The Cell Membrane
All cells are surrounded by a thin, flexible barrier known as the cell membrane. It regulates what enters and leaves the cell while also providing protection and support.
The composition of nearly all cell membranes is a double-layered sheet called a lipid bilayer which gives cell membranes a flexible structure that forms a strong barrier between the cell and its surroundings. Most cell membranes also contain protein molecules embedded in the lipid bilayer. Some of these proteins for channels and pumps that help to move material across the cell membrane. In addition, carbohydrate molecules are attached to many of these proteins, acting like chemical ID cards, allowing individual cells to identify one another.
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The Cell Wall
Cell walls are present in many organisms, including plants, algae, fungi, and many prokaryotes, but not in animals. The cell wall lies outside of the cell membrane and are porous enough to allow substances such as water, oxygen, and carbon dioxide to pass through. The main function of the cell wall is to provide support and protect the cell.
Most cell walls are made from fibers of carbohydrate and protein. Plant cell walls are comprised mostly of cellulose, a very tough carbohydrate. That cellulose is the primary component of both wood and paper!
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This site was last updated on Saturday, November 22, 2008.
