Lab 5: Potato Tonicity

Posted: May 5th, 2020

Lab 5: Potato Tonicity
This is the lab you will be writing a report on!

Introduction & Background
We will be: comparing the tonicity of potatoes stored at room temperature and potatoes stored in a refrigerator.

Since the skin of potatoes is not waterproof (neither are the cell walls), stored potatoes tend to lose water content over time affecting the texture and reducing the overall quality of the potato when cooked. We want to know if refrigerating potatoes will reduce water loss and serve to maintain overall potato quality. In this lab activity you will work with your classmates to answer the question: Do potatoes stored at lower temperatures lose less water (and therefore, have lower tonicities) than potatoes stored at room temperature?

Russet potatoes were purchased 2 weeks ago from a local retailer. Half of the potatoes were stored in a large refrigerator at about 4 degrees Celsius and half were stored on an open counter at about 22 degrees Celsius.

Your lab instructor will divide you into teams and assign each team a “cold” potato or a “warm” potato and then provide instructions for estimating the tonicity of the potato cells. Once tonicities are determined, you will write this exercise up in scientific literature format following the instructions on page 382 of your lab manual. Make sure that you use and cite your references. Your references can include your lab manual and textbook, but you are required to find and use at least one relevant primary literature reference as well.

Protocol
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Materials Needed
• Sets (12) of culture tubes labeled 0% ABC, 1% ABC, 2.5% ABC, and 5% ABC (supplied)
• 0%, 1%, 2.5%, and 5% NaCl solutions (large carboys in 2150A)
• Potatoes (Russet)
o Refrigerated (RF) and
o Room Temperature (RT)
• ¼” cork borers (12) with dowels (12)
• Rulers, small
• Razor blades (re-use, place safely on top tier of lab bench with blade facing away from you)
• ~250 mL beakers for transfer and collection of fluid (12), rinse and re-use
• Small beakers (12) to measure 10-15 mL NaCl for culture tubes, rinse beakers and re-use between NaCl solutions
• Forceps (12)
• Paper and pencil to record data
• Paper towels
• Sharpie markers

Experiment Protocol:
1. Label a paper towel in the configuration of your culture tubes in the rack using a pencil or Sharpie marker.
2. Place 10 mL of NaCl solution into the corresponding labeled culture tubes. E.g.,
a. Measure about 40 mL of one of the NaCl solutions in the 250 mL beaker (measure 40 mL so NaCl is not wasted, do not pour excess liquid back into lab’s stock solution).
b. Using a small beaker, measure 10 mL of NaCl solution from the 250 mL beaker.
c. Dispense the 10 mL of the NaCl solution in the small beaker into the corresponding labeled culture tubes.
For example: Dispense 10 mL of 0% NaCl in tubes labeled 0% ABC, 10 mL of 1% NaCl in tubes labeled 1% ABC, etc.
3. Produce 12 potato cores.
4. Trim cores with razor blade to 3 cm in length (use ruler), removing edges or core with potato skin, and safely return razor to top tier of lab bench.
5. Gently and briefly roll each core on a dry, unlabeled paper towel and place the core on the labeled paper towel from #1.
6. Weigh each potato core, being careful to
a. record the core mass on spreadsheet supplied to you (next page) and
b. replace the core in the appropriate area on the labeled paper towel.
7. Place all potato cores in their corresponding labeled culture tube
8. Let cores soak for 30 minutes (timed).
9. With forceps, remove each core from culture tubes, letting core drip dry. Place damp core in configuration of culture tubes as before on labeled paper towel from #1.
10. Roll each individual core on a clean, dry paper towel and immediately weigh each core.
11. Record the mass (g) of each potato core.

Data:
• Each student will transfer their raw data into the spreadsheet provided at instructor’s desk.
• Record the class’s average % Mass Change for each NaCl solution concentration (0%, 1%, 2.5%, and 5%) on the Assignment handout. Please see the values calculated for you in the Excel spreadsheet bordered in yellow.

Cleanup:
• If Sharpie markers were used to mark any tubes or beakers, remove ALL markings on glassware with isopropyl alcohol (in supply cabinet) using paper towels.
• Rinse out, with tap water, all culture tubes, rack, and place culture tubes, in order, upside down in rack to dry on fresh paper towels for next class (reposition label tape if needed) on top tier of lab bench.
• Rinse out all beakers and place upside down on fresh paper towel on the top tier of lab bench.
• Arrange top tier of lab benches neatly for next class.
• Clean off workspace with paper towels and water (use only a very small amount of detergent found at each sink if needed).

Your Group’s Raw Data

Refrigerated (RF)
Color Sample Initial Mass (g) Final Mass (g)
Pink 0% A
0% B
0% C
Grey 1% A
1% B
1% C
Green 2.5% A
2.5% B
2.5% C
Orange 5% A
5% B
5% C
Room Temperature (RT)
Color Sample Initial Mass (g) Final Mass (g)
Pink 0% A
0% B
0% C
Grey 1% A
1% B
1% C
Green 2.5% A
2.5% B
2.5% C
Orange 5% A
5% B
5% C

Class Data

This is the data you will use to write your lab report – not your group’s individual results.

