Questions related to gustation and olfaction.

Problem

Individuals heavily rely on their gustatory sense (taste) in everyday life. Taste is evolutionarily important in humans, since the ability to detect bitter compounds (which normally indicate a poisonous or toxic substance) is beneficial to survival, as is the ability to detect sweet compounds (indicating presence of sugar, an important source of energy). When a person’s sense of taste becomes impaired they are more likely to experience quality of life issues, and can also be more susceptible to serious issues related to dietary intake, like diabetes and heart disease. There are varying levels of taste impairment - hypogeusia, or partial loss of taste, is the reduced ability to detect sweet, sour, bitter, salty, or umami molecules. Ageusia is much more rare than hypogeusia, and is the total loss of taste detection. Dysgeusia is the distortion of flavors on the tongue, and can involve unpleasant or metallic taste. Taste disorders are usually caused by some type of injury or illness, but can sometimes be present at birth.
A researcher is interested in finding out more about taste disorders and their causes. He studies the patient records of 1500 adults who have been diagnosed with a taste disorder in the past two years, and is able to link the disorders to six broad causes. Table 1 outlines the percentage of taste disorders linked to each cause.
Cause of taste disorderPercent of patients
Head injury28, percent
Radiation therapy12, percent
Chemical exposure24, percent
Surgeries to the ear, nose, and throat5, percent
Poor oral hygiene and/or dental problems9, percent
Upper respiratory and/or middle ear infection12, percent
In a second study, the researcher examined the records of individuals who had parts of their tongue removed because of oral cancers, and attempted to quantify the loss of gustation compared to the amount of tongue removed. He found that the loss of taste correlated with the part of the tongue removed, more so than the amount of tongue removed. He concluded that his data supported previous work showing that taste receptors are preferentially localized in different parts of the tongue, mainly the anterior aspect of the tongue.
Individuals with hypogeusia have difficulty detecting umami tastes. Umami receptors are sensitive to which molecule?
Please choose from one of the following options.