Key concepts
Brain
Perception
Senses
Smell
Introduction
Whether it is freshly baked cookies, smoke from a wood fire or a bouquet of roses—your nose is an amazing smell detector! Your sense of smell cannot 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 is having 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? Try this activity to find out!
Background
Every day you are surrounded by a vast variety of odors that your nose is able to pick up. Your sense of smell, also called olfaction, is very powerful. Everything that has an odor releases specific chemicals, called odorants, into the air. These odorants eventually reach your nose, and when you inhale they get transported deep into the space behind your nose. There you have millions of smell receptors able to detect 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 scent 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 we can distinguish up to one trillion (an amount more than 100 times the world’s human population) 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 that, 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, such as vanilla, mint, almond and cinnamon extracts
- Four eight-ounce plastic cups or glasses
- 16 mini plastic cups with lids (two ounces)
- Water
- Spoon
- Medicine dropper
- Measuring cup
- Tablespoon
- Masking tape
- Permanent marker
- Several volunteers (optional)
Preparation
- Label eight mini cups so you have two for each flavor. Write the labels on the bottoms of the cups so you cannot see them from the top.
- Add one tablespoon of each extract to the respective mini cups.
- Put a lid on each cup and set them all aside. This is your first set of smell samples.
- For the second set label each of the four eight-ounce cups with one of your chosen flavors.
- Fill each eight-ounce cup with one half cup of room temperature water.
- Using the medicine dropper, add one drop of your first flavor to the respective cup and mix with a spoon.
- Repeat this step for the other flavors. Make sure to rinse the medicine dropper and spoon in between each flavor.
- Again, label eight mini cups so you have two mini cups for each flavor. Write the labels on the bottoms of the cups so you can't see them from the top. Add a "2" after each flavor to mark them as your second set of smell samples.
- Add one tablespoon of each of the flavored solutions into the respective labeled mini cups.
- Put a lid on each cup and set them aside. This is your second set of smell samples.
Procedure
- Take your first set of smell samples and shuffle them so you do not know which cup contains which flavor.
- 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 smell the sample. What flavor do you pick up? Can you easily identify it?
- 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?
- 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.
- Check the labels to see if your guess was right. Did you get all of your flavor pairs right?
- Put all the cups of the first sample set aside and get all the mini cups of the second sample set.
- Again, shuffle the cups, so you do not know which ones belong together. Spread the cups out in front of you and repeat steps the matching test with your second sample set. Again make sure you do not see the label of the cups while you smell the samples. Was it easier or 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 activity with more people. How well can they identify the flavors in the first sample set compared with the second set?
- Extra: Add more flavors to the game. What about banana extract or orange? 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 (for example, adding one drop to 10 cups of water, etcetera) and test if your nose is still able to pick up the odorants 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, lots of molecules move up into your nose and reach its 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 because each of the flavors has its unique flavor molecule that generates a very specific signal pattern in your brain. This allows us to differentiate among scents.
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 a half cup of water, which means 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
Your Nose, from KidsHealth
Human Nose Can Detect 1 Trillion Odors, from Scientific American
Small Molecules Make Scents, from Science in School
Flavor Lexicon, from Flavornet
Science Activity for All Ages!, from Science Buddies
This activity brought to you in partnership with Science Buddies
