1. Cell membrane outline Controls homeostasis Selectively permeable
Structure of membrane
1. lipid bilayer
2. transport proteins
3. cholesterol
drawing
Diffusion
Osmosis
1. isotonic
2. hypotonic
plant cells
animal cells
3. hypertonic

2. Summary Section 2 – pages 175-178
A cell’s survival depends on the cell’s ability to maintain necessary conditions inside itself
Maintaining these constant internal conditions is called--homeostasis
Summary Section 2 – pages

3. Summary Section 2 – pages 175-178
What controls homeostasis in a cell?
Plasma (Cell) membrane: the flexible boundary between the cell and its environment.
It allows-- water and nutrients to enter the cell and wastes to leave the cell
Summary Section 2 – pages

4. Summary Section 2 – pages 175-178
The cell membrane is selectively permeable.
Selective permeability--when a membrane allows some materials to pass through, while keeping others out.
Examples:
Spaghetti strainer—
allows water, but not
spaghetti to pass
through
Summary Section 2 – pages

5. Summary Section 2 – pages 175-178
mosquito netting—
allows air molecules to
pass through but not
mosquitoes

6. Summary Section 2 – pages 175-178
Selective Permeability
Plasma Membrane
Water
Summary Section 2 – pages

7. Structure of the Plasma Membrane
1. Lipid Bilayer--The cell membrane is 2 layers thick; made of phosopholipids

8. Lipid Bilayer Polar heads face out and are attracted to water
Nonpolar tails face in
and repel water
This arrangement makes the
membrane selectively permeable.

9. 2. Transport proteins: embedded in the membrane, they monitor which molecules enter and exit the cell

10. Summary Section 2 – pages 175-178
3. Cholesterol- stabilizes the cell membrane by preventing lipids from sticking together
Cholesterol
Summary Section 2 – pages

11. Draw and label the parts of the cell membrane below:

12. Diffusion and Osmosis What needs to cross a cell membrane?
water, nutrients, oxygen
How do materials cross the cell membrane?
Diffusion or osmosis

13. Diffusion
Random movement of particles to establish dynamic equilibrium (balanced movement and concentration)
Occurs from high to low concentration gradient (moves from area where there is a lot to an area where there is little)
ex. Oxygen diffuses into bloodstream because higher conc. in lungs

14. Section 8.1 Summary – pages 195 - 200
Osmosis
Osmosis--Diffusion of water across a selectively permeable membrane
Review--Diffusion occurs from an area of HIGH concentration to an area of LOW concentration
Section 8.1 Summary – pages

15. Section 8.1 Summary – pages 195 - 200
Osmosis Diagram
Section 8.1 Summary – pages

16. Section 8.1 Summary – pages 195 - 200
Example of osmosis?
After
Osmosis
Before
Osmosis
Selectively permeable membrane
Water molecule
Sugar molecule
Section 8.1 Summary – pages

17. Section 8.1 Summary – pages 195 - 200
3 Types of Osmotic Solutions
Isotonic Solution--Equal concentrations of water, inside and outside of the cell. Water moves in and out of cell equally
H2O
H2O
Water Molecule
Dissolved Molecule
Section 8.1 Summary – pages

18. Cells in an isotonic solution
Shape of isotonic cell--Normal
Section 8.1 Summary – pages Section 8.1 Summary – pages

19. Section 8.1 Summary – pages 195 - 200
Cells in a hypotonic solution
Hypotonic solution—More water outside the cell than inside the cell; water diffuses into the cell
H2O
H2O
Water Molecule
Dissolved Molecule
Section 8.1 Summary – pages

20. Section 8.1 Summary – pages 195 - 200
Cells in a hypotonic solution
Shape of hypotonic cell—swells
Section 8.1 Summary – pages

21. Plant cells have cell walls that allow a lot of water to enter without bursting; they stay plump and crisp (this is why grocers mist produce)
Animal cells do NOT have cell walls and could burst

22. Section 8.1 Summary – pages 195 - 200
Cells in a hypertonic solution
Hypertonic cell-- More water on inside of cell than outside of cell. water moves out of cell
H2O
H2O
Water Molecule
Dissolved Molecule
Section 8.1 Summary – pages

23. Section 8.1 Summary – pages 195 - 200
Cells in a hypertonic solution
Shape of hypertonic cell—Shriveled; this is why plants wilt
Section 8.1 Summary – pages