Functions Of Cell Membranes.

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Functions Of Cell Membranes

A cell membrane other wise known as a Plasma Membrane is a thin molecular layer that surrounds all living cells. The plasma membrane separates the cell from its surroundings, protects it from changes in the chemical and physical environment, and regulates the traffic of molecules into and out of the cell.

The cell membrane moves materials in and out of the cell in several ways.

Diffusion - Certain small molecules are able to move through the membrane by diffusion. This is a process in which molecules randomly move from an area where there are many of them (high concentration) into an area where there are fewer. Diffusion is a fairly slow process since there is no energy used to push the molecules, and it only works if the molecules are small enough to pass through tiny pores in the membrane. How the molecules pass through the membrane is also affected by whether they are fat soluble or water soluble. Some of the membrane proteins form channels that help water soluble molecules pass through the hydrophobic lipid interior of the membrane.

Facilitated Diffusion - Certain important molecules such as the glucose sugar needed to provide energy to all cells can be transported through the membrane in a process called facilitated diffusion. Protein channels help to move the molecules down the concentration gradient from areas of high concentration to low.

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Active Transport - In some cases the concentration of molecules is greater on one side of the membrane than the other, but the cell still needs to move even more molecules through the membrane, against the concentration gradient. In this case the cell membrane can actually use energy to push the molecules from lower to higher concentrations. This is called active transport. Root cells use active transport when they bring in certain minerals. Nerve cells use a "sodium pump" to actively transport ions when they send messages.

The plasma membrane forms an extremely effective seal around the cell. Only ...

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