enzymes

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UMUC Biology 102/103

Lab 4: Enzymes

INSTRUCTIONS:

· On your own and without assistance, complete this Lab 4 Answer Sheet electronically and submit it via the Assignments Folder by the date listed in the Course Schedule (under Syllabus).

· To conduct your laboratory exercises, use the Laboratory Manual located under Course Content. Read the introduction and the directions for each exercise/experiment carefully before completing the exercises/experiments and answering the questions.

· Save your Lab 4 Answer Sheet in the following format: LastName_Lab4 (e.g., Smith_Lab4).

· You should submit your document as a Word (.doc or .docx) or Rich Text Format (.rtf) file for best compatibility.

Pre-Lab Questions

1. How could you test to see if an enzyme was completely saturated during an experiment?

2. List three conditions that would alter the activity of an enzyme. Be specific with your explanation.

3. Take a look around your house and identify household products that work by means of an enzyme. Name the products, and indicate how you know they work with an enzyme.

Experiment 1: Enzymes in Food

This experiment tests for the presence of amylase in food by using Iodine-Potassium Iodide, IKI. IKI is a color indicator used to detect starch. This indicator turns dark purple or black in color when in the presence of starch. Therefore, if the IKI solution turns to a dark purple or black color during the experiment, one can determine that amylase is not present (because presence of amylase would break down the starch molecules, and the IKI would not change color).

concept_tab_2

Materials

(1) 2 oz. Bottle (Empty) (1) 100 mL Graduated Cylinder 30 mL Iodine-Potassium Iodide, IKI Permanent Marker Ruler 2 Spray Lids 30 mL Starch (liquid) *Cutting Board

 

*2 Food Products (e.g., ginger root, apple, potato, etc.) *Kitchen Knife *Paper Towel *Saliva Sample *Tap Water

*You Must Provide

Procedure:

1. Remove the cap from the starch solution. Attach the spray lid to the starch solution.

2. Rinse out the empty two ounce bottle with tap water. Use the 100 mL graduated cylinder to measure and pour 30 mL of IKI into the empty two ounce bottle. Attach the remaining spray lid to the bottle.

3. Set up a positive control for this experiment by spraying a paper towel with the starch solution. Allow the starch to dry for approximately one hour (this time interval may vary by location).

4. In the mean time, set up a negative control for this experiment. Use your knowledge of the scientific method and experimental controls to establish this component (hint: what should happen when IKI solution contacts something that does not contain starch?) Identify your negative control in Table 1.

Note: Be sure to space the positive and negative controls apart from each other to prevent cross-contamination.

5. When the starch solution has dried, test your positive and negative controls. This step establishes a baseline color scale for you to evaluate the starch concentration of the food products you will test in Steps 7 – 11. Record your results in Table 1.

6. Select two food items from your kitchen cabinet or refrigerator.

7. Obtain a kitchen knife and a cutting board. Carefully cut your selected food items to create a fresh surface.

Figure 3: Sample set-up.
Figure 3: Sample set-up.

8. Gently rub the fresh/exposed area of the food items on the dry, starch-sprayed paper towel back and forth 10 – 15 times. Label where each specimen was rubbed on the paper towel with a permanent marker (Figure 3).

9. Wash your hands with soap and water.

10. Take your finger and place it on your tongue to transfer some saliva to your finger. Then, rub your moistened finger saliva into the paper towel. Repeat this step until you are able to adequately moisten the paper towel. Note: You should always wash your hands before touching your tongue! Alternatively, if you do not wish to put your hands in your mouth, you may also provide a saliva sample by spitting in a separate bowl and rubbing the paper towel in the saliva. Be sure not to spit on the paper towel directly as you may unintentionally cross-contaminate your samples.

11. Wait five minutes.

12. Hold the IKI spray bottle 25 – 30 cm away from the paper towel, and mist with the IKI solution.

13. The reaction will be complete after approximately 60 seconds. Observe where color develops, and consider what these results indicate. Record your results in Table 1.

