In principle, just about all substances diffuse, with a variation of rates. Diffusion is the process in which the particles are uniformly distributed or at equilibrium, and the process of random movement toward a state of equilibrium. In diffusion, motions are uniquely at random can produce a net mevement-always a direction from a diffusion of water from high concentration to low concentration through a selectively permeable membrane. This process of diffusion of water is a passive process, meaning without any use of energy. Diffusion is imperative for the distribution of ion and other solutes within a cell. Small molecules and ions may move from one end of an organelle to another in a fraction of a millisecond, or from the center of a cell to its surface almost as fast. There are two types of diffusion across the membrane barrier:.
OSMOSIS:.
It depends on concentration of solutes in an aqueous solution on the two sides seperated by a membrane. Solute concentration is related to osmotic pressure. Greater the solute concentration, greater the osmotic pressure, and greater the tendency to absorb water.
Hyperosmotic Solution (hypertonic):.
A solution with a higher concentration of solutes.
Hypoosmotic Solution (hypotonic):.
The solution with lower solute concentration.
Isosmotic Solution (isotonic):.
The solutions containing equal concentrations of solutes.
FACILITATED DIFFUSION:.
Utilizes membrane protein to allow charged molecules to freely diffuse in and out of the cell. The channels come into greatest use with small ions like K+, Na+, Cl-. The speed of facilitated transport is limited by the number of protein channels available, whereas the speed of diffusion is dependent only on the concentration gradient. Facilitated Diffusion: Carrier Proteins and Ion Channels.
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Glucose, sodium ions and choride ions are just a few examples of molecules and ions that must efficently get across the plasma membrane but to which the lipid bilayer of the membrane is virtually impermiable.
