WEEK 3 EXPERIMENT ANSWER SHEET
Please submit to the Week 3 Experiment dropbox no later than Sunday midnight.
SUMMARY OF ACTIVITIES FOR WEEK 1 EXPERIMENT ASSIGNMENT
Experiment 3 Exercise 1 Diffusion: Movement of Solutes across a Membrane
Experiment 3 Exercise 2 Osmosis: Movement of Water across a Membrane
Experiment 3 Exercise 1: Diffusion - Movement of Solutes across a Membrane
We will be using dialysis tubing to simulate a semipermeable membrane. This tubing
allows small molecules (e.g., water, ions, glucose) to pass while preventing large
molecules (e.g., macromolecules like proteins, starch, glycogen) from moving across.
Be sure you have read over the suggested material before starting this exercise and
that you have reviewed the following animations
A. The dialysis bag we will use is permeable to water and small molecules (e.g.
less than 500 g/mol) and impermeable to large molecules (e.g., more than 500
B. The dialysis bag is filled with a mixture of glucose (molecular weight = 180
g/mol) and protein (molecular weight = 10,000 g/mol) dissolved in water. A small
subsample of the dialysis bag contents is saved and will be used in Step 4.
C. The dialysis bag is then placed into a beaker of water. A small subsample of
beaker water is also saved and is to be used in Step 4 as well.
The presence or absence of glucose and protein will be determined using indicators.
Indicators change colors in the presence certain materials. The two tests that well use
are the Benedicts test for simple sugars (e.g., glucose) and the Biuret test for the
presence of proteins.
If glucose is present, the Benedicts indicator will turn green. If no glucose is
present, the solution will be blue.
If protein is present, the Biuret indicator will turn violet. If the solution remains
clear, then no protein is present.
D. The subsample of dialysis bag solution and the beaker water are tested for the
presence of glucose and protein. See Table 1 below for the results.
E. The dialysis bag is then left in the beaker of water for 60 minutes.
F. At the end of 60 minutes, the dialysis bag solution and the beaker water are
again tested for the presence of glucose and protein. See Table 1 below for the
Table 1. Results of testing of the dialysis bag and beaker contents at the beginning and
end of the Experiment.
Test for Glucose
Test for Protein
1. Summarize the results regarding the presence (+) or absence (-) of glucose and
protein in the dialysis bag and beaker in Table 2 below (4 pts)
2. Explain the movement or lack of movement of protein and glucose across the
dialysis bag membrane (4 pts)
3. Which solution, that in the bag or that in the beaker, is hypotonic compared with
the protein solution (2 pts)?
4. What factors affect the movement of molecules across a semipermeable
membrane? Which factor plays the greatest role in biological systems (4 pts)?
5. Briefly explain what active transport is and how it differs from passive transport
especially in terms of concentration gradients (4 pts).
Experiment 3 Exercise 2: Osmosis - The Movement of Water across a Membrane
Before starting, lets 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
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
B. ReadovertheinformationpresentedandthenClick on
C. Then, Click on. Read through the information
presented and be sure to click on Animate beneath the illustration.
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).
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.
4. Describe the net movement of water molecules when cells are placed in a
hypotonic solution. Explain why water moves this way (3 pts).
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.
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
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.
7. Describe the net movement of water molecules when cells are placed in a
hypertonic solution. Explain why water moves this way (3 pts).
J. Click on
K. Read through the information presented and be sure to click on Animate
beneath the illustration. Answer the following 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).
Level of Detail: Only answer needed
Other Requirements: The number of questions are unimportant as long as the answers are in complete sentences.