1. Chapter 7 Cell Structure & Function
Section 7-3
Movement Through The Membranes

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

3. The Cell Membrane
Key Concept:
The cell membrane regulates what enters and leaves the cell and also provides protection and support

4. The Cell Membrane
The cell takes in nutrients and expels wastes plus cell products through the cell membrane
The Basic Structure Of Nearly All Cell Membranes Is The LIPID BILAYER

5. LIPID BILAYERS
Form Automatically When Certain Lipids Are Dissolved In Water
Tough Flexible Structure
Strong Barrier Between Cell Contents And Its Surroundings

6. LIPID BILAYERS

7. LIPID BILAYERS

8. In Addition To The Bilayer, The Cell Membrane Contains:
Fluid Mosaic Model
In Addition To The Bilayer, The Cell Membrane Contains:
Proteins That Form
Channels & Pumps
Proteins with Carbohydrates That Form
Antigenic Sites
Communication Sites

10. Diffusion All Living Cells Contain And Are Surrounded By Liquid.
THE CELL MEMBRANE REGULATES THE MOVEMENT OF MOLECULES FROM ONE SIDE OF THE MEMBRANE TO THE OTHER

11. Is A Solution Of Many Different Substances In Water
Cytoplasm
Is A Solution Of Many Different Substances In Water

12. A liquid mixture of 2 or more substances evenly mixed.
Solution
A liquid mixture of 2 or more substances evenly mixed.
Solvent
The liquid in which the substances are mixed
Solute
Substances dissolved in the Solvent

13. Concentration Of Solution
Mass of the solute in a given volume of solvent.
Mass/Volume e.g.
12 g. of NaCl dissolved in 3L H2O =
12g./3 l or g/L

14. In A Solution Molecules Are Moving Constantly
They Collide and Bounce off each other
This causes them to spread out randomly
Resulting In:
Movement from an area of higher concentration to and area of lower concentration

15. DIFFUSION
Molecules move away from an area of Higher Concentration to area’s of Lower Concentration
Equilibrium
Concentration of a solute is the same throughout the solution

16. Diffusion

17. Diffusion Causes Many Substances To Move Across A Cell Membrane But:
Key Concept:
Diffusion Causes Many Substances To Move Across A Cell Membrane But:
Does NOT Require The Cell
To Use Energy

18. Diffusion across a membrane

19. Diffusion & Cells
Substances that can diffuse across cell membranes will do so until equilibrium is reached
Diffusion continues after equilibrium but the rates in and out are equal

20. OSMOSIS

21. Osmosis Permeable Membrane Impermeable Membrane
Substance Can Easily Cross
Impermeable Membrane
Substance Can NOT Cross
Selectively Permeable Membrane
Some Substances Can Cross, Others Can Not

22. The Diffusion Of Water Through A Selectively Permeable Membrane
OSMOSIS
Key Concept:
The Diffusion Of Water Through A Selectively Permeable Membrane

24. The Tonics Hypotonic Isotonic Hypertonic Less concentrated solution
Equally concentrated solution
Hypertonic
More Highly concentrated solution

25. The Tonics

26. The Tonics

27. Osmotic Pressure
Pressure exerted on the hypertonic side of a selectively permeable membrane
May cause cells to shrink or burst

28. Osmotic Pressure
Cell Walls
Contractile Vacuoles

29. Facilitated Diffusion
Molecules that can easily diffuse across the cell membrane:
Alcohol
Water
Small Lipids

30. Facilitated Diffusion
Other molecules can not pass through the cell membrane but still get into the cell.
HOW?

31. Facilitated Diffusion
Thru Protein Channels in the Cell Membrane that allow a substance to cross.
Allows Diffusion In Both Directions
Each Channel Substance Specific
DOES NOT REQUIRE ENERGY

32. Facilitated Diffusion
Protein Channel Is Substrate Specific
Substrate Can Move Either Direction Depending On Concentration. Always from area of Higher Concentration to area of Lower Concentration!

33. Active Transport Moves Material Across A Cell Membrane
Against A Concentration Gradient
(from area of Lower concentration into an area of Higher concentration)

34. Active Transport
Requires Energy

35. Energy Molecule

36. Active Transport

37. Active Transport Endocytosis Exocytosis
Used to bring in large molecules, food, and whole cells
Exocytosis
Membrane surrounded material from inside the cell fuses with the cell membrane, releasing the contents.