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Lesson 6. NYS Diffusion through a Membrane State Lab, Part 2, Osmosis
Objective: to gather evidence to support the concepts of isotonic, hypertonic, and hypotonic
conditions and their effects on living cells.
EQ: What effect do hypertonic, hypotonic, and isotonic conditions have on living cells?
Bridge: Define the words in the beginning of the lab
Mini Lesson: Give expectations for the lab. If you do not have access for students to watch the
video on their own, give them a set time for finishing each part of the lab and then comparing it
to the video….. this can be done in chunks (after viewing once, they can watch that portion of
the video as a group or just show it at the end of the lab before they do the analysis.
I built in the video component for comparison because often the microscopes are not of the best
quality or the students do not do a good job of changing out the solutions and the purpose of the
lab gets lost on them to frustration and well I didn’t see that. If they know what they should be
looking for then they do seem to actually see the plasmolysis on their slides and often they will
go back and re-prepare slides/repeat the experiment until they do see it and then the objective has
been met.
Work Period: Complete part 2 of the lab.
Summary: Answer the EQ
Closing: Answer the following questions
1. What changes would you expect to see in the outcome of the lab if we had done this with
animal cells instead of plant cells?
A student cut three identical slices from a potato. She determined the mass of each slice. She
then placed them in labeled beakers and added a different solution to each beaker. After 30
minutes, she removed each potato slice from its solution, removed the excess liquid with a paper
towel, and determined the mass of each slice. The change in mass was calculated and the results
are shown in the data table below.
2. Identify the process that is responsible for the change in mass of each of the three slices. [1]
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3. Explain why the potato slice in beaker 1 increased in mass. [1]
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Independent Practice: Regents questions on full lab.
Name ____________________________________
Living Environment
School
Date ___________________
NYS Mandated Lab: Diffusion Through A Membrane, Modified from its original form
Part II. Osmosis
Define the following terms:
Osmosis:
Concentration:
Cell wall:
Hypotonic:
Hypertonic:
Isotonic:
Identify the difference between plant cells and animal cells that would allow for a plant cell NOT
to lyse (explode) when placed in distilled (pure) water.
Question: What effect do hypertonic, hypotonic, and isotonic conditions have on living cells?
Prediction/Hypothesis:
Experimental Design
Materials: microscope, slide, pipettes, saline solution, 20% salt solution, distilled water, slides,
something to view the video clip on
Procedure:
1. View the clip of the onion cell prior to adding the salt water
2. Prepare a wet mount slide of an onion. View it under 10X. Compare it to what you saw
in the video.
3. Draw what the cell looks like, labeling the cell wall, cell membrane, and the cytoplasm in
the data section.
4. Salt water is then added to the cell using the following method, so that the coverslip does
not need to be removed:
5. View the clip of what happens after the salt water was added to the cell.
6. Take the slide that you prepared from step 2. Add the 20% salt solution to your slide
using the technique pictured above (called pulling a stain).
7. View the slide under 10x. Compare it to the cell you saw during the video clip.
8. Draw what it looks like, again labeling the cell wall, cell membrane, and the cytoplasm in
the data section.
9. The same method is used to then add distilled water to the onion cell. View the clip of
the onion cell as the distilled water is added.
10. Using the same microscope slide and the same technique, add distilled water to your
slide.
11. View the slide under 10x. Compare it to the cell you saw in the video clip.
12. . Draw what the cell looks like, labeling the cell wall, cell membrane, and the cytoplasm
in the data section.
Data
Cell in Saline Solution
Cell in 20% or more
Salt Solution
Cell in Distilled Water
Analysis: Describe in words what happened to the cell at each stage. Answer your question
here.
Evaluation: After you have completed your evaluation, answer all of the following questions.
A wet mount of red onion cells as seen with a compound light microscope is shown below.
7. Which diagram best illustrates the technique that would most likely be used to add salt to
these cells?
8. In the space below, sketch what cell A would look like after the addition of the salt. [1]
9. Which substance would most likely be used to return the cells to their original condition?
(1) starch indicator
(2) dialysis tubing
(3) glucose indicator solution
(4) distilled water
A wet-mount slide of red onion cells is studied using a compound light microscope. A drawing
of one of the cells as seen under high power is shown below.
10. On the diagram below, label the location of each of the cell structures listed. [1]
cell wall
cytoplasm
cell membrane
11. Describe the proper way to add a saltwater solution to the cells without removing the
coverslip. [1]
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12. In the space below, sketch how the cell would look after the saltwater solution is added
to it. [1]