Cell Membrane
The cell membrane encloses the cell from extracellular fluid, just like how our skin encloses the rest of our body from the outside. Modern science accepts the fluid mosaic model of cell membrane structure. In this model, the main components of the cell membrane are phospholipids. A bilayer of phospholipids side by side forms the "fluid" portion of the cell membrane. Their hydrophilic ("water-loving" or "polar") heads face either inwards toward the cytoplasm or outwards toward the extracellular fluid. On the contrary, their hydrophobic ("water-fearing" or "non-polar") tails are located around the centre of the bilayer. The phospholipid bilayer allows small molecules to diffuse according to the concentration gradient. The strength of the membrane helps the cell maintain its shape.
A variety of proteins are embedded in the phospholipid bilayer. These proteins can selectively transport desired molecules and ions in and out of the cell, even against the concentration gradient. Some carbohydrates are also embedded in the bilayer. These short chains of polysaccharides act to identify the cell and and helps the cell communicate with other cells.
In short, the cell membrane separates the inside of the cell from the outside; it is selectively permeable; it helps maintain shape, and it identifies the cell.
A variety of proteins are embedded in the phospholipid bilayer. These proteins can selectively transport desired molecules and ions in and out of the cell, even against the concentration gradient. Some carbohydrates are also embedded in the bilayer. These short chains of polysaccharides act to identify the cell and and helps the cell communicate with other cells.
In short, the cell membrane separates the inside of the cell from the outside; it is selectively permeable; it helps maintain shape, and it identifies the cell.