TASTE AND SMELL

Why does food seem tasteless when you have a cold?

How do we perceive tastes and smells? How are taste and smell connected to communication?
Peggy and David seek out a connection between our senses of taste and smell.

Contents

Insights & Connections
Vocabulary
Resources
Main Activity
Try This

INSIGHTS

Have you ever wondered why food loses its flavor when you have a cold? It’s not your taste buds’ fault. Blame your stuffed-up nose. Seventy to seventy-five percent of what we perceive as taste actually comes from our sense of smell. Taste buds allow us to perceive only bitter, salty, sweet, and sour flavors. It’s the odor molecules from food that give us most of our taste sensation.

When you put food in your mouth, odor molecules from that food travel through the passage between your nose and mouth to olfactory receptor cells at the top of your nasal cavity, just beneath the brain and behind the bridge of the nose. If mucus in your nasal passages becomes too thick, air and odor molecules can’t reach your olfactory receptor cells. Thus, your brain receives no signal identifying the odor, and everything you eat tastes much the same. You can feel the texture and temperature of the food, but no messengers can tell your brain, “This cool, milky substance is chocolate ice cream.” The odor molecules remain trapped in your mouth. The pathway has been blocked off to those powerful perceivers of smell--the olfactory bulbs.

Of all our senses, smell is our most primal. Animals need the sense of smell to survive. Although a blind rat might survive, a rat without its sense of smell can’t mate or find food. For humans, the sense of smell communicates many of the pleasures in life--the aroma of a pot roast in the oven, fresh-cut hay, a rose garden. Smells can also signal danger, fear, or dread.

Although our sense of smell is our most primal, it is also very complex. To identify the smell of a rose, the brain analyzes over 300 odor molecules. The average person can discriminate between 4,000 to 10,000 different odor molecules. Much is unknown about exactly how we detect and discriminate between various odors. But researchers have discovered that an odor can only be detected in liquid form. We breathe in airborne molecules that travel to and combine with receptors in nasal cells. The cilia, hairlike receptors that extend from cells inside the nose, are covered with a thin, clear mucus that dissolves odor molecules not already in vapor form. When the mucus becomes too thick, it can no longer dissolve the molecules.

Animals depend on odors secreted from their bodies to communicate. For humans, odors communicate a variety of messages, depending on the odor and the person receiving it. The aroma of a baking apple pie sends one message when someone is hungry and quite another when that person has just finished a six-course meal!

CONNECTIONS

1. You cannot smell food very well when you have a cold, but why is taste bland or even absent?
2. Think of some smells you like. When might those smells be unpleasant to you?
3. Have you ever smelled natural gas? Why do you think gas utility companies give it an unpleasant odor?
4. In what ways are odors like language?

Vocabulary

molecule

the smallest particle into which a substance can be divided without chemical change

nasal passages

pathways between the nose and mouth which carry odor molecules to olfactory cells

odor molecules

comprise specific smells; stimulate smell receptors

olfactory

pertaining to or contributing to the sense of smell

receptor

a nerve ending that senses or receives stimuli

RESOURCES

• Alvin, V., & Silverstein, R. (1992) Smell, the subtle sense. New York: William Morrow & Company.
• Ardley, N. (1992) The science book of the senses. San Diego: Harcourt Brace Jovanovich.
• Gibbons, B. (1986, Sept) The intimate sense of smell. National Geographic, pp. 324-360.

Additional sources of information

• Chemical Sources Association 1620 First St. NW, Suite 925 Washington, DC 20006 (202) 293-5800
• Fragrance Foundation 145 E. 32nd St. New York, NY 10016 (212) 725-2755 (request publication: Living well with your sense of smell)
• Monell Chemical Senses Center 3500 Market St. Philadelphia, PA 19104-3308 (215) 898-4236
• National Geographic Educational Services PO Box 98019 Washington, DC 20090 (800) 368-2728 (videotapes from the 1982 Human Senses series: A Matter of Taste, #51124, and On the Nose, #51161)

Community resources

• Physician specializing in ear, nose, & throat
• Psychologist or psychotherapist who practices aroma therapy

WHERE’S THE FLAVOR?

Challenge your taste buds and nose to a flavor competition.

Main Activity

Test your classmates’ senses of taste and smell to find out which sends the clearest message to the brain.

Materials

• 6 small paper bags
• 6 small scoops of mini jelly beans in three different flavors (lemon, grape, cherry)
• marking pen

1. With the marking pen, identify the bags as either taste or smell bags. Write “taste #1,” “taste #2,” and “taste #3” on three of the sacks and “smell #1,” “smell #2,” and “smell #3” on the other three sacks.
2. Divide jelly beans among the bags so that you have a “taste” bag and a “smell” bag for each of the three flavors. Taste #1 and smell #1 jelly beans should be the same, taste #2 and smell #2 should be the same, and so on. Crush a few of the “smell” jelly beans so the odor molecules can escape into the bag. Close the bags by folding down the top.
3. Before Testing: Choose three of your classmates as testers and give them each a sheet of paper. Instruct them to draw a data table with three columns and three rows. The columns should read: “smell only”; “taste only”; and “taste and smell.” The three rows should read: “flavor 1”; “flavor 2”; and “flavor 3.”
4. Taste Test: Instruct the testers to close their eyes and plug their noses. Choose one of the taste bags and instruct each tester to chew on a sample from this bag. In five seconds, ask them to record on their data table what flavor they believe the sample to be. Repeat the procedure for the remaining taste bags. A small sip of water between samples will help clear away the previous flavor and provide a more accurate test. If they cannot tell the flavor, have them record “unknown.”
5. Smell Test: Choose one of the “smell” sample bags. Have testers close their eyes, open the bag, and inhale the aroma for 10 seconds. Remove the bag and close the top tightly. Have your testers record the flavor of the sample on the data table. Make sure each of them repeats this procedure for the other two samples.
6. Smell and Taste Test: Use the #8220t;taste” bags again. Repeat the procedure as in step # 4, “Taste Test,” but do not have your testers hold their noses shut. Be sure, however, that they have their eyes closed. Ask them to record their guesses in the appropriate column on their data table.

Questions

1. Which sense, taste or smell, identified the correct flavor most often?
2. How were the “taste” messages your brain received different from the “smell” messages?
3. How do you think candy makers simulate fruit flavors?
4. Why do you taste more flavor when you chew a jelly bean than when you suck on it? 5. If you took the Smell and Taste Test with your eyes open, do you think you could recognize the flavor of a purple jelly bean that has an orange flavor? What data from your tests support your conclusion?

Recapture a “smell” memory. Put a number of different, fragrant items in separate paper bags--a pine bough, broken cinnamon sticks, mothballs, a cloth sprinkled with baby powder, lemons. Sniff each bag until one brings a strong memory to mind. Write about this memory.

Create a survey to identify the favorite smells and tastes of your friends. Conduct your survey and display the results on a graph. Which smells and tastes were most popular? Now place your results in a Venn diagram. Do you see any overlap between favorite smells and favorite tastes?

Can you tell the difference between an apple and a potato by using only the sense of taste? Cut an apple and a potato into the same size pieces. Close your eyes, plug your nose, and lick one of the pieces. Can you tell what it is? Next, unplug your nose and eat the piece. Can you identify it now?

Animals and insects use smells to send messages. Cats and dogs, for example, put their own personal smell stamp on objects to communicate the message “no trespassing.” Ants lay down odor trails to mark the pathway to food. The monarch butterfly and ladybug produce odors that say, “I don’t taste as good as I look.” Research an animal by reading and thinking about how it uses smell to communicate.

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