In a system, there is a tendency to progress to increasing disorder or entropy. Energy cannot be created or destroyed but it can be transformed to other types of energy. Therefore, if solar energy is absorbed by plants, some is stored in the chemical energy bonds of glucose and some is released as heat energy. This heat increases the entropy of the system as it dissipates. It is now unavailable to do work. As energy is transferred or transformed more and more of it is wasted resulting in a more disordered state, or increased entropy. When a substance diffuses across a membrane this occurs due to a gradient being present on either side of the membrane. One side will have a high concentration relative to the other side. Molecules move from higher to lower concentrations. The random movement of molecules will cause them to become evenly distributed on both sides of the membrane. However, originally, the highly concentrated solute had lower entropy and the randomly distributed solute after diffusion has higher entropy.