Table 1: Substance vs. Starch Presence
Substance Resulting Color Presence of Starch?
Positive Control: Starch Dark Purple Yes
Negative Control : Cellulose Brownish red color  No
Food Product: Apple Dark Purple  yes
Food Product: Potato Dark Purple  yes
Saliva: Amylase Brownish red color  No

Post Negative Control -Lab Questions

1. What were your controls for this experiment? What did they demonstrate? Why was saliva included in this experiment?

2. What is the function of amylase? What does amylase do to starch?

3. Which of the foods that you tested contained amylase? Which did not? What experimental evidence supports your claim?

4. Saliva does not contain amylase until babies are two months old. How could this affect an infant’s digestive requirements?

5. There is another digestive enzyme (other than salivary amylase) that is secreted by the salivary glands. Research to determine what this enzyme is called. What substrate does it act on? Where in the body does it become activated, and why?

6. Digestive enzymes in the gut include proteases, which digest proteins. Why don’t these enzymes digest the stomach and small intestine, which are partially composed of protein?

Experiment 2: Effect of Temperature on Enzyme Activity

Yeast cells contain catalase, an enzyme which helps convert hydrogen peroxide to water

Figure 4: Catalase catalyzes the decomposition of hydrogen peroxide to water and oxygen.
Figure 4: Catalase catalyzes the decomposition of hydrogen peroxide to water and oxygen.

and oxygen. This enzyme is very significant as hydrogen peroxide can be toxic to cells if allowed to accumulate. The effect of catalase can be seen when yeast is combined with hydrogen peroxide (Catalase: 2 H2O2 → 2 H2O + O2).

In this lab you will examine the effects of temperature on enzyme (catalase) activity based on the amount of oxygen produced. Note, be sure to remain observant for effervescence when analyzing your results.

Materials

(2) 250 mL Beakers 3 Balloons 30 mL 3% Hydrogen Peroxide, H2O2 Measuring Spoon Permanent Marker Ruler 20 cm String

 

3 Test Tubes (Glass) Test Tube Rack Thermometer Yeast Packet *Hot Water Bath *Stopwatch *You Must Provide

Procedure

1. Use a permanent marker to label test tubes 1, 2, and 3. Place them in the test tube rack.

2. Fill each tube with 10 mL hydrogen peroxide. Then, keep one of the test tubes in the test tube rack, but transfer the two additional test tubes to two separate 250 mL beakers.

3. Find one of the balloons, and the piece of string. Wrap the string around the uninflated balloon and measure the length of the string with the ruler. Record the measurement in Table 2.

4. Create a hot water bath by performing the following steps:

a. Determine if you will use a stovetop or microwave to heat the water. Use the 100 mL graduated cylinder to measure and pour approximately 200 mL of water into a small pot or microwave-safe bowl (you will have to measure this volume in two separate allocations).

b. If using a stovetop, obtain a small pot and proceed to Step 4c. If using a microwave, obtain a microwave-safe bowl and proceed to Step 4e.

c. If using a stove, place a small pot on the stove and turn the stove on to a medium heat setting.

d. Carefully monitor the water in the pot until it comes to a soft boil (approximately 100 °C). Use the thermometer provided in your lab kit to verify the water temperature. Turn the stove off when the water begins to boil. Immediately proceed to Step 5. CAUTION: Be sure to turn the stove off after creating the hot water bath. Monitor the heating water at all times, and never handle a hot pan without appropriate pot holders.

e. If using a microwave, place the microwave-safe bowl in the microwave and heat the water in 30 second increments until the temperature of the water is approximately 100 °C. Use the thermometer provided in your lab kit to verify the water temperature. Wait approximately one minute before proceeding to Step 5.

5. Place Tube 1 in the refrigerator. Leave Tube 2 at room temperature, and place Tube 3 in the hot water bath.

Important Note: The water should be at approximately 85 °C when you place Tube 3 in it. Verify the temperature with the thermometer to ensure the water is not too hot! Temperatures which exceed approximately 85  °C may denature the hydrogen peroxide.

6. Record the temperatures of each condition in Table 2. Be sure to provide the thermometer with sufficient time in between each environment to avoid obscuring the temperature readings.

