ap-bio-4-osmosis-diffusion

AP® Investigation #4

Diffusion & Osmosis – Teacher’s Guide

Kit # 3674-04

Table of Contents Call “Us” at 1.800.962.2660 for Technical Assistance

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Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 General Overview . . . . . . . . . . . . . . . . . . . . . . 1 Recording Data. . . . . . . . . . . . . . . . . . . . . . . . 2 Material Requirements/Checklist . . . . . . . . . . . . . . 4 National Science Education Content Standards. . . . . . . 5 Correlation to AP Content Standards. . . . . . . . . . . . 5 Time Requirements . . . . . . . . . . . . . . . . . . . . . . 5 Learning Objectives. . . . . . . . . . . . . . . . . . . . . . 6 Safety Precautions. . . . . . . . . . . . . . . . . . . . . . 7 Pre-Lab Preparations. . . . . . . . . . . . . . . . . . . . . 8 Notes to the Instructor. . . . . . . . . . . . . . . . . . . 10 Before Class. . . . . . . . . . . . . . . . . . . . . . . . . 10 Background. . . . . . . . . . . . . . . . . . . . . . . . . 11 Part 1: Cell Size & Diffusion. . . . . . . . . . . . . . . . . 13 Part 2: Modeling Osmosis in Living Cells. . . . . . . . . . 17 Part 3: Osmosis in Living Plant Cells . . . . . . . . . . . . 21 Additional Questions (Optional) . . . . . . . . . . . . . . 24 Further Inquiry Investigations. . . . . . . . . . . . . . . 23 Teacher’s Answer Key. . . . . . . . . . . . . . . . . . . . 24 Vocabulary Guide. . . . . . . . . . . . . . . . . . . . . . 26 MSD SHEETS. . . . . . . . . . . . . . . . . . . . . . . . . . .

LIVE MATERIAL CARE SHEETS . . . . . . . . . . . . . . . . . . . .

**AP® and the Advanced Placement Program are registered trademarks of the College Entrance Examination Board. The activity and materials in this kit were developed and prepared by WARD’S Natural Science Establishment, which bears sole responsibility for their contents..

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Diffusion & Osmosis: Teacher’s Guide

Kit # 3674-04

abstract This lab addresses the properties of osmosis and diffusion and their function in maintaining homeostasis in the cell. Students use two phospholipid bilayer models to simulate the movement of water and nutrients across a cell membrane and observe osmosis in living tissue. In Part 1, students calculate the surface area-to-volume ratios of differently-sized cuboidal cell models.

In Part 2, the movement of molecules across a membrane is simulated using dialysis tubing and solutions of varying composition. In Part 3, students directly observe osmosis in a living specimen.

In all parts of this lab, after performing a guided activity, students are then directed to design their own experiments, to further develop their understanding of the topics explored. The students’ understanding of these exercises will allow them to explain how cell size and shape affect rates of diffusion, as well as pose scientific questions about the selective permeability properties of cell membranes.

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Diffusion & Osmosis: Teacher’s Guide

Kit # 3674-04

general Overview The College Board has revised the AP Biology curriculum to begin implementation in the fall of 2012. Advanced Placement (AP) is a registered trademark of the College Entrance Examination Board. The revisions were designed to reduce the range of topics covered, to allow more depth of study and increased conceptual understanding for students. There is a shift in laboratory emphasis from instructor-designed demonstrations to student-designed investigations. While students may be introduced to concepts and methods as before, it is expected that they will develop more independent inquiry skills. Lab investigations now incorporate more student-questioning and experimental design. To accomplish this, the College Board has decreased the minimum number of required labs from 12 to 8 while keeping the same time requirement (25% of instruction time devoted to laboratory study). The College Board has defined seven science practices that students must learn to apply over the course of laboratory study. In brief, students must: 1. Use models 2. Use mathematics (quantitative skills) 3. Formulate questions 4. Plan and execute data collection strategies 5. Analyze and evaluate data 6. Explain results 7. Generalize data across domains The College Board published 13 recommended laboratories in the spring of 2011. They can be found at: http://advancesinap.collegeboard.org/science/biology/lab Many of these laboratories are extensions of those described in the 12 classic labs that the College Board has used in the past. The materials provided in this lab activity have been prepared by Ward’s to adapt to the specifications outlined in AP Biology Investigative Labs: An Inquiry-Based Approach (2012, The College Board). Ward’s has provided instructions and materials in the AP Biology Investigation series that complement the descriptions in this College Board publication.

We recommend that all teachers review the College Board material as well as the instructions here to get the best understanding of what the learning goals are. Ward’s has structured each new AP investigation to have at least three parts: Structured, Guided, and Open Inquiry. Depending on a teacher’s syllabus, s/he may choose to do all or only parts of the investigations in scheduled lab periods.

The College Board requires that a syllabus describe how students communicate their experimental designs and results. It is up to the teacher to define how this requirement will be met. Having students keep a laboratory notebook is one straightforward way to do this.

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Diffusion & Osmosis: Teacher’s Guide

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Recording Data in a Laboratory Notebook All of the Ward’s Investigations assume that students will keep a laboratory notebook for studentdirected investigations. A brief outline of recommended practices to set up a notebook and one possible format is provided below.

1. A composition book with bound pages is highly recommended. These can be found in most stationary stores. Ward’s offers several options with pre-numbered pages (for instance, item numbers 32-8040 and 15-8332). This prevents pages from being lost or mixed up over the course of an experiment.

2. The title page should contain, at the minimum, the student’s name. Pages should be numbered in succession.

3. After the title page, two to six pages should be reserved for a table of contents to be updated as experiments are done so they are easily found.

4. All entries should be made in permanent ink. Mistakes should be crossed out with a single line and should be initialed and dated. This clearly documents the actual sequence of events and methods of calculation. When in doubt, over-explain. In research labs, clear documentation may be required to audit and repeat results or obtain a patent.

