Shine the flashlight on a student's tongue. Take a photo of the tongue. Then zoom into the photos to look closely and find the taste buds.
Optional: drip one drop of food colouring on the tongue, then rinse the mouth with water. The pink taste buds will contrast with the blue tongue.
Look for the bumps on the tongue.
These bumps detect tastes.
There are five established basic tastes, from separate taste buds detecting different molecules or ions.
Sweet detects sugar/protein when they bind.
Sour detects hydrogen ions, when they enter the taste bud.
Salt detects Na+, K+ or Li+ ions when they enter the taste bud.
Bitter from molecules binding a receptor.
Umami is glutamic acid binding a receptor.
The tongue can detect other sensations, not classically described as taste: spiciness, temperature, coolness (minty), numbness, astringency, metallicness, calcium, fattniess, starchiness (Wikipedia: Taste)
Note that the traditional division of the tongue into different areas (salt one region, sweet another) are wrong. All the tastes are distributed all over the tongue.
(Explanation: the original paper showed tiny differences in detection levels across the tongue, but this was misunderstood and reported in textbooks as a difference in sensitivity.)
Different students will have different densities of taste buds.
Super tasters have the greatest density of taste buds, normal tasters have fewer and non-tasters have the least.
(More than about 30 fungiform papillae they are considered a supertaster, if they have around 15 to 30 papillae they are an average taster, and if they have fewer than 15 papillae they are a non-taster. Of world population 25-30% are thought to be supertasters, 40-50% average tasters, and 25-30% non-tasters.)
To supertasters, foods may have much stronger flavors, which often leads to supertasters having very strong likes and dislikes for different foods. Supertasters often report that foods like broccoli, cabbage, spinach, grapefruit and coffee taste very bitter. The opposite of supertasters are non-tasters. Non-tasters have very few taste buds and, to them, most food may seem bland and unexciting.