1. Cell Walls

2. Movement Through the Plasma Membrane
Selective permeability
allows intracellular fluid to differ from extracellular fluid
nutrients enter, wastes exit
intracellular concentrations of substances must be maintained within norms

3. Passive transport processes
1. solutes, solvents, and solutions
2. diffusion: movement of solute molecules from areas of high concentration to areas of low concentration.
a. concentration gradient: measure of the difference in solute concentrations between two points

5. b. may involve membrane channels

6. 3. osmosis
a. diffusion of water across a selectively permeable membrane
b. water diffuses from low [solute] to high [solute]

7. c. osmotic pressure: pressure created by movement of water across a membrane
- cell walls can allow cells to withstand

8. Tonicity Hypotonic solutions
have a lower concentration of solutes than cytoplasm
lysis

9. Tonicity Hypotonic solutions Hypertonic solutions
have a lower concentration of solutes than cytoplasm
lysis
Hypertonic solutions
have a higher concentration of solutes than cytoplasm
crenation

10. Tonicity Hypotonic solutions Hypertonic solutions Isotonic solutions
have a lower concentration of solutes than cytoplasm
lysis
Hypertonic solutions
have a higher concentration of solutes than cytoplasm
crenation
Isotonic solutions
concentration of solutes is the same as cytoplasm

12. Selective Transport Mechanisms
Facilitated Diffusion
1. Moves molecules with the gradient through membrane protein.
2. Requires a specific transport protein.

13. Active Transport 1. Moves solutes against the gradient.
2. Results in increased [solutes] on one side of membrane.
3. Requires energy input (ATP) and a transport protein.

14. Bulk Transport Endocytosis is an energy-requiring process
cell “takes-in” substances
can involve pseudopodia
a membrane-bound vesicle is formed

15. Endocytosis Subtypes: 1. phagocytosis pseudopodia
large vesicles formed
contents of vesicle digested

16. Endocytosis Subtypes: 2. pinocytosis invagination of cell membrane
takes in liquid material
smaller vesicles

17. Exocytosis 1. products “packaged” into transport (secretory) vesicles
2. vesicles fuse with cell membrane
3. contents “spilled” outside of cell (secretion)

20. Membrane Proteins Used in Communication
Receptor proteins (on surface)
1. recognize specific molecules (like hormones)
2. receptor often changes shape
3. causes a change in cell activity (signal transduction)

21. Membrane Proteins Used in Communication
Gated channels
1. gated (may be open or closed)
2. allow passage of ions (current)
3. used in neurons and muscle cells