We have done some extensive experiments on taste buds: how they are categorized, what tastes they recognize, and we have even mapped their location on your tongue. But we haven’t yet mentioned this fact: not all people can taste the same flavors!


So today we will check to see if you have a dominant or recessive gene for a distinct genetic characteristic. We’ll do this by testing your reaction to the taste of a chemical called phenylthiocarbamide (or PTC, for short). The interesting thing about PTC is that some people can taste it – and generally have a very adverse reaction. However, some people can’t taste it at all.


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Here’s what you need


      • 1 vial of PTC paper
      • family members



Download Student Worksheet & Exercises


Here’s what you do


  1. Put the PTC paper in your mouth. If you have the dominant gene, it will usually taste pretty bitter. It might also be sour or even a little sweet. If it tastes like a piece of paper, you have a recessive gene.
  2. After testing your paper, be sure to note whether you are a taster or non-taster.
  3. Now test at least five more people in your family and note their reactions as tasters or non-tasters. Also note their relationship to you.
  4. If you have enough PTC paper, make a genetic tree of your responses. Put Mom and Dad at the center and list you and your siblings branching out beneath them. Then list both sets of grandparents above each of your parents. Circle the names of family members who test positive and leave the negative testers uncircled.

What’s going on?


The gene that determines whether or not you can taste PTC is a part of your DNA (deoxyribonucleic acid). It is the genetic blueprint that you were born with and it determines everything about you: from hair color to the size of your feet. But DNA also plays an important role in how your five senses function. Colorblindness is a genetic deficiency in which a person cannot see colors has a difficult time with distinguishing them. It can range in severity. Some people who are colorblind can’t tell the difference between colors like red and green, but some see no colors at all. Everything looks like a black and white movie to them. Just like colorblindness, our taste sensitivity can vary. Maybe this explains why some people like liver and brussel sprouts and others can’t stand them!


So to relate this to our test, the ability to taste PTC comes from a gene. We know that if both of your parents can taste it, there is a high likelihood that you will be able to taste it, too. About 70%, or 7 out of 10, people can taste it. But what does it mean?  In truth, not a lot. It doesn’t mean you have a highly developed palate or a better sense of taste. It just means you are lucky enough to have inherited a gene that allows you to taste a disgusting, bitter chemical on a piece of paper. Congratulations!


Exercises


  1. What are the tiny hair-like organelles that send taste messages to your brain called?
  2. What are the bumps on your tongue called?
  3. What kind of trait does this experiment test?

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Digestion starts in your mouth as soon as you start to chew. Your saliva is full of enzymes. They are a kind of chemical key that unlock chains of protein, fat, and starch molecules. Enzymes break these chains down into smaller molecules like sugars and amino acids.


In this experiment, we will examine how the enzymes in your mouth help to break down the starch in a cracker. You will test the cracker to confirm starch content, then put it in your mouth and chew it for a long time in order to really let the enzymes do their job. Finally you will test the cracker for starch content and see what has happened as a result of your chewing.


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Here’s what you need


    1. 1 package of soda crackers
    2. 1 5” pie tin
    3. 1 craft stick
    4. 1 0.5 oz bottle of iodine
    5. 1 pre-form tube
    6. 1 1 mL plastic pipette
    7. water



Download Student Worksheet & Exercises


Here’s what you do


  1. Take a cracker from the package and put it in the pie tin. Use your thumb to mash it up, making the pieces as small as possible. Add a small amount of water with the pipette. Mix everything up with the craft stick to make a mash of cracker.
  2. Now fill the pipette with iodine. When iodine comes in contact with starch, it changes in color from reddish-brown to a dark blueish-black. Take the pipette and squeeze a few drops onto the cracker mash in various spots. Record what you see in your experiment data.
  3. Take another cracker and chew it up for about 2 minutes. Do you notice any flavor changes as you are chewing? If so, note this. Be particularly aware of any sweet flavors.
  4. Spit the mash into the pre-form tube once you have chewed for 2 minutes. Use the pipette of iodine to add a few drops of iodine to the chewed mash. Note any change in color. If there is no starch, the iodine will stay reddish-brown in color. If starch is present, you will see the color change to a very dark blue-black as it did in step 2. Record what you see in your data.

What’s going on?


This lab gives you a good idea of what happens in digestion, which starts as soon as food enters your mouth. Actually, the process can start even before this as your body prepares for food. Have you ever had a wonderful smell make your mouth water? This is your body’s way of getting ready to get to work digesting that delicious food.


Once you take a bite and the enzymes start to do their job of breaking large, more complex molecules into smaller particles. In this experiment, starch got broken down into simple sugars that your body could easily move around and use as fuel.


There are three sets of saliva-secreting glands in your mouth. They include a gland in the back of your throat called the parotoid gland, one in your lower jaw called the submandibular gland, and the sublingual gland which is under your tongue. The three work together to secrete up to 2 liters of saliva each day.


