Name
Nutrient Testing Lab
Biology
Background information: In order for a cell (or an organism) to live and survive, it
needs a supply of energy. The source of this energy is in the form of chemical
compounds called nutrients. A food such as bread, milk, or meat is not a single substance
but a complex mixture of these chemical compounds. When a cell metabolizes these
nutrients, energy is produced and the chemical compounds become part of a living cell.
Among the organic molecules present in living cells are carbohydrates, proteins, and
lipids (fats and oils). The common elements to all three of these organic molecules are
carbon, hydrogen, and oxygen. Carbohydrates have a 1:2:1 ratio of carbon to hydrogen to
oxygen atoms. In lipids, the ratio is much greater. Proteins can be recognized by the
presence of nitrogen among other atoms.
Carbohydrates provide organisms with their basic source of energy. Starch is a
complex carbohydrate composed of smaller glucose units, all bonded together in chains.
This molecule is an important source of carbon atoms for the synthesis of other organic
molecules for the cell.
Proteins are larger and more complex than carbohydrates. They are made up of
amino acid units bonded together. Very little energy is obtained in the metabolizing of
proteins and their greatest role is in the making up of many of the cell's organelles.
Gelatin is an example of a protein.
Lipids are large and complex also. They are composed of a molecule of glycerol
bonded with three fatty acids. These molecules make up a large part of several cell
structures such as the cell membrane. Olive oil is an example of a lipid.
There are tests that can be used to aid in the identification of these nutrients. In
this lab, you will learn to perform tests for the presence of starches, sugars, proteins, and
fats.
Purpose: Students will determine what nutrients are found in various kinds of foods.
Materials:
hot water bath
Biuret's solution
Benedict's solution
Lugol’s iodine
4 test tubes
chem. Plates
paper towels
foods to test
Hypothesis: For each of the foods being tested, hypothesize which nutrients each
contains.
Procedure:
Part A- Test for Starch
1. Place a small quantity of food in one well of the chem. plate.
2. Place 1-2 drops of iodine solution of the food.
3. Note whether the iodine turns a purplish-blue color or a blue-black color. This
indicates the presence of a starch.
Part B- Test for Sugar
4. Place 30 drops of food-water solution in a test tube.
5. Add 5-10 drops of Benedict's solution to the test tube.
6. Place the test tube in the hot water bath that the teacher has set up for 4 minutes.
7. Remove the test tube with a test tube holder. Note whether the solution turned green,
yellow, orange, or orange-red. The color change to any of these colors indicates a
positive result. If the Benedict's solution remains blue it is a negative test- simple
sugars are not present.
Part C- Test for Proteins
8. Place a small quantity of each food into clean wells of the chem. plate.
9. Add 5-10 drops of Biuret's solution.
10. Note whether the mixture has turned a violet or blue-black color. This indicates the
presence of protein. If there is no color change, protein is not present.
Part D- Test for Lipids (fats, oils, or waxes)
11. Place a few drops of food onto a piece of paper towel and label what type of food is
being tested on the paper towel.. Place a few drops of water on another section of
the paper towel.
12. Allow the towel to dry and then hold the paper up to the light and look at the water
and food spot. Note whether the spot is greasy and translucent. This indicates the
presence of a fat.
13. Reexamine the spots after a few minutes. The water spot will evaporate and
disappear, but the fat spot does not disappear.
Data Table One- Test for Starches
Food tested
Color with Lugol’s iodine
Is starch present?
Data Table Two- Test for Simple Sugars
Food Tested
Color with Benedict’s +
Are simple sugars
Heat
present?
Data Table Three- Test for Proteins
Food Tested
Color with Biuret’s
Is protein present?
Data Table Four- Test for Lipids
Food Tested
Translucent spot?
Is fat present?
Questions:
1. Of the foods you tested, which contained starch? How do you know?
2. Of the foods you tested, which contained simple sugars? How do you know?
3. Of the foods you tested, which contained protein? How do you know?
4. Of the foods you tested, which contained fats? How do you know?
5. What purpose do starches and sugars serve in one’s diet?
6. Did any of the foods you tested contain all 4 organic molecules? List those that did.
7. Could you stay healthy by eating only 1 kind of food that contained all 4 organic
molecules? Explain your answer.
8. Which foods would a diabetic need to monitor or keep record of eating? Why?
9. Which foods would be included in a high protein diet? How does the body use
protein?
10. Why must fat be included in a person’s diet? What foods might include healthy fats?