fluid balance

        For this to happen the concentration must be different; this is known as concentration gradient. Concentration gradient is the difference between opposing concentrations. The greater the concentration gradient, the rate of diffusion will be faster, however it will not happen instantly. This is because the numbers of molecules become more evenly distributed, but the net movement of molecules will slow down and eventually come to a stop.

The cell membrane is a very selective “molecular gatekeeper”. It contains a continuous layer of  and  molecules that act as a selective barrier to regulate the cell’s chemical composition. The passage of most dissolved substances is regulated via special protein molecules, called transport or carrier proteins, which are embedded within the thickness of the layer. The substance attaches to the carrier on one side of the membrane. In active transport, the carrier protein uses energy to “pump” the substance through the membrane against the concentration gradient, into the area of higher concentration on the other side. The energy is provided by the cell’s standard energy-carrying substance,  (ATP). This transfers its energy to the carrier protein, and is itself converted to the lower-energy form, adenosine diphosphate (ADP). Meanwhile, the carrier protein uses the energy to change its shape, or configuration, flipping the substance through the membrane and releasing it on the other side. Some substances, such as  and  ions, have their own dedicated carrier proteins and pumping mechanisms. ().

Material will also move through the body because of osmosis. The physics definition of osmosis is slow change in concentration: the diffusion of a solvent through a semi permeable membrane from a dilute to a more concentrated solution () so in a simpler term it is a net movement of water molecules through the cell membrane and then moves down the concentration gradient like diffusion.