Instructions:
Please answer the questions interspersed below, found under the Activities headings, in a Word document. If you need to add pictures, graphs, etc., go ahead and add them directly into the Word document that you upload. Your answers need to be in your own words.
For this lab, there are some perishable items that you will be providing outside of your lab kit. Most everything you might have on hand or can be purchased cheaply at your nearest convenience store or dollar store. If you are having trouble finding items, message me, and I will help you find some alternatives.
The following video will help you get set up for the lab. Please watch this first.
Objectives:
Explain the importance of the four macromolecules of life: carbohydrates, nucleic acids, lipids, and proteins.
Detect carbohydrates, proteins, and lipids in various foods.
Introduction:
The food we eat is packed full of nutrients, and those nutrients come in the form of molecules. Molecules can be either organic or inorganic. Organic molecules typically come from living organisms and contain the elements carbon (C) and hydrogen (H) together, like glucose (C6H12O6) and methane (CH4). Inorganic molecules lack carbon and hydrogen together, like water (H2O) or oxygen gas (O2).
The big molecules that are found in all life are called macromolecules–proteins, carbohydrates, lipids, and nucleic acids are macromolecules. Macromolecules are polymers or long chains of repeating organic subunits called monomers. Proteins have many different functions in an organism, including physical structures, muscle contractions, and chemical reactions. Carbohydrates and lipids are used for energy storage. Nucleic acids are molecules that store genetic information and can provide energy for cellular reactions.
Use the table below to record your results for Activities 1-3.
Table 2.1 Results of Macromolecule Tests
Food Sample Simple Sugar Results (+/-) Simple Sugar Test Changes Observed (Color Change) Complex Sugar Results (+/-) Complex Sugar Test Changes Observed Protein Results (+/-) Protein Test Changes Observed (Color Change) Lipid Results Lipid Test Changed Observed
Water
Glucose Solution
Starch Solution
Albumin Solution
Vegetable/ Olive Oil
Milk
Broth
Fruit Juice
Flour
Soda
Diet soda
Activity 1: Carbohydrates
Carbohydrates are commonly referred to as sugars and are built from repeating units known as monosaccharides. Glucose is a monosaccharide that is used by cells as a quick form of energy. It can be linked together repeatedly to form polymers, longer chains of polysaccharides that can be used to store energy and provide structural support.
In this activity, you will be testing different foods for the presence of carbohydrates. To test for simple sugars, we use Benedict’s reagent. The reagent is blue, but in the presence of monosaccharides and disaccharides, it can change to green, yellow, orange, or red, depending on how much sugar is present. Green and yellow represent less sugar, while orange and red represent more sugar.
To test for complex sugars, we use iodine. The reagent itself is an amber color, but in the presence of starch, it will turn dark blue to black.
Materials:
Food samples: milk, chicken broth, fruit juice, flour, soda, and diet soda
Deionized water (distilled water) – negative control
Glucose solution – positive control
8 Test tubes and rack
Droppers/Pipettes (it is important to label these for each reagent, food item, etc., and not use for more than one item without thoroughly washing between)
Benedict’s reagent
Beaker (or glass cup that your test tubes will fit into)
Hot water
You will use the beaker to warm up water in the microwave to get it to hot but not yet boiling, around 1-2 minutes.
Remember to prepare the solutions, i.e., Glucose solution. You will be combing the powdered glucose in your glucose packet with 5mL of water measured from your graduated cylinder. Just pour the water directly into the bag and mix it together. For the flour use 1/2 teaspoon to 5mL of water.
Answer the following questions:
Activity 1A
Procedure:
Label the 8 test tubes near the top for each of the food samples (found in your table above), the positive control, and the negative control. Place the test tubes into the rack.
Add 0.25mL of Benedict’s to each test tube, using a graduated pipette to transfer.
Add 0.5mL of distilled water to the proper test tube, again using a graduated pipette.
Add 0.5mL of glucose solution to the proper test tube using a graduated pipette.
