Honors Biology Chapter 5 Lab: Observing Osmosis
Ms. DeCandia received a goldfish for her birthday and she accidentally placed it into a tank full
of salt water. Unfortunately, the fish did not live very long! After disposing of the fish, Ms. DeCandia
went to the pet store and purchased a new goldfish. She asked for advice from the pet store
worker. The worker told her that goldfish required a freshwater tank. So, Ms. DeCandia
hurried home and placed the goldfish in a tank full of distilled water. Once again, the fish died!
Why did Ms. DeCandia’s goldfish die both times?
Obviously, we cannot use living goldfish cells for this experiment. So, we will use the cells
from an onion. This will allow you to observe the effects of both salt water and distilled water on cells. Your
job is to design and carry out an experiment that will explain why the goldfish died in both solutions. Make
sure that the experiment has a control!
Problem: What happens to cells that are placed in hypotonic and hypertonic solutions?
Hypothesis: Write your hypothesis before you begin writing your procedure.
Materials:
1. microscope
2. slides
3. cover slips
4. onion
5. tap water
6. salt water
7. distilled water
8. pipettes
9. stain
Procedure:
1. Write a step-by-step procedure for this lab.
2. Make sure that your experiment has a control. Each group must get my approval before performing the
experiment.
3. When placing onion in experimental solutions, wait 30 minutes before observing cells under microscope.
Data: Draw a detailed picture of each slide (3 drawings) that you observe (high power).
Be sure to label each drawing with the type of solution.
Analysis
Read the following ofur statements before answering the questions:
a. Elodea cells normally contain 1% salt and 99% water on the inside.
b. Tap water used in this investigation contains 1% salt and 99% water.
c. Salt water used in this investigation contains 6% salt and 94% water.
d. Salt water has a higher concentration of salt than fresh water or elodea cells.
Answer the following questions about the cell in tap water.
1. What is the percentage of water outside the cell?
2. What is the percentage of water inside the cell?
3. How do the percentages compare?
4. Did the cell change shape? Explain. What is the name of this condition?
Answer the following questions about the cell in salt water.
5. What is the percentage of water outside the cell at the investigation start?
6. What is the percentage of water inside the cell at the investigation start?
7. Is the percentage of water (concentration) inside higher or lower than the percentage outside?
8. When will water move across the cell’s membrane?
9. Which direction will the water move?
10. Did the shape of the cell change? Explain. What is the name of this condition?
Conclusion: Write a conclusion that answers the problem. Make sure that you explain what happened
during this experiment.
Your conclusion should answer the following questions:
1. Identify each of your groups, what conditions did you keep constant between experimental groups?
2. Identify the dependent and independent variables.
3. Describe the position of the cell membrane and nucleus in each drawing.
4. Classify the three solutions as isotonic, hypotonic, or hypertonic. EXPLAIN!
5. Was your hypothesis supported by your data, explain.
6. Do plant cells appear to be able to maintain their shape in a variety of salt solutions?
7. If this experiment were done with living animal cells, what would you observe for each solution?
8. In the poem, "The Rhyme of the Ancient Mariner," is a line "Water, water, everywhere and not a drop to
drink." In terms of this investigation, what does this line mean?
A formal laboratory report is due for this lab.
Data Sheet: (Include in lab report)
Identify the types of solutions the plants were place in, and the result of each type of solution on the cells:
Solution
Result
plain water
sodium chloride solution
distilled water
DATA: Make a drawing of the onion cells under each of these conditions.
Dry
Sodium Nitrate
Distilled Water