Download Osmosis Lab

Osmosis Lab
Purpose: Describe the purpose of this lab in 1-2 sentences.
Background Info: 1) Define and contrast osmosis and diffusion. 2) Explain the difference between solute and solvent. 3) Describe the
difference between hypotonic, isotonic, and hypertonic solutions.
Hypothesis: Predict what will happen…
1) When you place a decalcified egg in a hypertonic, isotonic, and hypotonic solution? Why?
2) To Elodea cells when salt water is added to the slide? Distilled water? Why?
Materials:
1 decalcified egg
6 different concentrations of corn syrup and
distilled water: 0%, 20%, 40%, 60%, 80%, 100% corn
syrup
paper towels
250-mL beaker or plastic cup
electronic balance
plastic spoon
salt solution
compound light microscope
Elodea leaf in aquarium water
slide
cover slip
pipette
Procedures:
Part 1 – Osmosis in an egg
1.
Obtain a decalcified egg from your teacher. Gently blot it on a paper towel and determine the mass, using the correct
procedure (use weighing paper or a tray on the balance).
2.
Record initial mass of the egg in the Data Table 1. Record the corn syrup solution percentage that your group is assigned.
3.
Place the egg in a beaker. Fill this beaker with your solution to just cover the egg.
4.
Place your beaker in the specified area for 24 hours, then GO TO PART 2.
5.
After 24 hours, carefully remove the egg from the beaker with a spoon and set it on a paper towel.
6.
Carefully blot the egg with a paper towel and determine the mass of the egg. Record the mass in the Data Table 1.
7.
Determine the percent change in mass of the egg by using the following formula:
(mass after immersion – initial mass) X 100
initial mass
8.
Record the percent change in mass in Data Table 1.
9.
After you have determined the final percent change in mass for your solution percentage, send one student to your teacher to
record the information in an Excel spreadsheet.
10. Record the final mass changes for all the different solutions in your Data Table 2.
11. On a separate piece of graph paper, graph the corn syrup % (x-axis) versus percent change in mass (y-axis) of each egg.
Answer questions 1-8.
Part 2 – Osmosis in Elodea
1.
Remove a single leaf from near the tip of an Elodea plant. Place the leaf on a slide. Add a drop of aquarium water to the slide.
Lower a cover slip at a 45° angle into over the leaf.
2.
Center and focus leaf under scanning power. The eyepiece magnification should be at its highest setting. The diaphragm should
be at its highest setting.
3.
Then observe the leaf under low power (10X). Find a section of the leaf where you can clearly focus on one layer of cells. Now
switch to high power and examine the plant cells.
4.
In the Data and Results section of your lab write-up make a drawing of 4-5 Elodea cells in aquarium solution at high power.
Don’t forget to list total magnification and title of the drawing. Label the following plant structures, be sure labels are all
on one side, and have labels at the end of the line: cell wall, cell membrane, (not clearly visible because it is pressed
against the cell wall by the cell contents), cytoplasm, chloroplasts. Answer question 9 in the Data section of your write-up.
5.
Remove the slide from the microscope. Do not remove the cover slip or the leaf. Add two drops of salt water to one edge of
the cover slip. Place a piece of paper towel at the opposite edge of the cover slip to draw the saltwater solution under the
cover slip. See illustration below. Wait a few minutes for the concentration difference to affect the cells.
6.
Switch back to low power and examine the leaf. Before you switch to high power, be sure you see a change in the cells. If you
are not sure, ask your instructor for help. Answer questions 10-12 in your Data section
7.
Make another drawing at 400X of the Elodea cells in the observation section and label the same structures as step 4.
8.
Remove the slide from the microscope. Lift off the cover slip and gently rinse off leaf with distilled water into the sink. Be
careful not to drop or wash the leaf into the sink.
9.
Make a wet mount using the distilled water as your mounting solution. Wait a few minutes for the distilled water to cause
changes in the cells.
10. Switch back to low power and examine the leaf. Before you switch to high power, be sure you see a change in the cells. If you
are not sure, ask your instructor for help. Answer questions 13-17 in your Data section.
11. Make another drawing at 400X of the Elodea cells in the observation section and label the same structures as step 4.
12. Clean up your lab station, the floors and counters around your station as well as the sink well. Set microscope to scanning
power and wrap the chord around the base. Clean and dry the slide and slide cover and return materials to appropriate
spot on cart.
Data Collection:
Data Table 1: Your Egg Data
Solution % _______________
Mass of egg (grams)
Initial mass:
% change in mass
---------------------------------------------
After 24 hours:
Data Table 2: Your Class Data
Solution corn syrup %
0%
20%
40%
60%
80%
100%
Your Class % Change in Mass
Class Average % change in
mass
Data Analysis:
1.
What affect did the vinegar have on the egg?
2.
Did any egg gain mass over time? If so, which one(s)?
3.
Did any egg lose mass over time? If so, which one(s)?
4.
What passive transport method was demonstrated?
5.
What material passed through the egg membrane?
6.
Define isotonic, hypertonic, and hypotonic.
7.
In which instance was the egg in the most hypertonic solution?
8.
In which instance was the egg in the most hypotonic solution?
9.
What kind of solution would you describe the original aquarium solution in comparison to the plant cell? (hypertonic,
hypotonic, or isotonic) What observations support your answer? (2 pts)
10. How are the cells in the salt water solution different from the cells you first observed in aquarium solution?
11. What kind of solution would you describe the salt water solution in comparison to the original plant cell? (hypertonic,
hypotonic, or isotonic) What observations support answer? (2 pts)
12. Does the movement of water into or out of the Elodea cells change the shape of the cell walls? Explain why or why not?
hint: what are the cell walls made out of (2 pts)
13. How are the cells in the distilled water solution different from the cells you observed in salt water solution? *based on
your observations
14. What kind of solution would you describe the distilled water solution in comparison to the original plant cell? (hypertonic,
hypotonic, or isotonic) What observations support answer? (2 pts)
15. How would osmosis account for the crispy, fresh vegetables in the grocery store that has been sprayed with fresh water?
16. How would osmosis affect the growth of bacteria in an open jar of honey? Hint: honey is almost pure sugar, i.e. very little
water.
17. Why would gargling with salt water speed recovery from a bacterial throat infection?
Conclusion:
1.
Address your hypothesis. Be specific by using the terms isotonic, hypotonic, and hypertonic to explain the changes in
mass of the eggs and the changes in your Elodea leaf cells.
2.
Error analysis
3.
Suggestions for future labs