(b)+Membrane+Structure

media type="custom" key="10551312" Membranes consist of phospholipid molecues, which are made up of a phosphate head, and two fatty acid tails.

A phospholipid molecule is composed of 2 main parts : Membranes consist of two layers of phospholipids, or a phospholipid //bilayer//. When the phospholipid molecules are put together, these chemical properties cause the molecules to quickly rearrange so all Hydrophobic tails are together in the center, away from the surrounding water molecules, and all Hydrophilic heads are facing out on both sides of the membrane.
 * Hydrophilic (hydros = "water" + philia = "love") Head → ATTRACTS water
 * Hydrophobic (hydros = "water + phobos = "fear") Tail → REPELS water

media type="custom" key="10551316" align="center" None of the phospholipid molecules are bound together, and so they continually move around the cell surface membrane. They cannot leave the double layer due to their Hydrophobic tails. This is called the** Fluid Mosaic ** model because the molecules are free to move, similar to water particles on the surface of a pond.

media type="custom" key="10551322" align="center" The chemical properties of the phospholipid bilayer effectively block both polar and non-polar molecules from entering the cytoplasm of the cell. However, the cell still has a method to exchange materials with its environment: Proteins.
 * **Integral Proteins** are embedded in the phospholipid molecules
 *  → Interact with the cytoplasm & external molecules outside the cell
 * **Peripheral Proteins** are attached to the surface
 *  → Interact with the phosphate heads

The 2 other features of the plasma membrane are :
 * **Glycoproteins** : proteins with a carbohydrate group attached to them
 * **Cholesterol** : a large molecule positioned between the tails of the phospholipid
 * → reduces fluidity & permeability

//When the cell membrane breaks, cellular lysis occurs and the insides of the cell are released into the outside environment.//

// __**Functions of Membrane Protiens:**__ //
 * Integral Proteins - interact with the cytoplasm inside the cell and the molecules outside the cell
 * Peripheral Proteins - interact with the phosphate heads
 * Glycoproteins - cell to cell recognition, the ability of cells to recognize what the other cell is
 * Cholesterol - helps to build and maintain the membranes

Work Cited :
"2.4 Membranes." //Bio IBID Textbook//. 21-22. PDF file.

Yang, Na Yeong. "The Cell Surface Membrane." 15 Mar. 2010. Grade 9 One Note Document file.