lecture8 for BGYA01

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Biological Sciences
Clare Hasenkampf

BGYA01 LECTURE 8 OCTOBER 4, 2007 WE HAVE NOW LOOKED AT STRUCTURES INSIDE THE CELL NOW LETS LOOK OUTWARD. Cells often secrete important materials outside the cell, these materials can be very important to the structure of the cell and to the health of the organism. [Remember just because something is outside the cell, it does not mean it is outside the organism.] One important structural feature outside of cells of many eukaryotes is the cell wall. Animals do not have cell walls but plants, fungi, and most groups of protists do. The cell wall is a semi-rigid structure outsidef the plasma membrane. Cell walls are made of polysaccharides and proteins, but the different kingdoms use different polysaccharides. Plant cell walls have cellulose as the dominant polysaccharide, while fungal cell walls have the modified polysaccharide chitin as its major component. Lets take a quick look at a plant cell wall. Figure 4.24, page 91 and figure 4.7, page 77 The cell wall provides support for the cell, and limits the cells volume by its relative rigidity. The cell wall also acts as a barrier against infection [by fungi and other organisms that can cause plant diseases]. Even though cell walls surround the cells the wall does not isolate the cell from its neighbor cells. The neighboring cells are not isolated, because adjacent cells are connected by channels within the cell walls. The cell walls have gaps in them that are 20-40 nm in width. These organized gaps are called plasmodesmata. In Figure 4.7, page 77. You can see the cell walls and the plasmodesmata. A plasmodesmata is a gap in the cell walls of neighboring cells that allows the cytoplasm of neighboring cells to be continuous. Not only is there a gap in the cell wall at plasmodesmata, but the cells plasma membranes fuse in this region so that the cytoplasm of the neighbors is continuous. Thus the neighboring plant cells are very intimately associated. Similarly the neighboring cells of fungi and multicellular algae are also intimately associated. www.notesolution.com
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