Chemoreceptors

Exercise 1: Taste Receptors & Interaction of Taste and Smell

The stimuli interpreted by the brain as the basic tastes, sweet, sour, bitter, salty and possibly umami are important in our over all health.  The various tastes help us respond appropriately to foods.  For instance, the sweet taste of sugar makes us want to eat carbohydrates and also evokes physiological responses in our body like the release of insulin that prepare our body to digest and use ingested nutrients. 

Just as importantly, our universal revulsion of things that taste bitter may protect us from eating poisonous foods since many toxic compounds have intensely bitter tastes.  Our avoidance or dislike of sour may help us avoid foods that are spoiled or spoiling.  Some recent research even suggests that we may think things we nutritionally need actually taste better than usual and we may openly seek them out. 

Tasting food is a complex process.  Food strikes different taste buds in the mouth and "taste" results when the chemicals in the food dissolve in saliva and contact taste cells through a taste pore.  But taste is even more complex than that, for chemoreceptors called olfactoryreceptorsin the nasal passage also play a vital role in taste.  Smell is actually part of the complete taste of a food; without smell, some foods with subtle chemical stimuli may be difficult to identify.  Have you noticed that when you have a cold and your sense of smell is poor, food tastes differently and seems uninteresting?

PROCEDURE   

1.     Label three sealable containers as "potato," "apple," and "onion."  Cut twelve 1-cm cubes each of apple, potato, and onion and place them in their corresponding container.  Seal each container with its cover and keep it sealed when not in use. 

2.     Create data tables like those below to record your data.

Smell Versus Taste for First Partner

Smell Versus Taste for Second Partner

3.     Blindfold your partner and have him/her sit and hold his or her nose closed through out this part of the experiment.  Ask your partner not to breathe through his/her nose until you get to step 7.  With a toothpick spear a piece of one of the foods and place it in your partner's mouth.  Your partner should chew the food slowly and swallow it. 

4.     Ask your partner to identify the food. If it is identified correctly, record a plus sign ( +) in that food's row under the column heading "Taste Only."  If the food is not identified correctly, record a minus sign ( - ). 

5.     Repeat Steps 3 and 4 with the other two foods.  Remember to keep the containers sealed except when you are removing a piece of food. 

6.     Repeat Steps 3, 4, and 5 but select the foods in a different order so your partner cannot anticipate which food he or she tastes.  You will now have a total of six taste only tests, two for each food. 

7.     Have your partner sit blindfolded but this time without holding his/ her nose.  Use a toothpick to spear a piece of one food and hold it just under your partner's nose. 

8.     Ask your partner to identify the food.  If it is identified correctly record a plus sign in the row for the food and under the column heading "Smell Only."  If the food is not identified correctly record a minus sign.  Discard the food and the toothpick. 

9.     Repeat Steps 7 and 8 with the other two foods. Keep the containers covered except when removing food.  Then as before, repeat these steps, but select the foods in a different order.  You will now have a total of six smell only tests, two for each food. 

10. Have your blindfolded partner sit without holding his or her nose.  With a toothpick spear a piece of one of the foods and place it in your partner's mouth.  Your partner should chew the food slowly and then swallow it. 

11. Ask your partner to identify the food.  If it is identified correctly, record a plus sign in for the food and under the "Taste and Smell" column.  If the food is not identified correctly, record a minus sign. 

12. Repeat Steps 11 and 12 with the other two foods. Then as before, repeat these steps, but select the foods in a different order.  You will now have a total of six taste and smell tests, two for each food. 

13. Reverse roles with your partner and repeat Steps 3 through 12.