Cell Membranes Page # 46-47

Cell Membranes 1. Provide protection and compartmentalization. 2. Support. 3. Regulate what goes in and out of cell!

Compartmentalization External- Membrane around the cell. Keep things needed inside. Keep things harmful outside. Separates internal environment from the external. Example- The double layer cell membrane (walls around classroom)

Internal- Membrane around smaller objects inside the larger object to keep each individual thing separate. Example: Organelles (sandwich bag in a lunchbox)

How do membranes keep things in or out? The membrane is mostly made up of phospholipids that have a hydrophilic heads and two hydrophobic tails.

Phospholipid Phosphate group Glycerol Two Fatty acid chains

Phospholipids- Special fat molecules. Hydrophilic- Attracted to water. Facing out from middle of membrane towards water. Hydrophobic- Afraid of water. Found facing into the center of membrane

Phospholipid Bilayer Hydrophilic Phospholipids arrange themselves in a bilayer that has a hydrophobic interior region and hydrophilic exterior. Hydrophilic Hydrophilic

Water molecules are small enough to pass through the bilayer membranes. Other molecules are too large to easily pass through the membrane.

Semi-permeable – will only let certain things (molecules) go through. Soooo….. So this means that membranes are semi-permeable. Semi-permeable – will only let certain things (molecules) go through.

Major points of semipermeable membranes are: bilayer nature of biological membranes. water can go through with no problems. many solutes( dissolved stuff), because they are too large, will not go through the membranes without help. this is called a semi-permeable membrane.

1) Which is the Hydrophobic part of the membrane?

3) Which is the Hydrophilic part of the membrane?

2) Which molecule will not be able to pass through the membrane?