7. Let the tubes sit for 15 minutes.

8. During the 15 minutes prepare the balloons with yeast by adding ¼ tsp. of yeast each balloon. Make sure all the yeast gets settled to the bulb of the balloon and not caught in the neck. Be sure not spill yeast while handling the balloons.

9. Carefully stretch the neck of the balloon to help ensure it does not rip when stretched over the opening of the test tube.

10. Attach the neck of a balloon you prepared in step 8 to the top of Tube 2 (the room temperature test tube) making sure to not let the yeast spill into the test tube yet. Once the balloon is securely attached to the test tube lift the balloon and allow the yeast to enter the test tube. Tap the bulb of the balloon to ensure all the yeast falls into the tube.

11. As quickly and carefully as possible remove the Tube 1 (cold) from the refrigerator and repeat steps 9 – 10 with Tube 1 using a balloon you prepared in step 8.

12. As quickly and carefully as possible remove Tube 3 (hot) from the hot water bath and repeat steps 9 – 10 with Tube 3 using a balloon you prepared in step 8.

13. Swirl each tube to mix, and wait 30 seconds.

14. Wrap the string around the center of each balloon to measure the circumference. Measure the length of string with a ruler. Record your measurements in Table 2.

Table 2: Balloon Circumference vs. Temperature
Tube Temperature (°C) Balloon Circumference (Uninflated; cm) Balloon Circumference (Final; cm)
1 – (Cold)      
2 – (RT)    
3 – (Hot)    

Post-Lab Questions

1. What reaction is being catalyzed in this experiment?

2. What is the enzyme in this experiment? What is the substrate?

3. What is the independent variable in this experiment? What is the dependent variable?

4. How does the temperature affect enzyme function? Use evidence from your data to support your answer.

5. Draw a graph of balloon diameter vs. temperature. What is the correlation?

6. Is there a negative control in this experiment? If yes, identify the control. If no, suggest how you could revise the experiment to include a negative control.

7. In general, how would an increase in substrate alter enzyme activity? Draw a graph to illustrate this relationship.

8. Design an experiment to determine the optimal temperature for enzyme function, complete with controls. Where would you find the enzymes for this experiment? What substrate would you use?

 
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UMUC Biology 102 / 103 Lab 6: Taxonomy ANSWER KEY

This contains 100% correct material for UMUC Biology 103 LAB06. However, this is an Answer Key, which means, you should put it in your own words. Here is a sample for the Pre lab questions answered:

Pre-Lab Questions

 

1. Use the following classifications to determine which organism is least related out of the three. Explain your rationale. (1 pts)

 

 

The Eastern Newt is the least related organism out of the three. While all three are classified into the same domain, kingdom, phylum and class the Eastern Newt is in a different order than the American Green Tree Frog and the European Fire-Bellied Toad.

 

2. How has DNA sequencing affected the science of classifying organisms? (1 pts)

DNA sequencing has allowed for the comparison of genes at the molecular level as opposed to physical traits at the organism level. Physical traits can be misleading when classifying how related two organisms are. DNA sequencing can also trace relatedness through generations and more accurately assess how closely related two organisms are.

 

3. You are on vacation and see an organism that you do not recognize. Discuss what possible steps you can take to classify it. (1 pts)

The organism’s physical features can be used to compare it to known organisms. Some physiological features can even possibly be used to help classify it.

 

The rest of the questions in the lab are answered as well:

Experiment 1: Dichotomous Key Practice

Data Tables and Post-Lab Assessment

Table 3: Dichotomous Key Results

Organism Binomial Name
i  

Selasphorus platycercus

ii  

Mus musculus

iii  

Vaccinium oxycoccos

iv  

Ramphastos vitellinus

v Quercus abla
vi  

Evathlus smithi

vii  

Helix aspersa

viii  

Taeniopygia guttata

ix  

Lonicera japonica

xi  

Oryctes nasicornis

xii  

Taeniopyga guttata

xiii  

Musa acuminata

 

Seems like x was omitted, which would have been Carduelis tristis.

