1. Cell Membranes Structure, Function and Transport

2. TEM picture of a real cell membrane.
Cell Membranes
ALL CELLS HAVE A CELL MEMBRANE
Why do all cells need a cell membrane?
Functions:
1. Controls what enters and exits
2. Provides protection and support for the cell
TEM picture of a real cell membrane.

3. Let’s Look at the Structure
Lipid Bilayer –2 layers of phospholipids (chocolate chip ice cream sandwich)
Fatty acid tails (ice cream)
Phosphate head (cookie)
Proteins- embedded in membrane: (chocolate chips)
Carbohydrates-sticking out (label)
Phospholipid
Lipid Bilayer

4. B A D C F G H E

5. Fluid Mosaic Model of the cell membrane
Polar heads love water & dissolve.
Membrane movement animation
Non-polar tails hide from water.
Carbohydrate cell markers
Proteins

6. Structure of the Cell Membrane
Outside of cell
Carbohydrate
chains
Proteins
Lipid
Bilayer
Transport
Protein
Phospholipids
Inside of cell
(cytoplasm)
Animations
of membrane structure
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7. Cell Membranes
Cell membranes allow some molecules to move through but not others. This is called being Selectively Permeable.
How is a cell membrane like a screen door?
Pores

8. Types of Cellular Transport
Animations of Active Transport & Passive Transport
high
low
Weeee!!!
Passive Transport
cell doesn’t use energy
Diffusion
Facilitated Diffusion
Osmosis
Active Transport
cell does use energy
Protein Pumps
Endocytosis
Exocytosis
High to Low
Low to High
high
low
This is gonna be hard work!!

9. Traits of Passive Transport
Cell uses no energy
Molecules move randomly
Molecules spread out from an area of high concentration to an area of low concentration. HIGH  LOW
Continues until all molecules are evenly spaced (equilibrium)-Note: molecules will still move around but stay spread out.

10. 3 Types of Passive Transport
Diffusion -solutes move
Facilitated Diffusion – solutes move with the help of transport proteins
Osmosis – water moves
HIGH LOW

11. Passive Transport: Diffusion
Simple Diffusion Animation
Passive Transport: Diffusion
Random movement of particles (particles are always bumping into each other) from an area of high concentration to an area of low concentration.
(High  Low)
Particles move through pores (spaces) in cell membrane
Molecules will still move around but stay spread out.

12. Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer)
Passive Transport: Facilitated Diffusion A B
Movement of specific particles through Transport Proteins
Transport Proteins are specific – they “select” only certain molecules to cross the membrane
Transports larger or charged molecules that can’t move through pores.
Facilitated diffusion (Channel Protein)
Diffusion (Lipid Bilayer)
Carrier Protein

13. Passive Transport: Facilitated Diffusion
Glucose
molecules
Cellular Transport From a-
High
High Concentration
Channel Proteins animations
Cell Membrane
Low Concentration
Protein
channel
Low
Transport Protein
Through a 
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14. Passive Transport: Osmosis
Osmosis animation
diffusion of WATER ONLY through a selectively permeable membrane
Water moves from high to low concentrations
Continues until concentration reaches equilibrium
Water moves freely through pores.
Solute (green) to large to move across.

15. Traits of Active Transport
Cell uses energy
Actively moves molecules to where they are needed
Movement from an area of low concentration to an area of high concentration LOW  HIGH
Doesn’t move toward equilibrium

16. 3 Types of Active Transport
Protein Pumps-move solutes through membrane channels in either direction
Endocytosis-move materials out
Exocytosis-move materials in
LOW HIGH

17. Types of Active Transport
Sodium Potassium Pumps (Active Transport using proteins)
Protein Pumps -transport proteins that require energy to do work
Example: Sodium / Potassium Pumps are important in nerve responses.
Protein changes shape to move molecules: this requires energy!

18. Types of Active Transport
Endocytosis (endo=in): taking bulky material into a cell
A.K.A.“cell eating”
Cell membrane in-folds around food particle
forms food vacuole
This is how white blood cells eat bacteria!

19. Types of Active Transport
Exocytosis (exo=out): Forces material out of cell
Membrane surrounding the material and forms a vacuole
This fuses with cell membrane
Materials are forces out
Hormones or wastes released from cell
Endocytosis & Exocytosis animations

20. Effects of Osmosis on Life
REMEMBER: Osmosis is the diffusion of water through a selectively permeable membrane
HIGH CONC  LOW CONC
This is great is most cases but can also cause some BIG PROBLEMS!

21. Osmosis Animations for isotonic, hypertonic, and hypotonic solutions
Hypotonic: The solution the cell is found in has a lower concentration of solutes (hypo-low) and a higher concentration of water than inside the cell.
(Low solute = High water) Which direction does the water move?
Result: Water moves from the solution to inside the cell): Cell Swells and can burst open (cytolysis)!

22. Osmosis Animations for isotonic, hypertonic, and hypotonic solutions
Hypertonic Solution
Hypertonic: The solution the cell is found in has a higher concentration of solutes (hyper-high) and a lower concentration of water than inside the cell. (High solute = Low water) Which direction does the water move?
shrinks
Result: Water moves from inside the cell into the solution: Cell can shrink drastically (Plasmolysis)!

23. Osmosis Animations for isotonic, hypertonic, and hypotonic solutions
Isotonic Solution
Isotonic: The concentration of solutes in the solution the cell is found in is equal (iso-same) to the concentration of solutes inside the cell.
Which directions does the water move?
Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)
This condition maintains HOMEOSTASIS!!!

24. B C A What type of solution are these cells in? hypertonic isotonic
hypotonic

25. How Organisms Deal with Osmotic Pressure
Paramecium (protist) removing excess water video
Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure.
A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding.
Salt water fish pump salt out of their specialized gills so they do not dehydrate.
Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.