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The Functions of Cell Membrane

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THE FUNCTIONS OF CELL MEMBRANE The cell membrane is about seven mm wide and is a functional organelle which serves as a boundary between the cell and its environment, thereby separating the contents of cells from their external environment, controlling exchange of materials such as nutrients and waste products between the two. Membranes act as receptor sites for recognizing hormones, neurotransmitters and other chemicals, either from the external environment or from other parts of the organism. One of the major properties of the cell membrane is that it is partially permeable, which is its ability to permit different substances to pass across it at different rates. Thus, it allows the passage of substances like glucose, amino acids, fatty acids, glycerol and ions along with water. The cell membrane is almost entirely made up of proteins and phospholipids. The hydrophobic tails of phospholipids project inwards forming phospholipid bilayers which provide the basic structure of cell membranes in addition to restricting entry and exit of polar molecules and ions. ...read more.


Therefore, these components of the cell membrane contribute to the various functions of the cell membrane. In addition to this, cell membranes also present barriers to the movement of ions and molecules, particularly polar molecules which are repelled by the non-polar hydrophobic lipids of membranes. This prevents the aqueous contents of the cell from escaping. However, transport still occurs across membranes to obtain nutrients, to excrete waste substances, to secrete useful substances and to maintain a suitable pH and ionic concentration. Thus transport is one of the major functions of membranes and it occurs in four different ways, namely, diffusion, osmosis, active transport and bulk transport. Apart, from the whole cell having a membrane, there are numerous cell organelles too consisting of a membrane, the structure of which is the same as the cell membrane. These organelles are called membranous organelles, one of the major features of eukaryotic cells. The nucleus is one of the most prominent features of the cell which is bounded by a double membrane, the nuclear envelope, the outer membrane being continuous with the endoplasmic reticulum. ...read more.


These membrane sheets provide a large surface area for chemical reactions as well as transport of materials through the cell. Furthermore, vacuole is also a membranous organelle and is bound by a single membrane called the tonoplast. The membranes of mitochondria and chloroplasts have an energy transfer system where proteins take part for respiration and photosynthesis respectively. These membranous organelles confer a few advantages: the rate of any metabolic pathway inside an organelle can be controlled by regulating the rate at which the membrane of the organelle allows the first reactant to enter; many metabolic processes involve enzymes being embedded in a membrane. As cells become larger, the proportion of membrane area to cell volume is reduced. This proportion is increased by the presence of organelle membranes. Thus, cell membranes are an extremely important part of the cell since they isolate the cell contents from the outside, select what is allowed in and out, hold enzyme complexes, increase the surface area fro metabolic processes to take place and perform a variety of other significant functions, as explained before. ...read more.

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