5. It is good practice to permanently adhere a laboratory safety contract to the front cover of the notebook as a constant reminder to be safe.

6. It is professional lab practice to sign and date the bottom of every page. The instructor or lab partner can also sign and date as a witness to the veracity of the recording.

7. Any photos, data print-outs, or other type of documentation should be firmly adhered in the notebook. It is professional practice to draw a line from the notebook page over the inserted material to indicate that there has been no tampering with the records.

For student-directed investigations, it is expected that the student will provide an experimental plan for the teacher to approve before beginning any experiment. The general plan format follows that of writing a grant to fund a research project.

1. Define the question or testable hypothesis.

2. Describe the background information. Include previous experiments.

3. Describe the experimental design with controls, variables, and observations.

4. Describe the possible results and how they would be interpreted.

5. List the materials and methods to be used.

6. Note potential safety issues. (continued on next page) ©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

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Diffusion & Osmosis: Teacher’s Guide

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Recording Data in a Laboratory Notebook (continued) After the plan is approved: 7. The step by step procedure should be documented in the lab notebook. This includes recording the calculations of concentrations, etc., as well as the weights and volumes used.

8. The results should be recorded (including drawings, photos, data print outs).

9. The analysis of results should be recorded.

10. Draw conclusions based on how the results compared to the predictions.

11. Limitations of the conclusions should be discussed, including thoughts about improving the experimental design, statistical significance and uncontrolled variables.

12. Further study direction should be considered.

The College Board encourages peer review of student investigations through both formal and informal presentation with feedback and discussion. Assessment questions similar to those on the AP exam might resemble the following questions, which also might arise in peer review: •

Explain the purpose of a procedural step.

•

Identify the independent variables and the dependent variables in an experiment.

•

What results would you expect to see in the control group? The experimental group?

•

How does XXXX concept account for YYYY findings?

•

Describe a method to determine XXXX.

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Diffusion & Osmosis: Teacher’s Guide

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Materials checklist Units per kit

Description

MATERIALS NEEDED BUT NOT PROVIDED

1 pkg./72

Preclean microscope slides,

String

1

22 mm plastic coverslips,

Scale

4

Dialysis tubing, 10 ft. roll,

Graduated cylinder, 1 L

1

Cork borer, 3/16”

Plastic beakers, 250 mL

1 pkg./100

1000 mL disposable beaker

Water

2 pkgs./15

9 oz. plastic cup with lid

Compound microscope

1

Sodium chloride, lab grade, 500 g

Paper towels

1

ScholAR Chemistry New MSDS CD

Sweet potato

1 pkg./30

Wooden sticks, 6”

16 celery sticks (for pre-lab demonstration

1

Albumin (Egg), lab grade, 100 g

White potato

1

Sucrose, lab grade, 500 g

OPTIONAL MATERIALS ( NOT PROVIDED)

1

Food coloring, pkg. of 4 bottles, 3 oz. each

Other materials as determined by students’ experimental design

8

White vinylite plastic ruler,

1

Disposable Petri dishes, pkg./20

1

Vinegar, 473 mL, white

8

Plastic knife

8

Plastic spoon

1

Glucose anhydrous, lab grade, 500 g

1

Sucrose solution set

1

Live/Perishable Items Fulfillment Coupon*: Includes coupon for Elodea densa tips, agar cubes

1

Instructions (this booklet)

* - It is recommended that you redeem your coupon for live/ perishable materials as soon as possible and specify your preferred delivery date. Generally, for timely delivery, at least a week’s advance notice is preferred.

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Diffusion & Osmosis: Guided Inquiry Lab Activity – Teacher’s Guide

Kit # 3674-04

This lab activity is aligned with the 2012 AP Biology Curriculum (registered trademark of the College Board).

Listed below are the aligned Content areas (Big Ideas and Enduring Understandings), the Science Practices, and the learning objectives of the lab as described in AP Biology Investigative Labs: An Inquiry Approach (2012). This is a publication of the College Board that can be found at http://advancesinap.collegeboard.org/science/biology/lab.

Curriculum alignment Big Idea ‹ 2. Biological systems utilize energy and molecular building blocks to grow, to reproduce, and to maintain homeostasis.

Enduring Understandings ‹ 2.B. Growth, reproductions, and dynamic homeostasis require that cells create and maintain internal environments that are different from their external environments. ‹ 2B.1: Cell membranes are selectively permeable due to their structure. ‹ 2.B.2: Growth and dynamic homeostasis are maintained by the constant movement of molecules across membranes.

Science Practices ‹ 2.2 The student can apply mathematical routines to quantities that describe natural phenomena. ‹ 4.2 The student can design a plan for collecting data to answer a particular scientific question. ‹ 4.3 The student can collect data to answer a particular scientific question. ‹ 4.4 The student can evaluate sources of data to answer a particular scientific question. ‹ 5.1 The student can analyze data to identify patterns or relationships. ‹ 5.2 The student can refine observations and measurements based on data analysis. ‹ 11.3 The student can evaluate the evidence provided by data sets in relation to a particular scientific question.

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Diffusion & Osmosis: Teacher’s Guide

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Learning objectives ‹ The student is able to use calculated surface area-to-volume ratios to predict which cell(s) might eliminate wastes or procure nutrients faster by diffusion (2A3 & SP 2.2). ‹ The student is able to explain how cell size and shape affect the overall rate of nutrient intake and the rate of waste elimination (2A3 & SP 2.2). ‹ The student is able to use representations and models to pose scientific questions about the properties of cell membranes and selective permeability based on molecular structure (2B1 & SP 4.2, SP 4.3, SP 4.4).

