Read Laboratory%208.pdf text version

Laboratory 8: Banana Lab

Ripening Bananas: What's Happening and Can We Control It?

(This lab was revised by Laura B. Sonnichsen & Sheryl Drake, Parkland College) Reference: Davis-McGibony, C.M.; Bennett, R.R.; Bossart II, A.D.; Deal, S.T. J. Chem. Educ., 2006, 83, 1543.

Report Requirement: Answer all of the questions/do all the computations requested in italics. Questions not in italics do NOT need to be answered. You do NOT have to write a formal lab report. You should write your answers into a word processing program and save the file. Go into the Lab #8 Report and cut and paste the answers to each question in the appropriate space. (Lab #8 Report can be found on the Content page or under Assignments Quizzes.) The data table for Question 1 will be submitted to the Lab #8 Dropbox (found under Content page or under Assignments -> Dropbox.) Labs not submitted in the appropriate area will not be graded.

Report Scoring: 20 points total. Questions valued as marked. Working with a Partner: You are permitted to work with a partner. If you do so, the

experimental data reported may be the same, but you need to write your own answers to each question. At the beginning of each question you should note that you worked with a partner by writing "Lab Partner (fill in name)."

Goals:

1. Predict which bananas will have the highest sugar content and the highest starch content. 2. Draw valid conclusions on whether the hypotheses were supported or refuted based on gathered data and calculations 3. Use Keto-Diastix reagent test strips and color chart to determine sugar content 4. Apply significant figures and units to measurements and calculations Materials: Bananas ­ need 2 bananas of different ripeness (green, yellow, or black). Plastic cups (4). Screw top test tubes (2) ­ From CHE 106 Lab Kit Funnels ­ from Patriotic Colors kit. Coffee Filter Paper ­ from provided supplies (or you may purchase) Acetone or Nail Polish remover ­ this is optional. Distilled Water Patuer Pippettes (2) - From CHE 106 Lab Kit Commercial Glucose Test Strips (2-3) ­ from provided supplies (or you may purchase) Our laboratory uses Bayer Keto-Diastix brand test strips. They are sold 50 strips per bottle. Each test strip contains the following components: 2.2% w/w Glucose Oxidase (Microbial, 1.3 IU); 1.0% w/w Peroxidase (Horseradish 3300 IU): 8.1% w/w Potassium Iodide; 69.8% w/w Buffer; 18.9% w/w Nonreactive Ingredients. The strip is impregnated

with the components listed and a blue background dye. The oxygen liberated in the final reaction binds with the dye to produce a series of color changes 30 seconds after wetting the strip with urine (or sugar solution). The test strips must be stored at temperatures between 59- 86°F (15-30°C) and out of direct sunlight.

Background:

If you are a banana eater, you know that the flavor of a green banana is much different than the flavor of a brown banana. You also know that if you buy bananas well ahead of when you plan to eat them, they may well turn black before you get the chance to eat them. What you may not know is that bananas are shipped to the US as hard, green, sour, unripened fruits. They ship better that way, and they arrive into a distributor's warehouse without bruises. Once they reach the warehouse, the bananas are allowed to ripen by the addition of a small amount of ethylene. Ethylene, a ripening agent, is a simple hydrocarbon gas (H2C=CH2) that ripening fruits make and shed into the atmosphere. Sometimes a wound will cause rapid ethylene production; thus picking a fruit will sometimes signal it to ripen, as will an infection of bacteria or fungi on the fruit. This ethylene signal causes developmental changes that result in fruit ripening. Once the ethylene signal is detected and the banana begins to ripen, new enzymes are made. These include hydrolases to help break down chemicals inside the fruits, amylases to accelerate hydrolysis of starch into sugar (the reason a green banana tastes tart and a ripe banana sweet), pectinases to catalyze degradation of pectin (the glue between cells), and so on.1 As you may know, you can control the ripening of your bananas (both the skin and the fruit inside) by storing them in various ways. The most common methods of storage are on a banana stand, in the refrigerator, in a cool dark drawer, or in a brown paper bag.