Add 0.5mL of milk to the proper test tube using a graduated pipette. Repeat for each food sample in the appropriate tubes, one food sample per tube.
Microwave a beaker of about 30mL tap water for 1-2 minutes. (You just need enough water to cover the solutions in the test tubes without the water getting into the test tube itself.) Place the tubes in the water while it is still hot and let them sit for 2 minutes.
Record the colors of each test tube after boiling and determine if sugars are present in the table above. Take a picture of your tubes and add that to your document.
Materials:
Food samples: milk, chicken broth, fruit juice, flour, soda, and diet soda
Deionized water (distilled water) – negative control
Starch solution – positive control
8 Test tubes and rack
Droppers/Pipettes (it is important to label these for each reagent, food item, etc., and not use for more than one item without thoroughly washing between)
Iodine
Answer the following questions:
Activity 1B
Procedure:
Label the 8 test tubes near the top for each of the food samples, the positive control, and the negative control.
Add 2mL of distilled water to the proper test tube.
Add 2mL of starch solution to the proper test tube.
Add 2mL of milk to the proper test tube. Repeat for each food sample in the appropriate tubes, one food sample per tube.
Using a pipette, add 3 drops of iodine to each tube.
Record the colors of each test tube immediately in your table and determine if starch is present. Take a picture of your tubes and add that to your document.
Activity 2: Proteins
Proteins have the most diverse functions in a cell. They can have structural roles like collagen in the skin, chemical roles like enzymes that speed up chemical reactions, and transport roles like in the cell membrane, to name a few. The monomers of proteins are amino acids, and they are bonded together to make the polymer or protein.
To test for proteins, we use Biuret reagent. The reagent is blue, but in the presence of protein, it turns purple.
Materials:
Food samples: milk, chicken broth, fruit juice, flour, soda, and diet soda
Deionized water (distilled water) – negative control
Albumin solution – positive control
8 Test tubes and rack
Droppers/Pipettes (it is important to label these for each reagent, food item, etc., and not use for more than one item without thoroughly washing between)
Biuret
Answer the following questions:
Activity 2
Procedure:
Label the 8 test tubes near the top for each of the food samples, the positive control, and the negative control.
Add 0.25mL of Biuret to each test tube.
Add 0.5mL of distilled water to the proper test tube.
Add 0.5mL of albumin solution to the proper test tube.
Add 0.5mL of milk to the proper test tube. Repeat for each food sample in the appropriate tubes, one food sample per tube.
Record the colors of each test tube immediately in your table and determine if the protein is present. Take a picture of your tubes and add that to your document.
Activity 3: Lipids
Lipids are often referred to as fats in the non-science world. Fats are known for their hydrophobic nature, or ability to repel water. In the body, lipids play many roles in the body like form membranes like phospholipids, store energy like fatty acids, and act as chemical messages like steroids. Fatty acids can be referred to as saturated, when they are composed of single covalent bonds between the atoms, or unsaturated when they are composed of at least a few double covalent bonds.
To test for lipids, we will be adding drops of the food substances onto a paper towel, then we will examine the spots for whether or not they appear shiny or whether or not they dry.
Materials:
Paper towel
Pipette
Food samples: milk, chicken broth, fruit juice, flour, soda, and diet soda
Deionized water (distilled water) – negative control
Vegetable or Olive oil – positive control
Answer the following questions:
Activity 3
Procedure:
Draw 8 circles on your paper towel and label them for each food substance, the positive control, and the negative control.
Use a clean pipette to add a drop of water to the paper towel in the proper circle.
Use a clean pipette to add a drop of vegetable or olive oil to the paper towel in the proper circle.
Use a clean pipette to add a drop of milk to the paper towel in the proper circle. Repeat for each food sample in the appropriate circles, one food sample per circle.
Record the appearance of each substance in your table and determine if lipid is present. Compare each item in appearance to your positive control to determine if lipids are present. Take a picture of your paper towel and add that to your document.
