1. Homeostasis Maintenance of a stable internal environment
Maintaining the proper balance
Cell membrane helps maintain the cell’s homeostasis by regulating the movement of substances across the membrane

2. Homeostasis Cell membrane is SEMIPERMEABLE
The cell controls what comes in or goes out

3. Cell Membrane Phospholipid Bilayer Phospholipid Bilayer
Phosphate “head”
Two fatty acid “tails”
Bilayer
Two layers

4. Cell Membrane Phosphate “head” Two fatty acid “tails” Hydrophilic
Hydro = Water
Philic = Attraction
“Water-loving”
Two fatty acid “tails”
Hydrophobic
Phobic = opposite of attraction = aversion
“Water Hating”

5. Cell Membrane Barrier to outside
Only very small substances can pass through it

6. Cell Transport
Cells need to move substances in and out of the cell for many reasons
Get food, to remove waste, to maintain homeostasis
Variety of ways that substances can move across cell membrane
Passive transport
Active transport

7. Passive Transport
Substances move across the membrane without an energy input – Passive
Equilibrium
State of balance, stability
Chemical equilibrium = equal concentration
If concentrations are not equal…
Cell membrane will move substances to create equilibruim

8. Passive Transport
If the concentration on one side of the cell membrane is higher than the other, a CONCENTRATION GRADIENT exists
Substances will move from high concentrations to low concentrations
DIFFUSION
Moving down the concentration gradient
No energy input

10. Two Types of Diffusion Simple Diffusion Facilitated Diffusion
Small nonpolar substances can move directly through the phospholipid bilayer
Facilitated Diffusion
Other substances cannot pass through the lipid bilayer
They require assistance in movement across the membrane

11. Facilitated Diffusion
Required assistance
Cannot just move the membrane wherever it wants
Proteins are present in cell membrane
Two types of proteins can give assistance:
Channel Proteins
Carrier Proteins

12. Facilitated Diffusion
Channel Proteins
Proteins located in the lipid bilayer that act as tunnels
Each protein is made for the transport of a certain substance
Sodium ions pass through sodium ion channels

13. Facilitated Diffusion
Carrier Proteins
Proteins located in the lipid bilayer that bind to certain substances
After the substance binds to its binding site, the protein changes shape
This change in shape moves the substance across the membrane

14. Channel Proteins vs Carrier Proteins

15. Osmosis Water can move in and out of the cell too
Water can diffuse across the cell membrane through osmosis

16. Osmosis Water is polar Water uses channel proteins
(only nonpolar substances can move directly across the membrane)
Water uses channel proteins
Water moves down the concentration gradient for water

17. Osmosis
If the sugar were to move down its concentration gradient it would move which direction?
If the water were to move down its concentration gradient which way would it move

18. Osmosis in a Cell HYPERTONIC Hyper = excessive
Tonic = solution with concentration
High solute concentration outside the cell
INSIDE OUTSIDE
High water Low water
Low solute high solute
Water moves OUT

20. Osmosis in a Cell HYPOTONIC Hypo = low
Tonic = solution with concentration
Low solute concentration outside the cell
INSIDE OUTSIDE
Low water High water
High solute Low solute
Water moves IN

22. Osmosis in a Cell ISOTONIC Iso = equal
Tonic = solution with concentration
Equal solute concentration outside the cell
INSIDE OUTSIDE
Same water Same water
Same solute Same solute
Water does NOT move
Equilibrium

24. Active Transport
Sometimes substances have to move against the concentration gradient
Working against the concentration gradient requires energy input from the cell
ACTIVE

25. Active Transport
Facilitated diffusion uses carrier proteins to move substances WITH the concentration gradient
No energy needed
Active Transport can use carrier proteins to move substances AGAINST the concentration gradient
Energy required

26. Pumps
Carrier proteins that move substances against the concentration gradient are called PUMPS
The substance to be moved attaches to the carrier protein
ATP is added for energy
The carrier protein then changes shape and moves the substance

27. ACTIVE TRANSPORT - Pumps

29. ACTIVE TRANSPORT - Vesicles
Vesicles can trap substances from outside the cell and bring them into the cell
Movement into a cell via vesicles
ENDOCYTOSIS
Movement out of a cell via vesicles
EXOCYTOSIS

30. ACTIVE TRANSPORT - Vesicles

31. ACTIVE TRANSPORT - Vesicles

32. CONCENTRATION
GRADIENT
CARRIER
PROTEIN

33. Homework
DR Cell Transport : 7-17