Time Requirements Structured Inquiry: 5 minutes Part 1: Diffusion and Osmosis

Guided Inquiry: 45 minutes Open Inquiry: Will vary, depending on students’ experimental designs Structured Inquiry: 45 minutes

Part 2: Modeling Osmosis

Guided Inquiry: 45 minutes Open Inquiry: Will vary, depending on students’ experimental designs Structured Inquiry: 45 minutes

Part 3: Osmosis in Living Plant Cells

Guided Inquiry: 45 minutes Open Inquiry: Will vary, depending on students’ experimental designs

Analyzing Results and Class Discussion

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45 minutes

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Diffusion & Osmosis: Teacher’s Guide

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Safety Precautions Lab-Specific Safety ‹ White vinegar and phenolphthalein agar are used in this kit. Both are irritants to the skin and eyes. Use with caution. Review the Material Safety Data Sheets (MSDSs) for additional safety precautions, handling procedures, storage, and other information. MSDSs are provided at the end of this booklet. Addtionally, visit : www.scholarchemistry.com for the latest and most up-to-date MSDSs. General Safety ‹ The teacher should be familiar with safety practices and regulations in their school (district and state). Know what needs to be treated as hazardous waste and how to properly dispose of nonhazardous chemicals or biological material. ‹ Consider establishing a safety contract that students and their parents must read and sign off on.

This is a good way to identify students with allergies to things like latex so that you (and they) will be reminded of what particular things may be risks to individuals. A good practice is to include a copy of this contract in the student lab book (glued to the inside cover). ‹ Students should know where all emergency equipment (safety shower, eyewash station, fire extinguisher, fire blanket, first aid kit etc.) is located. ‹ Make sure students remove all dangling jewelry and tie back long hair before they begin. ‹ Remind students to read all instructions, MSDSs, and live care sheets before starting the lab activities, and to ask questions about safety and safe laboratory procedures. Appropriate MSDSs and live care sheets can be found on the last pages of this booklet. Additionally, the most updated versions of these resources can be found at www.wardsci.com, under Living Materials http://wardsci.com/article.asp?ai=1346. ‹ In student directed investigations, make sure that collecting safety information (like MSDSs) is part of the experimental proposal. ‹ As general laboratory practice, it is recommended that students wear proper protective equipment, such as gloves, safety goggles, and a lab apron.

At end of lab: ‹ All laboratory bench tops should be wiped down with a 20% bleach solution or disinfectant to ensure cleanliness. ‹ Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

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Diffusion & Osmosis: Teacher’s Guide

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Pre-Laboratory Preparation PREP Tip (FOR PART I) ‹ In this portion of this lab activity you will use phenolphthalein agar cubes.

Prior to starting this lab activity, submit your live/perishable material redemption coupon via mail, fax, or simply calling into customer service at 1-800962-2660. It is recommended that you do this at least one week before the lab. ‹ The phenolphthalein agar cubes are already prepared and cut to the appropriate size for this lab activity. The phenolphthalein agar cubes were prepared with 2% sodium hydroxide (NaOH).

Part 1: Diffusion and osmosis 1. Soak eight sticks of celery in water overnight.

2. Soak eight sticks of celery in saltwater (1 M) overnight.

3. Make sure that you have redeemed your coupon and have received your phenolphthalein agar cubes. ‹ Remove the cubes from the jar and, for every lab group, place one of each size cubes into a disposable cup. Each lab group should receive one cup with three phenolphthalein cubes of different sizes (1 x 1 cm, 2 x 2 cm, and 3 x 3 cm). ‹ Cover each cup with cellophane.

4. To save time, measure and pour 100 mL of white vinegar into a cylinder or addtional plastic cup for each lab group. Label the cups “white vinegar.”

Part 2: Modeling Diffusion by Osmosis 1. Prepare solutions for laboratory: ‹ 1 M Sucrose – In a 1 L (or larger) beaker, dissolve each sucrose package labeld for 1 M in 500 mL of distilled water. After the sucrose has completely dissolved, bring the volume up to 1 liter of distilled water. ‹ 1 M Sodium chloride (NaCl) – In a 1 L (or larger) beaker, dissolve 58.44 g of NaCl in 500 mL of distilled water. After the NaCl has completely dissolved, bring the volume up to 1 liter of distilled water.

Prep Tips (For part II) ‹ Store the egg albumin in the refrigerator to avoid clumping of the powder. ‹ The pores of the dialysis tubing are extremely small, and can be easily clogged by any oil or dirt on your fingers or hands. Wash your hands before handling the dialysis tubing and keep the physical contact to a minimum.

©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

‹ 1 M Glucose - In the beakers provided dissolve 180 g of glucose in 500 mL of distilled water. After the glucose has completely dissolved, bring the volume up to 1 liter of distilled water. ‹ 5% Egg albumin – In the beakers provided, dissolve 50 g of egg albumin in 500 mL of distilled water. After the egg albumin has completely dissolved, bring the volume up to 1 liter of distilled water.

2. Prepare the dialysis tubing: ‹ Cut five 20 cm pieces of dialysis tubing for each lab group. ‹ Soak the dialysis tubing overnight in paper or plastic cups.

Keep the pieces in water until they are needed.

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Diffusion & Osmosis: Teacher’s Guide

PREP Tip (FOR PART III) ‹ In this portion of this lab activity you will use Elodea tips. Prior to starting this lab activity, submit your live/perishable material redemption coupon via mail, fax, or simply calling into customer service at 1-800-962-2660. It is recommended that you do this at least one week before the lab. ‹ A french fry cutter can be used to cut the potato into more uniform pieces. Peel the potato before cutting it into pieces.

Kit # 3674-04

Pre-Laboratory Preparation (continued) Part 3: Osmosis in Living Plant Cells 1. Make sure that you have redeemed your coupon and have received your Elodea tips.

2. You may wish to prepare the potato cylinder in advance, to save time during the lab. Peel the potato. Then, using cork borer, cut four cylinders from a potato for each solution to be used. Cut each cylinder to a length of 3 cm for greater accuracy. Place the cylinders in a covered cup or beaker until they are ready to be used.

