LABORATORY PRACTICE EVALUATION
NAME:
DATE:
TEACHER:
GRADE:
Lab report structure:
1. Title
2. Personal Engagement
3. introduction
-objective
4. methodology
- list of materials
- procedure steps
- variables
- hypothesis
- ethical and/or environmental implications
5. Results:
-Raw data
- Processed data
6. Discussion
7. Conclusion and Evaluation
8. References
9. Appendix
Osmolarity
I. Objectives
After completing this lab, you should be able to:
1. Describe a selectively permeable membrane, and explain its role in osmosis.
2. Define hypotonic, hypertonic, and isotonic in terms of relative concentrations of
Osmotic active substances.
3. Discuss the influence of the cell wall on osmotic behavior in cells.
4. Observed, measure and manipulate equipment
5. Explain how incubation of plant tissues in a series of dilutions of sucrose can give an
approximate measurement of osmolarity of tissue cells.
6. Explain why osmosis is important to cells.
II. Introduction
III. EXERCISE 1.
Estimating the Osmolarity of Plant Cells by Change in Weight
Frequently, plant scientists need to determine the optimum water content for normal physiological
processes in plants. They know that for normal activities to take place, the amount of water
relative to osmotic active substances in cells must be maintained within a reasonable range. If
plant cells have reduced water content, all vital functions slow down.
In the following experiments, you will estimate the osmolarity of known cells. You will incubate pieces
of the known cell in sucrose solutions of known molarity. The object is to find the molarity at
which the weight of the potato tuber tissue does not change, indicating that there has been no
net loss or gain of water. This molarity is an indirect measure of the osmolarity of the known
cell.
Introduction
In this experiment, you will determine the weight of several cells and incubate them in a series of sucrose
solutions. After the cylinders have incubated, you will weigh them and determine if they have
gained or lost weight. This information will enable you to estimate the osmolarity of the cell
tissue.
Materials and Equipment
1 known cell
7 250-mL beakers
Sharpie
forceps
balance
metric ruler
potato /beetroot / carriot
petri dish
sucrose solutions: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 M
razor blade
cork borer
deionized (DI) water (0 molar)
paper towels
aluminum foil
Procedure
1. Label 7 beakers as follows: 0.0M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M and 0.6M.
2. Add 100 mL of the sucrose solutions to the correct beaker. (Note: DI water is 0.0M).
3. Use a sharp cork borer to obtain seven cylinders of the known cell.
Push the borer through the length of the cell, twisting it back and forth. When the borer is filled, remove
from the cell and push the cell cylinder out of the borer. You must have seven complete,
undamaged cylinders which are at least 5 cm long.
*Cork borers and razor blades can cut! Use them with extreme care! To use the cork borer, hold
the potato in such a way that the borer will not push through the potato in your hand.
4. Line up the potato cylinders and, using a sharp razor blade, cut all cylinders to a
uniform length, about 5 cm, removing the peel from the ends.
5. Place all seven potato samples in a petri dish, and keep them covered to prevent
their drying out.
*In subsequent steps, treat each sample individually. Work quickly. To provide consistency, each
person should do one task to all cylinders (one person wipe, another weigh, another
slice, another record data).
6. Remove a cylinder from the petri dish, and place it between the folds of a paper
towel to blot sides and ends.
7. Weigh it to nearest 0.01 g on the aluminum sheet on the balance. Record
the weight in Table 1 in the Results section.
8. Immediately cut the cylinder lengthwise into two long halves.
9. Transfer potato pieces to the water beaker.
10. Note what time the potato pieces are placed in the water beaker. Time _______
11. Repeat steps 6 to 8 with each cylinder, placing potato/beetroot/carriot pieces in the appropriate
incubating solution from 0.1 to 0.6 M.
*Be sure that the initial weight of the cylinder placed in each test solution is accurately recorded.
12. Incubate 1.5 hours. (As this takes place, you will be performing other lab
activities.)
13. Swirl each beaker every 10 to 15 minutes as the potato pieces incubate.
14. At the end of the incubation period, record the time when the potato pieces are removed. Time:
_______. Record the approximate incubation time in Table 1.
15. Remove the potato pieces from the first sample. Blot the pieces on a paper towel, removing excess
solution only.
16. Weigh the potato pieces and record the final weight in Table 1.
17. Repeat this procedure until all samples have been weighed in the chronological order in which they
were initially placed in the test solutions.
18. Record your data in the Results section.
Prediction / hypothesis
Predict the results of the experiment based on your hypothesis (if…then… because…).
Results
Raw Data: Complete the table below
Table 1. Data for Experiment Estimating Osmolarity by Change in Weight.
Sucrose Molarity
0.0
0.1
0.2
0.3
0.4
0.5
Final weifInitial weght
(g)
0.6
Initial weiFinal weight
(g)
Table 2.
0.0
0.1
NaCl Molarity
0.2
0.3
0.4
0.5
0.6
Final weifInitial weght
(g)
Initial weiFinal weight
(g)
Data Processed
To calculate percentage change in weight, use this formula:
Percentage change in weight = weight change X 100
initial weight
If the sample gained in weight, the value should be positive. If it lost in weight, the value should be
negative.
Table 3: Mass percent change. Using the following formula= [final w - initial w) initial
w] 100.
0.0
Weight chChange in
weight (g)
in weig
Sucrose and NaCl Molarity
0.1
0.2
0.3
0.4
0.5
0.6
Graph Results
Figure 1. Figure shows the data of the change in mass in percentage after having
carried out the experiment.
Table 4: Chart showing the results of procedure with the different solutions and
their physical description
Solution (Molarity)
Cell description
A
B
C
D
Solution
A
B
C
Cell description
Discussion
1. At what sucrose molarity does the curve cross the zero change line on the graph?
2. Explain how this information can be used to determine the osmolarity of the potato tuber tissue.
3. Estimate the osmolarity of the potato tuber tissue.
Analysis
Conclusion
References
Appendix