Key Concepts
Smell, perception, brain, senses, olfaction

Introduction

Take a deep breath: freshly baked cookies, smoke from a wood fire, or a bouquet of roses—your nose is an amazing smell detector! Your sense of smell can not only identify a huge variety of odors, but it is also incredibly sensitive. Think about how easily you can detect if someone in your neighborhood has a barbecue just by smelling hints of smoke from a faraway grill. But how good is your nose when it comes to differentiating individual smells? Do this activity to find out!

This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Background

Every day you are surrounded by a vast variety of smells that your nose is able to pick up. Your sense of smell, also called olfaction, is very powerful. Everything that has an odor or smell releases specific chemicals, called odorants, into the air. These odorants eventually reach your nose and when you breathe in, they get transported deep into the space behind your nose. There, you have millions of smell receptors able to identify specific odorants. You can imagine this process like a lock-and-key mechanism where each odor molecule fits into one specific receptor inside your nose. Once the receptor binds to the chemical, it communicates with the brain by sending a signal, and your brain is able to identify the specific odor.

But what makes one smell different from another? Thousands of chemicals exist that trigger the sensation of smell, and each individual one—and combinations between them—will result in a different smell and signal pattern in your brain. Researchers now believe that we can smell up to 1 trillion (this is more than 100 times as many people as there are in the world!) different scents, meaning individual odorants as well as mixtures! Sometimes only a single chemical distinguishes a specific smell and many people, especially in the food industry, try to produce them to make artificial scents. One example is a chemical molecule called vanillin, which, as you might guess, smells like vanilla.

It is not only the individual molecule that matters—its concentration is also important. You are much more likely to smell a specific odor if there are many of the odor molecules around. If there are only a few, you probably will not even notice them. Put your nose to the test in this fun game of flavor memory!

Materials

  • Four different flavor extracts, for example
  • Vanilla extract
  • Mint extract
  • Almond extract
  • Cinnamon extract
  • Four 8 oz. plastic cups or glasses
  • 16 mini plastic cups with lids (2 oz.)
  • Water
  • Spoon
  • Medical dropper
  • Measuring cup
  • Tablespoon
  • Masking tape
  • Permanent marker
  • Optional: Several volunteers

Preparation

  1. Label eight mini cups, so you have two for each flavor. Write the label on the bottom of the cups so you cannot see it from the top.
  2. Add one tablespoon of each extract to the respective mini cups.
  3. Put a lid on each cup and set them all aside. This is your first set of smell samples.
  4. For the second set, label each of the 8 oz. cups with one of your chosen flavors.
  5. Fill each cup with 0.5 cups room temperature water.
  6. Using the medical dropper, add one drop of your first flavor to the respective cup and mix with a spoon.
  7. Repeat step 6 for the other flavors. Make sure to rinse the medical dropper and spoon in between each flavor.
  8. Again, label eight mini cups, so you have two mini cups for each flavor. Write the label on the bottom of the cups so you can't see it from the top. Add a "2" after each flavor to mark them as your second set of smell samples.
  9. Add one tablespoon of each of the flavored solutions into the respective labeled mini cups.
  10. Put a lid on each cup and set them aside. This is your second set of smell samples.

Procedure

  1. Take your first set of smell samples and shuffle them so you do not know which cup contains which flavor.
  2. Now the game begins. Pick up one cup, bring it close to your nose, open the lid and smell inside. Close your eyes, or make sure not to see the label of the cup while you are smelling the sample. What flavor do you pick up? Can you easily identify it?
  3. Next, you have to find the second cup with the same flavor. Pick up each cup and smell its contents until you find the one cup that you think contains the same flavor. Put the matching flavor pair aside without looking at the labels. Was it difficult or easy to find the matching flavor?
  4. Now move on to the next flavor and try to find the matching cup again. Repeat this with all the remaining cups, until you have found all the four matching flavors.
  5. Check the labels to see if your guess was right. Did you get all of your flavor pairs right?
  6. Put all the cups of the first sample set aside and get all the mini cups of the second sample set.
  7. Again, shuffle the cups, so you do not know which ones belong together. Spread the cups out in front of you and repeat steps 2-5 with your second sample set. Again, make sure you do not see the label of the cups while you are smelling the samples. Was it easier of more difficult to identify the flavors this time? Why do you think this was the case? Were you able to identify all the matching flavor pairs?

Extra: If you have volunteers, repeat the whole experiment with more people. How well can they identify the flavors in the first sample set compared to the second sample set?

Extra: Add more flavors to the game. What about banana extract or cinnamon? Does it make the game easier or more difficult?

Extra: What if you added a third sample set, where you add one drop of each flavor to four cups of water. Can you still identify and match all of the flavors? If yes, try to make even more dilutions (adding one drop to 10 cups of water, etc.) and test if your nose is still able to pick up the flavor in these samples.

Observations and Results

You probably thought this game was very easy with the first sample set. The flavors in the extracts are very concentrated. This means that in each of the solutions there are a lot of flavor molecules. When you smell these cups, all of these molecules move up into your nose and reach the smell receptors. Once the molecules bind to the receptors, your brain is able to identify the specific smell. It should not have been a problem for you to find the matching flavor pairs, as each of the flavors has its unique flavor molecule that generates a very specific signal pattern in your brain. This allows us to differentiate between flavors.

In the second sample set, it was probably more difficult to find the matching flavor pairs. This is because you diluted your flavor extract by adding one drop to 0.5 cups of water, which means that there were fewer odor molecules in each of your samples than before. There needs to be a certain amount of odorant in the air—the odor threshold concentration—before smell receptors can send enough signals to the brain to identify a specific odorant. This threshold can differ between people as well as flavors because of their different chemical properties. If you still smelled all your samples correctly in the second sample set, try to find your odor threshold for each of the flavors by diluting the samples even more!

Cleanup

You can dispose of all your flavor solutions in the sink.

More to Explore

Credits

Svenja Lohner, PhD, Science Buddies

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Key Concepts
Smell, perception, brain, senses, olfaction
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