3. Prepare solutions for laboratory: ‹ The kit provides prepackaged sucrose to make solutions of 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M. In the beakers provided, dissolve each sucrose package in 500 mL of distilled water. After the sucrose has completely dissolved, bring the volume up to 1 liter with distilled water. ‹ In order to keep the solution concentrations unknown from the students, add food coloring to the solutions. Use the chart below to create colored solutions.

©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

Solution Concentration

Color

0.2 M 0.4 M 0.6 M

Red Orange Yellow

0.8 M

Green

1.0 M 0M

Blue Clear

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Number of Food Coloring Drops and Color Red - 1 drop Red -1 drop and Yellow - 1 drop Yellow - 1 drop Yellow - 2 drops Blue - 1 drop Blue - 1 drop –––––––

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Diffusion & Osmosis: Teacher’s Guide

Kit # 3674-04

Background OBJEcTIVES ‹ Use calculated surface area-tovolume ratios to predict which cell(s) might eliminate wastes or procure nutrients faster by diffusion. ‹ Explain how cell size and shape affect the overall rate of nutrient intake and the rate of waste elimination. ‹ Use representations and models to pose scientific questions about the properties of cell membranes and selective permeability based on molecular structure.

Figure 1: Plant cell in hypertonic solution.

Net movement of H O

The cell is plasmolyzed.

Why are cells so small? Most cells grow, but upon reaching a certain size, a cell will divide becoming two smaller cells. This is how multicellular organisms, like humans, grow. But why do cells stop growing once they reach a certain size? Why does a cell divide and multiply rather than simply growing bigger? One possible answer can be found in the relationship between cell size and the diffusion of substances across the cell membrane.

The absorption of nutrients, excretion of cellular wastes, and the exchange of respiratory gases are life processes which depend upon efficient transport of substances into, out of, and throughout living cells. Diffusion is one of the most common and efficient means by which substances are passively transported between cells and their aqueous environment. Diffusion is the movement of a substance (liquid or gas) along a concentration gradient from high to low concentration. Diffusion is vital to many life functions of a cell.

Diffusion allows the transport of vital nutrients and compounds without the expenditure of energy.

The cell membrane is the selectively permeable barrier whose total surface area is important to regulating the substances that diffuse into or out of the cell. Small, neutrally charged molecules such as oxygen, carbon dioxide, and glucose can pass freely through the membrane, while the diffusion of other materials is restricted. Materials that cannot diffuse across the membrane or need to be transported against a diffusion gradient can be actively transported across the membrane with the expenditure of energy. Osmosis is a special kind of diffusion that occurs as water is separated by a selectively permeable membrane with different solute concentrations on either side of the membrane. During osmosis, water moves from regions of low solute concentration to regions of high solute concentration without the expenditure of energy.

Organisms rarely exist in environments with solute concentrations that match their cytoplasm; there are usually more or fewer dissolved particles in one of two compared solutions separated by a membrane, such as a cell and the media in which it exists. A hypertonic solution is a solution in which the solute concentration is higher outside of the cell; therefore, water will flow to the external environment, causing the cell to shrink. Hypotonic solutions consist of a low concentration of solutes outside the cell; therefore, water will flow into the cell, causing cellular expansion. In the case of plant cells with cell walls , expansion is restricted, so pressure builds. This pressure is called turgor pressure. (continued on next page)

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Diffusion & Osmosis: Teacher’s Guide Figure 2 Plant cell in hypotonic solution.

Net movement of H O

Kit # 3674-04

Background (continued) Isotonic solutions, on the other hand, are solutions in which the solute and solvent concentrations are at equilibrium: there is no net flow of materials across the selectively permeable membrane.

Only a solute’s relative concentration, or water potential (y), affects the rate of osmosis. Water potential consists of two components – pressure potential (y p) the exertion of pressure on a solution; and solute (or osmotic) potential (ys), the relative concentration of solutes within the two solutions.

Water Potential (y) = Pressure Potential (yp) + Solute Potential (ys)

The cell is turgid.

Figure 3 Plant cell in isotonic solution.

Net movement of H O

Net movement of H O

Water moves from an area of high water potential (free energy) to an area of lower water potential. For example, in Figure 4 the water initially enters the tube because there is a negative solute potential in the sugar–water solution. However, the force of gravity begins to exert pressure on the rising column; when the force of gravity, pressure potential, equals the solute potential, the sugar-water solution in the column stops rising. The water potential is at zero and dynamic equilibrium has been established. The pressure potential can be determined from the height of the column. With the water potential and the pressure known, solute potential can be experimentally determined.

The solute potential can be calculated as yys = –i CRT, where:

Figure 4

i = ionization constant (number of ions Na+Cl– = 2, sucrose = 1) C = Molar concentration R = pressure constant (0.0831 Liter bars/mole, ° Kelvin) T = Temperature in Kelvin (273 + temp C)

Water Potential in a Tube.

Selective Permeable Membrane

bar = measure of pressure 1 bar = 1 atmosphere at sea level

Water Sugar Molecule

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Diffusion & Osmosis: Teacher’s Guide

Notes

Kit # 3674-04

Safety Precautions ‹ As general safe laboratory practice, it is recommended that you wear proper protective equipment, such as gloves, safety goggles, and a lab apron. ‹ As general lab practice, read the lab through completely before starting, including any Materials Safety Data Sheets (MSDSs) and live materials care sheets at the end of this booklet as well as any appropriate MSDSs for any additional substances you would like to test. One of the best sources is the vendor for the material.

For example, for chemicals purchased at Ward’s, searching for the chemicals on the Ward’s website will direct you to a link for the appropriate MSDSs. At the end of the labs: ‹ All laboratory bench tops should be wiped down with a 20% bleach solution or disinfectant to ensure cleanliness. ‹ Wash your hands thoroughly with soap and water before leaving the laboratory.

