![]() ![]() Each theory was improved in the following decades: the apposition (or lamination) theory by Eduard Strasburger (1882, 1889), and the intussusception theory by Julius Wiesner (1886). Carl Nägeli (1858, 1862, 1863) believed that the growth of the wall in thickness and in area was due to a process termed intussusception. Hugo von Mohl (1853, 1858) advocated the idea that the cell wall grows by apposition. The mode of formation of the cell wall was controversial in the 19th century. Before, it had been thought that cells shared walls and that fluid passed between them this way. Link proved that cells had independent cell walls. However, "the dead excrusion product of the living protoplast" was forgotten, for almost three centuries, being the subject of scientific interest mainly as a resource for industrial processing or in relation to animal or human health. HistoryĪ plant cell wall was first observed and named (simply as a "wall") by Robert Hooke in 1665. Unusually, diatoms have a cell wall composed of biogenic silica. Fungi possess cell walls made of the N-acetylglucosamine polymer chitin. The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers, pseudopeptidoglycan, or polysaccharides. ![]() In bacteria, the cell wall is composed of peptidoglycan. Algae possess cell walls made of glycoproteins and polysaccharides such as carrageenan and agar that are absent from land plants. Often, other polymers such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. The primary cell wall of land plants is composed of the polysaccharides cellulose, hemicelluloses and pectin. The composition of cell walls varies between taxonomic group and species and may depend on cell type and developmental stage. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters. Cell walls are absent in many eukaryotes, including animals, but are present in some other ones like fungi, algae and plants, and in most prokaryotes (except mollicute bacteria). It provides the cell with both structural support and protection, and also acts as a filtering mechanism. ![]() It can be tough, flexible, and sometimes rigid. CytoskeletonĪ cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. ![]()
0 Comments
Leave a Reply. |