diffusion& osmosis

diffusion is the movement of molecules from high concentration gradient to low concentration gradient without the requirement of energy until the even distribution.

osmosis is the net movement of water molecules from high water potential to low water potential through the permeable membrane without the requirement of energy until egual water potential.

Diffusion可以係普通d gas都得,eg:放屁d味由high concentration到low concentration.
而 Osmosis只係water potential,個水net movement經過d permeable membrane

兩者不需要energy

隨此之外,仲有active transport
active transport is movement of molecules from low concentration gradient to high concentration gradient with the need of energy through the selectively membrane.

diffusion個陣係會消秏particles的kinetic energy(internal energy)...

Diffusion
Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion. Consider two containers of gas A and B separated by a partition. The molecules of both gases are in constant motion and make numerous collisions with the partition. If the partition is removed as in the lower illustration, the gases will mix because of the random velocities of their molecules. In time a uniform mixture of A and B molecules will be produced in the container.

Diffusion is the net action of matter (particles or molecules), heat, momentum, or light whose end is to minimize a concentration gradient. The process of diffusion, therefore, minimizes thermodynamic Gibbs free energy (though, it is not a chemical reaction), and is thus a spontaneous process (more familiarly known as a "passive" form of transport, rather than "active").

The different forms of diffusion can be modeled quantitatively using the diffusion equation, which goes by different names depending on the physical situation. For instance - steady-state bi-molecular diffusion is governed by Fick's law, steady-state thermal diffusion is governed by Fourier's law. The diffusion of electrons in an electrical field leads essentially to Ohm's law that is further explained by Einstein relation. The generic diffusion equation is time dependent, and as such applies to non-steady-state situations as well.

Diffusion can be measured, by the means of concentration gradient. A concentration gradient is the difference between the high concentration and the low concentration. It also determines how fast diffusion occurs.


Osmosis
If two solutions of different concentration are separated by a semi-permeable membrane which is permeable to 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 called osmosis.

Osmosis is of great importance in biological processes where the solvent is water. The transport of water and other molecules across biological membranes is essential to many processes in living organisms. The energy which drives the process is usually discussed in terms of osmotic pressure.
Osmotic Pressure
Osmosis is a selective diffusion process driven by the internal energy of the solvent molecules. It is convenient to express the available energy per unit volume in terms of "osmotic pressure". It is customary to express this tendency toward solvent transport in pressure units relative to the pure solvent.

If pure water were on both sides of the membrane, the osmotic pressure difference would be zero. But if normal human blood were on the right side of the membrane, the osmotic pressure would be about seven atmospheres! This illustrates how potent the influence of osmotic pressure is for membrane transport in living organisms.

The decision about which side of the membrane to call "high" osmotic pressure is a troublesome one. The choice made here is the opposite of that made in many biology texts, which attribute "high" osmotic pressure to the solution and zero osmotic pressure to pure water. The rationale for the choice is that the energy which drives the fluid transfer is the thermal energy of the water molecules, and that energy density is higher in the pure solvent since there are more water molecules. The thermal energy of the solute molecules does not contribute to transport, presuming that the membrane is impermeable to them. The choice is also influenced by the observed direction of fluid movement, since under this choice the fluid transport is from high "pressure" to low, congruent with normal fluid flow through pipes from high pressure to low.

diffusion & osmosis 都係 passive transport 唔洗energy

osmosos 係 water pass through a region of high concentration to a region of low concentration with selectively permerable membrane 先得

diffusion only係 substance pass through a region of high concentration to a region of low concentration 唔洗一定係水 同埋唔洗 with selectively permerable membrane

osmosis係一定要有水先得ge~~而diffuision就唔只係水~air都得~~