Starter

1. What are the two categories of cells? 2. How are they different?3. What are examples of each?

The Cell Membrane

AKA – Plasma Membrane

Cell Membrane Structure

• Phospholipid Bilayer– Double layer of phospholipids• Phosphate heads

– Hydrophilic

• 2 Fatty Acid Tails attached to the head– Hydrophobic

• Tail to tail

– Embedded proteins and carbohydrates

Function

• Regulates the movement of substances in and out of the cell– Semi-permeable

• Molecules that like lipids (gases) can pass through the lipid bilayer

• Separates intracellular components from extracellular components.– a.k.a. skin!

• Helps cells adhere to other cells• Holds proteins for different functions

Membrane Protein Functions

• Cell to cell communication

• Cell to cell contact

• Enzyme activity

• Transporting substances across membrane

Fluid Mosaic Model

• Phospholipids move almost effortlessly– Fluid

• Made up of small “things”– Mosaic

• The cell membrane is not stationary! Everything moves together!

The cell can only be so big because of the surface area-to-volume ratio.

Volume increases faster than its surface area

More volume means more stuff in the cell means more activity means more stuff needs to come in and out of the cell

Cell must be small because cell membrane wouldn’t be able to keep up if it was larger.

1. What passes through the membrane easily? Why?

2. What doesn’t pass through the membrane easily? Why?

3. Describe why surface area-to-volume ratio controls the size of the cell? Is a higher or lower ratio better?