2020年2月20日雅思阅读真题+题目+答案：Biology of Bitterness

2020年2月20日雅思阅读真题+题目+答案：Biology of Bitterness

To many people, grapefruit is palatable only when doused in sugar. Bitter Blockers like adenosine monophosphate could change that.

A.

There is a reason why grapefruit juice is served in little glasses: most people don’t want to drink more than a few ounces at a time. aringin, a natural chemical compound found in grapefruit, tastes bitter. Some people like that bitterness in small doses and believe it enhances the general flavor, but others would rather avoid it altogether. So juice packagers often select grapefruit with low naringin though the compound has antioxidant properties that some nutritionists contend may help prevent cancer and arteriosclerosis.

B.

It is possible, however, to get the goodness of grapefruit juice without the bitter taste. I found that out by participating in a test conducted at the Linguagen Corporation, a biotechnology company in Cranbury, New Jersey. Sets of two miniature white paper cups, labeled 304and 305, were placed before five people seated around a conference table. Each of us drank from one cup and then the other, cleansing our palates between tastes with water and a soda cracker. Even the smallest sip of 304 had grapefruit ‘s unmistakable bitter bite. But 305 was smoother; there was the sour taste of citrus but none of the bitterness of naringin. This juice had been treated with adenosine monophosphate, or AMP, a compound that blocks the bitterness in foods without making them less nutritious.

C.

Taste research is a booming business these days, with scientists delving into all five basics-sweet, bitter, sour, salty, and umami, the savory taste of protein. Bitterness is of special interest to industry because of its untapped potential in food. There are thousands of bitter -tasting compounds in nature. They defend plants by warning animals away and protect animals by letting them know when a plant may be poisonous. But the system isn’t foolproof. Grapefruit and cruciferous vegetable like Brussels sprouts and kale are nutritious despite-and sometimes because of-their bitter-tasting components. Over time, many people have learned to love them, at least in small doses. “Humans are the only species that enjoys bitter taste,” says Charles Zuker, a neuroscientist at the University of California School of Medicine at San Diego. “Every other species is averse to bitter because it means bad news. But we have learned to enjoy it. We drink coffee, which is bitter, and quinine [in tonic water] too. We enjoy having that spice in our lives.” Because bitterness can be pleasing in small quantities but repellent when intense, bitter blockers like AMP could make a whole range of foods, drinks, and medicines more palatable-and therefore more profitable.

D.

People have varying capacities for tasting bitterness, and the differences appear to be genetic. About 75 percent of people are sensitive to the taste of the bitter compounds phenylthiocarbamide and 6-n-propylthiouracil. and 25 percent are insensitive. Those who are sensitive to phenylthiocarbamide seem to be less likely than others to eat cruciferous vegetables, according to Stephen Wooding, a geneticist at the University of Utah. Some people, known as supertasters, are especially sensitive to 6-n-propylthiouraci because they have an unusually high number of taste buds. Supertasters tend to shun all kinds of bitter-tasting things, including vegetable, coffee, and dark chocolate. Perhaps as a result, they tend to be thin. They’re also less fond of alcoholic drinks, which are often slightly bitter. Dewar’s scotch, for instance, tastes somewhat sweet to most people. ” But a supertaster tastes no sweetness at all, only bitterness,” says Valerie Duffy, an associate professor of dietetics at the University of Connecticut at Storrs.

E.

In one recent study, Duffy found that supertasters consume alcoholic beverages, on average, only two to three times a week, compared with five or six times for the average nontasters. Each taste bud, which looks like an onion, consists of 50 to 100 elongated cells running from the top of the bud to the bottom. At the top is a little clump of receptors that capture the taste molecules, known as tastants, in food and drink. The receptors function much like those for sight and smell. Once a bitter signal has been received, it is relayed via proteins known as G proteins. The G protein involved in the perception of bitterness, sweetness, and umami was identified in the early 1990s by Linguagen’s founder, Robert Margolskee, at Mount Sinai School of Medicine in New York City. Known as gustducin, the protein triggers a cascade of chemical reactions that lead to changes in ion concentrations within the cell. Ultimately, this delivers a signal to the brain that

registers as bitter. “The signaling system is like a bucket brigade,” Margolskee says. “It goes from the G protein to other proteins.”

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Questions 1-8

The reading Passage has seven paragraphs A-I.

Which paragraph contains the following information?

Write the correct letter A-I, in boxes 1-8 on your answer sheet.

1 Experiment on bitterness conducted

2 Look into the future application

3 Bitterness means different information for human and animals

4 Spread process of bitterness inside of body

5 How AMP blocks bitterness

6 Some bitterness blocker may help lower unhealthy impact

7 Bitterness introduced from a fruit

8 Genetic feature determines sensitivity

Question 9-12

Complete the following summary of the paragraphs of Reading Passage, using no more than two words from the Reading Passage for each answer. Write your answers in boxes 9-12 on your answer sheet.

The reason why grapefruit tastes bitter is because a substance called 9【】 contained in it. However, bitterness plays a significant role for plants. It gives a signal that certain plant is 10 【】. For human beings, different person carries various genetic abilities of tasting bitterness. According to a scientist at the University of Utah, 11 【】 have exceptionally plenty of 12 【】, which allows them to perceive bitter compounds.

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