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Overview

How do people experience taste? Some people savor the flavor of beets while others grimace in disgust. What accounts for the difference? In this lesson, students will investigate the genetic basis of taste by testing their ability to taste a bitter compound (PTC) and by sampling food.

Objectives

Students will be able to:

• define the term taste receptor
• explain how genes can influence our taste perception
• describe how taste and smell combine to create a flavor sensation

Grade Level: 9–12

Suggested Time

• 45–60 minutes

Media Resources

• NOVA: scienceNOW: The Science of Picky Eaters Video (12:45)
• The Sense of Taste QuickTime Video
• HHMI: Taste Lecture Video (6:00)

Materials

• PTC paper (available from biological supply companies)
• one type of baby food for the class to taste (e.g., peas, carrots)
• a spoon to dispense the baby food
• small paper cups for samples of baby food (one per student)
• straws or small spoons for tasting the food sample (one per student)
• mint oil (e.g., peppermint, spearmint, wintergreen, or eucalyptus, available at grocery stores) or a tin of strong-smelling breath mints
• cotton swabs (one per student)
• Picky Eaters Student Handout PDF Document

Before the Lesson

• order PTC paper from a biological supply company
• Make copies of the Student Handout (one per student)
• obtain all materials for the taste test
• cover the baby food container label so the food's identity is hidden
• Read the Teacher Notes—Picky Eaters PDF Document for background information and assessment tools
• Bookmark the Web sites for the media resources

The Lesson

1. Informally survey students about their taste preferences. For example, ask students to raise their hand if they:

• love ice cream
• enjoy eating broccoli
• hate spicy, hot, or strongly flavored foods
• have a hard time deciding what to order at a restaurant
• always ask for sauces and dressings on the side
• dive right into their food after being served
• carefully taste each food on their plate
• add a lot of salt
• have ever been called a picky eater

2. Explain that their responses might be based on their genes. Show them The Science of Picky Eaters Video, The Sense of Taste Video, and HHMI Taste Lecture Video.

3. If appropriate for your students, point out the genetics underlying taste. For example:

1. Genes are segments of double-stranded, complementary DNA, made of the nucleic acids adenosine (A), thymine (T), guanine (G), and cytosine (C)
2. To decode DNA, the complementary strand of DNA is transcribed into messenger RNA (mRNA)
3. To translate mRNA into amino acids, every three nucleic acids (called codons) are decoded using a chart
4. Amino acids, in a specific sequence and 3-D structure, form proteins

4. Tell students that special proteins on the surface of taste cells in our tongue help us detect specific flavors. These proteins (which are made up of amino acids) are called taste cell receptors. Mention that students will test factors influencing their ability to taste and to perceive flavor.

5. Give each student a copy of the Picky Eaters Student Handout PDF Document and a piece of PTC paper. Have them follow the instructions on the handout and answer the questions. For step 3, help students tally class PTC responses. Draw the following chart on the board:

6. For step 5 of the handout, give each student a spoonful of baby food in a cup and a cotton swab dipped in mint oil (e.g., peppermint, spearmint, wintergreen, or eucalyptus) or a very strong breath mint. Do not reveal the identity of the food. Students should smell the mint as they taste the food. Next, they should taste the food sample while holding their nose.

7. When students have finished the taste test, reveal the identity of the food and tally the number of correct responses. Discuss difference between taste and flavor. One way to describe it might be that taste is sensed by our tongues, whereas flavor is constructed by the brain, based on stimuli from the tongue and nose.

8. Discuss the role of genetics in our sense of taste and perception of flavor. Ask:

• Did all students who were able to taste PTC experience the same bitter flavor?
• Were tasters who could taste PTC better or worse at identifying the food sample?
• How do genes influence our food choices?
• Even if our genes predispose us to dislike certain foods, can we still choose to eat healthy meals?

Point out that generic difference, such as number of taste buds, play a role in flavor perception and ability to smell. Other external factors, such as temperature, can affect how we experience food.

9. Optional Extension Activities:

1. Ask students to design and carry out their own taste test, involving one or more of the following:

   • different flavors (e.g., bitter, sweet, salty)
   • sight (e.g., use food coloring to change the color of clear soda)
   • texture (e.g., prepare and compare puréed and whole foods)
   • temperature (e.g., taste the same food hot, cold, and room temperature)

   Challenge students to create tests that weigh one variable at a time, use experimental controls, and collect quantitative data.

2. Discuss how genes can influence our behaviors (such as food choice), and ask students whether genes determine our choices. Our susceptibility to become addicted to certain drugs, including alcohol and cigarettes, seems to have a genetic basis. Understanding our family history is important so that we are aware of our own vulnerabilities. Point out that although our genes might make us more likely to engage in certain behaviors, many factors, such as our parents, our peers, the media, and cultural norms, influence our choices.

   • According to one study, smokers who were less sensitive to bitter taste (PTC) rated taste as a strong reason for smoking, and those who were sensitive to bitter taste were less likely to smoke for taste.
   • One genetic variation found in over 40 percent of people is associated with impulsivity, low self-control, binge drinking, and substance use.
   • Brain cells have receptors for dopamine, a molecule that makes us feel good. Research has shown that people with a particular gene for a certain type of dopamine receptor (called DRD2) are more likely to be addicted to alcohol or cocaine.

Check for Understanding

Discuss how genetics can influence our taste perception, while taste and smell combine to create the sense of flavor. You can also use the answer key and rubric in the Teacher Notes—Picky Eaters PDF Document to assess each student's work on the handout.