BIO LABS

Experiment Cell Structure and Function: Tonicity and pH

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Cell Structure and Function: Tonicity and pH Margaret E. Vorndam, M.S. Version 42-0038-00-01

Lab Report Assistant This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Observations

Data Table 1: Comparison of States of Tonicity

Test Tube

Solute/Solvent

Appearance of Potato Strip

Type of Tonicity Gradient: Is the potato strip in a Hypertonic, Hypotonic, or Isotonic at the beginning of this exercise?

1

2

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

Solute/Solvent

Scientific Term for Condition:

Is the leaf in a Hypertonic, Hypotonic, or Isotonic at the beginning of this exercise?

Appearance of Cells at End of Procedure

Water

10% Sodium Chloride, NaCl solution

Experiment Cell Structure and Function: Tonicity and pH

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

Test Tube Contents Beginning pH Ending pH Total drops of 0.1 N HCl added

1 Water

2 Buffer (inorganic) solution)

3

Buffered protein Albumen (organic) solution

Data Table 4: Results of Acid Addition to Buffered Solutions

Total Drops of HCl Added Beaker #2 pH Beaker #3 pH

0

5 - initial addition while in test tube

10 - after solution is placed in beaker and 5 more drops of HCl are added

15

20

25

30

35

40

45

50

Experiment Cell Structure and Function: Tonicity and pH

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Figure 1: Graph of pH Change in Response to Buffering

p H

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14 0 5 10 15 20 25 30 35 40 45 50

Drops of HCl

Experiment Cell Structure and Function: Tonicity and pH

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Exercise 1: The Case of the Limp Vegetable Questions

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 exercise 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.

Experiment Cell Structure and Function: Tonicity and pH

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

Exercise 2: Turgor Questions

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? Into the cell. 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.

Experiment Cell Structure and Function: Tonicity and pH

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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 Questions

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?

Experiment Cell Structure and Function: Tonicity and pH

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Discussion

A. Did this exercise 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?