Name: ______________________________________________________________ Date: __________ Period:___ Lab #___ Egg Osmosis Lab Background Information: The cell membrane is a selectively permeable membrane that regulates what materials enter and leave the cell. When substance is able to pass through a membrane, we say that the membrane is permeable to that substance. Membranes may be more permeable to some substances like oxygen and carbon dioxide than to others, these membranes are said to be selectively permeable or semi-permeable. In other words, these membranes have different permeability to different substances. Perhaps a small urea molecule will pass easily, but not a large starch molecule. Sometimes, membranes do not permit substances to pass through at all. Then they are said to be impermeable to that substance. Water also is permeable to the membrane and can cross freely. Whether the net movement of water is into or out of the cell is a function of osmosis. Osmosis is the special process of water moving across a membrane. When materials are impermeable to the cell membrane and are not in equilibrium, there is a net movement of water across the membrane. The rule of thumb is “Water likes to dilute”. Water, like other substances, will cross the membrane from where the water is most concentrated to an area where it is least concentrated. If a semi-permeable membrane separates two solutions and those solutions are different in their concentrations, one can expect that there will be a net movement of water. The solution that has the greatest concentration of solutes is said to be hypertonic relative to the other side. The solution that has the least concentrations of solutes is said to be hypotonic relative to the other side. The net movement of water will be from hypotonic side of the membrane to the hypertonic side of the membrane as “water dilutes” the side with greater amount of solutes. In other words, whatever side of the membrane has more solutes, is hypertonic. And whatever side of the membrane has less solutes is hypotonic. Purpose: You are going to be working in groups of 3-4 people to investigate the process of osmosis through a semi-permeable cell membrane. It explores changes in the mass, percentages, circumference, and volume of an egg when placed in different types of solutions (example: salt water, corn syrup, Shasta Cola, sugar water, colored water, vegetable oil, distilled water, vinegar, etc.) Roles: Resource Manager, Time Keeper, Scribe. Pre-Lab Questions: (Answer all questions professionally and in complete sentences) 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 for a chick to develop correctly? 4. What would happen to the developing chick if the egg membrane did not work correctly? I. Investigative Question: II. Hypothesis: Write hypothesis to answer your lab question for each egg. Rewrite the purpose into an investigative lab question. This is a prediction of what you think will happen to the egg. If _________________________________________________________________________ (write: what YOU ARE GOING TO DO in this lab) then _______________________________________________________________________ (write: what you think WILL HAPPEN in the lab) because ______________________________________________________________________. III. Experimental Design a. Variables i. Independent (This is the thing that the scientist changes before the experiment): ___________________________________________________________________ ii. Dependent (This is what happens because of the change and it is measurable): ___________________________________________________________________ b. Materials: write the materials with quantities that you will use. o _______ egg o ____________ o Solutions: Colored Water, Coke, Colored Salt Water, Corn Syrup, Shasta Coke, Sugar Water o Common Sense (Be Careful!) c. Procedures: Write accurate, numerical, and detailed steps to test out your hypothesis Safety: Be sure to wash your hands after handling raw eggs. Salmonella is bacteria commonly found in poultry and eggs. To avoid food poisoning, one should always wash their hands after handling raw eggs. Day One 1. Obtain a raw egg that has already been soaked in vinegar overnight. You should note that the egg shell has been dissolved leaving behind the surrounding outer membrane. Carefully handle the egg and dry it off with a napkin. 2. Put on your safety goggles, tie hair back, and wear aprons. 3. Place the egg on the protective tray and place on a scale. Determine the mass of the raw egg to the nearest 0.1 g. Record the mass of raw egg in DATA TABLE. 4. Carefully measure the circumference of the egg to the nearest 0.1 cm using a small string. 5. Place the egg inside a 400-mL beaker and carefully pour 250 mL on the chosen solution. Make sure to completely cover it. 6. On a piece of masking tape write your team name and solution. Neatly place this onto the beaker. 7. Repeat procedures for Egg #2. 8. Clean up your work station. Be sure to wash your hands after handling the eggs. Day Two 1. After two days, observe what has happened to the egg and how it has changed. Note your qualitative results on the Data Handout. 2. Remove the egg from the beaker. Carefully rinse and dry taking care not to break the membrane. 3. Place the egg on the protective tray and place on a scale. Determine the mass of the egg to the nearest 0.1 g. Record the mass of raw egg in Data Table(s). 4. Carefully measure the circumference of the egg and record in Data Table(s). 5. Calculate the percentage change of the mass and circumference using the following formula: % change= (Final Mass – Initial Mass) X 100 Initial Mass 6. Place your egg for display back into the beaker. 7. Clean up your work station. Be sure to wash your hands after handling the eggs. 8. Answer the remainder of the qualitative and quantitative analysis questions on the Data Handout. 9. Get together with your assigned group and begin working on data analysis poster. IV. Data a. Data Tables Table 1. Observations & Measurements of Egg #1 in _________________________ Circumference (cm) Mass (g) Day 1 Day 3 Amount of Change (Day 3- Day 1= Change) Percentage of Change Table 2. Observations & Measurements of Egg #2 in _________________________ Volume (optional) (mL) Circumference (cm) Mass (g) Volume (optional) (mL) Day 1 Day 3 Amount of Change (Day 3- Day 1= Change) Percentage of Change Egg Osmosis Lab Data Analysis Handout b. Qualitative Observations 1. Write descriptors of what happened to the egg(s) after placed in solutions. (example: Color, size, texture, smell, etc.) 2. Draw pictures of the changes you saw. c. Quantitative Observations 3. What happened to the mass of the eggs after it was left in the solution? Explain what accounts for the change in the mass of the egg. 4. What happened to the circumference of the eggs after it was left in the solution? Explain what accounts for the change in the mass of the egg. 5. Based on the data, Egg #1 is in a hypertonic/ hypotonic/ isotonic (circle one) solution. Explain why? 6. Based on the data, Egg #2 is in a hypertonic/ hypotonic/ isotonic (circle one) solution. Explain why? d. Analysis Questions (Use the data/observations collected in your lab to help you): 1. What is diffusion? What is osmosis? 2. A patient comes into the emergency room. She is unconscious and dehydrated. Explain what sort of intravenous solution (IV) you would inject into your patient and why? 3. If carrot sticks are put into water and refrigerated, they become turgid (stiff). If red blood cells are given the same treatment, they explode. Account for the difference in the results with evidence. (Hint: Pay attention to the different structures of the cells.) 4. Why if you were in a life boat on the ocean and thirst, would it be harmful to drink the ocean water? Justify your reasoning & provide evidence. V . Conclusion: Conclude your lab by typing up your lab report. In two separate paragraphs conclude your lab by: 1. Answering the Investigative Question of your lab using evidence from your experiment. 2. Summarize and analyze the results of your experiment for each egg. 3. Explain if your initial hypotheses were correct or incorrect? Justify why or why not. 4. What real life connections do we observe osmosis and how can that affect us in our lives? 5. What experimental and human errors might have occurred during this? What could you have done to improve in your lab process? Explain how they affected the lab.
