The cell may be regarded as the basic unit of an organism it carries out the essential processes that make the organism a living entity. All cells share certain structyral and functional features and they are of almost universal occurance in living organi

Authors Avatar
GIVE AN ACCOUNT OF THE DISTRIBUTION & FUNCTIONS OF THE MEMBRANES OF EUKARYOTIC CELLS

The cell may be regarded as the basic unit of an organism, it carries out the essential processes that make the organism a living entity. All cells share certain structural and functional features and they are of almost universal occurrence in living organisms. Biologists have devoted a great deal of attention to its structure and the processes that go on inside it. They have recognised a major distinction between two types of cells, Eukaryotic cells that have a nucleus and Prokaryotic cells that do not have a nucleus. There are many other differences between these two cells, in particular eukaryotic cells have a full complement of membrane bound organelles in their cytoplasm and are characterised by the possession of these organelles. Eukaryotic cells are typical of a great majority of organisms including all animal and plant cells and it is this type of cell that we will be looking at. They are multicellular which means they are composed of groups of specialised cells each performing a particular function. They also show a high level of structural complexity that allows an elaborate division of labour, which has enabled them to reach high orders of functional complexity. The biological membrane and the various molecular complexes embedded in them must now be viewed as playing a central role in both cell structure and its functions

All cells whether animal or plant has a cell surface that is known as the plasma membrane. It is composed of a continuous double layer of phospholipids within which protein molecules are embedded. Phospholipids are polar molecules and are important in the formation of the plasma membranes, the non polar hydrophilic tails attract each other keeping the membrane relatively firm and in place. The formation of the proteins and phospholipids is called the lipid bylayer. The proteins take the form of globules dotted about in a mosaic pattern with some being attached to the urface of the membrane while others penetrate into it to varying extents. Some of these proteins act as enzyme catalysing chemical reactions within the membrane and also as pumps and channels transporting molecules into and out of the cell. The plasma membrane is perforated by pores and allows substances to pass in and out of the cell by Diffusion Active Transport, osmosis, Endocytosis and Exocytosis. The external cell membrane contains lipids and proteins combined with sugar molecules called Glycolipids and Glycoproteins. The sugar molecules only attach to the outside of the cell membrane and form what is known as the Glycocalyx or cell coat. The Glycocalyx is sticky and enables animal cells to adhere to each other. In the development of organisms cells must migrate from one region to another and recognise what kind of cells are their proper neighbours and what kinds are not. This recognition ability appears to lie within the Glycocalyx.
Join now!


The endoplasmic reticulum is found in the cytoplasm of the cell and like the plasma membrane is composed of phospholipids and protein. ER is an intracellular transport system moving materials from one part of the cell to another. In certain parts of the cell the ER is continuous with the plasma and nuclear membranes providing a route by which materials might move from the nucleus to the cytoplasm. There are two types of ER, rough and smooth. On the cytosol side of the ER membrane there are ribosome's attached to it and this is known as Rough ER. ...

This is a preview of the whole essay