(a)+Membrane+structure+(Q1-8)

Q1 A phospholipid is a major part of a cell membrane. It consists of "a phosphate head which is bipolar and 'hydrophilic' and 2 fatty acid tails that are nonpolar and 'hydrophobic'." (IB Biology textbook, page 21)

hydrophilic head attracts water and hydrophobic tails repel water. []

Q2. What is significant & different about the 2 ends of a phospholipid? (use the proper words, ensuring that you explain / define them)
 *  The head of a phospholipid is hydrophilic (from hydrogen bonds with water also attracts water)
 *  The 2 tails of a phospholipid are hydrophobic (repel water)



Q3. What ends of the phospholipid always line up together inside the plasma membrane, and which ends always line up pointing to the outside? Why is this?

The phospolipids always line up together to form a layer of cell membrane, inside of which is the cytoplasm. The phospholipids combine to form a bilayer (a bilayer being a double layer of the phospholipids, with the hydrophilic heads on the exterior and the hydrophobic tails on the interior). The polar phosphate heads will be on the outside of the layer because they can interact with water; they are hydrophilic. The inside layer is where the non-polar, fatty acid tails line up - they are kept away from water because they are hydrophobic (water repellent/cannot interact with water). []

Q4

Q5. How many cell layers thick is the plasma membrane?  The plasma membrane is bi-layer (two layers). Q6. Describe the **fluid mosiac model** of membrane structure. - The phospholipids in the membrane are made up of many different types of molecules such as integral and peripheral proteins, phospholipids, cholesterol and glycoproteins thus the membrane is mosaic. The cell membrane is in a constant fluid state enabling the cell to change shapes. Also the fluidity allows vesicles to be pinched off or fused to the membrane.

Q7 __**What happens if a hole is made in the plasma membrane?**__ Seeing as the plasma membrane acts as a wall between the contents of the cell and the environment around the cell, if a hole is created (or the cell is ruptured), there is no longer a solid "wall" to stop the substances inside and outside of the cell from mixing. This defeats the purpose of a plasma membrane, which is supposed to regulate the entrance and exit of substances from and to the cell. A hole can also be made in the plasma membrane through viral reproduction. Therefore, if a hole is made in the plasma membrane, it is subject to viruses and any other infectious diseases/bacteria in its surroundings. It also does not have any control of what passes in and out of the cell. Even with the pannels for passive/active transport and the phospholipid bilayer to stop molecules from going in and out of the cell, there is a new 'free passage-way' for anything and everything to get in and out of the cell, let alone the plasma membrane.

8. Draw a simple 2-dimensional diagram of the plasma membrane (Showing both types of membrane proteins). Refer to IB 2.4.1 for what you need to include.

__**﻿**__ __**Glucomproteins**__ are proteins with a carbohydrate attached. 