Greetings Astute Progenies of CS, All cells, plant and animal have cell membranes. In addition plant cells have a cell wall. Animal cells *never* have a cell wall.
The cell membrane: Limiting the cytoplasm of all cells, both plant and animal, is a delicate structure known as the *plasma membrane*. This membrane, which is only about 10 millimicrons thick, is composed of three layers. These three layers are like a sandwich, the outer layers are protein and the inner layer is of lipid, a fatty material. The cell membrane controls and restricts the passage of materials into and out of the cell. It separates the interior of the cell from the external environment. All animal cells are capable of independent movement, they are mobile, when seperated from other cells. The cell wall: With few exceptions, plant cells have an outer cell wall surrounding the cell membrane. This cell wall gives support and stiffness to the plant structure. This wall is constructed by the cell of glucose. The glucose deposited as *cellulose* can never be used again by the plant as nourishment, since the plant has no enzymes to digest the cellulose. When the cell dies the wall remains. Some plant cells have a secondary cell wall, used for conducting fluids, as in bark. The cell wall is perforated by holes through which strands of cytoplasm are threaded. These cytoplasm threads are called *plasmodesmata* and connect the cells together and permit the passage of materials. After the plant cell has matured and stopped expanding the cell wall hardens and forms the supporting structure for the plant. The cell wall prevents plant cells from being mobile. Plant cells are mobile if removed from the cell wall. Bless you Bob Lee -- oozing on the muggy shore of the gulf coast [email protected] -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] List maintainer: Mike Devour <[email protected]>
