Name______________________________________
Date_______________________ Hr__________
Grade Level: 10
Points: 100
Course: Biology B, Chapter 7.3
Objective: B1.1b
Benchmark: B2.6a
Osmosis
DIRECTIONS: Work in groups to develop the best lab possible to answer the following question.
Description
The Main ingredient in most eye drops is saline solution, which is a solution of salts dissolved in
water. You might think that salt water would irritate the eyes. But saline solution and cells at the
surface of your eyes are isotonic, which means that they have the same concentration of solutes.
Because saline solution and the cells in your eyes are at "equal strength", using the eye drops does
not change the balance of water in the eyes. What happens when solutions are NOT isotonic with he
cells that they bathe?
In this lab, you will make a wet mount of red onion cells and observe the cells. Then, you will
compare the effect of a 10% salt solution and of a distilled water on the onion cells.
Problem/Purpose/Question
What effect does the concentration of solutes outside of plant cells
have on the cells?
Hypothesis
Use this space to write your hypothesis (your answer to the question) then tell how you will prove if your
answer is true.
Materials
List all the materials your lab group used.
Initial Observations
Answer the following questions.
1. What is osmosis?
2. When water is distilled, any solutes dissolved in the water are left behind. Is distilled water hypertonic or
hypotonic compared to tap water? Please explain your answer
3. What is the purpose of the iodine solution?
Procedure
A general procedure is given on the powerpoint. Use this as a guide and tell exactly what you or members in
your lab group did to test your hypothesis. Be sure to include what your control was, what the independent
and dependent variables were, what variable you controlled so they would not effect your data and all details
some one would need to duplicate your lab. Please use good grammar and write clearly. You may do this
either in paragraph form or as a numbered list of steps. Include a drawing of how you hold a small piece of
paper towel to draw the salt solution underneath the coverslip.
Data Collection
Draw the cells in the field of view before and after the experiment. Choose one cell and label the cell wall,
nucleus and cytoplasm. Be sure to note and describe whether the cytoplasm completely fills the cell.
Results/Trends/Graphs/Calculations
Write an short description of what you expect the lab reader to see in your drawings of the cells from the data
section.
Speculate on what has occurred to create the difference inside the cells.
Analysis
Answer the following questions.
1. a. How were the cells different after you added the salt solution?
b. What happened after you added the distilled water?
2. a. What caused the changes you observed when the onion cells were surrounded by the salt solution?
b. Was the salt solution hypertonic or hypotonic compared to the cells?
3. a. What caused the changes you observed when the onion cells were surrounded by distilled water?
b. Was the distilled water hypertonic or hypotonic?
Conclusion
Please write a short essay including whether the experiment supported or failed to support your hypothesis
and why. Be sure to include references to the data drawings that "show" your view. Also include any
unfortunate errors that may have occurred and how these errors may have wrongly changed your data or
results.
Additional Information
Answer the following questions that apply what you learned about plant cells to other types of cells.
1. When a red blood cells is placed in distilled water (or distilled water is accidently injected into a persons
blood stream) the red blood cells will swell and burst. What prevented the onion cells from bursting when they
swelled with the distilled water?
2. Some communities no longer use salt to prevent a buildup of ice on roads. The road salt can pollute water
supplies and then harm plants (just as it did the onion cells) that grow along the side of the roads. Explain
HOW road salt could harm these plants?
Lab Partners and Tasks
List all members of your lab and mention what tasks each member performed. Remember sometimes a task
was done by more than one member.
Evaluation
Extra Credit option
If you would like, (totally optional) you may design an experiment to determine what percentage of salt in a
solution produces an solution that is isotonic. Include why a business or industry might be interested in this
information.