Diffusion

Diffusion is the process by which molecules spread from the region of high concentration, to the region of low concentration. When the molecules are even throughout a space it is called as EQUILIBRIUM

Concentration gradient is the difference between concentrations in a space. The process of osmosis is the diffusion of water. Water will move in direction where there is a high concentration of solute (and therefore a lower concentration of water). Osmosis and Diffusion are both the types of PASSIVE TRANSPORT - which means that, no energy is needed for the molecules to move into or out of the cell. At times, large molecules cannot cross the plasma membrane, and are "helped" across by the carrier proteins - this process is known as facilitated diffusion. Diffusion refers to the method by which the molecules mix together as a result of their kinetic energy of random motion. Consider 2 containers of gas A and B separated by a partition. The molecules of both the gases are in motion constantly and make numerous collisions with the partition. If the partition is removed, gases will mix owing to the random velocities of their molecules. In time a uniform mixture of A and B molecules will be generated in the container. The tendency toward diffusion is very strong even at room temperature because of the high molecular velocities linked with the thermal energy of the particles. As the average kinetic energy of different types of molecules which are at thermal equilibrium is the same, then their average velocities are different. Their average diffusion rate is expected to depend upon that average velocity, which gives the relative diffusion rate. If 2 solutions of different concentration are separated by a semi-permeable membrane which is permeable to the smaller solvent molecules but not to the larger solute molecules, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution. This process is termed as osmosis. Osmosis is of great importance in biological processes where water is the solvent. The transport of water and other molecules across the biological membranes is essential for many processes in living organisms. The energy which drives the process is commonly discussed in terms of osmotic pressure.