Introduction:

Each person will choose two bananas to test [green (unripe), yellow (ripe), or black (overripe)] for starch and glucose content. You will discover what happens to the chemical composition of a banana as it ripens.

Procedure:

For each banana, isolate the soluble sugars and the starch, and then determine the amount of each. In order to do so, you will need to perform Parts 1, 2 & 3 on both bananas (separately, of course!). Make sure that your bananas are not in the same state of ripening. You must test a minimum of two of the three types of bananas (unripe, ripe and overripe). You may earn 2 extra credit points if you test all three types.

1

For more information on the ethylene signaling pathway the following references have been provided. Bleecker, A.B. and Kende, H. Annual Review of Cell and Development Biology, 2000, 16, 1-18. Guo, H. and Ecker, J.R. Current Opinion in Plant Biology 2004, 7, 40-49. Koning, R. E. Plant Physiology Information Website. http://koning.ecsu.ctstateu.edu/plants_human/fruitgrowripe.html (accessed October 2005) Sauter, M. Ethylene. http://www.biologie.uni-hamburg.de/b-online/e31/31g.htm (accessed October 2005).

Part 1: Isolation of soluble sugars from bananas: 1. Obtain an unripe (green), ripe (yellow), or overripe (brown) banana. 2. Weigh out approximately 1 g of banana on a top-loading balance in a small plastic cup (saved from Lab #3). Don't forget to tare the cup before adding the banana. Note: It is not necessary to weigh out exactly 1 g of the banana, however it is important to know the exact mass of your sample. 3. Record the mass of the banana sample on your data sheet. 4. Add 6 mL of distilled water and thoroughly grind the sample using a spoon. 5. Pour the sample from the cup into a screw-top tube. Make sure that you are careful when transferring the banana suspension. You need to get all the liquid & solid into the tube. 6. Rinse the cup with 6 mL of fresh distilled water and add the rinse to the same tube. 7. Tape the tubes inside a washing machine, and use the spin cycle to centrifuge the tubes. Keep spinning until all the banana is a solid pellet at the bottom of the tube. Note: If you don't have a washing machine with a vertical tub, you can try taping the tubes to a ceiling fan instead (put the cap end towards the center) and turn on medium. 8. Decant (pour carefully) the supernatant (the liquid) into a cup. Make sure that all of the solid stays in the tube. If you can't do this by pouring, use a pipette to transfer the liquid. 9. Wash the pellet (the solid left behind) with 6 mL of fresh distilled water by adding the water to the centrifuge tube or test tube and thoroughly breaking the pellet up with a pipette. Make sure that you don't draw anything up into the pipette. 10. Centrifuge the suspension again in the washing machine (as described above). 11. Add this supernatant to the one from the previous centrifugation (in the same cup) and set the pellet aside to use in Part 2 below. 12. Using a graduated cylinder, carefully measure the volume of the combined supernatants. Record this volume in your data table. 13. Pour the solution back into the cup, label it and set it aside for use in Part 3. Part 2: Isolation of the insoluble starch: 1. Obtain 10 mL of distilled water. Add a small portion (approx. 3 mL) to the tube and use the pipette to re-suspend the pellet from Part 1. 2. Obtain a coffee filter and prepare it for using as filter paper by spreading it out, then folding in half and then in half again (to give ¼). Cut the filter paper so that it fits in the funnel. You may have a small about above the funnel. Write your name on it in pencil, mass the paper and record this mass on the data sheet. 3. Place the filter paper in the funnel and open it to form a cone. Now filter the re-suspended pellet. 4. Add another small portion of distilled water to the centrifuge tube, rinse, and pour this through the funnel trying to transfer as much solid as possible. Keep rinsing until all of the solid is transferred, or until all of the 10 mL of water is used. 5. If solid remains in the test tube, obtain a second 10 mL of distilled water. Again, using small portions, rinse the tube, and pour this through the funnel until all the solid is transferred or until all 10 mL has been used. 6. Once all of the water has gone through the filter, remove the filter paper from the funnel and unfold it. Lay the filter paper flat on a plate and let dry overnight. Record the mass of the filter paper plus banana solid on your data sheet. DO NOT mass until the filter paper and banana solid are completely dry.

