A solute is any molecule which is dissolved in a solvent such as water. A solution containing the same solute concentration as the cell is called isotonic, solutions with solute concentrations higher than and lower than that found in the cell are called hypertonic and hypotonic solutions, respectively. The movement of molecules which are unable to cross the plasma membrane by diffusion is dependent on membrane transport proteins, each type of membrane has its own characteristic proteins. Main difference between these two is the way they discriminate solutes. Active Transport Energy is required to move molecules against their concentration gradient.
Reactions proceed in the body according to the energy difference between reactants and products.
When the products store less energy than the reactants, energy is released, these are called exergonic reactions, they occur spontaneously. When the products store more energy than the reactants, outside energy is required for the reaction to proceed, this is an endergonic reaction. In the body, endergonic reactions must be coupled with exergonic reactions. If activation energy did not exist, our components would spontaneously break down into simpler molecules and we would all burst into flames. Proteins called enzymes lower the amount of energy needed to overcome the energy barrier preventing the exergonic reactions from occurring.