1. Movement across the Cell Membrane

2. First free response (FRQ)
The selectively permeable plasma membrane is composed of phospholipids and protein, which allow for its unique functions.
A) DESCRIBE the structure and properties of phospholipids and EXPLAIN the important roles of phospholipids in the plasma membrane.
B) EXPLAIN why proteins are an important component of the cell membrane, based on their structure and properties.

3. Diffusion Lab homework
Read lab packet
Highlight all vocabulary in background section
Read procedures
Complete #1 on page 15.
TODAY: Part A
Procedures on page 6
Table 1 on page 12

4. Iodine reacts with starch causing a blue-black color.
Diffusion lab results
Color
Glucose
Time
Bag
Beaker
Start
clear
amber + -
30 minutes
Iodine reacts with starch causing a blue-black color.

5. Part B: Make 6 cells Then…day 3 of egg lab

6. Part b DIFFUSION lab data
This is what you graph
CLASS DATA FOR % CHANGE IN MASS
Water
0.2 M
0.4 M
0.6 M
0.8 M
1.0 M

9. #2: Iodine diffused into the bag (blue/black); Glucose diffused out of the bag into the environment; Osmosis was also occurring bc it went into the bag as glucose diffused out
#3: Yes, iodine and glucose diffused, but the starch could not diffuse bc it was too big
#4: Osmosis occurred which caused a net flow of water into the bag increasing its mass; More water because the environment was hypotonic (less solute). Equilibrium was reached.
#5: Hypotonic because it had less solute than the bags

10. Change in mass
water
.2 M
.4 M
.6 M
.8 M
1.0 M

11. Part C Class averages class avg Water 0.2 M 0.4 M 0.6 M 0.8 M 1.0 M
CLASS DATA FOR % CHANGE IN MASS OF POTATOES
Water
0.2 M
0.4 M
0.6 M
0.8 M
1.0 M

12. Percent change in mass of potatoes at different sucrose molarities
individual
class average
% Change in Mass
Sucrose Molarity (moles/liter)

13. PLASMOLYSIS turgor pressure
Plant cells losing water in hypertonic solutions
Shrinking
Cell membrane pulls away from outer cell wall
Very rare
Opposite?
turgor pressure

16. PASSIVE TRANSPORT
Movement of a substance across a membrane with no energy investment
Direction depends on concentration
High concentrations to low concentrations
DOWN or WITH its concentration gradient
Types: diffusion, osmosis, facilitated diffusion
Movement from high concentration of that substance to low concentration of that substance.

17. Diffusion Movement from high to low concentrations
2nd Law of Thermodynamics governs biological systems
universe tends towards disorder (entropy)
Movement from high concentration of that substance to low concentration of that substance.

18. movement of water
diffusion
osmosis

19. Osmosis is diffusion of water
Water is very important to life, so we talk about water separately
Diffusion of water from high concentration of water to low concentration of water
across a semi-permeable membrane

20. Concentration of water
Direction of osmosis is determined by comparing total solute concentrations
Hypertonic - more solute, less water
Hypotonic - less solute, more water
Isotonic - equal solute, equal water
hypotonic
hypertonic
water
net movement of water

21. Managing water balance
Cell survival depends on balancing water uptake andloss
freshwater
balanced
saltwater

22. Osmosis…
.05 M
.03 M
Cell (compared to beaker)  hypertonic or hypotonic
Beaker (compared to cell)  hypertonic or hypotonic
Which way does the water flow?  in or out of cell

23. Managing water balance
Isotonic
animal cell immersed in mild salt solution
example: blood cells in blood plasma
problem: none
no net movement of water
flows across membrane equally, in both directions
volume of cell is stable
balanced

24. Managing water balance
Hypotonic
a cell in fresh water
example: Paramecium
problem: gains water, swells & can burst
water continually enters Paramecium cell
solution: contractile vacuole
pumps water out of cell
ATP
plant cells
turgid
ATP
freshwater

25. Water regulation
Contractile vacuole in Paramecium
ATP

26. Managing water balance
Hypertonic
a cell in salt water
example: shellfish
problem: lose water & die
solution: take up water or pump out salt
plant cells
plasmolysis = wilt
saltwater

27. Aquaporins 1991 | 2003 Water moves rapidly into & out of cells
evidence that there were water channels
Peter Agre
John Hopkins
Roderick MacKinnon
Rockefeller

28. Diffusion across cell membrane
Cell membrane is the boundary between inside & outside…
separates cell from its environment
NO!
Can it be an impenetrable boundary? IN
OUT
food
carbohydrates,
sugars, proteins
amino acids,
lipids, salts, O2, H2O
waste
ammonia
salts
CO2
H2O
products
cell needs materials in & products or waste out

29. Diffusion through phospholipid bilayer
What molecules can get through directly?
fats & other lipids
inside cell
outside cell
What molecules can NOT get through directly?
polar molecules
H2O
ions
salts, ammonia
large molecules
starches, proteins
lipid
salt
NH3
sugar aa
H2O

30. Channels through cell membrane
Membrane becomes semi-permeable with protein channels
specific channels allow specific material across cell membrane
inside cell
H2O aa
sugar
salt
outside cell
NH3

31. Facilitated Diffusion
Diffusion through protein channels
channels move specific molecules across cell membrane
no energy needed
facilitated = with help
open channel = fast transport
Donuts!
Each transport protein is specific as to the substances that it will translocate (move).
For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer.
Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane.
These channel proteins allow fast transport.
For example, water channel proteins, aquaporins, facilitate massive amounts of diffusion.
high
low
“The Bouncer”

32. conformational change
Active Transport
Cells may need to move molecules against concentration gradient
shape change transports solute from one side of membrane to other
protein “pump”
“costs” energy = ATP
conformational change
Some transport proteins do not provide channels but appear to actually translocate the solute-binding site and solute across the membrane as the protein changes shape. These shape changes could be triggered by the binding and release of the transported molecule. This is model for active transport.
low
high
ATP
“The Doorman”

33. Active transport Many models & mechanisms ATP ATP antiport symport
Plants: nitrate & phosphate pumps in roots.
Why?
Nitrate for amino acids
Phosphate for DNA & membranes
Not coincidentally these are the main constituents of fertilizer
Supplying these nutrients to plants
Replenishing the soil since plants are depleting it
antiport
symport

34. Getting through cell membrane
Passive Transport
Simple diffusion
diffusion of nonpolar, hydrophobic molecules
lipids
high  low concentration gradient
Facilitated transport
diffusion of polar, hydrophilic molecules
through a protein channel
Active transport
diffusion against concentration gradient
low  high
uses a protein pump
requires ATP
ATP

35. Transport summary simple diffusion facilitated diffusion
ATP
active transport

36. How about large molecules?
Moving large molecules into & out of cell
through vesicles & vacuoles
endocytosis
phagocytosis = “cellular eating”
pinocytosis = “cellular drinking”
exocytosis
exocytosis

37. Endocytosis fuse with lysosome for digestion phagocytosis
non-specific process
pinocytosis
triggered by molecular signal
receptor-mediated endocytosis

38. The Special Case of Water Movement of water across the cell membrane

39. Any Questions??