Read the entire exercise and organize time, materials, and work space before beginning. Remember to review the safety sections and wear goggles when working with chemicals.
Allow at least 90 minutes to perform this exercise.
Objective
- To demonstrate the interaction of chemoreceptors for taste and smell.
Materials From: |
Qty |
Item Description: |
Student Provides |
1 |
An assistant |
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1 |
Fresh apple, potato and onion |
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3 |
Sealable containers |
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1 |
Blindfold scarf or fabric |
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1 |
Toothpicks |
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1 |
Pencil, marking |
Discussion and Review
Receptors in our body that respond to chemical stimuli are called chemoreceptors. The chemoreceptors for smell respond to air-borne chemicals while the chemoreceptors for taste respond to chemicals placed in the mouth.
Until recently, it was thought humans had four different types of taste receptors, segregated on different parts of the tongue that responded to four groups of stimuli commonly called sweet, sour, bitter and salty. For almost a century scientists erroneously believed that each of these tastes could be discerned only by taste buds located on specific areas of the tongue and that each taste bud could detect only one type of taste stimuli. From these beliefs a "tongue map" was created which indicated that sweet taste could be detected only by the tip of the tongue, salt tastes only by the sides of the tongue near the front, sour tastes only further back on the sides of the tongue, and bitter tastes only at the back of the tongue.
In 1975, American scientist Virginia Collings re-examined the differences in taste perception across the tongue. She determined that while individual taste buds do react more strongly to one particular taste, each taste bud can actually detect all four taste stimuli. In other words, the "tongue map" was wrong in segregating tastes to specific areas of the tongue and researchers now know taste buds are even found on the soft palate and other parts of the mouth.
Further research suggests there may be a fifth receptor for a taste called umami and hints there may be a sixth, as yet unnamed, receptor for fats. The taste sensation attributed to umami was identified by Japanese scientist Kikunae Ikeda in 1908, but it has only recently begun to gain acceptance in the West. Scientists are still unsure if it is a universal "taste" since only the Japanese and Chinese have a word for it. The taste of umami is that of glutamate, an amino acid found in meat, cheese, and other protein-heavy foods as well as in monosodium glutamate (MSG). Umami roughly translates to "meaty" or "savory".
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