Post Lab #2: Diffusion and Osmosis Further Discussion of Part A and Part B AP Biology Ms. Day...
-
Upload
aldous-wilkinson -
Category
Documents
-
view
221 -
download
0
Transcript of Post Lab #2: Diffusion and Osmosis Further Discussion of Part A and Part B AP Biology Ms. Day...
Post Lab #2: Diffusion and Osmosis
Further Discussion of Part A and Part B
AP Biology
Ms. Day
10/8/14
PART A: Diffusion and Dialysis Tubing
• What happened to the STARCH?• Iodine moved into bag (high low [
])• Starch too big do NOT move• STARCH + Iodine = BLACK COLOR
• What happened to the GLUCOSE?• Moved out of bag (high low [ ])• Benedict test has POSITIVE result in
presence of glucose • it was cloudy and changed color• Not a lot of glucose present
PART B: Osmosis and Dialysis Tubing
• As sucrose molarity increased, % change in mass also increased.
• WHY???– Solutions were getting more and
more hypertonic IN bag• Water moved INTO bag to maintain
equilibrium
PART B GRAPH: Osmosis and Dialysis Tubing…
What do you expect?
Post Lab #2: Diffusion and Osmosis
Further Discussion of Water Potential
AP Biology
Ms. Day
10/8/14
PART C: Osmosis and Potato Cores
RECALL: Water Potential (Ψ)
• Botanists use this term when predicting the movement of water into/out of plant cells.
• Abbreviated by Ψ (“psi”) Ψ = Ψp + Ψs
water potential = pressure potential + Solute (osmotic)
potential
Plants & Water PotentialPlants & Water Potential (water potential) combines the effects
of 1.) solute concentration 2.) physical pressure placed on cell
= psi = water potential
• What are the units for ? –measured in megapascals (MPa) or
Bars
Solute Potential (Solute Potential ( S)
• Solute potential is also called the osmotic potential because solutes affect the direction of osmosis.
S of any solution at atmospheric pressure ( p = 0) is always negative!
WHY?• Answer = less free water molecules to do
work
Recall: What are Recall: What are ““freefree”” water water molecules?molecules?
• Solutes bind water molecules reducing the number of free water molecules lowers waters ability to do work (ex: move)
Pressure Potential (Pressure Potential (P)
P is the physical pressure on a solution where cell is located.
• P can be negative transpiration in the xylem tissue of a plant (“pulling” pressure)
P can be positive water in living plant cells is under positive pressure by cell wall pushing on cell membrane (“pushing” pressure)
Standard for measuring Standard for measuring
• Pure water is the standard.
• Pure water in an open container has a water potential of zero at one atmosphere of pressure.
Therefore, assume …Therefore, assume …ΨΨp p is zero b/c is zero b/c solution is at atmospheric pressure solution is at atmospheric pressure (unless told otherwise in problem)(unless told otherwise in problem)
RECALL: Water MovementRECALL: Water Movement
• Water will ALWAYS move from an area of HIGHER Ψ to an area of LOWER Ψ
(more positive Ψ more negative Ψ )
– Water diffuses DOWN a water potential gradient
•Higher Ψ – More “free” water molecules; more solutes
•Lower Ψ – Less “free” water molecules; more solutes
PART C:Graphing Potato Core Data
• Graph your data using positive and negative value for % change in Potato Core Mass
• Connect the “dots” between all data points
• The point at which the line CROSSES the X-AXIS represents the molar [ ] of sucrose INSIDE potatoe cell
0.0 0.2 0.3 0.4 0.60.6
Isotonic Solution is at ZERO indicated the amount of solutes in
potato cells (THIS IS YOUR MOLAR [ ] of solutes INSIDE the potato)
PART D: Calculating the PART D: Calculating the Water Water ΨΨ from Experimental from Experimental
DataData• Remember: Ψ = Ψp + Ψs
HOW DO YOU FIND THE SOLUTE POTENTIAL?
• Solute potential Ψs = -iCRT• i = ionization CONSTANT (for sucrose it is = 1)• C = Molar concentration (determined from graph)• R = Pressure CONSTANT (0.0831 L bars/ mol•K)• T = Temperature in Kelvin (273 + ºC)
• Units will all cancel so Ψs is in bars!
So…..So…..• Knowing the Ψs , you can figure
out water potential Ψ.
•NOTE: NOTE: ΨΨp p is zero b/c solution is zero b/c solution is at atmospheric pressureis at atmospheric pressure
• Use Ψ = Ψp + Ψs
• Water potential values are important b/c it allows us to predict the direction of the flow of water.
Bozeman Biology-Review of Water Potential
• https://www.youtube.com/watch?v=nDZud2g1RVY
Water Potential Practice Problems
AP Biology
Ms. Day
10/8/14
Water Potential: an artificial model
• (a) addition of solutes on right side reduces water potential. S = -0.23
• Water flows from “hypo” to “hyper”
• Or from hi on left
to lo on right
Water Potential: an artificial model
• (b) adding +0.23 pressure with plunger no net flow of water
• (c) applying +0.30 pressure increases water potential solution now has of +0.07
• Water moves right to left
• (d) negative pressure or tension using plunger decreases water potential on the left.
• Water moves from right to left
Water Potential: an artificial model
Animal vs. Plant Cells• Animal cells can take in water until it
BURSTS (or lyses)
• Plant cells take in water and exert a PRESSURE on cell due to constrictions by cell wall– Cell wall prevents cells from BURSTING.
Instead, pressure build up! – This pressure will affect water movement.
This is called TURGOR PRESSURE. WHY IS WATER MOVEMENT WHY IS WATER MOVEMENT AFFECTED????AFFECTED????
Water relations in plant cells
• (b) Flaccid cell in pure waterpure water Water potential is into cell cell becomes turgid
Water relations in plant cells
• (a) Flaccid cell placed in hypertonichypertonic solution Water potential is out of cell plasmolysis
Hints & reminders
1. Remember water always moves from [hi] to [lo].
2. Water moves from hypo hypertonic.3. [Solute] is related to osmotic pressure.
Pressure is related to pressure potential.4. Pressure raises water potential.5. When working problems, use zero for
pressure potential in animal cells & open beakers.
6. 1 bar of pressure = 1 atmosphere