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The Effect of Sucrose Concentration on the Rate of Osmosis Through a Selectively Permeable Membrane in a Model Cell

Amanjot Saini and Jaslyen Singh
Biology Lab 111
October 26, 2011
Debbie Wheeler

Introduction:
The cell membrane functions in transport of materials in and out of the cell, recognition, communication and homeostasis. A wide variety of molecules and substances must pass through the cell membrane – large, small, hydrophobic and hydrophilic. Molecules of the same size must be sorted out and the cell must also be able to get large amounts of molecules in and out when necessary. The key to this process lies within the structure of the cell membrane.
The cell membrane consists of the fluid mosaic model of membrane structure. It is a remarkable structure which has the properties of both a solid and a liquid. The fluid parts are composed of side by side phospholipids arranged in a bilayer, forming a lipid bilayer. The phospholipids are amphipathic lipid molecules—they are part hydrophobic and part hydrophilic. The heads, which are polar and hydrophilic, face outward and the tails ,which are non- polar and hydrophobic, face inward (Farabee, 2007).This fluid part is where proteins and other molecules such as other lipids or carbohydrates are suspended or anchored at various points on its surface. Moreover, the solid or mosaic part is a variety of proteins wholly or partly embedded in the bilayer. Carbohydrates are strung together in chains are attached to proteins, glycoproteins, or lipids, glycolipids, on the membrane. They function as identification markers for cell recognition.
Due to the phospholipid bilayer being selectively permeable some molecules enter the cell while other molecules are not allowed to enter. The cell membrane can discriminate between different molecules that are the same size. There are three general means by which substances can enter and exit cells: diffusion, transport by carriers; active and facilitated and endocytosis... [continues]

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