Exercises


  1. What is the first step in the digestive process?
  2. How does saliva help to digest food?
  3. Name one or more of the main salivary glands and where they are located.

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The tongue has an ingenious design. Receptors responsible for getting information are separate and compartmentalized. So, different areas on the tongue actually have receptors for different types of tastes. This helps us to separate and enjoy the distinct flavors. In this experiment, you will be locating the receptors for sweet, sour, salty, and bitter on the tongue’s surface.


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Here’s what you need


  • 4 cotton swabs
  • 5 wax cups
  • 1 bag of black tea
  • 1 bottle of red vinegar
  • 2 packages of sugar
  • 2 packages of salt
  • 1 microwave
  • water
  • 1 spoon
  • 1 partner
  • 1 blindfold



Download Student Worksheet & Exercises


Here’s what you do


1. Put 3 ounces of water into the first of the wax cups. Bring it to a boil in the microwave and have an adult help you add a teabag. This will make your bitter cup. Let it sit for 5 minutes. While it is steeping, you can prepare the other cups.


2. Fill the remaining cups with 2 ounces of water each. Prepare them as follows:


A.      For the sweet cup, add two packages of sugar to the warm water in one of the cups. Stir until well dissolved.
B.      For the sour cup, add 2 ounces of red vinegar to another cup and stir well.
C.      For the salty cup, put two packages of salt into the final cup. Stir until dissolved.
D.      The last step in cup preparation is to discard the tea bag that has been steeping in the first cup.


3. Now put the blindfold on your partner and have them stick out their tongue.  Dip the first swab into the tea. Using the diagram as a guide, swab each area one at a time: A, B, C, and D.  Ask your partner to identify the flavors as sweet, sour, salty, bitter, or can’t tell  as you swab each individual area. Record your partner’s response for each area.


4.Your partner should rinse out their mouth with water after testing the bitter tea. Then test each of the remaining solutions, one at a time in the same manner.


What’s going on?


Humans can identify thousands of distinct tastes, but we only have four types of taste receptors. When you take a bite of something flavorful, your saliva starts to dissolve it immediately. This solution of flavor and saliva goes to your taste buds and is then interpreted by your brain as sweet, sour, salty, or bitter.


The taste buds have taste receptors which bind to the structure of certain molecules: sweet receptors recognize hydroxyl groups (OH) in sugars, sour receptors find acids (H+, such as the citric acid in a lemon), salt receptors respond to metal ions (like Na+ in table salt), and bitter receptors are triggered by alkaloids. These are bases which contain nitrogen.  It’s interesting to note the location of the bitter taste buds – they are on the back of the tongue.  Since many poisons are alkaloids, their bitter taste may actually trigger vomiting.


Anyone who’s had a stuffy nose can tell you that smell plays a big role in our ability to taste. This makes sense because we know that we can only really taste the 4 distinct true flavors of sweet, sour, salty, and bitter. Our nose works in partnership with our tongue to allow us to identify more complex flavors.


Exercises


  1. How many different types of taste receptors do we have? What are they?
  2. Can you still taste food when you have a stuffy nose?
  3. Which taste receptors recognize the hydroxyl group?

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Did you know that your tongue can taste about 10,000 unique flavors? Our tongues take an organized approach to flavor classification by dividing tastes into the four basic categories of sweet, sour, salty, and bitter.


For this experiment, you will need a brave partner! They will be blindfolded and will be attempting to guess foods. Relying only on their sense of taste, they will try to determine what kind of foods you are giving them.


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Here’s what you need


    • 1 partner
    • 1 blindfold
    • 1 cup of water
    • 1 plate
    • 1 lemon
    • 2 toothpicks
    • 1 sugar cube
    • 1 salty cracker
    • 1 piece of dark chocolate
    • 1 pencil



Download Student Worksheet & Exercises


Here’s what you do


  1. (NOTE: Make sure your partner is not around for the first step!) Prepare a plate with a piece of lemon on a toothpick, a sugar cube, a really salty cracker, and a piece of dark chocolate, which will also be on a toothpick.
  2. Blindfold your partner before they see the plate. Explain that you’re going to give them food samples. Their job is to taste each sample, one at a time, and then determine whether the food is sweet, sour, salty, or bitter. After they have provided a category, see if they can tell you the specific flavor of the food. They should use the water between samples in order to rinse their mouth and prepare for the next food.
  3. Record data and observations for each individual food item. Be sure to list each food, your partner’s group classifications (sweet, sour, salty, or bitter) and what specific flavors that they note.

 What’s going on?


When you put food in your mouth, saliva immediately begins to break it down. Saliva mixes with food and makes a solution, which then takes the food (and its flavor) to the taste pores. There, receptors determine the chemical structure and send this information to your brain, which then decodes and categorizes the taste. The exact nature of the secret code relayed between your taste receptors and your brain is still a mystery. Maybe someday you can help to figure out the science behind it!


