Don't Be Bitter: Exploring Factors that Impact the Sense of Taste!

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Objective

Students will investigate the various factors that influence the variation and diversity of tasting abilities in humans.

Big Idea

Receptors, nerve cell pathways, and taste areas of the brain are involved in the ability to process specific chemical tastants from the environment.

Introduction

Lesson Background & Justification:

       Taste buds are the clusters of bulbous nerve endings housed in tiny projections on the tongue called papillae. These projections which are located in the lining of the mouth (tongue, throat and roof of the mouth) provide the sense or perception of taste in animals. Taste buds detect chemicals dissolved in saliva from food in the mouth and throat and send this sensory information through neurons to the gustatory center of the brain. In this lesson, students learn to visualize papillae on their own tongues, assess differentiated tasting abilities of their classmates and gain an understanding of how genetics contribute to the variation of taste abilities. Command of this content further iterates how specialized systems and organs therein are interconnected in the body and how each separate system contributes in some fashion to the overall survival of organisms.  

Essential Prior Knowledge: Prior to experiencing this lesson, students should be familiar with the following content/concepts:

             a) Structure and Function of Neurons  

             b) Organization/Hierarchy of organisms   

Lesson Preparations:

 In the effort to prepare for this lesson, I make certain that I have the following items in place: 

a) A class set of The  Taste Blind Science Take Out Kit (One kit for each pair of students). 

b) A class set of blue lollipops, blue food dye and cotton swabs.

c) Student lab books.

d) A few mirrors for students who do not have cells phones. 

Common Core and NGSS Standards:

HS-LS1-2- Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

HS-LS4-2-Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment. 

SP2- Developing and Using Models.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

HS-LS3-3-Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.

MS-LS3-1Develop and use a model to describe why structural changes to genes (mutations) located on chromosomes may affect proteins and may result in harmful, beneficial, or neutral effects to the structure and function of the organism.

Standards Rationale:

       Modeling is the process by which scientists represent ideas about the natural world to each other, and then collaboratively make changes to these representations over time in response to new evidence and understandings. It is intimately connected to other scientific processes (asking questions, communicating information, etc.) and improves students ability to recall scientific jargon through association. In the classroom, it is important that teachers engage students in modeling practices, to set the foundation of success in a lesson or instructional unit. In this lesson modeling is used in concert with other science practices in the classroom to promote students’ reasoning and understanding of core science idea presented (the anatomy and function of the tongue). 

 

Engage

10 minutes

Section Sequence: 

       In this section of the lesson, my goal is to provide students with a discussion opportunity that helps them to process why humans and animals have differentiated tasting abilities.The idea is to provide a conduit for students to become engaged in the subsequent activity that investigates what and how they chemically process tastants. This activity proceeds as follows: 

a) Slide 1: Read the question on the slide and encourage students to consider the groups of feeders as they articulate their responses to the class. Inform students to keep these responses in mind as we will revisit later this logic later.

b) Share the following video with students:

     

c) Post video, discuss as a class how the video altered their initial thoughts and shared responses in step a. What didn't they consider prior to video?

Standards Covered:  

HS-LS4-2-Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment. 

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

Explore

30 minutes

Section Primer: 

      PTC or Phenylthiocarbamide, also is an organosulfur thiourea containing a phenyl ring. It has the unusual property that it either tastes very bitter or is virtually tasteless, depending on the genetic makeup of the taster. In this section of the lesson, students investigate their ability to taste this chemical and learn to describe and sequence the chemical events that either allows for them to taste the chemical or prohibit their abilities. This activity proceeds as follows:

Section Sequence: 

a) Slide 2: Say to the class: "Now that we have a general understanding of why we process flavors differently, let’s explore the specific events that occur between our tongue and brain which leads to this sense. We will start by assessing each of your ability to taste a special chemical called PTC".

b) Tell students to obtain The Taste Blind Science Take Out Kit  (One kit for each pair of students). Instruct them to complete Part 1 (page 1) and to stop when they finish this section.

c) Survey the class (by show of hands) to quantify the relative percents of the group that can taste the chemical versus those who can't. Allow for students to verbally propose hypothesis that explains the difference in numbers. Dispense one blue lollipop to each student and instruct students to slowly dissolve as they complete part two of the lab. 

d) Say to students: Let’s explore why we are able to taste in general. In other words, how do we get the PTC or blue sucker tastants to our brains for processing? Instruct students to complete Part 2 of the lab and to take a close up picture of their tongues once they conclude. Note: The nervous system diagrams can be seen on page vi (kit contents) but the kit has to be purchased in order to obain a full page copy. 

e) Ask the class: What did you discover about the process of tasting? Tell students to provide a sequence of events for the process without referencing their kits or lab books. Note that the last step doesn't implicate a specific part of the brain. So, use the image on the slide to direct students to the specific part of the brain that processes taste. Finally, prompt students to explain why some of them can taste PTC and some can not. Responses to all questions should be verbally shared and discussed as a class. 