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Diffusion & Osmosis: Teacher’s Guide

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Part 1: osmosis & Diffusion Notes

Materials List q q q q q q q q q

Celery stick soaked in water\ Celery stick soaked in saltwater 3 Phenolphthalein agar cubes: 3 x 3 cm, 2 x 2 cm, and 1 x 1 cm 1 Plastic knife 1 Plastic spoon 1 Plastic cup 1 Vinylite white plastic ruler, 6” metric system 1 White vinegar, 100 mL 1 Timer

Part 1A – Structured inquiry: Osmosis & Diffusion 1. Observe the celery stick that was soaked in water. Record your observations.

2. Break the celery stick that was soaked in water. Record your observations.

3. Observe the celery stick that was soaked in saltwater. Record your observations.

4. Break the celery stick that was soaked in saltwater. Record your observations.

Part 1A – guided inquiry: Osmosis & Diffusion ‹ The agar cubes have been prepared with 1% phenolphthalein, which is a pH indicator. The chart below indicates a color scale of pH for phenolphthalein. The blocks are pink because the agar blocks were soaked in 0.01 % sodium hydroxide.

Phenolphthalein Color Indicator Color Colorless Pink to Red

pH 0 - 8.2 8.2 – 12.0

Acid or Base Acidic or slightly neutral Basic

1. Obtain agar cubes in a plastic cup from your teacher.

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Be careful not to scratch any surface of the cubes. (continued on next page) US: www.wardsci.com Canada: www.wardsci.ca

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Diffusion & Osmosis: Teacher’s Guide Part 1B– guided inquiry: Osmosis & Diffusion (continued)

Formulas All formulas for calculations are listed below: ‹ Surface Area = Length x width x # of sides

‹ Volume =

2. Using the metric ruler, measure the dimensions of each agar cube and record the measurements in your lab notebook.

3. Place the three cubes carefully into a plastic cup. Add white vinegar (acidic solution) until the cubes are submerged. Using a plastic spoon, keep the cubes submerged for 10 minutes turning them frequently. ‹ Be careful not to scratch any surface of the cubes.

Length x width x height

‹ Surface Area Volume Ratio = Surface Area Volume

‹ Extent of Diffusion = Total Cube Volume –

Kit # 3674-04

Volume of cube that has not changed color x 100

Total Cube Volume

‹ Be sure to start the timer once the cubes are submerged.

4. As the cubes soak, calculate the surface area, volume, and surface area to volume ratio for each agar cube. Record this data in a table similar to the one below.

Block # Start 1 Start 2 Start 3 End 1 End 2 End 3

Length (cm)

Width (cm)

Height Surface Volume 2 (cm) area (cm ) (cm3 or mL)

5. After 10 minutes, use the spoon to remove the agar cubes and carefully blot them on dry paper towel. For more accurate measures of diffusion, use a knife to cut the cubes.

6. Using a metric ruler, measure the distance in centimeters (cm) that the white vinegar diffused into each cube. (Distance from surface) 7. Calculate the rate of diffusion for each cube in centimeters per minute (cm/min.).

8. Calculate the volume of the portion of each cube which has not changed color (in other words, the portion of the cube that is still pink).

9. Calculate the extent of diffusion into each cube as a percent of the total volume.

10. Graph the rate of diffusion relative to cell volume and surface area.

11. Graph the extent of diffusion relative to cell volume and surface area. ©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

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Part 1: OSMOSIS & Diffusion ASSESSMENT Questions 1. Why are celery sticks soaked in saltwater more flexible than those soaked in plain water?

Plain water is hypotonic to the inside of the cells, so water flows into the cell and expands, increasing turgor pressure. Salt is hypertonic to the inside of the cells, so cells become shrunken relative to the cell wall, and turgor pressure is decreased.

2. Examine your data from Part 1A: Guided Inquiry. What dimensions supported the fastest diffusion rate? Why?

The diffusion rate in this experiment is constant because the concentration of solute is constant.

The greatest surface to volume ration causes he biggest change in g total volume.

4. Construct a useful graph of the relationship between cell dimension to the extent of diffusion.

See graph at right.

5. Why can’t humans drink seawater for hydration?

Explain.

Extent diffusion or % total volume change

3. What dimensions supported the greatest diffusion percent total volume? Why?

Surface area/volume

Seawater is hypertonic to digestive system cells. Therefore, water will be drawn out of the cells to be excreted.

6. The size of some human cells is 0.01 mm. Using the formulas in this activity, calculate the surface to volume ratio of such a cell (assume 0.01 mm cube). Describe the extent of diffusion into this living cell as compared to the smallest agar cube. Explain.

The ratio is 600:1. The extent of diffusion will be considerably greater due to the much larger surface area to volume ratio. The cell will reach complete equilibrium before the agar cube does.

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Diffusion & Osmosis: Teacher’s Guide EXPERIMENT DESIGN Tips The College Board encourages peer review of student investigations through both formal and informal presentation with feedback and discussion. Assessment questions similar to those on the AP exam might resemble the following questions, which also might arise in peer review: ‹ Explain the purpose of a procedural step.

Part 1 C – OPEN inquiry: Osmosis & Diffusion What questions occurred to you as you investigated diffusion in agar blocks and the flexibility of the celery sticks? Design an experiment to investigate one of your questions. Questions may involve examining diffusion in different shapes of agar blocks, the effect of temperature on rates of diffusion, the amount of time it takes to make crisp celery limp, the effect of salt concentration on celery limpness, or the effect of other solutes on celery limpness.

Before starting your experiment, have your teacher check over your experiment design and initial your design for approval. Once your design is approved, investigate your hypothesis. Be sure to record all observations and data in your laboratory sheet or notebook.

‹ Identify the independent variables and the dependent variables in an experiment.

Use the following steps when designing your experiment.

‹ What results would you expect to see in the control group? The experimental group?

2. Describe the background information. Include previous experiments.

‹ How does XXXX concept account for YYYY findings?

•

Describe a method to determine XXXX.