 

Post-Lab Questions

1.    What do you notice about the options of each step as they go from number one up?

 

 

2.    How does your answer from Question 1 relate to the Linnaean classification system?

 

Experiment 2: Classification of Organisms

Data Tables and Post-Lab Assessment

Table 2: Key Characteristics of Some Organisms

Organism Kingdom Defined Nucleus Mobile Cell Wall Photosynthesis Unicellular
E. Coli       Yes   Yes
Protozoa   Yes Yes No   Yes
Mushroom   Yes   Yes    
Sunflower   Yes Yes Yes Yes  
Bear   Yes Yes      

 

 

 

 

 

 

Post-Lab Questions

1.    Did this series of questions correctly organize each organism? Why or why not?

 

 

2.    What additional questions would you ask to further categorize the items within the kingdoms (Hint: think about other organisms in the kingdom and what makes them different than the examples used here)?

 

 

 

3.    What questions would you have asked instead of the ones that you answered about when classifying the organisms?

 

 

 

 
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lab report

Experiment 2: Concentration Gradients and Membrane Permeability

In this experiment, you will dialyze a solution of glucose and starch to observe:

  • The directional movement of glucose and starch.
  • The effect of a selectively permeable membrane on the diffusion of these molecules.

An indicator is a substance that changes color when in the presence of a specific substance. In this experiment, IKI will be used as an indicator to test for the presence of starch.

 

Materials

(5) 100 mL Beakers
10 mL 1% Glucose Solution, C6H12O6
4 Glucose Test Strips
(1) 100 mL Graduated Cylinder
4 mL 1% Iodine-Potassium Iodide, IKI
5 mL Liquid Starch, C6H10O5
3 Pipettes
4 Rubber Bands (Small; contain latex, handle with gloves on if allergic)

 

 

Permanent Marker
*Stopwatch
*Water
*Scissors

*15.0 cm Dialysis Tubing

*You Must Provide
*Be sure to measure and cut only the length you need for this experiment. Reserve the remainder for later experiments.

 

 

   

 

Attention!

Do not allow the open end of the dialysis tubing to fall into the beaker. If it does, remove the tube and rinse thoroughly with water before refilling it with the starch/glucose solution and replacing it in the beaker.

 

Note:

If you make a mistake, the dialysis tubing can be rinsed and used again.

Dialysis tubing must be soaked in water before you will be able to open it up to create the dialysis “bag.” Follow these directions for this experiment:

1.      Soak the tubing in a beaker of water for ten minutes.

2.     Place the dialysis tubing between your thumb and forefinger, and rub the two digits together in a shearing manner. This motion should open up the “tube” so that you can fill it with the different solutions.

 

Procedure

1.     Measure and pour 50 mL of water into a 100 mL beaker using the 100 mL graduated cylinder. Cut a piece of dialysis tubing 15.0 cm long. Submerge the dialysis tubing in the water for at least ten minutes.

2.     Measure and pour 82 mL of water into a second 100 mL beaker using the 100 mL graduated cylinder. This is the beaker you will put the filled dialysis bag into in Step 9.

3.     Make the glucose/sucrose mixture. Use a graduated pipette to add 5 mL of glucose solution to a third 100 mL beaker and label it “dialysis bag solution.” Use a different graduated pipette to add 5 mL of starch solution to the same beaker. Mix by pipetting the solution up and down six times.

4.     Using the same pipette that you used to mix the dialysis bag solution, remove 2 mL of the dialysis bag solution and place it in a clean beaker. This sample will serve as your positive control for glucose and starch.

a.     Dip one of the glucose test strips into the 2 mL of glucose/starch solution in the third beaker. After one minute has passed, record the final color of the glucose test strip in Table 3. This is your positive control for glucose.

b.     Use a pipette to transfer approximately 0.5 mL of IKI into the 2 mL of glucose/starch solution into the third beaker. After one minute has passed, record the final color of the glucose/starch solution in the beaker in Table 3. This is your positive control for starch.

5.     Using a clean pipette, remove 2 mL of water from the 82 mL of water you placed in a beaker in Step 2, and place it in a clean beaker. This sample will serve as your negative controls for glucose and starch.

a.     Dip one of the glucose test strips into the 2 mL of water in the beaker. After one minute has passed, record the final color of the glucose test strip in Table 3. This is your negative control for glucose.

b.     Use a pipette to transfer approximately 0.5 mL of IKI into the 2 mL in the beaker. After one minute has passed, record the final color of the water in the beaker      in Table 3. This is your negative control for starch.

