Exercise 1: The Case of the Limp Vegetable

Table 1: Comparison of States of Tonicity

A. How does each potato strip look? Which one is limp and which one is crisp?

B. How can the difference be explained?

C. What caused the change in appearance of each strip?

Discussion:

A. Did the experiment support or refute the initial hypothesis? Explain why.

B. Explain why vegetables stored in a refrigerator over time become limp.

C. In this exercise two of the three types of tonicity gradients were observed. Suggest an experiment to provide an example of the third type of tonicity gradient in action.

D. What kinds of cell environmental conditions might affect tonicity in cells?

Exercise 2: Turgor

Table 2: Comparison of Turgor Pressure States in Elodea Leaf Cells

A. How can the differences in appearance of the cells in the two solutions be explained?

B. What caused the appearance of the cell to be altered by using 10% NaCl solution instead of water?

C. In what direction did the water move in the hypotonic solution? In the hypertonic solution?

D. Plasmolysis refers to the movement of water out of the cell, thus causing the central vacuole to become smaller. The volume of the entire cell is reduced and the plasma membrane may be visible, separated from the cell wall, because it pulls away from the cell wall with the reduction in volume. In which turgor state would this be most likely to occur?

Discussion:

A. Did this exercise support or refute the initial hypothesis? Explain.

B. Where might an example of this turgor pressure adjustment be observed happening in nature or around your home?

Exercise 3: Buffering Effect and pH

Table 3: Initial and Ending pH Comparison for Test Tube Solutions

Table 4: Results of Acid Addition to Buffered Solutions

A. What was the initial pH of the water in test tube #1?

B. What was the pH of the water after the addition of acid?

C. What was the initial pH of test tube solutions #2 and #3?

D. What was the pH after adding 5 drops of acid in each of test tubes #2 and #3?

E. When did the pH appreciably change?

F. What caused this dramatic shift in pH?

Figure: Graph of pH Change in Response to Buffering

A. Did this experiment support or refute the initial hypothesis? Explain.

B. Why did this pattern occur?

C. What was the difference between solutions #2 and #3?

D. What difference was observed in the way the two solutions reacted to the addition of acid?

E. Why is the buffering capacity of organic substances so important to living organisms, including humans?

Laboratory Summary:

What did you learn from doing this laboratory?