Diffusion

Diffusion:
It is the net movement of molecules or ions from a region where they are more highly concentrated, to a region where they are less concentrated.
It occurs when there is a high concentration of molecules/ions in one place and less in another, and, through random movement, the particles spread out evenly over time, under the concentration is in equilibrium.
The factors that affect the rate of diffusion are: Concentration Gradient (The greater the difference, the faster the rate), Area over which the diffusion takes place (The larger the area of an exchange surface, the faster it can take place), and the thickness of the exchange surface (the thinner the exchange surface, the faster the rate of diffusion.)
The nature of the plasma membrane can also affect it. How many pores it has and how it is composed, etc. The size and nature of the molecule diffusing affects it too. Smaller ones go through quicker, and lipid soluble ones go through faster then the water soluble ones, as they can pass straight through the membrane, and not a protein.
Facilitated diffusion differs from simple diffusion in that it only occurs at specific points down the membrane, where there are special protein molecules. They are filled with water and allow water soluble molecule and ions to pass through. These channels only open to specific molecules. If that substance is not present, it remains closed. This means there is control over what goes in. Carrier proteins can also be used. When the right proteins show up, it bind to the carrier protein, and changes its shape in a way that releases it to the inside.

1) Three factors that affect diffusion are: Surface area (if there’s a large surface area, the rate of diffusion is quicker.) The thickness of the membrane/diffusion distance (the thinner it is, the quicker the rate of diffusion.) Also, there is the difference is concentration. The greater the distance, the faster the rate of diffusion.
2) Facilitated diffusion differs from diffusion in that it only occurs at certain points along the membrane, and involves proteins, whereas simple diffusion only uses the phospholipids.
3) Facilitated diffusion is passive because it only uses the kinetic energy of the molecules involved; it doesn’t involve anymore being produced then what it already has.