to produce different product molecules: AB+C->AC+B. An exchange reaction occurs when ATP reacts with glucose and transfers its end phosphate group to glucose, forming glucose-phosphate. Then the ATP becomes ADP. Oxidation reduction reacts are also very important. They are decomposition reactions in that they are the basis of all reactions in which food fuels are catabolized for energy. Electrons are exchanged between the reactants. The reactant losing the electron is said to be oxidized and the reactant taking up the transferred electrons is said to become reduced. These reactions mostly occur when ionic compounds are formed.