responsible for homeostasis. The membrane has a selective permeability

which means what moves in and out of the cell is regulated. Amino

acids, sugars, oxygen, sodium, and potassium are examples of substances

that enter the cell. Waste products and carbon dioxide are removed from

the cell. All of these substances cross the membrane in a variety of

ways. From diffusion and osmosis, to active transport the traffic

through the cell membrane is regulated.

Diffusion is the movement of molecules form one area of higher

concentration to an area of lower concentration. Concentration gradient

causes the molecules to move from higher concentration to a lower

concentration. The side of the membrane that has the higher

concentration is said to have the concentration gradient. It drives

diffusion because substances always move down their concentration

gradient. The pressure gradient also plays a role in diffusion. Where

this is a pressure gradient there is motion of molecules. The pressure

gradient is a difference in pressure between two different points. If

the concentration of one side of the membrane is greater than the

protein is specialized for the solute it is carrying, just as enzymes

one side of the membrane to the other fast enough for the cell's

The third way a substance can cross the cell membrane is through

solutes dissolved in the water across the membrane by using active

solutions have different concentration of solutes then the one with less

endocytosis, where only specific substances attach to the receptor

is digested. In the next step, called pinocytosis, the cell engulfs the

substances across the cell membrane. The cell has the ability to

Some common words found in the essay are:
, Proteins ATP, active transport, cell membrane, concentration gradient, plasma membrane, facilitated diffusion, substances cross, pressure gradient, lower concentration, transport protein, transferring phosphate protein, proteins facilitate diffusion, diffusion transport protein, move concentration, cross cell membrane, concentration lower concentration,
Approximate Word count = 857
Approximate Pages = 3 (250 words per page double spaced)