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Enrichment 3-1: Teacher Activity Notes

Exploring Osmosis

PLAN

Summary

Students explore osmosis using the selectively permeable membrane surrounding an uncooked egg and a dialysis membrane. Students compare the effects of osmosis in different concentrations of sugar solution and relate these experiments to osmosis that occurs inside cells.

Objectives

Students:

\checkmark explain the process of osmosis.

\checkmark compare the effects of different concentrations of sugar solution on osmosis.

\checkmark relate these experiments to osmosis that occurs inside cells.

Student Materials

  • Activity Guide
  • Resource (Optional)
  • Activity Report
  • Containers [5]
  • Tap water [500 ml]
  • Raw egg without shell (soaked in vinegar) [5]
  • Sugar solution (concentrated such as corn syrup) [500 ml]
  • Sugar solution (10%) [250 ml]
  • Sugar solution (20%) [250 ml]

Teacher Materials

  • Activity Report Answer Key
  • Corn syrup
  • Vinegar
  • Resource, dialysis tubing (pieces IS-cm long), string, and scissors (Optional)

Advance Preparation

Review the Procedure in the Activity Guide on TE page 48 and decide if you want students to explore osmosis further using this activity.

Purchase chicken eggs. Prepare sugar solutions. Collect containers.

One or two days before doing activity, remove shells from eggs by placing them in a container. Pour enough vinegar into the container so that the eggs are completely submerged in the vinegar. Place container in a refrigerator overnight.

The acetic acid (HAc) in the vinegar will react with the calcium carbonate (CaCO_3) of the shell to dissolve it, releasing bubbles of carbon dioxide (CO_2). Once the shell has been removed, the egg membrane will be exposed and very easily punctured. Be careful when handling these eggs without their shells.

Review the Procedure on the student Activity Guide on TE page 48 and decide if you want students to explore osmosis further using this activity. If you choose to have students do the activity extension, cut dialysis tubing into 15-cm lengths, one per team. Soak dialysis tubing in water for 15-30 minutes before using to make it easier for students to work with the tubing. Make dialysis tubing and copies of the student Activity Guide available to students.

Estimated Time

2 class periods

Prerequisites and Background

Students should have some knowledge of the process of osmosis. Knowledge of the structure of the cell, particularly the cell membrane and its role in regulating passage of materials into and out of the cell, is important.

IMPLEMENT

  • Provide students with a copy of the Activity Guide. You may want to review the Procedure with your students, including percent sugar calculations before they begin the activity. Make sure students do Day 1, Parts A, B, and C during the first class period. Then have them do Day 2, Parts A, B, and C during the next day's class period.
  • Share with students how the eggshell was removed.
  • Remind students to be careful with the solutions and the eggs.
  • Upon completion of the activity, encourage students to design an experiment to demonstrate osmosis using dialysis tubing (a selectively permeable membrane). Use the Resource provided.

Helpful Hints

  • Encourage students to investigate the effects of other osmotic environments. As an example, students could compare the effects of water (hypotonic), concentrated salt solution (hypertonic), and a water solution with just a trace of salt on eggs without shells.
  • Students can investigate the effects of osmosis using a plant cell such as the aquarium plant elodea.
  • Ask students to think of examples of osmosis that we see in our daily lives, such as in the grocery store where vegetables are often sprayed with water, kept moist, in order to help cells retain water and remain crisp.
  • Explain to students that saline solution, with a 0.9% salt concentration, is often used to replenish blood volume in an IV. Ask them to explain why this is used instead of water. They determine that the blood normally must be slightly salty and, therefore, must receive an infusion of saline that has a similar salt concentration in order to maintain homeostasis and intact blood cells. An infusion of pure water would cause the red blood cells to burst due to too much water flowing into the cells.
  • Ask students to compare osmosis in plant cells (having a cell wall) and in animal cells (having no cell walls).

ASSESS

Use the completion of the activity and the written answers on the Activity Report to assess if students can

\checkmark explain the process of osmosis.

\checkmark compare the effects of different concentrations of sugar solution on osmosis.

\checkmark relate these experiments to osmosis that occurs inside cells.

Enrichment Activity 3-1: Exploring Osmosis – Activity Report Answer Key

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. Why are vegetables sprayed with fresh water in your local grocery store? What if you substituted salt water for fresh water? Explain.
  2. Explain why it is a good idea to wait until the last minute to add salad dressing to a lettuce salad.
  3. When salt is poured on a snail or slug, bubbles (foam) appear. How would you explain this?
  4. Why is it important in making jam or jelly to add additional sugar? Could you substitute salt? Explain.
  5. What is the relationship between salt intake and high blood pressure?

Enrichment 3-1 Activity Guide: Exploring Osmosis (Student Reproducible)

Introduction

What is osmosis? Why is it important? How is it different from diffusion? Osmosis, like diffusion, requires a difference in concentration and molecular motion of a substance. Osmosis is a special kind of diffusion. In addition to concentration and molecular motion, osmosis requires the substance to be water moving through a selectively permeable membrane.