Standards Covered:

HS-LS1-2- Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

SP2- Developing and Using Models.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

MS-LS3-1Develop and use a model to describe why structural changes to genes (mutations) located on chromosomes may affect proteins and may result in harmful, beneficial, or neutral effects to the structure and function of the organism.

Explain

15 minutes

Section Sequence: 

    In this section of the lesson, students learn how to describe the molecular and chemical events that allow for the tongue to selectively receive and process various tastes including sour, sweet, umami, salty and bitter. This section proceeds as follows:  

a) Slide 3: Provide students with a copy of the tongue diagram handout and draw students attention to the papillae at the top of the page. Instruct for students to locate these bumps on the image of their tongues (it will appear as pink spots in the blue dyed areas of the tongue since papillae can not be stained with blue dye).  Ask-where are they concentrated? Is this where you experience taste? 

b) Ask- What do you think happens on a chemical level in these bumps when you taste things?Share that this the unit that makes chemical transmission possible and that in order to understand its function, that they need to learn the different parts. Instruct students to label the part of the taste buds from the projected diagram. Then play the following animation which illustrates the process that occurs in the dots or papillae that students have observed.

                

c) As students watch, pause at the following times and ask the following questions:

19 seconds: What are the protrusions or hills seen here.

25 seconds: Why are the cells different colors?

45 seconds: What happens when the blue dot or tastant passes each taste bud? What are the yellow extensions and where are they going? Why?

d) Ask-Do you think that there are more on the tongue? Discuss. Let’s find out. Provide students with a q tip and apply one drop of blue food coloring on each of their tongues. Instruct students to use their phones to view their tongues as they  evenly coat their tongues and to take a second image of their tongues. 

e) Slide 4: Tell students to examine the second photo. Ask- Can you see your ______ receptors? Fill in the blank with the names of the receptors projected at the top of the slide. Ask students why is tasting ability relatively uniform in each area. Encourage them to notice taste bud loads in each area. Discuss. 

f) Bring students attention to the flavor distribution image at the bottom. Ask- What does it show us about the distribution of taste? How is it different from what you learned in your earlier years? Show Slide 5 and instruct students to explain why we can taste in all areas of the mouth. 

g) Project the following website to the class and use the images on the site that explains how differentiated gustatory cells in taste buds and their receptors process salt, sweet and bitter differently. Guide students through summarizing each image into 3 basic steps.

h)  Finally, encourage students to think about the engagement question again and to verbally restructure their responses based on what they have learned.  

Standards Covered: 

HS-LS1-2- Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

Extend

25 minutes

Section Sequence: 

       In this section of this lesson, students learn to explain the genetic basis of taste differences in humans. The section proceeds as follows:

a) Slide 6: Ask- How do we know if we have our taste genes or not? Let's review and simulate the technologies that aid in our ability to understand the genetic connections to taste. 

b) Instruct students to proceed with sections 3 and 4 of the lab as outlined on the slide. Share out student summaries developed in step d and discuss how their summarized results impacts the validity of their hypothesis. Ask: Would you reconstruct your hypothesis? Why or why not? 

Standards Covered:

HS-LS4-2-Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment. 

SP2- Developing and Using Models.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

HS-LS3-3-Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.

MS-LS3-1Develop and use a model to describe why structural changes to genes (mutations) located on chromosomes may affect proteins and may result in harmful, beneficial, or neutral effects to the structure and function of the organism.

Evaluate

10 minutes

Section Sequence:

Slide 7: Read the instructions for the evaluation activity as presented on the slide. Students should record the responses in their lab books. As an instructor, you should look for students ability to articulate that similarly, the chemical stimuli received and processed by taste and smell receptors transmits information to the same region of the brain but differ by specific reception factors (organ, receptors, etc.). See student examples for well constructed responses.    

HS-LS1-2- Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.