Testing Macromolecules

Objectives: Students will be able to determine the compounds of various macromolecules found in food substances. Through background knowledge and chemical tests.

Expectations: Students must complete lab activity proficiently and accurately in groups of four or five. Students must remain vigilant to all dangers that may arise in the lab and always use appropriate lab technique.

Googles and lab aprons must be worn at all times!

Hypothesis:Create a hypothesis through observations on which macromolecules you believe correspond to each labeled item.

Role designation: Determine which student will be responsible for the following tasks. If a student is selected twice, 2nd place must take that the role.

Collect materials- Person who is the tallest.

Collect data- Person whose birthday is furthest from today

Clean materials- Person who is wearing the brightest/most colorful shirt

Safety- Person whose first name has the most letters

Materials

  • 6 test-tubes (per group)
  • 1 test-tube rack
  • Iodine solution
  • Biuret solution
  • Benedict’s solution
  • Ethanol
  • Water
  • Gloves
  • Apron
  • Goggles
  • Test Tube Holders
  • Large Beaker

Pre-lab questions:

1. What is an indicator?

2. When testing for monosaccharides, what indicator will you use?

3. What will you see if monosaccharides are present?

4. When testing for starch, what indicator will you use?

5. What will you see if starch are present?

6. What will you do to test for lipids?

7. How will you tell if lipids are present?

8. When testing for proteins, which indicator will you use?

9. What will you see if proteins are present?

10. For which test will you need to put test tubes in a hot-water bath and wait 5 minutes before you see results?

Lab Overview

  1. Collect one pipette full of each of the sample Items (A-E) in your test tubes. You will repeat this step for each of the various test. Make sure to clean out test tubes between tests.
  2. Sample A will serve as your control to make sure all your indicators are accurate.
  3. Follow the instructions for each of the tests you must conduct.
  4. Create a data table to collect your results in your science notebook
  5. Once all test are completed determine what your results showed for the samples A-E
  6. Complete extension activity

Extension #1:

Collect one mystery sample (1-6) and test it by using the various indicators to determine its components.Explain your results.

Indicator Tests

Iodine Test

This test will determine the presence of starch in your samples.

1. Add 2-3 drops of your iodine solution to each of your samples.

A positive result will result in your solution becoming blue/black (give the solution a couple of seconds for the reaction to take place

A negative result will result in your solution remaining yellow/orange

  • In your science notebook draw and label your observations

Biuret Test

This test will determine the presence of proteins in your samples

1. Add 2-3 drops of your Biuret solution to each of your samples.

A positive result will result in your solution becoming purple/lilac (give the solution a couple of seconds for the reaction to take place

A negative result will result in your solution remaining light blue

  • In your science notebook draw and label your observations

Ethanol Test

This test will determine the presence of fats in your samples

1. Add 2ml of ethanol solution to each of your samples. The SHAKE VIGOROUSLY! (Be careful not to spill and wear gloves!)

2. Add 2 ml of water and observe changes

A positive result will result in your solution creating a white emulsion (precipitate) that has separated from your solution.

A negative result will result in your solution remaining liquid.

  • In your science notebook draw and label your observations

Benedict’s test(conduct this test last/ due to time)

This test will determine the presence of sugar in your samples

1. Add 2-3 drops of your benedict’s solution to each of your samples.

2. Place your samples in a water bath for approximately 5-8 minutes to observe changes. [Obtain a beaker with hot water from your teacher. BE CAREFUL!]

A positive result will result in your solution becoming green then yellow then orange then red, depending on the amount of sugar (give the solution a couple of seconds for the reaction to take place

A negative result will result in your solution remaining blue

  • In your science notebook draw and label your observations