16. A synthesis reaction is when atoms or molecules combine to form a larger more complex molecule. A synthesis reaction always involves bond formations and can be represented as A+B=AB. A decomposition reaction occurs when a molecule is broken down into smaller molecules or its constituent atoms A decomp reaction would look like AB=A+B. Exchange or displacement reactions involve both synthesis and decomposition as bonds are both made and broken. It would look like AB+C=AC+B or AB+CD=AD+CB. Oxidation reduction reactions (redox) are the basis of all reactions in which food fuels are catabolized for energy. The reactant losing the electrons is said to be oxidized.
17. Chemical reactions in the body are often irreversible because once a reaction has occurred the state of the reaction usually goes into chemical equilibrium which means that there is no further net change between the reactants and the products so molecules are still broken down but the results remain unchanged.
18. Water and salts are important to body homeostasis because they assist in maintaining it. Some of the properties that make water vital are high heat capacity, high heat of vaporization, polar solvent properties, reactivity and cushioning. Salts are important because when they dissolve into water, they dissociate into their component ions.