Experiment 3 Exercise 2: Osmosis – The Movement of Water across a Membrane
Before starting, let’s see what you know about the terms hypotonic, isotonic and hypertonic. Examine the diagrams below. Note that the small green circles represent dissolved solutes like salt, glucose, and amino acids. You can assume that the additional space surrounding the solutes is water and that the tan area is INSIDE the cell.
Question
1. Define each term below in terms of solute concentration outside compared to the inside of the cell. You do not need to explain which direction water will move (3 pts).
a. Hypotonic –
b. Isotonic –
c. Hypertonic –
Procedure
A. Open the following website to get started:
The Biology Place. No Date. Osmosis: Movement of Water across Membranes http://www.phschool.com/science/biology_place/biocoach/biomembrane1/osmosis.html
B. Read over the information presented and then Click on
C. Then, Click on . Read through the information presented and be sure to click on Animate beneath the illustration.
Questions
2. What concentration of salt is isotonic to animal cells (1 pts)?
3. When cells are in isotonic solution, is there movement of water into or out of the cell? If so, describe this movement (3 pts).
Procedure (continued)
D. Click on .
E. Read through the information presented and be sure to click on Animate beneath the illustration. When ready, answer the following question.
Question
4. Describe the net movement of water molecules when cells are placed in a hypotonic solution. Explain why water moves this way (3 pts).
Procedure (continued)
F. Click on
G. Read through the information presented and be sure to click on Animate beneath each of the illustrations. Answer the following questions. Your answers should incorporate the terminology used in the animations.
Questions
5. What happens to an animal cell when placed in a hypotonic solution (2 pts)?
6. What happens to plant cells when placed in a hypotonic solution? What accounts for the difference in outcomes between animal cells and plant cells (3 pts)?
Procedure (continued)
H. Click on
I. Then, Click on . Read through the information presented and be sure to click on Animate beneath the illustration. Answer the following question.
Question
7. Describe the net movement of water molecules when cells are placed in a hypertonic solution. Explain why water moves this way (3 pts).
Procedure (continued)
J. Click on
K. Read through the information presented and be sure to click on Animate beneath the illustration. Answer the following questions.
Questions
8. Compare and contrast what happens to plant and animal cells when placed in a hypertonic solution. Be sure to use proper terminology (4 pts).
9. Based on what you learned in this exercise, explain why salt might make a good weed killer (3 pts).
Week 3 Experiment Grading Rubric
| Component | Expectation | Points |
| Experiment 3 Exercise 1 | Interpretation of results and demonstrated understanding of diffusion (Table 2 and Questions 1-5). | 18 pts |
| Experiment 3 Exercise 2 | Demonstrates understanding of isotonic solutions and no net movement of water (Questions 1-3). | 7 pts |
| Demonstrates understanding of hypotonic solutions and the movement of water (Questions 4-6). | 8 pts | |
| Demonstrates understanding of hypertonic solutions and the movement of water (Questions 7-9). | 10 pts | |
| TOTAL | 43 pts |