Kit # 3674-04

1. Define the question or testable hypothesis.

3. Describe the experimental design with controls, variables, and observations.

4. Describe the possible results and how they would be interpreted.

5. List the materials and methods to be used.

6. Note potential safety issues.

After the plan is approved by your teacher: 7. The step by step procedure should be documented in the lab notebook. This includes recording the calculations of concentrations, etc. as well as the actual weights and volumes used.

8. The results should be recorded (including drawings, photos, data print outs).

9. The analysis of results should be recorded.

10. Draw conclusions based on how the results compared to the predictions.

11. Limitations of the conclusions should be discussed, including thoughts about improving the experimental design, statistical significance and uncontrolled variables.

12. Further study direction should be considered.

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Part 2: Modeling osmosis Introduction In this lab activity, you will construct and simulate model cells in an external environment, to relate solutes passing through a semipermeable membrane in hypertonic, hypotonic, and isotonic solutions.

MATERIALS LIST PER LAB GROUP q q q q q q q q q q

Procedure Tips ‹ Record all data immediately in your laboratory notebook. ‹ Wash your hands before handling the dialysis tubing, and keep physical contact with the tubing to a minimum. ‹ Remember to label your model cells. Record the pairs in your laboratory notebook in their respective order of your lab set-up. ‹ If you choose to tie off the end of the dialysis tubing with string, tie two knots, about 1/4” apart, to prevent leaking.

1 1 1 5 7 ft.

250 mL 250 mL 250 mL 250 mL 500 mL

Roll of String Balance Graduated Cylinder Disposable beaker, 1000 mL Piece of Dialysis Tubing, 20 cm 1M Sucrose Solution 1M Sodium Chloride (Salt) 1M Glucose Solution 5% Albumin Solution (Protein) Distilled OR Tap Water

PART 2A – Procedure: STructured INquiry The pores in dialysis tubing allow some molecules to freely diffuse across the membrane and some to be restricted. In this lab, you will use dialysis tubing as a model cell membrane.

1. Obtain five pieces of pre-soaked dialysis tubing from the beaker of water. Tie a tight knot in one end of each piece of tubing, or use a piece of string to tie off the end.

2. Measure and pour 10 mL of each of the four prepared solutions into a separate graduated cylinder. The solutions are salt, glucose, sucrose, and protein.

3. Open the tubing by rubbing the untied end between your fingers.

Pour 10 mL of prepared solution into the tubing. Carefully tie a knot in the open end to form a closed cell membrane (similar to a bag). Be sure to leave enough space in the bag for expansion.

Minimize air enclosed in the tubing.

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PART 2A – Procedure (continued) 4. Fill a beaker about 100 mL of the solutions to be paired with your model cell. Use either water or salt. (See sample data table below for parings.)

Paired Extra-Cellular Solution (in cup) Cell 1 (protein)

Salt

Cell 2 (sucrose)

Water

Cell 3 (water)

Water

Cell 4 (glucose)

Salt

Cell 5 (salt)

Water

Cell Weight (g) Start time After 30 0 minutes

% Change Final Mass - Initial Mass x 100 Initial Mass

5. Repeat Steps 3 and 4 for the remaining four cells.

Notes

‹ Remember to clean the graduated cylinder between solutions.

6. Determine the initial weight of each cell and record in a table similar to the one shown below.

7. Completely immerse the model cells in their pairing solutions in the beaker or cup. Start your timer.

8. Given what you know about solute concentration, predict whether each “cell” volume will grow, shrink, or remain constant. Record your predictions in your laboratory notebook.

9. Allow the “cells” to soak for 30 minutes. Record any observations in your laboratory notebook.

10. When 30 minutes has passed, remove the model cells from the solution, pat dry, and determine the final weight of each of the model cells. Record the final weights and any additional observations.

11. Calculate the percent change in weight and record your results in your laboratory notebook. ‹ Do not discard any of your solutions from this part of the lab activity as they will also be used in Parts 2B, 2C, and Part 3 of this investigation.

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Diffusion & Osmosis: Teacher’s Guide

Notes

Kit # 3674-04

PART 2B – modeling osmosis Procedure: guided INquiry 1. Repeat Part 2A of this lab, but pair intracellular and extracellular solutions as you like, and make predictions about how the “cells” will behave.

PART 2B – modeling Osmosis: assessment 1. Examine the initial and final weights of the model cells. What cause the mass of the dialysis bags to change? Was there more or less water in the dialysis bags at the conclusion of the experiment? Explain.

Answers will vary, but the students should account for the change in mass to the water entering and leaving the model cell.

Students should conclude which solutions have the greatest and least water potential inside and outside of the model cell.

2. From your results, which solutes, if any, diffused across the membrane and which, if any, were restricted? Why do you think this occurred?

Protein is restricted since its concentration does not drive water either way. Protein is much larger than simple molecules, and will not pass through the pores of the membrane.

3. How is dialysis tubing different from a cell membrane?

©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

Answers will vary. They may include:

Dialysis tubing is much less complex; it is not a lipid bilayer; it does not use energy to pump materials against a concentration gradient.

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Diffusion & Osmosis: Teacher’s Guide EXPERIMENT DESIGN Tips

Kit # 3674-04

Part 2C – OPEN inquiry: modeling osmosis

The College Board encourages peer review of student investigations through both formal and informal presentation with feedback and discussion. Assessment questions similar to those on the AP exam might resemble the following questions, which also might arise in peer review:

What questions occurred to you as you investigated osmosis through a permeable membrane? Design an experiment to investigate one of your questions. Questions may involve examining different types of solutes that do not cross the membrane, effects of variation in pressure, effects of different types of ions in solutions, or the behavior of different types of solutes. Before starting your experiment, have your teacher check over your experiment design and initial your design for approval. Once your design is approved, investigate your hypothesis.

Be sure to record all observations and data in your laboratory sheet or notebook.

‹ Explain the purpose of a procedural step.

Use the following steps when designing your experiment.

