Cell Membrane

Cell Membrane

The cell membrane is a phospholipid bilayer that surrounds both eukaryotic and prokaryotic cells. It is made up of a double layer of phospholipids which forms a selectively permeable barrier between two aqueous compartments, allowing only certain molecules to pass. Embedded within this bilayer are proteins which have carry out specific functions. Integral proteins act as pathways for ion and molecules. Peripheral proteins act as cell to cell recognition sites. Transmembrane protein channels and transporters allow nutrients such as sugars and amino acid to enter the cell. Carbohydrates attach to the external surface of integral proteins holds cells together as well as acting as a site where viruses or chemical messengers can attach themselves.

Passive Transport

Passive transportation is the transportation of molecules or atoms through a cell membrane without requiring chemical energy. The rate of passive transport is determined by the permeability of the cell membrane.

Diffusion

Diffusion is the movement of molecules from an area of high concentration to an area of lowest concentration. Diffusion takes place at the cellular level of living things. For example, simple animals that do not have internal circulatory systems rely on diffusion to exchange gases and obtain the nutrients need to survive and grow. The root cells of plants obtain their water from the soil by method of diffusion. Diffusion requires no energy from the cell to occur.

Diffusion occurs naturally once certain conditions occur at the molecular level. Molecules move constantly and randomly, mixing together with different types and thus depend on the amount of kinetic energy present in each molecule. As molecules move and mix together, they noticeably f...

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Works Cited

Alford, D. & Hill, J. 2010, Excel Preliminary Biology, Pascal Press, Sydney, NSW, Australia

Bruno, L.C. 2001, U.X.L. Complete Life Science Resource, Vol 1, A-E, Gale Group, Farmington Hills, Michigan, USA

Bruno, L.C. 2001, U.X.L. Complete Life Science Resource, Vol 3, O-Z, Gale Group, Farmington Hills, Michigan, USA