Part 3: Measuring the amount of glucose in the Banana Extract: Most of the soluble material in your sample is glucose. Depending on the type of banana you test, it might be necessary to dilute your sample. The riper your banana is the more glucose it should contain. You will be using Keto-Diastix Reagent Test Strips to assay for glucose. 1. Remove one test strip from the bottle. DO NOT touch the test areas of the strip. 2. Dip the test strip into the Banana Extract solution you set aside in Part 1 and remove immediately (drawing the edge of strip against the rim of the beaker or flask). 3. Compare the glucose test area to the Glucose Color Chart (on bottle) exactly 30 seconds after wetting. 4. Record the amount of glucose in the data table. 5. If the amount of glucose exceeds 2000mg/dL, (brown color), then dilute your sample by adding an additional 10 mL of distilled water. Mix the solution well, and retest.

Question 1: (16 points) Prepare a table like the one shown below and fill in all of the information. Green text is hints on how to calculate the quantity. Only final values are needed ­ you don't have to show your calculations in your report. Save a copy of this table in .html, .rtf or .pdf format and submit to the Lab #8 Dropbox. Banana 1 Banana 2 Banana 3

(2 points extra credit)

Banana Type(Green, Ripe, Overripe) Color of Banana Skin Mass of Banana Sample Volume of Banana Extract (in mL) Mass of Filter Paper Mass of Starch and Filter Paper Mass of Starch

% Starch in Banana

(from part 1, #2) (from part 1, #12) (from part 2, #2) (from part 2, #6) (= final mass ­ mass of filter paper) (=Mass of starch/mass of banana x 100%) (from part 3, #4) (=concentration x volume of banana extract) (=Mass of glucose/mass of banana x 100%)

(from part 1, #2) (from part 1, #12) (from part 2, #2) (from part 2, #6) (= final mass ­ mass of filter paper) (=Mass of starch/mass of banana x 100%) (from part 3, #4) (=concentration x volume of banana extract) (=Mass of glucose/mass of banana x 100%)

(from part 1, #2) (from part 1, #12) (from part 2, #2) (from part 2, #6) (= final mass ­ mass of filter paper) (=Mass of starch/mass of banana x 100%) (from part 3, #4) (=concentration x volume of banana extract) (=Mass of glucose/mass of banana x 100%)

Concentration of Glucose in Banana Extract Total Grams of Glucose in Banana Extract % Glucose in Banana

Calculation Hint: To determine total grams of glucose, you will need to do some unit conversion. Before you multiply the concentration by the volume, make sure that the volume is in dL, not mL. Also, record your final answer in grams, not milligrams.

Question 2: (1 point) Based on your experimental results, what happens to the chemical composition of a banana as it ripens? Question 3: (1 point) What type of chemical reaction is taking place (inside the banana) as it ripens? The Lab #8 report will ask for a single word answer, you do not need a complete sentence here. Question 4: (1 point) What type of bond is cleaved during this process? The Lab #8 report will ask for a single word answer, you do not need a complete sentence here. Answer the following question: Question 5: (1 point) Please give constructive feedback regarding this lab. Were the directions clear? How long did it take you to complete this lab? How does this lab compare to the others in difficulty, time, enjoyment, & relation to class content? Did it illustrate CHE 106 concepts? What did you gain/learn from doing the experiments that you did not learn from the text alone? What would you keep/recommend in future semesters? What would you change? You should write your answers into a word processing program and save the file. Go into the Lab #8 Report and cut and paste the answers to each question in the appropriate space. (Lab #8 Report can be found on the Content page or under Assignments Quizzes.) The data table for Question 1 will be submitted to the Lab #8 Dropbox (found under Content page or under Assignments -> Dropbox.) Labs not submitted in the appropriate area will not be graded. This lab was revised by Laura Sonnichsen and Sheryl Drake from the lab in the article: DavisMcGibony, C.M.; Bennett, R.R.; Bossart II, A.D.; Deal, S.T. J. Chem. Educ., 2006, 83, 1543. You are welcome to copy and distribute the lab so long as credit is given. Ver.042013

Information

5 pages

Find more like this

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate

1185717


You might also be interested in

BETA