1. Cell Boundaries

2. Vocab Hypertonic Hypotonic Isotonic Protein channels
Facilitated diffusion
Active Transport
Concentration gradient
Endocytosis
Phagocytosis
Pinocytosis
Exocytosis
Cell membrane
(phospho)lipid bilayer
Cell wall
Prokaryote
Eukaryote
High Concentration
Low concentration
Solute
Solvent
Equilibrium
Diffusion
Osmosis
Selectively permeable

3. Objectives
1. What are the main functions of the cell membrane and the cell wall?
2. What happens during diffusion?
3. What is osmosis?

4. Cell Membrane
All cells are surrounded by a thin, flexible barrier known as the cell membrane.
The cell membrane regulates what enters and leaves the cell and also provides protection and support.

5. Cell Membrane

6. Cell Membrane
The composition of nearly all cell membranes is a double-layered sheet called a lipid bilayer.
It functions as a flexible barrier between the cell and its surroundings.
Lipid bilayer

7. Cell Membrane
Most cell membranes contain protein molecules embedded in the lipid bilayer.
Carbohydrates are for recognition purposes.
Protein channel

8. Cell Wall (plants)
The main function of the cell wall is to provide support and protection for the cell.

9. Cell Wall
Cell walls are found in plants, algae, fungi, and many prokaryotes.
The cell wall lies outside the cell membrane.
Most cell walls are porous enough to allow water, oxygen, carbon dioxide, and certain other substances to pass through easily.

10. Diffusion Through Cell Boundaries
The cell membrane regulates movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side.

11. Diffusion  
Particles move from an area of more concentration to an area of less concentration.
This process is called diffusion.
When the concentration of the solute is the same throughout a system, the system has reached equilibrium.

12. High vs Low Concentration

13. Diffusion
Substances diffuse across membranes without requiring the cell to use energy.

14. Diffusion
A) There is a higher concentration of solute on one side of the membrane as compared to the other side of the membrane

15. Diffusion B)
Particles move from the side of with a higher concentration to the side of the membrane with a lower concentration.
The solute particles will continue to diffuse across the membrane until equilibrium is reached.

16. Diffusion C)
When equilibrium is reached, solute particles continue to diffuse across the membrane in both directions.

17. Equilibrium is a balance of molecules on either side of the membrane.

18. Osmosis
Osmosis is the diffusion of water through a selectively permeable membrane.

19. Selectively Permeable
Cell membranes let some molecules enter a cell, but prevents other molecules from getting in.
Can Enter Can Not Enter
- Water
- Small Molecules (O2 & CO2)
- Non-polar lipids
- Macromolecules
- Ions (Na+,Cl-)
- Hydrophilic molecules (glucose)

20. Osmosis
Water tends to diffuse from a highly concentrated area of water to a less concentrated area of water.

21. Hypertonic
hypertonic (“above strength”): the more concentrated solution
SO,
- Water leaves the cell
- Animal cells shrink

22. c. Isotonic
isotonic (”same strength”): When concentrations of solutions are the same on both sides of a membrane
Water goes in and out at the same rate and pressure doesn’t change

23. Hypotonic
hypotonic (“below strength”): the more dilute solution
SO,
Water enters the cell
Animal cells expand and possibly burst

24. Types of Transport across a membrane

25. Simple Diffusion
Molecules move from an area of high concentration to a low concentration. Does NOT require Energy. Happens naturally.
(“Molecules move down its concentration gradient”)

26. Facilitated Diffusion
Cell membranes have protein channels that act as carriers, allowing certain molecules to cross.
The movement of specific molecules across cell membranes through protein channels is known as facilitated diffusion.

27. Facilitated Diffusion
Only specific materials can enter or exit through each type channel.

28. Active Transport
Sometimes cells move materials in the opposite direction from which the materials would normally move—that is against a concentration gradient.
This process is known as active transport.
Active transport requires ENERGY.

30. Active Transport Examples: Endocytosis is the process
of taking material into the cell.
Phagocytosis: Solids or large molecules moved
Pinocytosis: “to drink,” Liquids moved
Exocytosis removes materials from the cell.

32. Membrane Transport Summary
Types of molecules transported
Special channel required?
Energy reguired?
Diffusion
Osmosis
Facilitated diffusion
Active transport no no
Small molecules
water no no
yes no
ions, sugars (glucose), salts
yes
yes
ions (H+, K+, Na+, Ca2+)