learning objectives investigation 4: diffusion and · pdf file•to investigate osmosis in...

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


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.


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.



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.



Background



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


Bozeman Biology: Water Potential (10:00 min.)https://paul-andersen.squarespace.com/water-potential


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?


PreLab


Getting Started:

• Complete LabBench Activity Lab 1 Diffusion & Osmosis in your CompBook (handout)- http://www.phschool.com/science/biology_place/

labbench/lab1/intro.html



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


Note - Please edit question 7 to read ...modified to facilitate the diffusion of materials which support life processes?


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



Procedure 2: Modeling Diffusion and Osmosis


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



• 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


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



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





Diagram 1: Leaf Cell Drawings CONTROL VARIABLEleaf cell in fresh water

EXPERIMENTAL VARIABLEleaf cell in _(solution)_

Observations Observations

Text



• Day of investigation:- Procedure steps 1-6- Record findings in your Data Table



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.



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



Your Design: Determining Water Potential of Plant Tissues



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



• 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)




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




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


Bozeman Biology: AP Biology Lab 1: Diffusion of Osmosis (8:00 min.)http://www.bozemanscience.com/ap-bio-lab-1-diffusion-osmosis


learning objectives investigation 4: diffusion and · pdf file•to investigate osmosis in...

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