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The Cell Membrane

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Sheena Shah (12L) The Cell Membrane The cell membrane is found in both animal and plant cells and carries out the same function in both. The main functions of the cell membrane is to control what goes in and out of the cell, to protect the rest of the cell and maintain the structure, allow cell recognition and to regulate transport. The cell membrane is a lipid bilayer, which contains proteins and cholesterols, which function as a sensitive barrier for entry and exit of selective substances. Other organelles such as chloroplast are also surrounded by a cell membrane. "A cell membrane consists of a double layer of phospholipid molecules arranged with their hydrocarbon chains inwards." (www.cellsalive.com). The phospholipid bilayers can be shown in a fluid mosaic model. It is called a fluid mosaic model, as the phospholipids are free to float around in the plane of the membrane, hence "fluid" and the proteins look like small pieces of tile, hence "mosaic". ...read more.


Tight junctions, which prevent movement of molecules between cells, forming a continuous seam. Gap junctions, which are specialised cell connections and protein channels that allow flow of ions or molecules between cells." (www.biology.arizona.edu) There are two types of proteins in cells- carrier proteins and transport proteins. Transport proteins are either active or passive. Passive transport uses no energy and substances diffuse through channels formed by proteins. Passive transport moves molecules down a concentration gradient, examples of this are diffusion, facilitated diffusion and osmosis. A concentration gradient is necessary for diffusion as the greater a gradient, the faster diffusion can take place. "Diffusion is the net movement of molecules or ions from a region of higher concentration to a region of lower concentration." (A New Introduction To Biology, page 24) When there is a higher concentration on one side of the membrane, a concentration imbalance is produced. Molecules continue to move across a concentration until equilibrium is reached- an equal distribution of molecules on either side of the membrane. ...read more.


A vesicle would separate from the edge of the Golgi apparatus in the cytoplasm and move towards the membrane where it would be pushed out of the cell. This is how hormones are secreted from cells. Another type of lipid in the membrane is cholesterol. The amount of cholesterol varies with the type of membrane. Cell membranes have one cholesterol per phospholipid molecule. Cholesterol makes the bilayer stronger, more flexible and more permeable. Cholesterol helps to pack phospholipids in the membranes, giving more firmness. Without cholesterol, a cell would need a cell wall as it decreases permeability to small water-soluble molecules. Another component of the membrane is carbohydrates. Glycoproteins have carbohydrates in the form of a polysaccharide attached to them in a covalent link. They are rich in sugars and store carbohydrates in animals. The cell membrane is vital for the protection and structure of animal and plant cells. It separates the cell from its surrounding environment and maintains the homeostasis of the cell. The whole cell counts on the membrane to get rid off toxins and take in important substances like oxygen. ...read more.

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