Note:The color results of these controls determine the indicator reagent key. You must use these results to interpret the rest of your results.

6.     After at least ten minutes have passed, remove the dialysis tube and close one end by folding over 3.0 cm of one end (bottom). Fold it again and secure with a rubber band (use two rubber bands if necessary).

7.     Test to make sure the closed end of the dialysis tube will not allow solution to leak out. Dry off the outside of the dialysis tube bag with a cloth or paper towel. Then, add a small amount of water to the bag and examine the rubber band seal for leakage. Be sure to remove the water from the inside of the bag before continuing.

  1. Using the same pipette that was used to mix the solution in Step 3, transfer 8 mL of the dialysis bag solution to the prepared dialysis bag.
Figure 4: Step 9 reference.
Figure 4:Step 9 reference.

9.     Place the filled dialysis bag in the 100 mL beaker filled with 80 mL of water, leaving the open end draped over the edge of the beaker as shown in Figure 4.

10.Allow the solution to sit for 60 minutes. Clean and dry all materials except the beaker holding the dialysis bag.

11.After the solution has diffused for 60 minutes, remove the dialysis bag from the beaker and empty the contents of the bag into a clean, dry beaker. Label the beaker “final dialysis bag solution.”

12.Test the final dialysis bag solution for the presence of glucose by dipping one glucose test strip into the dialysis bag. Wait one minute before reading the results of the test strip. Record your results for the presence of glucose in Table 4.

13.Test for the presence of starch by adding 2 mL IKI. After one minute has passed, record the final color in Table 4.

14.Use a pipette to transfer 8 mL of the water in the beaker to a clean beaker. Test the beaker water for the presence of glucose by dipping one glucose test strip into the beaker. Wait one minute before reading the results of the test strip, and record the results in Table 4.

15.Test for the presence of starch by adding 2 mL of IKI to the beaker water. Record the final color of the beaker solution in Table 4.

 

 

 

Table 3: Indicator Reagent Data
Indicator Starch Positive
Control (Color)
Starch Negative
Control (Color)
Glucose Positive
Control (Color)
Glucose Negative
Control (Color)
Glucose Test Strip n/a n/a    
IKI Solution     n/a n/a

 

Table 4: Diffusion of Starch and Glucose Over Time
Indicator Dialysis Bag After 60 Minutes Beaker Water After 60 Minutes
IKI Solution    
Glucose Test Strip    

 

Post-Lab Questions

1.     Why is it necessary to have positive and negative controls in this experiment?

 

 

 

 

 

2.     Draw a diagram of the experimental set-up. Use arrows to depict the movement of each substance in the dialysis bag and the beaker.

 

 

 

 

3.     Which substance(s) crossed the dialysis membrane? Support your response with data-based evidence.

 

 

 

 

4.     Which molecules remained inside of the dialysis bag?

 

 

5.     Did all of the molecules diffuse out of the bag into the beaker? Why or why not?

 

 

 

 

 

Experiment 1: Diffusion through a Liquid

In this experiment, you will observe the effect that different molecular weights have on the ability of dye to travel through a viscous medium.

Materials

1 60 mL Corn Syrup Bottle, C12H22O11
Red and Blue Dye Solutions (Blue molecular weight = 793 g/mole; red molecular weight = 496 g/mole)
(1) 9 cm Petri Dish (top and bottom halves)

 

Ruler
*Stopwatch
*Clear Tape

*You Must Provide

 

Procedure

1.     Use clear tape to secure one-half of the petri dish (either the bottom or the top half) over a ruler. Make sure that you can read the measurement markings on the ruler through the petri dish. The dish should be positioned with the open end of the dish facing upwards.

  1. Carefully fill the half of the petri dish with corn syrup until the entire surface is covered.
  2. Develop a hypothesis regarding which color dye you believe will diffuse faster across the corn syrup and why. Record this in the post-lab questions.
  3. Place a single drop of blue dye in the middle of the corn syrup. Note the position where the dye fell by reading the location of its outside edge on the ruler.
  4. Record the location of the outside edge of the dye (the distance it has traveled) every ten seconds for a total of two minutes. Record your data in Table 1 and use your results to perform the calculations in Table 2.
  5. Repeat the procedure using the red dye, the unused half of the petri dish, and fresh corn syrup.