Did you know that humans have about 7500 taste buds? That’s a lot compared to most chickens, which only have about 24, total. But it’s a pretty small amount compared to catfish. They have over 175,000 taste buds! Can you imagine what your favorite dessert might taste like if you had that many? I wonder if it would be a good thing, or maybe too much information. Perhaps we are better off with our own perfect number of taste buds!


Exercises


  1. How does saliva help with tasting?
  2. What helps to decode the chemical structure of a food so that the brain can determine its taste type?
  3. Why do foods sometimes become less strong as we age?

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What is happening when we feel hungry? Or when we feel thirsty?

What we are feeling are  hormones signaling our brain that we need food or water.

Hormones play a large role in our digestion process. They help maintain homeostasis by stimulating appetite, thirst, as well as many, many other bodily functions.

Digestion is the process of food (and drink) being broken down and absorbed. The mouth begins the digestion by breaking down food mechanically and chemically. Protein is digested in the stomach. The small intestine finishes the chemical digestion and absorption of food. The large intestine absorbs excess water from the waste and finally passes it through the anus.



What happens to those meals when they enter our mouths? There are the main things that happen:

  1. Digestion: Digestion involves the breakdown of what we consume into nutrients. The first step is mechanical digestion—chewing. After we mechanically break down the food with our teeth, we begin chemical digestion. Chemical digestion breaks down what we eat and drink chemically. Chemical digestion is mostly accomplished by proteins called enzymes.
  2. Absorption: After we’ve broken down the nutrients we need, we absorb them into our body. This step is called absorption.
  3. Elimination: Lastly, we excrete solid and liquid waste.
Digestion begins in the mouth. In the mouth, the teeth digest food mechanically, and the saliva digests starches chemically.  Enzymes are catalysts that make chemical reactions go faster. They are found at every important step of digestion. Amylase is found in our saliva, and it helps breaks down bread-like things (starches) into smaller sugar molecules. Pepsin helps us digest protein in our stomachs. Pancreatic lipase breaks down fats.

After the mouth, the food travels to the stomach through a narrow tube called the esophagus. The esophagus moves the ball of chewed and partially digested food into the stomach. Food is moved through the tube via muscle contractions. The muscle contractions start in the esophagus and end in the anus, moving in a wave called peristalsis. Peristalsis is the name of the movement of the muscle contractions moving the food through the tube.

Once in the stomach, the food is further chemically digested. The protein is digested with the enzyme pepsin. Pepsin, along with other chemicals such as hydrochloric acid (HCl) chemically digest the food. Water, salts, and simple sugars are absorbed through the walls of the stomach. The rest of the nutrients are absorbed after exiting the stomach.

The small intestine, about 7 ft long, has three parts. The large intestine takes the liquid waste from the small intestine, absorbs the excess water, and excretes the solid was through the anus. The large intestine is home to trillions of helpful bacteria. Although we often think of bacteria as harmful, most bacteria is helpful. The bacteria in our small intestines helps us digest food, and we provide the bacteria a place to live. Among other functions, the bacteria in our large intestines produce vitamins B12 and K, as well as break down poisons.

The liver is essential to digestion, and life. The liver detoxifies the blood, maintains the glucose balance, synthesizes proteins, and produces many chemicals needed for digestion.

Getting the right nutrients and getting fiber in your diet is extremely important. The nutrients keep your system running well, while fiber helps to move waste through your digestive system. If you do not get enough fiber you may become constipated; unable to pass waste.

Maintaining a healthy digestive system means a.) maintaining a healthy diet, and b.) taking care of any illnesses, allergies, or intolerances which arise.  

Eating and drinking are essential parts of our life. Part of maintaining a healthy lifestyle is making sure to eat and drink the right quantities of the six essential nutrients. Those nutrients are: protein, carbohydrates, lipids, vitamins, minerals, and water.




Does it mean to eat all vegetables? Does it mean to eat only meat? No. A healthy diet is a balanced diet. This is what MyPlate demonstrates. A balanced diet means getting the right amounts of nutrients. MyPlate guidelines are recommendations from the United States Department of Agriculture (USDA). Since 1958 the USDA has recommended a balanced diet in the form of the food pyramid. However, the pyramid proved to be too complicated for most Americans to efficiently use to create diets. In response, the USDA simplified its recommendations in 2011 into the MyPlate format.




We already know what a diet is—the sum of food and drink consumed. Now, what does it mean to have a healthy diet?




The specific advice of the USDA is:


  • Balance calorie intake.
  • Enjoy your food, but eat less.
  • Avoid oversized portions.
  • Eat certain foods.
  • Make half your plate fruit and vegetables.
  • Make at least half your grains whole grains.
  • Switch to fat-free or low fat (1%) milk.
  • Eat certain foods in moderation.
  • Compare sodium in foods like sodium, bread, and frozen meals—and choose the foods with lower numbers.
  • Drink water instead of sugary drinks.