‹ Identify the independent variables and the dependent variables in an experiment. ‹ What results would you expect to see in the control group? The experimental group? ‹ How does XXXX concept account for YYYY findings?

•

Describe a method to determine XXXX.

1. Define the question or testable hypothesis.

2. Describe the background information. Include previous experiments.

3. Describe the experimental design with controls, variables, and observations.

4. Describe the possible results and how they would be interpreted.

5. List the materials and methods to be used.

6. Note potential safety issues.

After the plan is approved by your teacher: 7. The step by step procedure should be documented in the lab notebook. This includes recording the calculations of concentrations, etc. as well as the actual weights and volumes used.

8. The results should be recorded (including drawings, photos, data print outs).

9. The analysis of results should be recorded.

10. Draw conclusions based on how the results compared to the predictions.

11. Limitations of the conclusions should be discussed, including thoughts about improving the experimental design, statistical significance and uncontrolled variables.

12. Further study direction should be considered.

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Part 3: osmosis in living plant cells Notes

introduction In this lab, you will microscopically observe an Elodea densa plant leaf and explore the effects of different solution concentrations on the cells.

You will then use the solutions to determine the water potential of plant tissues, such as white or sweet potato tubers.

Materials List q q q q q q q q q

1 Thermometer 1 Graduated cylinder 6 Plastic cups 150 mL Red mystery solution 150 mL Orange mystery solution 150 mL Yellow mystery solution 150 mL Green mystery solution 150 mL Blue mystery solution 175 mL Distilled water

q q q q q q q q q

1 5 1 1 1 1 6 1 1

Microscope slide Paper towels Pair of forceps Compound microscope Scalpel Coverslip Potato tubers Balance Ruler

Part 3A – Procedure: Structured inquiry 1. Using the forceps, remove an Elodea densa leaf from its stem and place it gently on a clean microscope slide.

2. Add two to three drops of distilled water to the slide and cover with a coverslip.

3. Examine the cell at 40X magnification and note the characteristics of the cells. In your lab notebook, draw several cells that show a good representation of the cells you observed. In your drawing, label all visible structures and organelles.

4. Remove the microscope slide. Choose one of the solutions from Part 2 of this lab. Add two to three drops of this solution across the leaf sample.

5. Allow the slide to sit for two to three minutes in the solution and reexamine the sample under the microscope. ‹ To speed up the reaction to the cells in solution, place a paper towel on the opposite end of the coverslip to wick your solution through the cells.

6. Note the appearance of the cells. In your lab notebook, draw several cells that show a good representation of the cells you observed. In your drawing, label all visible structures and organelles. ©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

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Label all visible structures and organelles in your drawings.

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Part 3B – Procedure: guided inquiry Notes

1. Make potato cores with a borer or use pre-made potato bores.

2. Weigh each core and measure the length of each core. Record your data in your laboratory notebook.

3. Place one or more potato cores in each of the mystery sucrose solutions.

4. Record your observations.

5. Wait 30 minutes.

6. After 30 minutes, re-weigh the cores, and calculate the changes in their weight. Record your data in your laboratory notebook.

Part 3B – assessment 1. Which color mystery solution had the highest concentration of sucrose? How do you know this?

The blue mystery solution had the highest concentration of sucrose, since the core weighed the least at the end of the 30 minutes.

2. Knowing that the mystery solutions were sucrose at concentrations of 0.2 M, 0.4 M, 0.6 M, 0.8 M , and 1.0 assume 0.3 M, calculate the water potential of the 0% potato core.

Show your calculations and explain your 0 0.2 0.4 0.6 0.8 reasoning.

1.0

See graph above. Assuming 0.3 M, water potential = 1 bar + (–7.3 bars) = –8.3 bars

3. If you looked at your potato cores under the microscope, describe what you think you would see.

©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

Expanded cells in 100% water; shrunken cells in the blue dyed, sucrose solutions.

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250-7454 v.1/12 Page 23

Diffusion & Osmosis: Teacher’s Guide EXPERIMENT DESIGN Tips The College Board encourages peer review of student investigations through both formal and informal presentation with feedback and discussion. Assessment questions similar to those on the AP exam might resemble the following questions, which also might arise in peer review: ‹ Explain the purpose of a procedural step. ‹ Identify the independent variables and the dependent variables in an experiment. ‹ What results would you expect to see in the control group? The experimental group? ‹ How does XXXX concept account for YYYY findings? ‹ Describe a method to determine XXXX.

Kit # 3674-04

Part 3C – OPEN inquiry: modeling osmosis What questions occurred to you as you investigated osmosis in living plant cells? Design an experiment to investigate one of your questions.

Questions may involve differences in water potential in cells from different plants, from different parts of plants, or from single celled organisms. Before starting your experiment, have your teacher check over your experiment design and initial your design for approval. Once your design is approved, investigate your hypothesis. Be sure to record all observations and data in your laboratory sheet or notebook.

Use the following steps when designing your experiment.

1. Define the question or testable hypothesis.

2. Describe the background information. Include previous experiments.

3. Describe the experimental design with controls, variables, and observations.

4. Describe the possible results and how they would be interpreted.

5. List the materials and methods to be used.

6. Note potential safety issues.

After the plan is approved by your teacher: 7. The step by step procedure should be documented in the lab notebook. This includes recording the calculations of concentrations, etc. as well as the actual weights and volumes used.

8. The results should be recorded (including drawings, photos, data print outs).

9. The analysis of results should be recorded.

10. Draw conclusions based on how the results compared to the predictions.

11. Limitations of the conclusions should be discussed, including thoughts about improving the experimental design, statistical significance and uncontrolled variables.

12. Further study direction should be considered.

©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

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Diffusion & Osmosis: Teacher’s Guide

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Live material care guide

Elodea Genus: Egeria or Elodea Family: Hydrocharitaceae Order: Hydrocharitales Class: Liliopsida Phylum: Magnoliophyta Kingdom: Plantae

Conditions for Customer Ownership We hold permits allowing us to transport these organisms. To access permit conditions, click here.

