1. Chapter 3A Cell Membranes
Cell Structure
Chapter 3A
Cell Membranes

2. Objectives
I will be able to describe the characteristics of a cell membrane.
I will be able to distinguish between passive transport and active transport.
I will be able to compare the processes of diffusion and osmosis.

3. Cytology
The study of cells

4. Cell Boundaries
The cell membrane is the outer boundary of most cells. Found in all cells.
A cell wall is a stiff structure outside the cell membrane that protects a cell from attack by viruses and other harmful organisms. Found in plant cells.

5. Cell membrane

6. Cell Membrane Functions
Senses and responds to changes in the environment
Protects cell from harmful substances
Allows needed materials into the cell

7. Cell Membranes Fluid mosaic model Phospholipids Lipid bilayer
Hydrophilic (point towards outside)
Hydrophobic (point towards middle)
Lipid bilayer

8. Fluid Mosaic Model

9. Selectively Permeable
A selectively permeable membrane allows certain molecules to pass through the membranes and others to not pass through

10. Selectively Permeable
Not all membranes are permeable to the same molecules.
However water, oxygen, and carbon dioxide are small and easily passes through most membranes.

11. How does a substance pass through a unit membrane?
Passive Transport
Active Transport

12. Passive Transport
Passive transport moves substances through a membrane without the use of the cell’s own energy.

13. PASSIVE TRANSPORT This is the main way.
Small molecules, such as oxygen and carbon dioxide, pass through membranes via passive transport.
Passive transport depends on the amount of substance on each side of a membrane.
This is the main way.

14. main forms of passive transport
Diffusion
Osmosis
Facilitated Diffusion

15. diffusion
the movement of molecules from an area of higher concentration to an area of lower concentration
diffusion
from Latin diffusionem, means “scatter, pour out”

16. diffusion
diffusion can be speeded up by such things as heat, movement, and pressure

17. Diffusion
Diffusion continues until the concentration of a substance is the same on both sides of the membrane. The substance is then in equilibrium.

18. The diffusion of water through a selectively permeable membrane
Osmosis
The diffusion of water through a selectively permeable membrane

19. Facilitated Diffusion
Facilitated diffusion occurs when molecules pass through a cell membrane using special proteins called transport proteins.
Carrier proteins are transport proteins that carry large molecules through the cell membrane.
Channel proteins are transport proteins that form pores through the cell membrane.

20. Facilitated Diffusion
The Plasma Membrane
11/12/2018
Facilitated Diffusion
*Is a type of passive transport
Doesn’t require energy
Uses transport proteins to move molecules from high to low concentration
Facilitated Diffusion- is the movement of larger molecules like glucose through the cell membrane  larger molecules must be “helped”
Examples: Glucose or amino acids moving from blood into a cell.
G. Podgorski, Biol. 1010

21. Facilitated Diffusion

22. ACTIVE TRANSPORT
Active transport requires the cell to use its own energy to move substances through a membrane.
(sometimes because of the size of the molecule being so large, or going against gradient)

23. This is going to be hard work!!
Active Transport
Requires Energy.
ATP (form of energy made by mitochondria).
Moves against the concentration gradient.
High
low
This is going to be hard work!!

24. Sodium Potassium Pump
Active transport goes AGAINST the concentration gradient
Low solute concentration to high solute concentration
The cell uses energy (ATP) to actively transport Na+ out of the cell and K+ into the cell against the concentration gradient

25. Sodium Potassium Pump

26. Endocytosis and Exocytosis
Endocytosis and Exocytosis is the mechanism by which very large molecules (such as food and wastes) get into and out of the cell
**ENERGY IS REQUIRED

27. Endocytosis Think endo- Think enter
Transporting material into a cell by the in folding of a membrane.
Think endo-
Think enter
To take inside of the cell

28. 2 Types of Endocytosis
Phagocytosis- Solid particles are ingested into the cell.
Pinocytosis – liquids and very small molecules are taken into the cell.

29. Endocytosis

31. Exocytosis
Moves materials out of the cell
Think exo-
Think exit

32. Exocytosis- moving things out.
The Plasma Membrane
Moving the “Big Stuff”
11/12/2018
Exocytosis- moving things out.
Molecules are moved out of the cell by vesicles that fuse with the plasma membrane.
This is how many hormones are secreted and how nerve cells communicate with one another.
G. Podgorski, Biol. 1010