The bitter receptor hTAS2R38 is activated by glucosinolates found in plants such as turnips and broccoli. Glucosinolates can block synthesis and transport of iodine. Before the advent of iodized salt, this was a particular problem in areas of the world that are naturally low in iodine. Why might the human population include different variants of the hTAS2R38 gene?

Question

A.  Areas of high iodine are generally coastal, and turnips and broccoli are not easily grown there.
B.  Iodine created mutations in the hTAS2R38 gene.
C.  Where iodine was low, eating plants rich in glucosinolates helped people metabolize iodine, but where iodine was high they avoided such foods.
D.  Where iodine was low, it was important to avoid foods with glucosinolates, but where iodine was plentiful, palatability of a wider range of plants was beneficial.

Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

Gather Content
What do you already know about taste receptors? What other information is related to the question?

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?

Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

D.  Where iodine was low, it was important to avoid foods with glucosinolates, but where iodine was plentiful, palatability of a wider range of plants was beneficial.


Clarify Question
What is the key concept addressed by the question?
        · Why are there variants in human bitter receptors?
What type of thinking is required?
            o This is an evaluate question because you have to weigh and judge the different reasons that variability in a human bitter taste receptor exist.

Gather Content
What do you already know about taste receptors? What other information is related to the question?
        · You already know that taste receptors are specific to different types of chemical that elicit different flavors (sweet, salty, umami, bitter). You know that it is hypothesized that bitter receptors evolved to detect compounds that are toxic. Glucosinolates are found in plants like turnips and broccoli which activate hTAS2R38 receptors. Although eating such vegetables has nutritional benefits, the glucosinolates contained in them can also block synthesis and transport of iodine. If an individual’s diet is low in iodine, this could become a problem as blocking what little iodine the individual produces can lead to diseases such as goiter. If an individual’s diet is high in iodine, then glucosinolates may not cause a problem. Thus natural selection on receptors for glucosinolates would vary by geographical region and food supply.

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
        · The case study presented here does not present any evidence that iodine produces mutations in genes. As glucosinolates block the synthesis and transport of iodine, it could not help people metabolize iodine no matter what the iodine levels were in their food. It is true that areas of high iodine are coastal, whereas mountainous regions have had much of the iodine washed from the soil, but turnips and broccoli can grow well in coastal areas. Thus the answer is that in areas were iodine levels are low, it was important to avoid foods with glucosinolates so as to not block what little iodine was available to the body, whereas in areas of high iodine, eating a wider range of plants in the diet could be beneficial by providing additional fiber and nutrients.

Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o Answering this question correctly depended upon your ability to weigh or judge the potential benefits and costs of having a diet high in glucosinolates. If you answered incorrectly, which answer did you choose? Did you misunderstand that glucosinates could help people metabolize iodine instead of blocking its synthesis and transport? Did you think that plants high in glucosinolates, like turnips and broccoli, could not be grown in coastal areas?