Never purchase living specimens without having a disposition strategy in place.

The USDA does not require any special permits to ship and/or receive Elodea except in Puerto Rico, where shipment of aquatic plants is prohibited. However, in order to continue to protect our environment, you must house your Elodea in an aquarium. Under no circumstances should you release your Elodea into the wild.

Primary Hazard Considerations Always wash your hands thoroughly before and after you handle your Elodea, or anything it has touched.

Availability Elodea is available year round. Elodea should arrive with a green color, it should not be yellow or “slimy.”

• Elodea canadensis—Usually bright green with three leaves that form whorls around the stem. The whorls compact as they get closer to the tip. Found completely submerged. Is generally a thinner species of Elodea. Has a degree of seasonality May–June.

• Egeria densa—Usually bright green with small strap-shaped leaves with fine saw teeth. 3–6 leaves form whorls around the stem and compact as they get closer to the tip. Usually can grow to be a foot or two long. Is thicker and bushier than E. canadensis.

Elodea arrives in a sealed plastic bag. Upon arrival, this should be opened and Elodea should be kept moist, or it should be placed in a habitat. For short term storage (1–2 weeks), Elodea should be placed in its bag into the refrigerator (4 °C). Regardless of its housing, do not allow your Elodea to dry out.

Captive Care Habitat: • When you receive your Elodea, remove it from the packaging and gently rinse away any debris or broken off pieces.

• Your Elodea is a freshwater organism that should be kept in de-chlorinated water. Water from the tap in most homes contains chlorine which can be detrimental to the health of your aquatic plant. Elodea should be fully submerged in de-chlorinated water.

De-chlorinate your water by using a commercial chemical designed to do so (such as Stress Coat 21 W 2338), or by leaving your water out in an open container for 24–48 hours.

• Elodea has a relatively undemanding light requirements, 10–12 hours a day . Elodea is typically kept at temperatures ranging between 50°F–77°F. • Elodea is an aquatic plant; submerge it into an established or de-chlorinated aquatic environment. It can grow un-rooted (free floating), however, it will grow more vigorously if rooted in a substrate.

Care: • Food: There is no need to feed; Elodea derives most of its nourishment from the water through its leaves and through light.

• Water: You should keep your Elodea fully submerged in water, so water in its habitat should be replenished as it evaporates with de-chlorinated water.

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Live material care guide To Root Elodea: • Place 2–3 inches of gravel on the bottom of the tank.

• Work the plants down into the gravel.

• Keep the plants secured in place by using small weights (they can be purchased at local pet stores) or stones or other heavy inert material until they can be secured with their own roots.

• The habitat should be cleaned once a month to ensure addition of fresh water into the habitat, and removal of any waste material that has fallen off the plant.

Information • Method of Reproduction: Elodea does not reproduce sexually (there are no flowers or seeds); instead, there are specialized nodal regions described as double nodes that occur at intervals along the sprig. Double nodes produce lateral buds, branches, and sprout roots. Only those shoot fragments can develop into new plants.

Wild Habitat Elodea is a submerged, freshwater perennial, generally rooted on the bottom in depths of up to 20 feet or drifting. It is found in both still and flowing waters, in lakes, ponds, pools, ditches, and quiet streams.

Aquarium Hobbyiest Use Elodea works well in many fish tanks. Elodea acts to increase the levels of oxygen in the water. It can also be a food source for different fish and aquatic snails. The leaves also absorb nutrients from the water that are normally considered a nuisance to other organisms in an aquarium (such as nitrogen).

Disposition Do one of the following: • Place Elodea in a freezer for 48 hours.

• Allow Elodea to “dry out” for 72 hours.

• Incinerate Elodea.

© 2008 Ward’s Natural Science Establishment. All rights reserved.

Rev. 9/08, 12/09

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AP Investigation #4: Diffusion & Osmosis Teacher’s Guide – Answer Key

Kit # 36-7404

Data Tables This table includes actual data from this lab. Your students’ data will vary somewhat.

Part 1: Cell Size & Diffusion Data Table 1: Agar Cubes Cube Size (cm)

Surface Area (cm2)

Volume (cm3)

Surface Area/Volume Ratio

3 2 1

54 24 6

27 8 1

2:1 3:1 6:1

JANET, SHOULD WE KEEP ANY OF THESE TABLES?

Data Table 2: Rate of Diffusion Cube Size (cm)

Depth of Diffusion (cm)

Time (min.)

Rate of Diffusion (cm/min.)

3 2 1

0.4 0.4 0.4

10 10 10

0.04 0.04 0.04

Data Table 3: Extent of Diffusion Total Volume of Cube (cm3)

Volume of Cube which has NOT Changed Color

Extent of Diffusion (%)

27 8 1

10.648 1.728 0.008

60 78 99

Part 2: Model Cells & Osmosis Solution

Dialysis Bag Initial Mass (g)

Dialysis Bag Final Mass (g)

Change in Mass (g)

% Change in Mass (g)

Water 1 M Sucrose 1 M Sodium Chloride 1 M Glucose 1 M Egg Albumin

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AP Investigation #4: Diffusion & Osmosis Teacher’s Guide – Answer Key

Kit # 36-7404

Data Tables (continued) This table includes actual data from this lab. Your students’ data will vary somewhat.

Part 3: Osmosis in living plant cells Potato Cylinders Initial Mass (g)

Final Mass (g)

Change in Mass (g)

% Change in Mass

Water

1.5

2.1

+0.6

+28.6

Mystery Red

1.5

1.6

+0.1

+6.3

Mystery Orange

1.5

1.3

-0.2

-15.4

Mystery Yellow

1.5

1.2

-0.3

-25.0

Mystery Green

1.6

1.1

-0.5

-45.5

Mystery Blue

1.5

0.9

-0.6

-66.7

Solution

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