Plasma Membrane

AP Biology

9/14/01

Plasma Membrane

The fluid mosaic of a plasma membrane is made up of a semi permeable double barrier of phospholipids called a bilayer. A phospholipid is a phosphorus element with two fatty acids acting as tails. Due to the hydrophilic property of phosphorous, and the hydrophobic property of the fatty acids, this causes the phospholipids to line up in two rows with the tails in together because there are aqueous solutions on either side. This causes a semi permeable barrier that is called the plasma membrane. Semi permeable means that some things are able to pass through while others are not. When molecules are transported though a membrane using either method, it is called diffusion.

Passive transport is called passive because it requires absolutely no energy transfer to move things through the membrane. It occurs when the membrane either separates and allows the molecules through, or a piece of the membrane breaks off and surrounds the molecule and brings it through. The reason that no energy is used, is that the concentration gradient is going the same way as