Name:____________________________ Date:______________ Period:_____________ Egg Osmosis Lab Introduction: Cells have an outer covering called the cell membrane. This membrane is selectively permeable; it has tiny pores or holes that allow objects to move across it. The cell membrane controls what moves in and out of the cell. Food and oxygen move into cells across the cell membrane through the process of diffusion. Diffusion is movement of a substance from an area of high concentration to an area of low concentration. Osmosis is a special type of diffusion; it is the diffusion of water across a selectively permeable membrane. Osmosis occurs when water moves from an area where it is more concentrated to an area where it is less concentrated. In this lab you will be using an egg with the shell removed. The shell-less egg will represent a cell and its selectively permeable membrane. You will remove the shell of the egg by soaking the egg in vinegar. The egg shell is made up of the mineral calcium carbonate. Calcium carbonate dissolves in acids such as vinegar. During this process it releases the gas carbon dioxide. After the shell has been dissolved, only the membrane will remain around the egg. Safety notes: 1. Raw eggs can carry salmonella (harmful bacteria). Be sure to wash your hands after handling the eggs. 2. Handle your egg very carefully so that it does not break Pre-Lab Questions: What happens when a cell is subjected to a solution where the water concentration is higher than that inside a cell (hypotonic solution)? What happens when a cell is subjected to a solution where the water concentration is lower than that inside a cell (hypertonic solution)? What happens when a cell is subjected to a solution where the water concentration is equal to that inside a cell (isotonic solution)? Hypothesis Predict how the egg will respond when it is soaked in the following solutions. Make sure to write a correct if then because statement for each solution. 1. Vinegar: 2. Corn Syrup: 3. Water: Procedure & Materials Student Sheet Materials: Marker Saran Wrap Balance 2 Egg 2 Plastic cups Water Vinegar Corn syrup Procedure: Day 1 1. Label your cups with your group’s name. 2. Weigh the eggs (individually) in grams. Record mass 3. Carefully place the eggs into their container and pour vinegar into the container, enough to cover the egg. Cover the cup with saran wrap. Allow them to soak for 24 hours. 4. Put your container in the designated space. 5. Clean up materials and wash your hands Day 2 1. 2. 3. 4. 5. 6. Carefully remove eggs from their container of vinegar. Remove any remaining bits of shell by gently running egg under water. Blot it dry with a paper towel Measure and mass your egg and record observations in data table Pour used vinegar down the drain. Rinse container Refill container with enough water in one cup and the other egg with corn syrup, enough to cover the egg. Carefully place the eggs back into their containers and allow it to soak for 24 hours, cover it with saran wrap. 7. Clean up materials and wash your hands. Day 3 1. 2. 3. 4. Take the egg gently out of each container, rinse gently under tap water, pat dry, and weigh. Measure and mass your egg and record observations in data table. . DO NOT put corn syrup down the drain. Dispose of eggs, used cups and corn syrup in the garbage can Table 1. Quantitative Data Weight start (grams) Soaking Solution Weight end (grams) Difference in Weight (end-start) % Change in Weight* Vinegar Water Corn Syrup * Calculate % Change in Weight = Difference in Weight x Weight start 100% * Note that % Change in Weight can be negative or positive Table 2. Qualitative Data Egg Observations before soaking Observations after soaking Vinegar Water Corn Syrup Analysis Questions: 1. Create a bar graph showing the difference in initial and final weight for each egg. Create a title, and properly label all axis. 2. How did the results compare to your pre-lab predictions? 3. In a controlled experiment, you should only change one variable and you hold others constant. List three variables you held constant during this experiment. 4. Which of the solutions was hypertonic? What is your evidence? 5. Which of the solutions was hypotonic? What is your evidence? 6. Draw an illustration for each set up, showing movement of water between the egg and each solution. 7. A student’s experiment showed that her egg gained mass overnight with the vinegar and distilled water. She had about a +1% change for vinegar and a +10% change for distilled water. She had hypothesized that the egg’s mass would not change significantly with vinegar. She concluded that her hypothesis about vinegar was not supported (because it did change in mass). Her teacher told her that the data indicated that her hypothesis was supported, especially with the 10% change for the distilled water. What did the teacher mean? 8. What is the biggest source of error for the lab? What improvements can be done to the lab?