Materials

  • Activity Report
  • Containers [5]
  • Tap water [500 ml]
  • Raw egg without shell (soaked in vinegar) [5]
  • Sugar solution (concentrated such as corn syrup) [500 ml]
  • Sugar solution (10%) [250 ml]
  • Sugar solution (20%) [250 ml]

PART A

Procedure for Observing Containers 1 and 2

DAY 1

Step 1 Design a data table that includes space to illustrate the procedure, predictions, and recorded observations for 5 eggs.

Step 2 Label and fill container 1 half full of tap water. You need enough water to cover an egg.

Step 3 Obtain a raw egg that has been soaked in vinegar to remove the shell and carefully place the egg in container 1.

Step 4 Repeat Steps 2 and 3 using container 2. Add 10-20 drops of food coloring.

Step 5 Predict what you think will happen to each egg. Give a reason for your prediction. Record your prediction and reason on your data table.

Step 6 Observe the eggs carefully and make a labeled drawing of your observations on your data table for both eggs.

Step 7 Place containers 1 and 2 in a safe place until tomorrow.

DAY 2

Step 8 Observe the eggs carefully and make a labeled drawing of your observations for both eggs. Note any changes in the eggs in containers 1 and 2 from day 1. Brainstorm with your lab partners to explain what happened to cause any changes.

Add descriptions on your data table to illustrate any changes you see.

Step 9 Save containers 1 and 2 containing tap water and eggs for use as controls for Parts B and C.

PART B

Procedure for Observing Container 3 (egg in concentrated sugar solution)

DAY 1

Step 1 Label and fill container 3 half full of concentrated sugar solution such as Karo syrup (light). You need enough sugar solution to cover the egg.

Step 2 Obtain a raw egg that has been soaked in vinegar to remove the shell and carefully place the egg into container 3.

Step 3 Observe the egg carefully and make a labeled drawing of your observations on your data table.

Step 4 Predict what you think will happen to the egg. Give a reason for your predictions. Record your prediction and reason on your data table.

Step 5 Place container 3 in a safe place until tomorrow.

DAY 2

Step 6 Observe the egg carefully and make a labeled drawing of your observations on your data table. Note any changes in the egg in container 3 from day 1. Brainstorm with your lab partners to explain what happened to cause any changes.

Be sure to add descriptions on your data table to illustrate any changes you see.

PART C

Procedure for Observing Containers 4 and 5 (eggs in a dilute sugar solution)

DAY 1

Step 1 Let a concentrated sugar solution represent a 100% sugar solution. What do you think would happen if you set up eggs without shells in varying concentrations of the sugar solutions?

For example:

a. 5 ml of a concentrated sugar solution combined with 95 ml of water. What is the percent sugar concentration of this solution?

\frac{\text{part}}{\text{total}} \times 100 = \text{percent} \qquad \frac{5}{100} \times 100 = 5 \ \text{percent}

b. 25 ml of concentrated sugar solution combined with 225 ml of water. What is the percent sugar concentration of this solution?

Step 2 Place 250 ml of a solution that has a sugar concentration of 10 percent into container 4 and label.

Step 3 Place 250 ml of a solution that has a sugar concentration of 20 percent into container 5 and label.

Step 4 Carefully place a raw egg without a shell into containers 4 and 5.

Step 5 Predict what you think will happen to the eggs in containers 4 and 5. Be sure to give a reason for your predictions. Record your predictions and your reasons on your data table.

Step 6 Place containers 4 and 5 in a safe place until tomorrow.

DAY 2

Step 7 Observe the eggs carefully and make a labeled drawing of your observations for both eggs. Note any changes in the eggs in containers 4 and 5 from day 1. Brainstorm with your lab partners to explain what happened to cause any changes.

Add descriptions on your data table to illustrate any changes you see.

Enrichment 3-1 Resource: Exploring Osmosis (Student Reproducible)

Procedure

Step 1 Working with your partner or group, design an experiment to demonstrate osmosis through a selectively permeable membrane. Your experimental design should (a) use a control, (b) test only one variable at a time, and (c) allow for the collection of data.

Step 2 Have your group agree on a hypothesis to be tested. Determine what materials you will need. A piece of dialysis tubing 15 cm long will represent the selective membrane. You may want to use selected sugar solutions from Part C.

Step 3 Check with your teacher for final approval of your experimental plan, required supplies, and hypothesis.

Step 4 Discuss and answer with your group the following questions.

a. What will be your control?

b. What variable are you going to test?

c. What data are you going to collect?

d. How did you design and make your data table?

e. What will be the responsibility of each group member?

Step 5 Carry out your experiment, recording your observations in your data table.

Step 6 Follow the directions of your teacher to clean up.

Enrichment 3-1 Activity Report: Exploring Osmosis (Student Reproducible)

1. Why are vegetables sprayed with fresh water in your local grocery store? What if you substituted salt water for fresh water? Explain.

2. Explain why it is a good idea to wait until the last minute to add salad dressing to a lettuce salad.

3. When salt is poured on a snail or slug, bubbles (foam) appear. How would you explain this?

4. Why is it important in making jam or jelly to add additional sugar? Could you substitute salt? Explain.

5. What is the relationship between salt intake and high blood pressure?

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