Transport Across the Membrane. ^__^

Diffusion and Facilitated Diffusion.

Hydrophobic small and uncharged could pass through a membrane, but larger ones has more difficulty.

Simple Diffusion: Where molecules diffuse across the lipid bilayer through channel proteins in the direction of their concentration gradient.

Facilitated Diffusion: Where protein carrier molecules within the membrane assist the passage of substances across the membrane in the direction of the concentration gradient.

All methods above are passive, which means no cellular energy is required.

Concentration Gradient means that stuff from areas where there a lot goes into the areas where there's more little. Kinda to even things out a bit.

The bigger the difference between one side of molecule, the bigger/ more dramatic the net movement. [AN: So, basically, if there's more to shift, it puts more into doing it and gets the job done quicker, right?]

Diffusion is continued until equilibrium is reached.

It is chance that it hits are protein channel in facilitated, so wit ha higher concentration/amount of ions/molecules, the higher the chance of hitting the channel.

If they can pass through the lipid bilayer they are lipid soluble.

The larger the surface area, the more diffusion that can take place.

If the temperature is higher there is more kinetic energy, so the particles move quicker and there is more collisions. (Link this to before paragraph.)

Steepness of concentration gradient also affects it. If it is lower, diffusion will be less strong/quicker.

The membrane thickness affects the rate of diffusion too. The thicker the membrane, the longer it takes, as there's more to travel through.

Fick's Law states that the Rate Of Diffusion = (Surface Area x Steepness of Concentration Gradient) / Thickness of Membrane.

In facilitated diffusion there are CARRIER MOLECULES involved. When carier molecules have reached their limit, they can't transport any more. Eg, like only being able to fit two kids in a double buggy. Unless you take one out, only then can another take it's place.


Thoughts & Additions?
-Nin. ^_^