Lesson One What do you taste? Created for SPICE by Deena Westbrook and Marbie Caruso KEY QUESTIONS: Can some people taste things that others can’t? Is it genetic? SCIENCE SUBJECT: Genetics, Anatomy and Physiology GRADE LEVEL: 7-9 SCIENCE CONCEPTS: Dominant/recessive alleles Inheritance Genetic/phenotypic diversity Control vs. experimental tests OVERALL TIME ESTIMATE: 50 minute class period plus next-day follow-up LEARNING STYLES: Visual and Kinesthetic VOCABULARY: Phenotype Genotype Allele Gene LESSON SUMMARY: Students will receive three test strips each, plus a neutral strip. They will taste each strip and record if they detect any flavor. Then, the nature of the phenotypic diversity for this trait will be examined. STUDENT LEARNING OBJECTIVES: 1) The students will become aware that there is a great deal of phenotypic diversity. 2) The students will observe the general correlation between some phenotypes in the same individual, and the lack of correlation between others. 3) Based on 2, the students will infer a genetic basis for some phenotypic traits. MATERIALS: Control taste test paper (1 per student) PTC taste test paper (1 per student) Sodium benzoate taste test paper (1 per student) Thiourea taste test paper (1 per student) What do you Taste? Lab worksheet BACKGROUND INFORMATION: The ability to taste PTC is a genetically heritable trait that follows basic Mendelian patterns. The students should understand the meaning of genes, alleles, genotypes, phenotypes, and dominance. A familiarity with working Punnett squares would be greatly helpful to the students prior to attempting this lab. See Lesson 3 for a reference. PTC is detected by the bitter tastebuds, which are located at the back of the tongue and in the throat. Unlike sweet, sour, and salty taste buds, there are many different types of bitter taste buds. Because of this, not everyone has all the same bitter tastebuds. Most of your students should be able to taste PTC. ADVANCE PREPARATION: In order to keep germ spreading to a minimum, it would be helpful to separate the taste strips into ziplock bags by lab group. Be sure you don’t mix two different strips in the same bag, otherwise you won’t be able to tell which is which. Copy student worksheets. PROCEDURE AND DISCUSSION QUESTIONS: 1) Outline the lab procedure for the kids, including the proper way to taste the strips, disposal of used strips, and the purpose of the control strip. The control strip is there so kids know what the paper tastes like. Each taste strip should be touched to all parts of the tongue, then removed and promptly put in the trash. Distinguish between having a taste for something (liking it) and being able to taste something. 2) Ask the students what the four major tastes are. Draw a diagram of the tongue, and ask where each type of taste bud is located. If they are having trouble, lead them on by asking them where or when they taste something. For instance, ask them why they get an aftertaste with medicine, and how it tastes. They should be able to figure out it’s a bitter taste, and that you only taste it in the back of the tongue. The same can be done with sour, if you ask what they feel when they eat something too sour. Most of them point to their ears, and they figure out they taste it on the back and sides of their tongue. 3) Inform them that there is only one type of sour taste bud (detectes H+), only one type of salt taste bud (detects Na+), and only one type of sweet taste bud (detects sugar), but there are many types of bitter taste buds. Then, ask them which ability to taste is likely to differ among people (bitter). 4) Ask them why they think different people will be able to taste different bitter tastes. You will probably get some strange answers, but their answers should boil down mostly to genetics or environment. Remind them of Mendelian laws, and review the necessary terms. 5) Review the procedure for the lab again. This is important, because if you don’t, you are likely to get saliva-soaked paper all over the place, and kids tasting the control strip last. Steps 1-5 should take 15-20 minutes maximum. 6) Have the kids go to their lab station and perform the tests. This can take 5-20 minutes, depending on the maturity of the class. 7) After everyone has finished the taste-testing and recording of their data, collect the class-wide data, and ask the following questions: a. Is there a relationship between the ability to taste one bitter substance and the ability to taste another? b. Do you think your family could taste the same flavors, or do you think their taste abilities will differ from yours? Why? c. Did everyone taste the same thing when they tasted sodium benzoate? Do you think this supports genetic or environmentally- associated abilities to taste? Step 7 can take ten to twenty minutes. If there is any time left over, the students can answer the questions on their lab sheet. SUNSHINE STATE STANDARDS: SC.F.1.3: The student describes patterns of structure and function in living things SC.H.1.3: The student uses scientific processes and habits of mind to solve problems SC.F.2.3: The student understands the process and importance of genetic diversity Provided by What do you taste? 1) Write a hypothesis about the differences in taste ability. Remember to use the “If, Then, Because” format. For each lab group member, follow this procedure to find out which compounds you can taste: 1) Take one control taste test strip from the bag marked “control”. 2) Place the taste strip on your tongue. Be sure to test all the regions of your tongue. You should not taste anything. If you taste something, it should taste like paper. Remember what it tastes like 3) Remove the taste test strip from your mouth, and immediately throw it in a trash can. Do not place it on your lab bench or desk! 4) Take one PTC taste test strip from the bag marked “PTC”. 5) Place the taste strip on your tongue. Be sure to test all the regions of your tongue. Do you taste anything? 6) Remove the taste test strip from your mouth, and immediately throw it in a trash can. Do not place it on your lab bench or desk! 7) Record whether or not you taste PTC in your chart. If you tasted nothing, or if it tasted the same as the control test, you are a non- taster. Otherwise, you are a taster. 8) Repeat steps 4-7 using the thiourea taste test strips. 9) Repeat steps 4-6 using the sodium benzoate taste test strips 10) Record whether or not you taste sodium benzoate in your chart. If you tasted it, record whether you tasted something sweet, salty, sour, or bitter. Sodium Benzoate Lab group members PTC Thiourea No taste Sweet Salty Sour Bitter Sodium Benzoate Class Data PTC Thiourea No taste Sweet Salty Sour Bitter Tasters Non-Tasters PTC, Sodium Sodium Thiourea, & PTC & Benzoate & Benzoate & Sodium Class Data Thiourea PTC Thiourea Benzoate Tasters Non-Tasters 2) In general, could those tasting PTC also taste thiourea? Is this evidence for or against your hypothesis? 3) In general, could those tasting PTC also taste sodium benzoate? Is this evidence for or against your hypothesis? 4) Was there a lot of variety in your classmate’s ability to taste? Is this evidence for or against your hypothesis? 5) Overall, do you think your hypothesis was supported? What would you conclude about the variety in people’s ability to taste? Make a conclusion about both the amount diversity and the source of the diversity.