Experiment 1: Tonicity and the Animal Cell

Experiment 1: Tonicity and the Animal Cell

In this experiment you will explore the effects of osmosis on eggs. An egg is surrounded by a permeable membrane and a hard shell. To observe the effects of osmosis the shell will first need to be removed.

Materials Acetic Acid (Vinegar) 4 Pieces of Aluminum Foil (to cover beakers) (4) 100 mL Beakers *Distilled water *4 Eggs 10 mL Graduated Cylinder

100 mL Graduated Cylinder 100% Sugar Solution (Corn Syrup) Stirring Rod *You Must Provide

Note: This lab requires at least one day to prep and at least one day for observations. For best results, please use a medium or large sized egg. Jumbo or extra large eggs are too large for the experimental set-up.

Procedure:

1. Set out four beakers with one egg in each beaker.

Note: Always wear gloves when handling raw eggs.

1. Cover each egg with acetic acid (vinegar).
2. Cover each beaker with a piece of foil and allow the eggs to sit for 24 hours. Keep foil for entire experiment. You will need it later in the experiment.

Figure 2:An egg that h as been soaked in vinegar and rinsed with water. Some white shell remains.

1. You will be placing eggs (cells) in different tonicities and observing the results. Develop a hypothesis and record it in the data section for this experiment.
2. After 24 hours, check to see if the egg shell is dissolved by gently taking out each egg and rinsing with a small amount of water. The eggs should have a yellow tint to them and you should be able to lightly squish the egg between your fingers (Figure 2). BE CAREFUL TO NOT BREAK THE EGG.
3. If any of the eggs still have a hard shell after 24 hours allow the eggs to sit for another 12 - 24 hours.
4. Once the egg shells have been dissolved remove them from the vinegar. HANDLE EGGS CAREFULLY. THEY CAN EASILY BREAK.
5. Rinse out and dry all four beakers.
6. Label one beaker “100 % distilled water”, one “100% corn syrup solution”, one “10% corn syrup/90% water solution” and one “control”.
7. In the beaker labeled “10% corn syrup/90% water solution”, prepare a 10% sugar solution by mixing 45 mL of distilled water with 5 mL of corn syrup. Mix well with a stirring rod. Record the initial volume in Table 1.
8. In the beaker labeled “distilled water”, measure and pour 50 mL of distilled water. Record the volume in Table 1. The egg should be covered. Add or reduce the amount of water if necessary. Record the initial volume in Table 1.
9. In the beaker labeled “100% corn syrup solution”, measure and pour 50 mL of corn syrup (100% sugar solution). The egg should be covered. Add more corn syrup if necessary. Record the initial volume of the solution in Table 1.
10. In the beaker labeled “control”, do not add any solution. Record the volume in Table 1.
11. Add one egg to each beaker and cover with foil.
12. Let the eggs sit for 24 hours. In the meantime, develop a hypothesis stating how you believe each egg will be affected by the solution in the beaker over the 24 hour period. Record your hypothesis in the Post-Lab Questions section.
13. After 24 hours have passed, observe the eggs. If you do not see any noticeable difference let the eggs sit for another 12 - 24 hours.
14. After the eggs have rested for 24-48 hours in the solutions carefully remove them from the beakers. Make sure to note which eggs came from each beaker. Be careful to not spill the solutions.
15. Record the final volume of each solution using a graduated cylinder and record your results in Table 1.
16. Observe the eggs. Draw your observations in the in Table 2 of data section.

Data

Hypothesis:

Table 1: Osmosis Results
Solution Type	Volume (mL) Before Osmosis	Volume (mL) After Osmosis
100% distilled water
100% corn syrup
10% corn syrup/ 90% distilled water
control

Table 2: Observations of Eggs After Osmosis
100% Distilled Water	100% Corn Syrup	10% Corn syrup/ 90% Distilled Water	Control

Post-Lab Questions

1. Record your hypothesis from Step 15 here. Be sure to include scientific reasoning to support your predictions.

1. How do each of the three eggs placed in solution compare to the control egg?

1. For each beaker, identify whether the solution inside was hypotonic, hypertonic, or isotonic in comparison to the control beaker.

1. What was the direction of osmosis in the beaker labeled “100% distilled water”? Did the egg in this beaker burst?

1. Was there a volume in the “control” beaker after 24-48 hours? If so, why do you think this is? If not, why do you think this is?

1. Which solution contained a dehydrated cell? Think about someone having a high sugar diet. Hypothesize how their cells might be affected by osmosis?

1. Osmosis is how excess salts that accumulate in cells are transferred to the blood stream so they can be removed from the body. Explain how this process works in terms of tonicity.