1. The Plasma (Cell) Membrane
What is the function?

2. Find a picture

3. Why must cells control materials that enter and leave the cell?
Cells need to maintain a balance (homeostasis)

4. Why do organisms have many small cells instead of a few large cells?
Cells are limited by surface-area-to-volume ratio
Smaller cells – higher ratio
Larger cells – lower ratio
Hint : Think of a pile of wet laundry

6. Relationship btwn surface area & volume
Surface area = 6 mm2 Volume = 1 mm3
Surface area = 24 mm2 Volume = 8 mm3
1 mm
2 mm
4 mm
Surface area = 96 mm2 Volume = 64 mm3
Not enough membrane to allow materials in/out

7. Then how can eukaryotic cells be bigger than prokaryotic cells?
Organelles bound by membranes - increases surface area
Organelles help divide jobs for the cell

8. Why is the Plasma Membrane so Important?
Allows cells to be alive
Separates life from non life

9. What is the main component of the cell membrane?
Lipids
(aka Fats, oils, and waxes)

10. Specialized Lipid- phospholipid
Glycerol Backbone
Two Fatty Acid Chains
Phosphate Group

11. Phospholipid bilayer Phosphate head (glycerol +phosphate)
hydrophilic – “water-loving”
2 Fatty acid tails
hydrophobic – “water-fearing”

12. Inside of cell
Outside of cell
protein
carbohydrate
cholesterol
phospholipid

13. Fluid Mosaic Model Molecules freely move sideways w/in each layer
Flexible
Proteins – communication & control movement of large molecules in/out
Cholesterol – increase stability & strength
Carbohydrates – identification & communication

14. Selectively Permeable aka semi-permeable
Allows some smaller materials to pass (ex. water, glucose)
Keeps out bigger materials (ex. starch, polymers)