To allow for cell wall expansion during growth, primary walls are thinner and less rigid than those of cells that have stopped growing. The primary wall is the cellulose-containing layer laid down by cells that are dividing and growing. The middle lamella serves as a cementing layer between the primary walls of adjacent cells. Mechanical propertiesĪll cell walls contain two layers, the middle lamella and the primary cell wall, and many cells produce an additional layer, called the secondary wall. What is the thin layer that forms the outer boundary of a cell? Where is the site of photosynthesis in a plant cell? Test your knowledge. The scope of this article is limited to plant cell walls. Unlike those of plants and algae, fungal cell walls lack cellulose entirely and contain chitin. Algal cell walls are similar to those of plants, and many contain specific polysaccharides that are useful for taxonomy. Bacterial cell walls are characterized by the presence of peptidoglycan, whereas those of Archaea characteristically lack this chemical. Such functions include: (1) providing the living cell with mechanical protection and a chemically buffered environment, (2) providing a porous medium for the circulation and distribution of water, minerals, and other small nutrient molecules, (3) providing rigid building blocks from which stable structures of higher order, such as leaves and stems, can be produced, and (4) providing a storage site of regulatory molecules that sense the presence of pathogenic microbes and control the development of tissues.Ĭertain prokaryotes, algae, slime molds, water molds, and fungi also have cell walls. Although often perceived as an inactive product serving mainly mechanical and structural purposes, the cell wall actually has a multitude of functions upon which plant life depends. The cell wall is responsible for many of the characteristics that distinguish plant cells from animal cells.
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