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Lab 3:  The Molecules of Life

Page history last edited by Derek Weber 11 years, 9 months ago

A. Learning Objectives

In this lab, students will:

• identify the presence of various macromolecules due to their structural properties.

• determine the identity of unknown food products based on their molecular make-up.


B. Textbook Correlation: 

Please review  Sections 3.2-3.5 of Chapter 3: Organic Molecules when preparing for the lab.


C.  Introduction:

Cells are the basic unit of life.  In order to understand the nature of cells, we have to appreciate their chemical make-up.  The four most abundant elements of life include oxygen, carbon, hydrogen and nitrogen.  These elements make up 96% of your body and can be organized into molecules through chemical bonding.  An example of a molecule that is essential in supporting life is H2O, otherwise known as water.  Other examples of biologically important molecules include amino acids, fatty acids, monosaccharides, and nucleotides.  These four molecules are the basic building blocks of the macromolecules used to construct our cells.  There are four types of macromolecules found within all cells:  carbohydrates, lipids, proteins, and nucleic acids.  These organic (carbon-containing) macromolecules are organized into a functional unit we call cells.  In this exercise, we will analyze the properties of the following macronutrients (required in large amounts): water, carbohydrates, lipids, and proteins. 


D.  Unknown Food Project

Throughout your introductions, you have emphasized the importance of macronutrients on our health and discussed the food products that contain each type.  We often classify food groups based on their nutrient content.   The goal is to determine the identity of the four unknown food products based on the nutrient make-up of each.   While certainly these unknowns may have more than one of the nutrients listed below, each food products is representative of each class of macromolecules. 


To accomplish this goal, you will have to devise experiments to detect the presence of these nutrients.  Below is a list of materials that will be available:

1. Test Tubes

2.  Plastic droppers

3. Hot plate and beaker of water containing boiling chips

4. Distilled H2O

5. Known food products: glucose, starch, egg, and vegetable oil

6. Chemical reagents for testing.  In the list of reagents below, I have included the volumetric ratio of test substance/reagent for each and included the order by which materials should be added to their respective tubes:

     a.  Biuret reagent: 20 drops (1mL) test substance/10 drops (0.5mL) of reagent

     b.  Lugol's solution: 60 drops (3 mL) test substance/10 drops (0.5 mL) of reagent

     c.  Benedict's solution:  40 drops (2 mL) test substance/40 drops (2 mL) of reagent

     d.  Sudan reagent:  60 drops (3 mL) of water/60 drops (3 mL) of test solution/10 drops (0.5 mL) of reagent/40 drops (2 mL) of water


Your job is to research these reagents before lab to determine the appropriate use for each.  You also need to determine if there are any special condition necessary (i.e. heat, pH) that are necessary.  You also need to specify the negative and positive control for each experiment.


In the space provided below outline the experiment you will use to detect the presence of each nutrient in the four unknown food products.  After the experimental section, you will record your data and write a conclusion for each experiment (i.e. which nutrient(s) was present in each unknown). 


A.  Simple Carbohydrates:

Experimental Design (outline the procedure for identifying simple sugars HERE.  Make sure to include both a negative and positive control.





B.  Complex Carbohydrates:

Experimental Design (outline the procedure for identifying complex sugars HERE.  Make sure to include both a negative and positive control.): 





C.  Proteins:

Experimental Design (outline the procedure for identifying proteins HERE.  Make sure to include both a negative and positive control.):  







D.  Fats:

Experimental Design (outline the procedure for identifying fats HERE.  Make sure to include both a negative and positive control.):   







E. Results and Conclusions

Please embed the presentation on the lab using the instructions provided in the syllabus.





Color Before Heating

Color After Heating

a.      distilled water



b.      glucose



c.       lactose



d.      starch



e.      orange juice



f.        soda



g.      diet soda



h.      unknown substance A



i.        unknown substance B



j.        unknown substance C



k.       unknown substance D




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