Students have been presented the concepts of diffusion, osmosis, passive transport, hypertonic, isotonic, hypotonic. This allows them to see these concepts through a macroscopic investigation. Subsequently, they are ready to use dialysis tubing as an example of a selectively permeable membrane.

THE CELL Cells have particular structures that underlie their functions. Every cell is surrounded by a membrane that separates it from the outside world. Inside the cell is a concentrated mixture of thousands of different molecules which form a variety of specialized structures that carry out such cell functions as energy production, transport of molecules, waste disposal, synthesis of new molecules, and the storage of genetic material.

Use of a triple beam balance or Electronic balance Observation Inference

Using fresh vinegar should remove the egg shell before the next class period. Check the shell to see if more vinegar should be added. The hydrochloric acid works better but you may not want to use this with your students.

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Name_____________________ Date ____________ Period _______________ Osmosis With an Egg Introduction: An egg is nothing more than a giant cell. A developing embryo has all the food it needs to grow into a little chicken. But it cannot survive without being able to get oxygen in and carbon dioxide out. The shell acts as a protective coat allowing this exchange to take place. When the shell is removed, other substances can also enter or leave the egg. Purpose: To predict and observe the effects of osmosis through the membrane of the egg. Materials: 1 egg vinegar or dilute HCl 1 balance (triple beam or electronic) distilled water 1 250 ml beaker Karo syrup 1 50 ml beaker Procedure: Day One: 1. Record which balance you are using. (You must use the same balance each day.) 2. The mass of the raw egg and shell is: ______________grams 3. Hypothesis: If the egg is left in the acid bath overnight, then _____________________________________________________________. 4. Place your raw egg with its shell into the 250 ml beaker. Pour either vinegar or dilute HCl (Your teacher will designate which to use.) onto the egg to cover it. If your egg wants to float to the top of the liquid, place the 50 ml beaker on top of it to hold it down. Is anything happening? Describe what you see. _____________________________________________________________ 5. Label the beaker and where your teacher indicates until the next class period. Day Two: 6. What has happened to your egg? __________________________________ Was this what you had hypothesized? _______________________________ 7. Carefully, so as not to damage the egg or get acid on your hands, pour off the acid bath and rinse the egg and the beaker in tap water. 8. Mass the egg being sure to use the same balance. ____________grams 9. Did the egg gain or lose mass? ________________ Explain why you think this happened? _______________________________ ______________________________________________________________ 10. Hypothesis: If the egg is now placed in distilled water, what will happen to the mass of the egg? _________________________________________ 11. Place your egg in the 250 ml beaker and pour distilled water on the egg to cover it. Again, if necessary, place the 50 ml beaker on top to hold the egg in the water. Put your egg and beaker in the designated area until the next class period. Day Three: 12. Carefully pour off the water in the beaker. 13. Mass the egg being sure to use the same balance. ___________grams 14. Was your hypothesis correct? ____________ Explain why you think your hypothesis was correct or incorrect. _________________________________ _____________________________________________________________ 15. Hypothesis: If the egg is now placed in Karo Syrup, what will happen to the mass of the egg? ___________________________________________ 16. Dry your beaker. Then place your egg into it and pour Karo Syrup to cover the egg. Again, if necessary, place the 50 ml beaker on top to hold the egg in the water. Put your egg and beaker in the designated area until the next class period. Day Four: 17. When you got your beaker, what did you observe has happened to the egg? _____________________________________________________________ 18. Remove the egg from the syrup. Rinse the egg very carefully. Mass the egg being sure to use the same balance. ___________grams 19. Was this what you had predicted (hypothesized)? __________ Explain your results and compare to what actually happened. _______________________ _____________________________________________________________ Analysis: 1. What effect did the acid have on the egg? ______________________________ _______________________________________________________________ 2. What passive process of moving molecules is demonstrated in this lab? _______________________________________________________________

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