1. 7-3 Cell Boundaries Objectives:
What are the main functions of the cell membrane and the cell wall?
What happens during diffusion?
What is osmosis?

2. Introduction Among the most important parts of a cell are its borders
Separate the cell from its surroundings
Cell membrane: all cells are surrounded by a thin, flexible barrier
Cell wall: a strong supporting layer around the membrane

3. Cell Membrane Function
Regulates what enters and leaves the cell
Provides protection and support
Almost all cell membranes are made of a double-layered sheet
Lipid bilayer: 2 layers of lipids
Flexible structure and strong barrier

4. Cell Membrane Cont’d Many kinds of molecules in cell membranes
Most have protein molecules and carbohydrates (etc.)

5. Cell Walls Outside the cell membrane
Most are porous to allow water, oxygen, carbon dioxide, and certain other substances to pass through easily

6. Cell Walls Cont’d Function Made Provide support and protection
Mostly of cellulose
Fibers of carbohydrate and protein
Main part of wood and paper
Inside the cell and then released at the surface of the cell membrane

7. Diffusion Through Cell Boundaries
One of the most important functions of the cell membrane is to regulate the movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side
Demo

8. Measuring Concentration
Cytoplasm is a solution of many different substances in water
Solution: a mixture of 2 or more substances
Solutes: substances dissolved in the solution
Concentration: the mass of solute in a given volume of solution
More solutes in a volume=greater concentration

9. Diffusion
Diffusion: Particles tend to move from an area of high concentration to an area of less concentration
Does not need cell energy
Equilibrium: when the concentration of the solute is the same throughout
Particles will continue to move until equilibrium is reached
Particles are in constant motion
Activity

10. BLUE TICKET QUESTION
What conditions are present when equilibrium is reached in a solution?

11. BLUE TICKET ANSWER
Equilibrium is reached when the concentration of the solute is the same throughout the solution

12. Osmosis
Some substances are too large or too strongly charged to cross the lipid bilayer
Permeable: a substance that is able to diffuse across a membrane
Impermeable: substances cannot pass across
Selectively permeable: some substances can pass across and others cannot
Osmosis: the diffusion of water through a selectively permeable membrane

13. How Osmosis Works Isotonic: “same strength
Hypertonic: “above strength”
Hypotonic: “below strength
Osmosis Activity

14. Osmotic Pressure
If cells are surrounded by fresh water, they will swell and burst
Plants and bacteria are surrounded by a cell wall which prevents bursting
Blood is isotonic so cells will not burst

15. Blue Ticket Question
What structures protect plant and bacterial cells from potential damage resulting from osmotic pressure?

16. Blue Ticket Answer
Cell walls

17. Facilitated Diffusion
Cell membranes have protein channels that make it easy for certain molecules to cross the membrane
Facilitated diffusion: help the diffusion of glucose across the membrane

18. Facilitated Diffusion Cont’d
100s of different protein channels have been found that allow particular substances to cross different membranes
Fast and specific

19. Facilitated Diffusion Cont’d
Will only happen if there is a higher concentration of the particular molecules on 1 side than on the other side
Does not use the cell’s energy
Lab

20. Active Transport https://www.youtube.com/watch?v=STzOiRqzzL4
Active transport: move materials against a concentration difference
Requires energy
Usually moves ions with transport proteins
Endocytosis and exocytosis move larger molecules and clumps of materials

21. Molecular Transport
A considerable portion of the energy used by cells in their daily activities is devoted to providing the energy for active transport

22. Endocytosis and Exocytosis
Endocytosis: taking material into the cell by means of infolding of the cell membrane

23. Endocytosis and Exocytosis Cont’d
Exocytosis: the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell

24. 7-3 Exit Ticket Answer the following questions.
Use complete sentences.
You may NOT use your book. You MAY use your notes.
This is a quiz grade.
What are the main functions of the cell membrane and the cell wall?
What happens during diffusion?
What is osmosis?