 

Table 1: Rate of Diffusion in Corn Syrup
Time (sec) Blue Dye Red Dye Time (sec) Blue Dye Red Dye
10     70    
20     80    
30     90    
40     100    
50     110    
60     120    
           

 

Table 2: Speed of Diffusion of Different Molecular Weight Dyes
Structure Molecular Weight Total Distance
Traveled (mm)
Speed of Diffusion
(mm/hr)*
Blue Dye      
Red Dye      

*Multiply the total distance diffused by 30 to get the hourly diffusion rate

 

Post-Lab Questions

  1. Record your hypothesis from Step 3 here. Be sure to validate your predictions with scientific reasoning.

 

 

 

  1. Which dye diffused the fastest?

 

 

 

  1. Does the rate of diffusion correspond with the molecular weight of the dye?

 

 

 

 

 

  1. Does the rate of diffusion change over time? Why or why not?

 

 

 

 

  1. Examine the graph below. Does it match the data you recorded in Table 2? Explain why, or why not. Submit your own plot if necessary.

 

https://nuonline.neu.edu/bbcswebdav/pid-9451339-dt-content-rid-14232100_1/courses/BIO1101.90155.201714/BIO1101.90155.201714_ImportedContent_20160930044714/CourseRoot/html/lab006s001.html

 

 

https://nuonline.neu.edu/bbcswebdav/pid-9451340-dt-content-rid-14232401_1/courses/BIO1101.90155.201714/BIO1101.90155.201714_ImportedContent_20160930044714/CourseRoot/html/lab006s002.html

 

https://nuonline.neu.edu/bbcswebdav/pid-9451341-dt-content-rid-14232402_1/courses/BIO1101.90155.201714/BIO1101.90155.201714_ImportedContent_20160930044714/CourseRoot/html/lab006s003.html

 

 

 

 

 
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Escience Labs BIO Diffusion Homework

An indicator is a substance that changes color when in the presence of the substance it indicates. In this experiment, IKI will be used an indicator to test for the presence of starch and glucose.

Materials

(5) 100 mL Beakers
10 mL 1% Glucose Solution, C6H12O6
4 Glucose Test Strips
(1) 100 mL Graduated Cylinder
4 mL 1% Iodine-Potassium Iodide, IKI
5 mL Liquid Starch, C6H10O5
3 Pipettes
4 Rubber Bands (Small; contain latex, handle with gloves on if allergic)

 

*Stopwatch
*Water
*Scissors
*15.0 cm Dialysis Tubing

*You Must Provide
*Be sure to measure and cut only the length you need for this experiment. Reserve the remainder for later experiments.

 

 

   

 

Attention!

Do not allow the open end of the dialysis tubing to fall into the beaker. If it does, remove the tube and rinse thoroughly with water before refilling with a starch/glucose solution and replacing it in the beaker.

Note:

  • Dialysis tubing can be rinsed and used again if you make a mistake.
  • Dialysis tubing must be soaked in water before you will be able to open it up to create the dialysis “bag”. Follow the directions for the experiment, beginning with soaking the tubing in a beaker of water. Then, place the dialysis tubing between your thumb and forefinger and rub the two digits together in a shearing manner. This should open up the “tube” so you can fill it with the different solutions.

