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Copyright © Rebecca Rehder Wingerden
Pearson Education, Inc., publishing as Person Benjamin CummingsCollege Board, AP Biology Curriculum Framework 2012-2013
AP Biology Investigative Labs: An Inquiry-Based Approach
Investigation 4: Diffusion and Osmosis
AP Biology Investigation 4: Diffusion and OsmosisLearning Objectives• To investigate the relationship among surface area, volume,
and the rate of diffusion
• To design experiments to measure the rate of osmosis in a model system
• To investigate osmosis in plant cells• To design an experiment to measure water potential in plant
cells• To analyze the data collected in the experiments and make
predictions about molecular movement through cellular membranes
• To work collaboratively to design experiments and analyze results
• To connect the concepts of diffusion and osmosis to the cell structure and function
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Background
• Cells must move materials through membranes and throughout cytoplasm in order to maintain homeostasis.
• The movement is regulated because cellular membranes, including the plasma and organelle membranes, are selectively permeable.
• Membranes are phospholipid bilayers containing embedded proteins.
• The cellular environment is aqueous.
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and OsmosisBackground
• Diffusion - solutes move from an area of high concentration to an area of low concentration
- simplest form of movement,
- directly related to molecular kinetic energy, and
- does not require energy input by cells.
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Background
• Osmosis - the diffusion of water- water moves from
an area of high potential (high free water concentration) and low solute concentration to areas of low potential (low free water concentration) and high solute concentration.
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Background
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Background
• Water Potential predicts which way water diffuses through plant tissue
- water potential (Ψ) is the free energy per mole of water and is calculated from two major components:• pressure potential (ΨP) which results from the
exertion of pressure - either positive of negative (tension) - on a solution
• solute potential (ΨS) which is dependent on solute concentration (osmotic potential)
Ψ = ΨP + ΨS
Copyright © 2012 Rebecca Rehder Wingerden
Bozeman Biology: Water Potential (10:00 min.)https://paul-andersen.squarespace.com/water-potential
Investigation 4: Diffusion and Osmosis
Complete the following before conducting this investigation:
I. Read Investigation 4: Diffusion and Osmosis and be ready to complete the all three Procedures.
II. Answer the following PreLab questions in Comp Book:
1. Summarize what you will be doing in this investigation (remember there are three parts).
2. What is the primary question you will be trying to answer in each part of this investigation?
Copyright © 2012 Rebecca Rehder Wingerden
PreLab
Investigation 4: Diffusion and Osmosis
Getting Started:
• Complete LabBench Activity Lab 1 Diffusion & Osmosis in your CompBook (handout)- http://www.phschool.com/science/biology_place/
labbench/lab1/intro.html
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Procedure 1: Surface Area and Cell SizeComplete Activity - Limits To Cell Size in your CompBook (handout)• Part 1:- Table 1: Cell Dimensions and Time for Diffusion- Calculations (show your work)
• Part 2: - Table 2: Cell Mass and Time for Diffusion- Calculations (show your work)
• Summary Questions: #1-9 in your CompBook
Copyright © 2012 Rebecca Rehder Wingerden
Note - Please edit question 7 to read ...modified to facilitate the diffusion of materials which support life processes?
Investigation 4: Diffusion and Osmosis
Procedure 2: Modeling Diffusion and Osmosis• Before conducting this part of the investigation:
- Complete Pre-Lab Questions 1-13 (handout)- Discuss the three bulleted questions at the top of
page S57 with your lab group- ReRead Procedure steps 1-4 (p. S57)- Choose the four pairs of different solutions that
your group will test in your cell models- Prepare Data Table to record your findings- Predict the direction of osmosis in EACH cell
model (You should have 5 different hypotheses)- Approval by Instructor
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Procedure 2: Modeling Diffusion and Osmosis
Copyright © 2012 Rebecca Rehder Wingerden
Number of Cell Model
SolutionSolution Mass of Dialysis (g)Mass of Dialysis (g)Percent
change in weight
Number of Cell Model
Inside Dialysis
Bag
Outside Dialysis
BagInitial Final
Percent change in
weight
1
2
3
4
5
Table 1: Percent Change in Weight of Cell Models
Predictions: Predict the direction of osmosis in each cell model
Investigation 4: Diffusion and Osmosis
Copyright © 2012 Rebecca Rehder Wingerden
• Day of investigation:- Procedure steps 1-4- Record findings in your
Data Table- Analysis: percent change
in weight calculations (show your work)
- Answer PostLab Questions: 1-6 (handout)
Procedure 2: Modeling Diffusion and Osmosis
Investigation 4: Diffusion and Osmosis
Procedure 3: Observing Osmosis in Living Cells
Elodea cell before and after plasmolysis
Plasmolysis of Elodea: http://www.csun.edu/scied/7-microscopy/elodea_plasmolysis/index.htmRed Onion Plasmolysis: http://teachertube.com/viewVideo.php?video_id=135394
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Procedure 3: Observing Osmosis in Living Cells• Before conducting this part of the investigation:
- Complete Pre-Lab Questions 1-4 (handout)- Read alternate procedure steps 1-6 for this part of
the investigation- Determine the solution your group will test- Write your hypothesis: If (rational for the
investigation), then (outcome that you would expect).
