www.TeachEngineering.org: Free Curriculum for K-12

North Carolina Math
- 4.01 Collect, organize, analyze, and display data (including line graphs and bar graphs to solve problems. (Grade 4) [2003]
- 4.04 Design experiments and list all possible outcomes and probabilities for an event. (Grade 4) [2003]
- 4.02 Compare and contrast different representations of the same data; discuss the effectiveness of each representation. (Grade 5) [2003]
- 4.01 Collect, organize, analyze, and display data (including box plots and histograms) to solve problems. (Grade 7) [2003]
North Carolina Science
- 1.01 Identify and create questions and hypotheses that can be answered through scientific investigations. (Grade 6) [2004]
- 1.06 Use mathematics to gather, organize, and present quantitative data resulting from scientific investigations:
  • Measurement. (Grade 6) [2004]
- 1.01 Identify and create questions and hypotheses that can be answered through scientific investigations. (Grade 7) [2004]
- 1.02 Develop appropriate experimental procedures for:
  • Student generated questions. (Grade 6) [2004]
- 1.05 Analyze evidence to:
  • Explain observations. (Grade 6) [2004]
- 1.02 Develop appropriate experimental procedures for:
  • Student generated questions. (Grade 7) [2004]
- 1.05 Analyze evidence to:
  • Explain observations. (Grade 7) [2004]
- 1.06 Use mathematics to gather, organize, and present quantitative data resulting from scientific investigations:
  • Measurement. (Grade 7) [2004]
- 4.05 Determine that foods are made up of a variety of components
  (Grade 4) [2004]
- 4.01 Analyze how human body systems interact to provide for the needs of the human organism:
  • Musculoskeletal. (Grade 7) [2004]

Does this curriculum meet my state's standards?

When we breathe through our noses, the inhaled air travels up through the nose and then makes a hairpin turn before it is pulled down the trachea and into the lungs. As the air makes the hairpin turn, it passes by two small areas, one at the top of each nostril, and each about the size of a postage stamp. These areas consist of thousands of olfactory receptor cells, and together they are responsible for the sense of smell.

In normal breathing, the inhaled air barely makes contact with the olfactory receptors. But when we make an effort to smell something, we inhale more sharply as we sniff the air. This forces the inhaled air straight up the nasal cavity, where it can make more complete contact with the olfactory receptors. Similarly, when we eat, the chewing motion of the jaw forces some of the air in the mouth up toward the olfactory sensors -- assuming we chew with our mouths closed! Holding the nostrils closed while eating greatly reduces the air flow past the receptors, so food loses most of its flavor in this event. Nasal congestion due to the common cold can produce the same result.

The taste receptors are more familiar to most people. These are located on the tongue, with different regions of the tongue able to detect sweetness (the tip of the tongue), saltiness (the sides just behind the tip), sourness (the sides further back on the tongue), and bitterness (the center back of the tongue). The receptors in both the tongue and the olfactory region of the nasal cavity are highly sensitive chemical receptors; they need only a few molecules to make contact with them before they will send a signal to the brain. For the tongue, it is molecules dissolved in saliva that are detected by cells within the taste buds.

For smell, however, it is volatile compounds in food that are detected by the receptor cells. These compounds are the chemical components that can change from their liquid state (within the saliva) to a gaseous state, or a vapor, at room temperature. It is the vaporized molecules that travel with the air up to the receptors. Therefore, it is the volatile compounds in foods that we smell most readily. We refer to these foods as being particularly aromatic, with flavors of mint, coffee, and cinnamon, being good examples. Blander foods, such as rice and mashed potatoes, contain far fewer volatile chemicals, and so we perceive them as both less aromatic and flavorful.

Anyone with a functional tongue can tell the difference between grains of salt and grains of sugar placed on the tongue, but the tongue alone cannot distinguish between the sweet flavor of a peach and the sweet flavor of a strawberry. It is the volatile compounds within the these fruits that give each its distinctive flavor, and so it is the sense of smell rather than the sense of taste that distinguishes one from the other.

Body of Lesson:

Ask your students why they think certain foods can trigger certain feelings, either pleasant or unpleasant, in humans. Ask if they think the first humans experienced similar sorts of responses to food. You may need to ask further questions that will allow them to understand that being able to remember foods that are good to eat, i.e., provide nutrition, is of benefit to humans. Likewise, being able to remember foods that are bad to eat, i.e., cause vomiting or nausea, is also of benefit to humans. The ability to identify both nutritious and noxious foods would have been of particular benefit to early humans, since they depended largely on plants that they gathered for their nutrition. Being able to distinguish by taste those foods that were good and those that were bad would have clearly been adaptive in an environment where the food supply was limited or food was difficult to obtain.

Then ask the class how the body's nervous system, particularly the senses, allows humans to identify foods. Students will most likely respond that humans are able to remember what foods taste like, smell like, and look like. At this point, ask for a student volunteer willing to taste and try to identify a common food (but first check for food allergies or special dietary constraints).

Before having the student taste the food, however, ask the class how you can make sure that only taste is involved in the determination. Students will probably respond that the taster should not be able to see the food, and they may also want to rule out smell. It is unlikely that they will name texture as a clue to what the food is, though. In that case, you can point out that if all foods were pureed until they had the texture of baby food, the sense of touch would also be eliminated. Also, by putting food on a spoon and feeding the volunteer, the taster would not be able to get information about what the food felt like to the hands.

Finally, ask the volunteer to close his or her eyes. Put some regular (unflavored) applesauce on a spoon and feed it to the volunteer. Then ask him or her to identify it. Next, have the student close his or her eyes and pinch his or her nose closed, and ask the student to remain this way until after he or she has stated what the food is. (This is important, because as soon as the nose is released the student will be able to identify the food.) Then using a spoon, put some flavored apple sauce (e.g., cherry or strawberry applesauce) in the taster's mouth. Remind the student to keep holding his or her nose until after the food has been swallowed and identified.

Most likely the student will not be able to correctly identify the flavored applesauce. He or she will probably think that it is applesauce, though, so be sure to ask what made him or her think that. The texture should be the main clue, but without the sense of smell, the student should not be able to distinguish between regular and flavored applesauce.

By now all students will probably be wanting to be tasters. Let them know that they will get a chance to do so when they conduct an experiment to see if smell is important to food recognition.