Docstoc

Title What do you taste (DOC)

Document Sample
Title What do you taste (DOC) Powered By Docstoc
					                              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.

				
DOCUMENT INFO