How will soaking gummy bears in saltwater affect the size of the candy? ______
3. How does osmosis occur in an egg cell? ______ 4. Is there a relationship ...
Lab # __________ Name __________________________________________ Date ______________ Period ________ Background: Diffusion is defined as the movement of molecules from an area of high concentration to an area of low concentration. Osmosis is a specialized form of diffusion involving the passage of water molecules through a selectively permeable membrane. It is difficult to see osmosis occurring in cells because of the small size of the cell. In this laboratory activity, we will be using several models to gain a better understanding of these processes in action. Question(s)/Problem(s): ______ 1. ______ 2. ______ 3. ______ 4.
How will soaking gummy bears in water affect the size of the candy? How will soaking gummy bears in saltwater affect the size of the candy? How does osmosis occur in an egg cell? Is there a relationship between temperature and the rate of diffusion?
Procedure: Part I – Modeling a Cell Membrane 1. 2. 3. 4.
Put on safety goggles Get 2 - 250 mL beakers . Label one beaker “cold” and the other “hot.” Add 90 mL of cool or lukewarm tap water to each beaker. In a larger beaker or flask, dissolve 1 teaspoon of cornstarch in 250 mL of water. Pour the mixture into two plastic bags, distributing it evenly among the bags. Seal the bags. 5. Add 10 mL of Lugol’s iodine to the “medium” beaker. CAUTIO : Lugol’s iodine is a poison and irritant. Avoid eye and skin contact. Do not inhale or ingest. This material also will stain skin and clothing. Use a thermometer to find the temperature of the water in the beaker. Record this initial temperature in Table 1. 6. Place a bag with the cornstarch solution in the “cold” beaker. Observe what happens in the beaker. Record your observations in Table 1. Include notes about how long it took noticeable changes to occur. 7. Place the “hot” beaker on a hot plate, and heat the water to boiling. CAUTION: A hot plate’s high temperature can cause injury. Make sure the electrical cord is not in the way of your movements. 8. Use an oven mitt to carefully remove the beaker from the hot plate. CAUTIO : Boiling water can cause injury. Place the beaker on a surface that is suited for high temperatures. 9. Repeat steps 5 and 6 for the “hot” and beaker. Record your results in Table 1. 10. Clean up your materials, and wash your hands before leaving the lab. Temperature and Diffusion Times Cold Initial temperature Observations
Hot
Analysis Questions: 1. What happened to the water inside the bag? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 2. Did the cornstarch diffuse out of the bag? How do you know? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 3. Explain how temperature affects diffusion. _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 4. Why is a warm body advantageous for a living thing? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________
Part II – Modeling a Cell Membrane Day 1- Preparation ____ Place the egg into the 500 ml beaker. Pour 250 ml of vinegar over the egg. Cover the beaker. ____ After 30 minutes, record your observations in the data table. ____ Let stand for two days. Day 2 – Soaking eggs in liquids ____ Label two separate sheets of paper towel “Egg 1” and “Egg 2.” Pour the vinegar from the beakers into the sink. ____ Using a tablespoon or tongs, remove the eggs and carefully rinse them with water.
