Diffusion Osmosis Lab

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Diffusion Osmosis Lab
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Osmosis

• Osmosis the movement of water molecules from a
  region of higher water potential to a region of
  lower water potential through a partially
  permeable membrane. Osmosis is considered in
  terms of water potential and solute potential.

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Water Potential

• Water potential a measure of the kinetic energy
  of water molecules. Here, water molecules are
  constantly moving in a random fashion. Some of
  them collide with cell membrane, cell wall,
  creating a pressure on its known as water
  potential.
• The higher their kinetic energy the more they
  move and hit the membrane, therefore higher the
  water potential

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Water potential
How does water move?
Why does water move?
1.
Downhill
Pressure potential
2.
Hose, straw
3.
Fresh salty
Osmotic/solute potential
4.
Sponge
Matric potential
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Components of Water Potential

• Pressure potential pushing (positive pressure,
  like the hose)
• sucking (negative
  pressure, like a straw) Major factor
  moving water through plants

• Osmotic, or Solute potential reduction in water
  potential due
• 
  to the presence of dissolved solutes
• Dissolved substances dilute pure water, so
• salty water has lower water potential (lower
  concentration) than pure water

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Water Potential

• Unit of measurement megapascals (Mpa)
• 1 MegaPascal 10 atm 145.1 psi
• Water potential for pure water 0
• Anything that lowers the free energyof water
  lowers it potential.
• -dissolved solutes

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Water potential pressure potential solute
potential
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Clarifying Water Potential Values

• (2) Factors to consider
• ?p pressure potential (outside inside)
• ?s solute potential
• ?system ?p ?s
• SO
• ? ?p results in value
• ? ?p results in - value

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Water Potential Values

• High water potential (Value)
• - less solute
• - more water
• - (hypotonic)
• Zero (0) Value
• - Pure water
• Low water potential (-Value)
• - More solute
• - less water
• - (hypertonic)
• Water will move across a membrane in the
  direction of the lower water potential

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Analysis of the Data Collected

• Mass Difference Final initial (absolute
  diff.)
• Change in Mass Final initial x 100
• initial
• Why do we use the change in mass instead of
  simply the straight difference?
• Plot your data on the graph.
• Determine the molar solute concentration of the
  potato cores. How???
• Where your line crosses the 0 mark

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Calculating Solute Potential

• Variables involved i, C, R, T
• i ionization constant NaCl 2.0 (Na
  Cl-)
• for sucrose it will be 1.0 (it doesnt ionize)
• C Molar concentration of your potato (graph)
• R rate constant 0.0821 L atm (bar)
• mol K
• T Temperature K

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Calculating the Solute Potential (?s)

• ?s - iCRT
• Sample Calc.
• A 1.0 M sugar solution _at_ 22 C under standard
  atmospheric conditions
• ?s -(1)(1.0mol)(0.0821 L bar )(295K)
• L mol K
• ?s -24.22 bars

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Typical Water Potential Values

• Outside air (50 humidity) -100 MPa
• Outside air (90 humidity) -13 MPa
• Leaf Tissue -1.5 MPa
• Stem -0.7 MPa
• Root -0.4 MPa
• Soil water -0.1 MPa
• Hydrated soil (Saturated) 2 - 5
  MPa
• When the soil is extremely dry what happens to
  the water potential and water movement into the
  plant?
• Does the value become more negative or more
  positive?

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Water Potential in Plants
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Water Balance (pg. 117-118)

• Osmoregulation control of water balance
• Hypertonic higher concentration of solutes
• Hypotonic lower concentration of solutes
• Isotonic equal concentrations of solutes
• Cells with Walls
• Turgid (very firm)
• Flaccid (limp)
• Plasmolysis plasma membrane pulls away from cell
  wall

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Dialysis Tubing Experiment
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An Artificial CellPermeable to monosaccharides
waterImpermeable to Disaccharides
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Introductory Questions 3 (Lab)

• Suppose you have an artificial cell that was
  permeable to monosaccharides and impermeable to
  disaccharides. What would happen to the cell if
  it had 0.80 M maltose and 0.85 M fructose in it
  and was placed in a solution containing 0.45 M
  glucose, 0.65 M fructose, and 0.40 M sucrose.
• a) Which direction would the water flow?
• b) Which area has a higher water potential?
• c) What would happen to the concentration of the
  maltose inside the cell (increase, decrease,
  remain the same)?
• What is the ionization constant (i) for sucrose?
• Determine the C value for your potato cores.
  (guidesheets)
• Graph your results
• change in mass vs. sucrose molarity within
  the beakers
• (guidesheets)

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Key Sections you need for your Lab

• Title
• Intro/Background Defining water potential
• Importance Sig. Of the lab
• Hypothesis reason for your prediction
• ID Experimental Variables
• Materials (diagram visual of set up optional)
• Procedure
• Data tables charts graphs
• Analysis- be thorough
• Conclusion Evaluation error improvements

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Introductory Questions (lab)

• Explain how potential energy is different from
  kinetic energy. What are some ways we can
  measure energy?
• 2) Define each variable in the equation
• ?G ?H T ?S
• 3) What is the difference between an exergonic
  reaction and an endergonic reaction?
• How is ATP associated with coupled reactions?
  What purpose does it serve?
• How is an electron carried from one molecule to
  the next? Name a molecule that can carry an
  electron.
• 6) How is Anabolism different from
  catabolism?
• 7) Briefly explain how the first two laws of
  thermodynamics apply to a living organism

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Lab 3 Water Potential Osmosis

• Read the Handout provided
• Go to my web site and click on
• Review of 12 AP Labs
• Click on the hyperlink shown on the worksheet
• Choose Lab 1 Diffusion Osmosis
• Go through the tutorial and READ each section.

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What to have Ready for Tomorrow

• Bring in a Large Potato (one per lab table)
• Have the Pre-lab finished w/quiz
• Write a statement of purpose or reason for doing
  this lab
• Materials list - review the handout
• Hypothesis
• Data Table review website or others for an
  idea.
• Need (2) Individual data class Data

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Introductory Questions 3 (Lab)

• Suppose you have an artificial cell that was
  permeable to monosaccharides and impermeable to
  disaccharides. What would happen to the cell if
  it had 0.80 M maltose and 0.85 M fructose in it
  and was placed in a solution containing 0.45 M
  glucose, 0.65 M fructose, and 0.40 M sucrose.
• a) Which direction would the water flow?
• b) Which area has a higher water potential?
• c) What would happen to the concentration of the
  maltose inside the cell (increase, decrease,
  remain the same)?
• What is the ionization constant (i) for sucrose?
• Determine the C value for your potato cores.
  (guidesheets)
• Graph your results
• change in mass vs. sucrose molarity within
  the beakers
• (guidesheets)

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Questions to answer from the Website- Prelab

• How many concepts are there?
• How many Exercises are there for
• designing the experiment?
• After looking at the Analysis Results portion
  of tutorial define each of following terms i
  C R T
• Do the 5 question quiz and print out your
  results.

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Answers for the Website- Prelab

• How many concepts are there? 8
• How many Exercises are there for
• designing the experiment? 5
• After looking at the Analysis Results portion
  of tutorial define each of following terms
• i ionization constant
• C molar concentration of the potato
• R rate constant 0.0821 L atm (bar)
• mol K
• T temperature (K) 273 ?C
• Do the 5 question quiz and print out your
  results.
• 1. C 2. D 3. E 4. B 5. A