1.

2. Cell Boundaries
Chapter 6
3. What are boundaries?
We have borders surrounding countries
We have boundaries on a playing field
Why are borders important?
4. What are the borders of a cell?
Cell membrane
Thin, flexible barrier
Cell wall
Plant, algae, fungi, prokaryotes
Strong supporting layer
5. Cell Membrane
What does it do for cell?
Controls what goes in and out
Regulates molecules moving from one liquid side of the cell to the other liquid side of the cell
Protects
Supports
6. Cell Membrane
Lipid bilayer
What are lipids?
What does bi- mean?
Whats a layer?
A cell membrane is made of two
layers of lipid molecules
7. Cell membrane
Phospholipids bilayer
Made of a negatively charged phosphate head
PO43-
Attracts water because the phosphate is charged (-)
Water is a polar , slightly positive ends and slightly negative ends
Attached to the phosphate group are 2 fatty acid chains
Hydrophobic= dont like water
So the inside of the cell membrane doesnt let water in but the outside allows cells to be dissolved in aqueous environments
8. 9. Other things in the membrane
Proteins embedded in lipid bilayer
Carbohydrates attached to proteins
So many different molecules in membrane, we call it a mosaic of different molecules
10. 11. Proteins
Proteins help things get across membrane
Kinda like a pump
12. Carbohydrates
Chemical identification cards
ID card of cell
Helps individual cells id each other
13. 14. Cell Walls
Outside cell membrane (does NOT replace membrane!!!)
Plants, algae, fungi, prokaryotes
Have pores to allow things in
Function: SUPPORT and PROTECT
15. 16. Cell walls made of
Protein and carbs
Plant cell walls made up of CELLULOSE
This is a tough carbohydrate
Wood and paper
17. A biological membrane
Cells exist in liquid environments
Things need to get in and out of cell
Different ways to do this.
The Cell Membrane
18. Concentration (conc.)
Solution
Mix of 2 or more substances
Solutes
Substance dissolved in solution
Concentration
Molarity (M) is # of Moles of a substance per liter of solution
6.02 x 1023 small things (molecules, atoms, ions, electrons, ions, etc)
Moles is a unit for measuring EXTREMELY small things
is mass of SOLUTE in a given volume of solution (g/L)
What is the concentration of 12 grams of salt dissolved in 3 liters of water?
12g/3L= 4g/L
19. Diffusion
Particles constantly move
Collide randomly
Spread out randomly
Diffusion is moving from area of HIGH conc. to area of LOW conc.
This is what we call the CONCENTRATION GRADIENT
20. 21. Equilibrium
When the conc. Of a system is the same throughout
(same conc. on both sides)
22. What happens when we reach equilibrium?
Particles continue moving across membrane but in both directions!***No more changes in concentration
23. If things can cross a membrane we call the membrane PERMEABLE
If things canNOT cross a membrane we call the membrane IMPERMEABLE
24. Biological membranes are
SEMI-PERMEABLE
A.K.A.
Selectively permeable
Cell membranes are picky
25. Whats this have to do with cells?
Cell have liquid inside and are found in liquid environment
We have substances (solutes) inside and outside cell
Unequal concentrations means we get DIFFUSION!!!
B/c diffusion depends on random particle movements, substances diffuse across membranes without requiring the cell to use energy
26. What diffuses across the membrane???
Small, uncharged (non-polar) molecules
Examples:
Carbon dioxide
Oxygen
27. Cells are always trying to Maintain Equilibrium by
PASSIVE Transport
Requires NO energy
Goes with Conc. Gradient
3 types:
SIMPLE DIFFUSION-
No protein required
Small, uncharged particles
FACILITATED DIFFUSION-
CHANNEL or CARRIER proteins
Trans-membrane protein channel
Protein with a specific shape; open-close mechanism
Ex. Osmosis and ligand-gated channels
ACTIVE Transport
REQUIRES Energy
Goes Against Conc. Gradient
ACTIVE TRANSPORT
Involves transporter membrane protein and ENERGY (ATP)
28. Osmosis
Water (H2O) can pass easily through most biological membranes
Def:
Diffusion of Water through a semi-permeable membrane
Small molecules of water can sometimes diffuse across easily (no protein needed)
AQUAPORIN:
What does aqua mean???
Protein in cell membrane that allows water through (speeds up diffusion of water across the membrane)
Type of Facilitated diffusion (more on this later)
29. How Osmosis works
We have water molecules and some other molecules, lets say sugar
If we have more water on one side of the membrane (HIGH conc. of H2O), then the water will diffuse across
Membrane will let water thru but not sugar
Water can move back and forth (not sugar)
30. Water moves from areas of HIGH conc. To areas of LOW conc.
Water moves across till equilibrium is reached
Isotonic:
when conc. Of both solutions is equal
Hypertonic: above strength
When we begin with more sugar in water
More concentrated sugar solution on side A
Hypotonic: below strength
When we end with less sugar
Dilute sugar solution on side A
31. 32. 33. Osmotic Pressure
Central vacuole fills with water and exerts and out ward pressure on cell membrane and cell wall
Cell wall does NOT allow cell to expand past a certain size
Osmoregulation

Osmoregulation

34. means by which cells keep the concentration of cell cytoplasm or blood at a suitable concentration.