1. Chapter 4: Cells and Their Environment

2. The Fluid Mosaic Model of the Plasma Membrane

3. Parts of the Plasma Membrane
Phospholipid – has a polar phosphate “head” which is hydrophilic.
It has two nonpolar lipid “tails” which are hydrophobic.

4. Parts of the Plasma Membrane
Cholesterol – helps to stabilize the membrane.
The only thing that keeps the plasma membrane together is the orientation of the lipid tails (they stay away from water)

5. Parts of the Plasma Membrane
Functions of Proteins:
Transport. They allow larger molecules and charged molecules/ions to go through the membrane.
They can act as markers that other cells can recognize.
They can act as enzymes.

6. Selective Permeability
Substances that can easily pass through are: O2
CO2
H2O
The plasma membrane is selectively permeable – it allows some substances to pass through, but not all. (It is selective).

7. Brownian Motion
Molecules are in constant, random motion, called Brownian motion.
Animation

8. Membrane (Cell) Transport
Transport of materials in and out of the cell
Passive Transport – requires no energy expenditure from the cell Active Transport – requires energy from the cell

9. Passive Transport
Three types: 1. Simple diffusion 2. Facilitated diffusion 3. Osmosis

10. What is Diffusion?
Diffusion – the net movement of particles from an area of high concentration to an area of low concentration

11. Concentration High concentration: a lot of molecules in a given space.
Low concentration: a few molecules in a given space.
Concentration gradient: a difference in the concentration of a substance.

12. Diffusion & Concentration Gradient
If molecules are going from an area of HIGH concentration to an area of LOW concentration, they are going down the concentration gradient.

14. Dynamic Equilibrium
A condition in which the concentration of a substance is equal throughout a space. The molecules are still moving, but there is no change in concentration.

15. What is Facilitated Diffusion?
Diffusion of substances across a membrane with the help of transport proteins
Facilitated diffusion

16. What is Osmosis?
Osmosis is the diffusion of water through a selectively permeable membrane.
NOT!

17. Osmosis
Note that osmosis ONLY refers to the diffusion of WATER!

18. Osmosis: Isotonic Solution
Isotonic solution has the same solute/ water concentrations in and out of the cell. Water is in a dynamic equilibrium.

19. Osmosis: Hypertonic Solution
Hypertonic solution: the water concentration is higher inside the cell than outside. Water will diffuse out of the cell. The cell will shrink (crenate)
“Hyper” means “more”: there is more solute outside of the cell (therefore, less water)

20. Osmosis: Hypotonic Solution
Hypotonic solution – the concentration of water is greater outside of the cell as compared to the inside. Water will enter the cell. The cell will expand and may burst.
“Hypo” means “less” or “under”. There is less solute outside of the cell.

21. Osmosis

22. Osmosis in Plants
Turgor pressure – pressure of water inside of a cell.
The large central vacuole in plants regulates the amount of water in the cell.
Is turgor pressure higher when a cell is in a hypertonic, hypotonic or isotonic solution?

23. Plasmolysis
A loss of turgor pressure is called plasmolysis

24. Plasmolysis in Elodea
Normal
Plasmolyzed

25. Plasmolysis in Red Onion
Red Onion Cells - normal
Red Onion Cells - plasmolyzed

26. Which solution is isotonic, hypertonic and hypotonic to the cell?B C

27. Active Transport
Examples:
1. Solute pumping – molecules go from an area of low concentration to an area of high concentration.
2. Endocytosis
Phagocytosis
Pinocytosis
Receptor-Mediated Endocytosis
3. Exocytosis

28. Contractile Vacuoles
Some species of protists live in a hypotonic environment (what will happen to them??)
Contractile vacuole – a structure in some protists that expels water.
Contractile vacuole

29. Endocytosis and Exocytosis
Endocytosis – the cell takes in particles
Exocytosis – the cell releases particles into its environment

30. Phagocytosis – How your immune cells get rid of some pathogens
Phagocytosis is a type of endocytosis in which a cell engulfs a large particle.
Your white blood cells engulf bacteria and then merge them with a lysosome to digest them.
Animation of Phagocytosis