Osmosis: An Eggcellent Example Introduction: Cells have an outer covering called the cell membrane that 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 via Passive or Active Transport. In passive transport, diffusion is the movement of substances like food, oxygen and waste across the membrane from a high to a lower concentration. Osmosis is the movement of water across the membrane from a high to a lower concentration. In this lab you will be using a shell-less egg to observe osmosis across a selectively permeable membrane. Facts about the egg: ● An egg is a single cell with its own cell membrane. ● The egg shell is made up of the mineral calcium carbonate. Calcium carbonate dissolves in acids such as vinegar. ● A chicken egg has 88% water in the white and 48% water in the yolk. Overall, a chicken egg is 74% water, which is similar to the ~70% water in typical animal cells. White vinegar is about 95% water and 5% acetic acid (Dewees 2011). 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. PROCEDURE PRELAB: Day One - Two Purpose: We will soak the eggs in vinegar for 2 days to remove the hard shell of the egg to expose the cell membrane of the egg. Material: ● 2 eggs ● 2 glass/plastic cups ● Distilled White Vinegar (Apple Cider Vinegar as a substitute) ● Saran wrap/aluminum foil Procedure: 1. Place one egg in each cup. 2. Add enough vinegar to cover 1cm over the egg. 3. Cover the top of the cup with saran wrap/aluminum foil. 4. Let sit for 2 days Day Three Purpose: Expose our shell-less eggs to a Hypertonic and a Hypotonic environment to determine what will happen to the egg. Additional Material: ● Water (Distilled or tap water) ● Corn syrup (or maple syrup or sugar water) ● Scale/Ruler (or pencil and paper to draw the egg’s measurements) Procedure Egg 1: 1. Remove egg from vinegar. Dump vinegar down the sink. Rinse excess shell off the egg. 2. Measure the egg (Quantitative Observation): a. Scale: Tare the scale, weigh the egg, record the mass in grams (g) b. Ruler: Measure the egg’s height ________(mm) and width ________(mm) c. None of the above: place your egg on a sheet of paper, draw marks to indicate the height and width of the egg for reference later (include a picture) 3. Write 3 descriptions of the egg (Qualitative Observation): a. b. c. 4. Place egg back into the cleaned cup. Add distilled or tap water to cover 1cm over the egg. 5. My prediction: I think the egg will shrink / grow / stay the same because distilled water represents a hypertonic / hypotonic / isotonic solution. Highlight 1 phrase per underline. Procedure Egg 2: 6. Remove egg from vinegar. Dump vinegar down the sink. Rinse excess shell off the egg. 7. Measure the egg (Quantitative Observation): a. Scale: Tare the scale, weigh the egg, record the mass in grams (g) b. Ruler: Measure the egg’s height ________(mm) and width ________(mm) c. None of the above: place your egg on a sheet of paper, draw marks to indicate the height and width of the egg for reference later (include a picture) 8. Write 3 descriptions of the egg (Qualitative Observation): a. b. c. 9. Place egg back into the cleaned cup. Add corn syrup, maple syrup, or sugar water to cover 1cm over the egg. 10. My prediction: I think the egg will shrink / grow / stay the same because distilled water represents a hypertonic / hypotonic / isotonic solution. Highlight 1 phrase per underline. Day ______ Purpose: Record data to support or reject your prediction. Today’s Material: ● Scale/Ruler (or pencil and paper to draw the egg’s measurements) Procedure Egg 1: 1. Remove egg from distilled water. Dump remaining contents down the sink. Dry off the egg. 2. Measure the egg (Quantitative Observation): a. Scale: Tare the scale, weigh the egg, record the mass in grams (g) b. Ruler: Measure the egg’s height ________(mm) and width ________(mm) c. None of the above: place your egg on a sheet of paper, draw marks to indicate the height and width of the egg for reference later (include a picture 3. Write 3 descriptions of the egg (Qualitative Observation): a. b. c. 4. Analyze Result: a. The egg shrank / grew / stayed the same. Highlight 1 underlined phrase. b. Distilled water represents a hypertonic / hypotonic / isotonic solution. Highlight 1 underlined phrase. 5. Conclusion: My hypothesis is supported / rejected. Highlight 1 underlined phrase Procedure Egg 1: 6. Remove egg from corn syrup. Dump remaining contents down the sink. Rinse and dry off the egg. 7. Measure the egg (Quantitative Observation): a. Scale: Tare the scale, weigh the egg, record the mass in grams (g) b. Ruler: Measure the egg’s height ________(mm) and width ________(mm) c. None of the above: place your egg on a sheet of paper, draw marks to indicate the height and width of the egg for reference later (include a picture 8. Write 3 descriptions of the egg (Qualitative Observation): a. b. c. 9. Analyze Result: a. The egg shrank / grew / stayed the same. Highlight 1 underlined phrase. b. Distilled water represents a hypertonic / hypotonic / isotonic solution. Highlight 1 underlined phrase. 10. Conclusion: My hypothesis is supported / rejected. Highlight 1 underlined phrase Analysis Questions 1. What material do you think moved in or out of the eggs to cause these size changes? What makes you think this? (2 pts) 2. Sketch the concentrations of the egg and its environment. One sketch per egg. a. Click on the picture b. Click “Edit” in the lower left corner c. Drag the correct phrase into the white oval (egg) or into the colored box (cup’s solution) d. Move the arrow to show the flow of osmosis (into the egg or out of th egg) e. Then click “Save and Close” Egg 1 (Distilled Water) Egg 2 (Corn Syrup