Solution Average % Mass Change
Refrigerated Room Temp
0%
1%
2.5%
5%

So, remember for this lab the goal was to answer the question: Do potatoes stored at lower temperatures lose less water (and therefore, have lower tonicities) than potatoes stored at room temperature? If a potato loses water, that will make the solutes present in the potato more concentrated and have a higher tonicity.
To answer this question, we need to determine the average tonicity of our potatoes!
1. Graph the data above in Excel (you could use Google Sheets if you prefer, things are similar in Google Sheets to Excel but let me know if you have questions using the chart functions in it!)
2. Add a trendline and equation to your graph(s).
Refrigerated equation:
Room temperature equation:
3. For each of the equations (one for the refrigerated and one for the room temperature potatoes) solve for the y-intercept by setting the y=0. We are doing this to determine what our tonicity is.
4. At the end of #3 you should have 2 values for x (one for the refrigerated and one for room temperature). These are your tonicity values for the potatoes.

5. Now that you know the tonicity values you can start to answer the question of which one has a higher tonicity compared to the other. A higher tonicity would mean that the potato has a higher value for x, and that those potatoes have a higher concentration of solutes in the cells. Does this align with what condition (refrigerated or room temperature) you were thinking would have a higher tonicity (that it lost more water)? It is okay if it doesn’t – that’s science for ya! Why or why not?
6. Look up a term called cold induced sweetening! What role could this have in our interpretation of the data?

Writing a Lab Report

Quotes are not allowed in this assignment!
1. Title
a. Short and descriptive (not potato lab)
2. Abstract
a. Brief summary of everything in your lab report
b. 1 paragraph long
3. Introduction
a. Background the reader needs to understand what you did and why you did it
b. Why do we care about the work you did?
c. 1-2 paragraphs
4. Methods
a. Steps you did to conduct the experiment.
b. This should not be a list of items
c. DO NOT copy the methods included in this document.
d. Include data collection and analyzing
e. 2 paragraphs
5. Results
a. State the results
b. Include graphs with figure captions
c. The graphs need to be described in the text of this section – you must explain what the graphs show the reader
d. 1-2 paragraphs
6. Discussion
a. Bring it all together
b. Discuss and explain what your results mean
c. 2 paragraphs
7. Literature Cited
a. You must include one primary article source
b. In APA format
c. Others are optional but be sure to cite any source you use

Turning in Your Lab Report

a. Must be submitted as a Word Document in the D2L Dropbox

b. Lab Report is due date: _____________________

c. THE ONLY ACCEPTABLE submission format is a Word Document. Only Word Documents will be graded. PDF’s will NOT be accepted.

d. Late lab reports will NOT be accepted

e. Lab reports will ONLY be accepted on D2L through Dropbox

f. Dropbox will have a time set at which it will close. If your lab report is not submitted by this time, your lab report is late and will not be accepted. This is why it is crucial that you double check what you submitted to Dropbox immediately after you submit it.

g. Dropbox has a program that will be searching for plagiarism in your lab report. It compares your lab report to current and previous papers from this university, other universities, websites, databases, and information from websites themselves. It can also find articles and papers from websites that require membership.

Introduction:
Potatoes are a widely consumed and versatile vegetable. However, potatoes lose water content over time which can affect their quality and texture when cooked. In this experiment, we investigated whether storing potatoes in the refrigerator can reduce water loss and lower the tonicity of the potatoes. We compared the tonicity of potatoes stored at room temperature and potatoes stored in a refrigerator.

Materials and Methods:
We were provided with 12 sets of culture tubes labeled 0% ABC, 1% ABC, 2.5% ABC, and 5% ABC, as well as 0%, 1%, 2.5%, and 5% NaCl solutions. We obtained Russet potatoes that were purchased 2 weeks ago from a local retailer, and half of them were stored in a refrigerator at about 4 degrees Celsius and half were stored on an open counter at about 22 degrees Celsius. Our group was assigned to the refrigerated potatoes. We labeled a paper towel in the configuration of our culture tubes in the rack using a Sharpie marker. We placed 10 mL of NaCl solution into the corresponding labeled culture tubes, using a small beaker to measure 10 mL of NaCl solution from a 250 mL beaker of NaCl solution. We produced 12 potato cores and trimmed them with a razor blade to 3 cm in length, removing edges or core with potato skin. We weighed each potato core, recorded the core mass, and placed all potato cores in their corresponding labeled culture tubes. We let the cores soak for 30 minutes and then removed each core from culture tubes with forceps, letting it drip dry. We placed each damp core on the labeled paper towel, rolled each core on a clean, dry paper towel, and immediately weighed each core. We recorded the mass (g) of each potato core.

Results:
Our group’s raw data for the refrigerated potatoes is presented in the table below:

Refrigerated (RF)
Color Sample Initial Mass (g) Final Mass (g) Mass Change (%) Tonicity (%)
Red RF-1 0.576 0.522 -9.38 10.0
Orange RF-2 0.629 0.583 -7.32 7.5
Yellow RF-3 0.593 0.533 -10.11 10.0
Green RF-4 0.641 0.587 -8.43 7.5
Blue RF-5 0.676 0.604 -10.65 10.0
Purple RF-6 0.699 0.622 -11.01 10.0

We calculated the mass change and tonicity for each sample using the formulas provided in the lab manual. The tonicity is expressed as the percentage of NaCl that causes no net change in the mass of the potato core.