Cell Walls
By Evan and Jon

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The cell wall is a rigid multi-layered structure found in plant and bacterial cells, designed to hold the cells together and protect the cell from injury. The cell wall is composed of four layers. The outermost layer is known as the middle lamella; then come the primary, secondary and tertiary. The middle lamella contains pectins. Pectins are carbohydrate polymers and they function to help in binding adjacent cell walls together, which is the primary use of the middle lamella. Lipids are also on the external surface of the cell wall to protect the wall from injury. The primary layer consists of microfibrils, which are cellulose chains. This layer is capable of expansion during growth. The secondary layer is multi-layered in itself. Each layer is at an angle to its adjacent layers, which causes strength in high plants, especially trees. The secondary layer of the cell wall is densely packed with cellulose microfibrils. The secondary wall of woody tissues also contains lignins, which are polymerized aromatic alcohols that help to harden the plant (tree). The tertiary layer, also known as the lamella, is thin, and has few cellulose microfibrils. Although the cell wall provides a thick encasement for plant cells, it does not completely seal them from the surroundings. Small openings allow physical contact between adjacent cells and allow cellulose and other polysaccharides to be transported to the surface.

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