- Prepare Data section: • Leaf Diagram (control) & Observations• Leaf Diagram (experimental) & Observations
- Approval by Instructor
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Procedure 3: Observing Osmosis in Living Cells
Copyright © 2012 Rebecca Rehder Wingerden
Diagram 1: Leaf Cell Drawings CONTROL VARIABLEleaf cell in fresh water
EXPERIMENTAL VARIABLEleaf cell in _(solution)_
Observations Observations
Text
Investigation 4: Diffusion and Osmosis
Copyright © 2012 Rebecca Rehder Wingerden
• Day of investigation:- Procedure steps 1-6- Record findings in your Data Table
Procedure 3: Observing Osmosis in Living Cells
- Answer PostLab Questions: 1-3 (handout)
Plant Cell Wall
Plant Cell Membrane
Onion @ 100xCopyright © 2012 Rebecca Rehder Wingerden
Plant Cell MembranePlant Cell Wall
Onion w/ NaCl @ 100xCopyright © 2012 Rebecca Rehder Wingerden
Designing and Conducting Your Investigation:• Design and experiment to identify the concentrations
of the sucrose solutions and use the solutions to determine the water potential of the plant tissues.
• You will then conduct your experiment, analyze your results and formulate a conclusion.
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Bozeman Biology: Osmosis Lab Walkthrough (8:00 min.)http://www.bozemanscience.com/osmosis-lab-walkthrough
• Before conducting this part of the investigation:- Complete Pre-Lab Questions Fun With Water
Potential (handout)- Discuss the seven bulleted questions at the bottom
of page S59 with your lab group- Design your investigation and get it approved
Your Design: Determining Water Potential of Plant Tissues• Purpose: method that will be used, independent and
dependent variable• Hypothesis: If (rational for the investigation), then
(outcome that you would expect).• Procedure: Design an experiment to (1) identify the
concentrations of the sucrose solutions and (2) determine the water potential of the plant tissues. Identify the (3) independent (levels), (4) dependent, and (5) standardized variables in your experimental design.
• Data: table(s) to record findings• Approval by Instructor
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Your Design: Determining Water Potential of Plant Tissues
Copyright © 2012 Rebecca Rehder Wingerden
Investigation 4: Diffusion and Osmosis
Solution Color
Solution Temperature ºC
Solution Temperature ºC Plant Cell Tissue CylindersPlant Cell Tissue CylindersPlant Cell Tissue CylindersPlant Cell Tissue Cylinders
Solution Color
Initial Final Initial Mass (g)
Final Mass (g)
Change in Mass (g)
% Change in Mass
Table 1: Plant Cell Tissue Water Potential
Investigation 4: Diffusion and Osmosis
Copyright © 2012 Rebecca Rehder Wingerden
• Day of investigation:- Complete your approved procedure- Record findings in your Data Table- Analysis:
• Calculations: Percent Change In Mass• Identify molarity of color-coded sucrose solutions• Graph: Plant Cell Water Potential• Identify approximate molar concentration of plant
tissue (graph)• Water potential of plant tissue (calculations)
- Answer PostLab Questions: 1-4 (handout)
Your Design: Determining Water Potential of Plant Tissues
Investigation 4: Diffusion and Osmosis
Graph 1: Change in Mass of Watermelon Cores for a Given Sucrose Concentration
What is the approximate molar concentration of the watermelon cell according to the graph? ~ 0.33 M
Copyright © 2012 Rebecca Rehder Wingerden
Your Design: Determining Water Potential of Plant Tissues
Investigation 4: Diffusion and Osmosis
Using the data from the graph and the formula for water potential, calculate the solute potential (Ys) of the sucrose solution in bars?
where:i = ionization constant (1 for sucrose, 2 for NaCl)C = molar concentrationR = .0831 (pressure constant)T = temperature in degrees K
Assume a room temperature of 27ºC
-1 0.33 mole 0.0831 L bar 300ºK
L mole ºK= = -8.23 bars
If the equilibrium point between the solution and the watermelon cells indicates the point where the two water potentials are equal, then what is the water potential of the watermelon cells? -8.23 bars
Copyright © 2012 Rebecca Rehder Wingerden
Bozeman Biology: AP Biology Lab 1: Diffusion of Osmosis (8:00 min.)http://www.bozemanscience.com/ap-bio-lab-1-diffusion-osmosis
Your Design: Determining Water Potential of Plant Tissues
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