Grade Level: 6th – 8th grade
Subject Matter: Physical Science
National Standards: NS.5-8.1, NS.5-8.2
Skunked? Forget The Tomato Juice
Plastic cups – 8 for each student, plus one for each group of students
Measuring cups and spoons
Coffee beans – enough for a plastic cup-full for each group of students
Pitcher of water
Amino acid tablets - available at health food stores
Permanent markers – one for each group of students
Oven mitts or gloves
Stove or hot plate
Olfaction: the sense of smell
Maillard (pronounced meh-YAR) reaction: a chemical reaction between amino acids and sugars created by heat. It is named for the French chemist Louis-Camille Maillard, who first described it around 1910.
Amino acids: compounds that form the basic structural units for all proteins.
Volatile: a substance prone to evaporation at relatively low temperature.
1. Begin the lesson by having students watch the Science Friday video “Skunked? Forget the Tomato Juice.” Begin a discussion with the students about how humans are able to smell. Why would it be advantageous for a human or other living creature to have the ability to smell?
2. Tell students that they will conduct an experiment to investigate how well they can smell and where smells come from.
1. Hand out eight cups to each student and have them label each with a number from 1 to 8 with a permanent marker. Place a small cup of coffee beans on each table for students to share. Tell students that they will need to sniff the coffee beans in between each smell test. Ask students what they think will happen if they do not.
2. Download copies of the chart at the end of this lesson, and give one copy to each student.
3. Have students fill cup #1 with one cup of vinegar, and cup #2 with ½ cup of vinegar and ½ cup of water. The vinegar-water solution is half concentrated, compared to the cup of pure vinegar. Ask students how they think this will affect the smell from each cup.
4. Have students smell each cup from the same distance and record on their chart whether the scent of vinegar is strong, not very strong, or if there is no smell at all.
5. Have students continue the experiment by following the measurements listed in their chart for each cup, and recording their observations on the degree of smell. Remind students to sniff the cup of coffee beans before each smell test in order to cleanse their nasal passages from previous smells. What do they predict will happen as the vinegar is diluted? Do they think that they will be able to smell the vinegar even in the smallest concentration?
6. Have students compare and contrast their smell charts. How were the results different or the same? Were some students able to smell even the smallest concentration of vinegar?
Note: Since this experiment requires the use of a hot stove and skillet, we recommend that an adult conducts it as a demonstration, or that the appropriate safety materials are used and safety guidelines are discussed prior to the experiment.
1. Place one teaspoon of corn syrup in a skillet, and place the skillet on a stove or hot plate. Turn the heat on low.
2. Open one of the amino acid caps and allow students to smell the powder inside the cap. Does it have a strong aroma?
3. Sprinkle the powder onto the corn syrup in the skillet and turn the heat up. What do students think will happen? What reactions do they think will occur?
4. Move the skillet back and forth to mix in the powder with the syrup. What do students smell? Do the odors change as the mixture continues to heat up on the skillet?
Smell involves the detection of volatile molecules as they float through the air and into the receptors in your nose. This means that the smell of baked chocolate chip cookies comes from a combination of odor molecules from the ingredients that have evaporated into the air. These odor molecules float into your nose and adhere to a receptor that allows your brain to perceive the smell.
• How does the loss of your sense of smell affect your other senses?
• Why do certain smells stir up memories?
• Why do we stop smelling an odor that we have been exposed to for a long period of time?
• Why does the scent of coffee beans clear your sense of smell?
• How do animals (ants, wolves, skunks, etc.) use their sense of smell to communicate or defend themselves?
Extend this experiment by having students try to place the cups in sequential order, from most pungent to least pungent, by sniffing them. Hide the right sequence under the cup to prevent students from seeing the correct order.