Name: ___________________________
Date Given: October 15th
Lab Section
Biology Level One
Compounds of Living Organisms
Introduction:
As you know from our recent class discussions, the cells of your body need a
combination of many different carbohydrates, proteins, and lipids, along with
vitamins and minerals, in order to survive. All living organisms must obtain
building blocks for making new macromolecules and energy to carry out the
essential processes of life. These building blocks and energy are found in the
organic compounds that make up food and that also make up living things:
carbohydrates, lipids, and proteins. In this lab you will perform chemical tests on
standard solutions of carbohydrates (glucose & starch solutions), proteins
(gelatin solution), and lipids (vegetable shortening). After recording the results
from these standard tests, you will then perform the same tests on some
ordinary foods to obtain determine the presence of carbohydrates (sugars &
starches), lipids, and proteins.
Materials:
6-9 test tubes
Test tube rack
Test tube holder
Test tube brush
Hot plate
Safety goggles
Stirring rod
Medicine droppers
3 ml 10% gelatin solution
3 ml 10% sugar solution
3 ml 10% starch solution
vegetable shortening
Dropper bottle of Benedict’s solution
Dropper bottle of Biuret reagents
Dropper bottle of Lugol’s solution
Square of brown paper
Mortal & pestle
Petri dish
Food samples:
Egg white
Egg yolk
Apple juice
Onion
Orange juice
Milk
Corn
Potato
unknown # ____ & # ______
Part A: Standard Solutions – Demonstrating the presence of
carbohydrates, proteins, and fats
1. Put on safety glasses before measuring/pouring/carrying/touching any chemicals.
Safety glasses must be worn throughout the lab.
2. Label three test tubes; one with ‘protein’, one ‘sugar’, and one ‘starch’. You will use
these tubes for your standard tests. Keep your standards until the completion of the lab,
as you will want to compare some of your other foods with the standards.
3. Follow the test procedure listed below.
Test for Protein
Put about 2 mL of gelatin into the test tube labeled ‘protein’. Add 3 drops of Biuret
solution. Hold the tube over white paper, and examine. Record the color in the data
chart below.
Test for Glucose and other reducing sugars (monosaccharides and some
disaccharides)
Put about 3 mL of sugar solution into the test tube labeled ‘sugar’. Add 10 drops of
Benedict’s solution. Use the test tube holder to place the test tube in boiling water. Wait
4 or 5 minutes. Use the test tube holder to remove the test tube from the water bath and
place it in a test tube rack. Record the color on the data chart on the below.
Color scale for Benedict’s Test
No sugar
amount of sugar
Highest
--+-------------+----------------+-----------+-------------+----------------+----------------+--------blue
blue-green
green
green-yellow
yellow
orange
brick red
Test for Starch (polysaccharide produced by plants)
Place about 3 mL of starch solution into the test tube labeled ‘starch’. Add 3 drops of
Lugol’s solution. Record the color on the data chart below.
Test for fat
Smear a small amount of vegetable shortening onto a piece of brown paper. Let the
smear stand for a few minutes to dry, and then hold the paper up to the light. Record
whether or not the spot is translucent on the data chart below.
Data
Standard Solution
Gelatin
Reagent Test
Biuret
Sugar
Benedict’s
Starch
Lugol’s
Vegetable Shortening
Brown paper
Results
Part B: Food Tests – Determining the presence of
carbohydrates, proteins, and fats
Procedure
1. Before testing, predict which compounds will be found in each food. Indicate your
predictions in the data chart below. Use (+) to indicate predicted presence, and (–) to
indicate predicted absence.
2. Use the procedures described in part A* to test each food for all four substances. For
example, you will add 3 mL of melted butter to each of three test tubes. In the first tube,
you will conduct the protein test. In the second you will conduct the glucose test, and in
the third you will conduct the starch test. You will also drop a small amount of butter
onto brown paper to conduct the fat test. Wash out your test tubes, repeat these tests, and
record the results for all of the foods listed in the attached data chart.
*If the food is a solid, you must grind it into as much “mush” as possible before adding it
to the test tube and conducting the test. You may also use the Petri Dish in place of a test
tube for some foods if necessary.
Part C: Testing of Unknowns
1. Before testing, predict which compounds will be found in each food. Indicate your
predictions in the data chart below. Use (+) to indicate predicted presence, and (–) to
indicate predicted absence.
2. Choose two of the unknowns and record their numbers on the data table. Repeat the
procedure in part A to test each unknown for all four substances.
Data Table:
Food
Prediction
/Result
Egg White
Prediction
Result
Egg Yolk
Prediction
Result
Apple juice Prediction
Result
Orange
Prediction
Juice
Result
Onion
Prediction
Result
Potato
Prediction
Result
Corn
Prediction
Result
Milk
Prediction
Result
Unknown
Prediction
#____
Result
Unknown
Prediction
#____
Result
Starch
Sugar
(Glucose)
Lipids
Proteins
Analysis Questions
1. Which compound is most common in foods that come from plants? Which
compound is most common in foods that come from animals?
2. What food do you believe your unknowns were, explain your answer.
3. What biomolecules are present in milk and corn? What biomolecules make up a
cow? How do you know this?
4. What chemical elements make up the biomolecules you listed in #3?
5. What chemical elements are needed to make a protein. Might it be possible to
make proteins if you don’t take in proteins? How would this be possible?
6. How can two different substances – corn and milk – be composed of many or
possibly all (depending on your results) of the same biomolecules?
7. Based on the results of your experiment create a diagram illustrating the possible
pathways that you think a cow uses corn to make milk.