Name ___________________________________ Period __________ Egg Cell Osmosis Lab Purpose: To soak an egg in various liquids and observe how the size of the egg changes as it gains or loses water through the membrane. 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 eggshell 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. Pre lab Questions: 1. What do you think would happen to a shell-­‐less egg if water passed into the egg through the membrane? 2. What do you think would happen to a shell-­‐less egg if water passed out of the egg through the membrane? 3. What substance must pass through the shell and membrane in order for a chick to develop correctly? 4. What would happen to the developing chick if the egg membrane did not work correctly? Hypothesis: Predict what will happen when an egg is submerged for 24 hours in each of the 4 different liquids. Day 1: I think that when I soak the egg in vinegar, the egg will ___________________________ (grow, shrink, stay the same) because ____________________________________________________________________________________. Day 2: I think that when I soak the egg in salt water, the egg will ___________________________ (grow, shrink, stay the same) because ____________________________________________________________________________________. Day 3: I think that when I soak the egg in corn syrup, the egg will ___________________________ (grow, shrink, stay the same) because ____________________________________________________________________________________. Day 4: I think that when I soak the egg in tap water, the egg will ___________________________ (grow, shrink, stay the same) because ____________________________________________________________________________________. 1 Example: Egg and cup 60g – empty cup 20g = egg 40g Data Collection: – = Day 1: Egg and cup ______g – empty cup ______g = egg ______g *This is your Egg’s Initial Mass data for Day 1 Day 2: Egg and cup ______g – empty cup ______g = egg ______g *This is your Egg’s Mass After 24 Hours Day 2 AND your Egg’s Initial Mass data for Day 2 Day 3: Egg and cup ______g – empty cup ______g = egg ______g *This is your Egg’s Mass After 24 Hours Day 3 AND your Egg’s Initial Mass data for Day 3 Day 4: Egg and cup ______g – empty cup ______g = egg ______g *This is your Egg’s Mass After 24 Hours Day 4 AND your Egg’s Initial Mass data for Day 4 Day 5: Egg and cup ______g – empty cup ______g = egg ______g *This is your Egg’s Mass After 24 Hours Day 5 Data and Observations: Solution Type Egg’s Initial Mass (g) Egg’s Mass After 24 Hours (g) Day 1 Day 2 Day 1 Day 2 Day 3 Day 2 Day 3 Day 4 Day 3 Vinegar Initial Observations Salt water Corn syrup Day 4 Tap water Day 5 Day 4 Observations after 24 hours Day 2 Day 3 Day 4 Day 5 2 y-­‐axis label: Graphing Your Data: Use a bar graph to show how each solution affected a change in the egg’s mass. (y-­‐axis for mass, x-­‐axis for solution type, and two bars for each solution: one bar for the egg’s initial mass and the second bar for its mass after 24 hours) Key: o = Initial Mass o = Mass After 24 Hours Title: _____________________________________________________________ x-­‐axis label: Graph Analysis: Write down 3 facts from your graph. (Should not include “There are bars”) 1. _______________________________________________________________________________________________________ 2. _______________________________________________________________________________________________________ 3. _______________________________________________________________________________________________________ 3 Conclusion: 1. Were your hypotheses right or wrong? (See p. 1 of your lab) Solution Right or Wrong Why? Vinegar Salt water Corn syrup Tap water 2. How did the mass of the egg change after sitting in each liquid for 24 hours? What caused the change in mass? Change in Mass Solution How many grams did it increase What caused the change in mass? (é) or decrease (ê) by? Vinegar Salt water Corn syrup Tap water 3. Explain the changes of the egg’s mass in terms of osmosis. (See the Introduction section on p. 1 for a description of osmosis.) 4. Why do grocery stores spray their produce with water? (Hint: It has something to do with the central vacuole. See p. 147 of the textbook for a description of what the central vacuole does.) 5. If a shipwrecked crew drank salt water, they could die. Explain why this could happen. 4