Procedure

  1. Measure and pour 50 mL of water into a 100 mL beaker. Cut a piece of dialysis tubing 15.0 cm long. Submerge the dialysis tubing in the water for at least 10 minutes.
  2. Measure and pour 82 mL water into a second 100 mL beaker. This is the beaker you will put the filled dialysis bag into in Step 9.
  3. While the dialysis bag is still soaking, make the glucose/sucrose mixture. Use a graduated pipette to add five mL of glucose solution to a third beaker and label it “Dialysis bag solution”. Use a different graduated pipette to add five mL of starch solution to the same beaker. Mix by pipetting the solution up and down the pipette six times.
  4. Using the same pipette that you used to mix the dialysis bag solution, remove two mL of that solution and place it in a clean beaker. This sample will serve as your positive control for glucose and starch.
    1. Dip one of the glucose test strips into the two mL of glucose/starch solution in the third beaker. After one minute has passed, record the final color of the glucose test strip in Table 3. This is your positive control for glucose.
    2. Use a pipette to transfer approximately 0.5 mL of IKI to into the two mL of glucose/starch solution in the third beaker. After one minute has passed, record the final color of the glucose/starch solution in the beaker in Table 3. This is your positive control for starch.
  5. Using a clean pipette, remove two mL of water from the 82 mL of water you placed in a beaker in Step 2 and place it in a clean beaker. This sample will serve as your negative control for glucose and starch.
    1. Dip one of the glucose test strips into the two mL of water in the beaker. After one minute has passed, record the final color of the glucose test strip in Table 3. This is your negative control for glucose.
    2. Use a pipette to transfer approximately 0.5 mL of IKI to into the two mL of water in the beaker. After one minute has passed, record the final color of the water in the beaker in Table 3. This is your negative control for starch.

Note: The color results of these controls determine the indicator reagent key. You must use these results to interpret the rest of your results.

  1. After at least 10 minutes have passed, remove the dialysis tube and close one end by folding over 3.0 cm of one end (bottom). Fold it again and secure with a rubber band (use two rubber bands if necessary).
  2. Make sure the closed end will not allow a solution to leak out. You can test this by drying off the outside of the dialysis bag with a cloth or paper towel, adding a small amount of water to the bag, and examining the rubber band seal for leakage. Be sure to remove the water from the inside of the bag before continuing.
  3. Using the same pipette which was used to mix the solution in Step 3, transfer eight mL of the solution from the Dialysis Bag Solution beaker to the prepared dialysis bag.
Figure 4: Step 9 reference.
Figure 4:Step 9 reference.
  1. Place the filled dialysis tube in beaker filled with 80 mL of water with the open end draped over the edge of the beaker as shown in Figure 4.
  2. Allow the solution to sit for 60 minutes. Clean and dry all materials except the beaker with the dialysis bag.
  3. After the solution has diffused for 60 minutes, remove the dialysis tube from the beaker and empty the contents into a clean, dry beaker. Label it dialysis bag solution.
  4. Test the dialysis bag solution for the presence of glucose and starch. Test for the presence of glucose by dipping one glucose test strip into the dialysis bag directly. Again, wait one minute before reading the results of the test strips. Record your results for the presence of glucose and starch in Table 4. Test for the presence of starch by adding two mL IKI. Record the final color in Table 4 after one minute has passed.
  5. Test the solution in the beaker for glucose and starch. Use a pipette to transfer eight mL of the solution in the beaker to a clean beaker. Test for the presence of glucose by dipping one glucose test strip into the beaker. Wait one minute before reading the results of the test strip and record the results in Table 4. Add two mL of IKI to the beaker water and record the final color of the beaker solution in Table 4.
Table 3: Indicator Reagent Data
Indicator Starch Positive
Control (Color)
Starch Negative
Control (Color)
Glucose Positive
Control (Color)
Glucose Negative
Control (Color)
IKI Solution   Dark Purple  Black n/a n/a
Glucose Test Strip n/a n/a  Light Green  Yellow

 

 

 

 

 

Table 4: Diffusion of Starch and Glucose Over Time
Indicator Dialysis Bag After 1 Hour Beaker Water After 1 Hour
IKI Solution    
Glucose Test Strip  Purple  

 

Post-Lab Questions

1.       Why is it necessary to have positive and negative controls in this experiment?

 

 

2.       Draw a diagram of the experimental set-up. Use arrows to depict the movement of each substance in the dialysis bag and the beaker.

 

 

 

 

3.       Which substance(s) crossed the dialysis membrane? Support your response with data-based evidence.

 

 

 

 

4.       Which molecules remained inside of the dialysis bag?

 

 

5.       Did all of the molecules diffuse out of the bag into the beaker? Why or why not?

 

 

 
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