____ Place each egg on the appropriately labeled paper towel. Measure the mass of each egg, and record the measurement in the last column of Table 1. ____ Record the appearance of the egg in the data table. ____ Return Egg 1 to its beaker, and add water until the egg is covered. ____ Return Egg 2 to its beaker, and add corn syrup until the egg is covered. ____ Store the beakers for 24 hours in the same place as before. ____ Clean up your work area and wash your hands before leaving the lab. Day 3 Measuring changes in the eggs ____ Predict how the mass of each egg has changed after 24 hours in each liquid. (Hint: An egg is surrounded by a membrane. Inside the membrane, the egg white consists mainly of water and dissolved protein. The yolk consists mainly of fat and water. Corn syrup is sugar dissolved in water. The protein, fat, andsugar are solutes.) Record your predictions in Table 2. • What will have occurred if your egg gains or loses mass? ______________________________________________________________
____ Observe your eggs. Record your observations in Table 2. Measure and record the final masses of the two eggs. Egg
Liquid
Predicted change after 24 h
Observations after 24 h
Final Mass of eggs
1 2 ____ Dispose of your materials according to your teacher’s instructions. ____ Clean up your work area, and wash your hands. Analysis Questions 1. What effect did the vinegar have on the eggs? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 2. What caused the change in appearance in Egg 1 after it is soaked in water? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________
3. What caused the mass of the egg to increase after soaking in the vinegar solution? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 4. What material seems to have moved through the membrane of Egg 2 after it soaked in the corn syrup? In what direction did the material move? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 5. How did your results compare with your prediction? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 6. Which egg was in a hypertonic solution? Explain. _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 7. Which egg was in a hypotonic solution? Explain. _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 8. Conclusions What do you think would happen to a red blood cell placed in a test tube of distilled water? Explain. _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ Part III – Osmosis in Gummy Bears Reminder: In this laboratory exercise, we will be using gummy bears to observe the process of osmosis. Gummy bears are popular candies made from gelatin, starch and sugar. DO OT eat your gummy bears. Make a Prediction (hypothesis). Explain your prediction based on the background information and your knowledge of science. Write in the “if…then…because” format. _________________________________________________________________________________ _________________________________________________________________________________
Day 1 ______ 1. Obtain two plastic cups and two different color bears. ______ 2. Use the masking tape to label your beaker with your name and class period. ______ 3. Using your ruler, find the height (cm) and width (cm) of your gummy bear. Measure carefully.
______ 4. Using the triple beam balance, find the mass of your gummy bear. i. Use a piece of wax paper to protect the pan of the balance. ii. Remember to subtract the mass of the wax paper. ______ 5.
Record your descriptive observations about your bear.
______ 6.
Fill your beaker approximately ½ full with water. Make sure the bear is fully covered.
______ 7.
Place the gummy bear into the beaker and allow the beaker to set for 24 hours.
______ 8.
Repeat Steps 1-5 using a saltwater solution.
Day 2 ______ 1. Gently remove the gummy bear from the beaker of water and pat it dry. Be extremely careful, as your gummy bear may now be easily broken. ______ 2. Using your ruler, find the height (cm) and width (cm) of your gummy bear. Measure carefully. ______ 3. Using the triple beam balance, find the mass of your gummy bear ______ 4. Use a piece of wax paper to protect the pan of the balance ______ 5. Remember to subtract the mass of the wax paper. ______ 6. Record your descriptive observations about your bear. ______ 7. Repeat Steps 1-3 for your bear in the saltwater solution.
Day 3 ______ 1. On the third lab day find the mass and dimensions of the bears using same procedure as DAY 2, and record in your data table.
Calculate the percent change in the size of the candy. % CHA&GE I& HEIGHT (distilled water) = (After soaking height – Before soaking height / Before soaking height) x 100 Sample 1: ( _________ - _________ / ________ ) x 100 = _____% Sample 2: ( _________ - _________ / ________ ) x 100 = _____% % CHA&GE I& WIDTH (distilled water) = (After soaking width – Before soaking width / Before soaking width) x 100 Sample 1: ( _________ - _________ / ________ ) x 100 = _____% Sample 2: ( _________ - _________ / ________ ) x 100 = _____% % CHA&GE I& MASS (distilled water) = (After soaking mass – Before soaking mass / Before soaking mass) x 100 Sample 1: ( _________ - _________ / ________ ) x 100 = _____% Sample 2: ( _________ - _________ / ________ ) x 100 = _____%
% CHA&GE I& HEIGHT (saltwater) = (After soaking height – Before soaking height / Before soaking height) x 100 Sample 1: ( _________ - _________ / ________ ) x 100 = _____% Sample 2: ( _________ - _________ / ________ ) x 100 = _____% % CHA&GE I& WIDTH (saltwater) = (After soaking width – Before soaking width / Before soaking width) x 100 Sample 1: ( _________ - _________ / ________ ) x 100 = _____% Sample 2: ( _________ - _________ / ________ ) x 100 = _____% % CHA&GE I& MASS (saltwater) = (After soaking mass – Before soaking mass / Before soaking mass) x 100 Sample 1: ( _________ - _________ / ________ ) x 100 = _____% Sample 2: ( _________ - _________ / ________ ) x 100 = _____% Create a bar graph showing the % change in height, width, and mass. Remember your labels.
Analysis Questions 1. What happened to the candy after soaking in water overnight? In saltwater? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 2. Why do you think you obtained these results? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 3. What do you think would have happened to the bears if, after the last day, they were again placed in distilled water? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________
