Diffusion is the driving force behind the movement of many substances across the cell membrane.The process by which particles move from an area of high concentration to an area of lower concentration is known as diffusion!.

As a result, the particles tend to move from an area where they are more concentrated to an area where they are less concentrated.They collide with one another and tend to spread out randomly.In any solution, solute particles move constantly.Cellular cytoplasm consists of many different substances dissolved in water.Equilibrium= when the amount of substances (concentration) is the SAME in both places.

Concentration Gradient= when the amount of substances (concentration) is different in two places.

Meaning, that some substances can pass across them and others cannot.

Most biological membranes are selectively permeable.

Although many substances can cross biological membranes, some are too large or too strongly charged to cross the lipid bilayer.

Act like chemical identification cards, allowing individual cells to identify one another.

Form channels or pumps that help move materials across the cell membrane.

Because the proteins embedded in the lipid bilayer can mover around and “float” among the lipids, and because so many different kinds of molecules make up the cell membrane, scientists call the cell membrane a “fluid mosaic”.

Embedded in the lipid bilayer of most cell membranes are protein molecules, carbohydrates molecules are attached to many of these proteins.

When these lipids are mixed with water, their hydrophobic fatty acid “tails” cluster together while their hydrophilic “heads” are attracted to water.

The fatty acid portion of a phospholipid is hydrophobic (“water-fearing”), while the opposite end of the molecule (the head) is hydrophilic (“water-loving”).

The layered structure of cell membranes reflects the chemical properties of the lipids that make them up.

The lipid bilayer gives cell membranes a flexible structure that forms a strong barrier between the cell and its surroundings.

All cells contain cell membranes, which almost always are made up of a double-layered sheet called a lipid bilayer.

Download free cell membrane structure