Lab

Lab 5: Diffusion, Osmosis and Enzymes

Objective: The objective of this lab is to introduce you to the concepts of diffusion, osmosis and enzyme activity.

Reading Assignment: Read 4.9 and 5.4; Diffusion and Osmosis and How Enzymes Work from the textbook Essentials of the Living World.

 

For this lab you will need to supply the following materials:

Camera or cell phone (you will upload pictures of your experiment)

Kitchen scale (food scale, it can weigh in either ounces or grams)

Microwave

Liquid measuring cup

Teaspoon

Tablespoon (3 Tsp = 1 Tbs)

Several Drinking cups (1 needs to hold at least 2 cups of liquid)

1 Potato

Knife

Blender or Potato masher

Zip lock sandwich bag (not a freezer bag)

Pancake syrup

Salt

Sugar

Vinegar

Hydrogen Peroxide (H2O2)

 

Solutions to prepare

Sucrose solution – add one tablespoon of sugar to 1 cup of water

 

Exercise 1 – Diffusion

· In this exercise you will observe the diffusion of water through a semipermeable membrane (a plastic bag)

Step 1. Place ¼ of a cup of pancake syrup into a plastic zip lock bag and seal the bag.

Step 2. Weigh the bag using a small kitchen scale and record the weight on your worksheet.

Step 3. Fill larger cup (2 cup measuring or equivalent) with 1 cup of water. Record the time.

Step 4. Place the syrup bag in the larger cup and leave overnight (12+ hours).

Step 5. Remove the bag, dry it off and weigh it using a small kitchen scale. Record weight on your worksheet and the time you ended the experiment. (Hint: The bag should gain weight. If it loses weight you may have had a puncture. You must redo this exercise).

Step 6. Take a picture of the completed exercise and upload to the worksheet. Make sure it includes the date, your name and a photo ID.

Exercise 2 – Osmosis

· In this exercise you will determine the result of putting cells into solutions of various tonicity.

Step 1. Cut (2) potato slices: 3 inches long, 1 inch wide, 0.5 inches thick.

Step 2. Prepare two coffee cups with the following solutions:

Cup 1 = add one cup of water

Cup 2 = add one cup of water and 1 teaspoon of salt

Step 3. Add one potato slice to each cup and let stand for 1 hour.

Step 4. Remove potato slices and determine if the slice is crisp or limp. Record your observations of the slices on the data sheet.

Step 5. Take a picture of the completed exercise and upload to the worksheet. Make sure it includes the date, your name, and a photo ID.

Exercise 3 – Enzyme Activity

· In this exercise you will observe factors that affect the enzyme activity of catalase. Catalase is found in potato cells.

H2O2 (hydrogen peroxide) 2 H2O + O2 (oxygen gas) when catalase is present.

Step 1. Place the remaining amount of potato in a blender with two tablespoons of water. Blend to a paste. If you don’t have a blender use a potato masher to make the paste.

Experiment 3-1

Step 2. Transfer one tablespoon of the paste to a small cup and add 1 tablespoon of hydrogen peroxide.

Step 3. Mix together by gently rotating the cup clockwise and record your observations on the data sheet

Step 4. Take a picture of the completed exercise and upload to the worksheet. Make sure it includes the date, your name and photo/student ID.

 

Experiment 3-2

Step 5. Transfer one tablespoon of the paste to a small cup and add 1 tablespoon of sucrose solution.

Step 6. Mix together by gently rotating the cup clockwise and record your observations on the data sheet.

Step 7. Take a picture of the completed exercise and upload to the worksheet. Make sure it includes the date, your name and photo/student ID.

 

Experiment 3-3

Step 8. Transfer one tablespoon of the paste to a small cup and add 1 tablespoon of vinegar (an acid).

Step 9. Next add 1 tablespoon of hydrogen peroxide.

Step 10. Mix together by gently rotating the cup clockwise and record your observations on the data sheet.

Step 11. Take a picture of the completed exercise and upload to the worksheet. Make sure it includes the date, your name and photo/student ID.

 

Experiment 3-4

Step 12. Transfer one tablespoon of the paste to a small cup and add 1 tablespoon of water.

Step 13. Microwave on high for 1 minute.

Step 14. Remove from microwave (careful it’s hot) and allow 5 minutes to cool.

Step 15. Next add 1 tablespoon of hydrogen peroxide.

Step 16. Mix together by gently rotating the cup clockwise and record your observations on the data sheet.

Step 17. Take a picture of the completed exercise and upload to the worksheet. Make sure it includes the date, your name and photo/student ID.

 

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