You should spend about 20 minutes on Questions 28-40, which are based on Reading Passage 3 below.
The Search for the Anti-aging Pill
In government laboratories and elsewhere, scientists are seeking a drug able to prolong life and youthful vigor. Studies of caloric restriction are showing the way
As researchers on aging noted recently, no treatment on the market today has been proved to slow human aging — the build-up of molecular and cellular damage that increases vulnerability to infirmity as we grow older. But one intervention, consumption of a low-calorie*yet nutritionally balanced diet, works incredibly well in a broad range of animals, increasing longevity and prolonging good health. Those findings suggest that caloric restriction could delay aging and increase longevity in humans, too.
Unfortunately, for maximum benefit, people would probably have to reduce their caloric intake by roughly thirty per cent, equivalent to dropping from 2,500 calories a day to 1,750. Few mortals could stick to that harsh a regimen, especially for years on end. But what if someone could create a pill that mimicked the physiological effects of eating less without actually forcing people to eat less? Could such a ‘caloric-restriction mimetic’, as we call it, enable people to stay healthy longer, postponing age-related disorders (such as diabetes, arteriosclerosis, heart disease and cancer) until very late in life? Scientists first posed this question in the mid-1990s, after researchers came upon a chemical agent that in rodents seemed to reproduce many of caloric restriction’s benefits. No compound that would safely achieve the same feat in people has been found yet, but the search has been informative and has fanned hope that caloric-restriction (CR) mimetics can indeed be developed eventually.
The benefits of caloric restriction
The hunt for CR mimetics grew out of a desire to better understand caloric restriction’s many effects on the body. Scientists first recognized the value of the practice more than 60 years ago, when they found that rats fed a low-calorie diet lived longer on average than free-feeding rats and also had a reduced incidence of conditions that become increasingly common in old age. What is more, some of the treated animals survived longer than the oldest-living animals in the control group, which means that the maximum lifespan (the oldest attainable age), not merely the normal lifespan, increased. Various interventions, such as infection-fighting drugs, can increase a population’s average survival time, but only approaches that slow the body’s rate of aging will increase the maximum lifespan.
The rat findings have been replicated many times and extended to creatures ranging from yeast to fruit flies, worms, fish, spiders, mice and hamsters. Until fairly recently, the studies were limited to short-lived creatures genetically distant from humans. But caloric-restriction projects underway in two species more closely related to humans — rhesus and squirrel monkeys — have made scientists optimistic that CR mimetics could help people.
calorie: a measure of the energy value of food
The monkey projects demonstrate that, compared with control animals that eat normally, caloric-restricted monkeys have lower body temperatures and levels of the pancreatic hormone insulin, and they retain more youthful levels of certain hormones that tend to fall with age.
The caloric-restricted animals also look better on indicators of risk for age-related diseases. For example, they have lower blood pressure and triglyceride levels (signifying a decreased likelihood of heart disease), and they have more normal blood glucose levels (pointing to a reduced risk for diabetes, which is marked by unusually high blood glucose levels). Further, it has recently been shown that rhesus monkeys kept on caloric-restricted diets for an extended time (nearly 15 years) have less chronic disease. They and the other monkeys must be followed still longer, however, to know whether low-calorie intake can increase both average and maximum life spans in monkeys. Unlike the multitude of elixirs being touted as the latest anti-aging cure, CR mimetics would alter fundamental processes that underlie aging. We aim to develop compounds that fool cells into activating maintenance and repair.
How a prototype caloric-restriction mimetic works
The best-studied candidate for a caloric-restriction mimetic, 2DG (2-deoxy-D-glucose), works by interfering with the way cells process glucose. It has proved toxic at some doses in animals and so cannot be used in humans. But it has demonstrated that chemicals can replicate the effects of caloric restriction; the trick is finding the right one.
Cells use the glucose from food to generate ATP (adenosine triphosphate), the molecule that powers many activities in the body. By limiting food intake, caloric restriction minimizes the amount of glucose entering cells and decreases ATP generation. When 2DG is administered to animals that eat normally, glucose reaches cells in abundance but the drug prevents most of it from being processed and thus reduces ATP synthesis. Researchers have proposed several explanations for why interruption of glucose processing and ATP production might retard aging. One possibility relates to the ATP-making machinery’s emission of free radicals, which are thought to contribute to aging and to such age-related diseases as cancer by damaging cells. Reduced operation of the machinery should limit their production and thereby constrain the damage. Another hypothesis suggests that decreased processing of glucose could indicate to cells that food is scarce (even if it isn’t) and induce them to shift into an anti-aging mode that emphasizes preservation of the organism over such ‘luxuries’ as growth and reproduction.
Do the following statements agree with the claims of the writer in Reading Passage 3?
In boxes 28-32 on your answer sheet, write
YES if the statement agrees with the claims of the writer
NO if the statement contradicts the claims of the writer
NOT GIVEN if it is impossible to say what the writer thinks about this
28 Studies show drugs available today can delay the process of growing old.
29 There is scientific evidence that eating fewer calories may extend human life.
30 Not many people are likely to find a caloric-restricted diet attractive.
31 Diet-related diseases are common in older people.
32 In experiments, rats who ate what they wanted led shorter liver than rats on a low-calorie diet.
Classify the following descriptions as relating to
A caloric-restricted monkeys
B control monkeys
C neither caloric-restricted monkeys nor control monkeys
Write the correct letter, A, B or C, in boxes 33-37 on your answer sheet.
33 Monkeys were less likely to become diabetic.
34 Monkeys experienced more chronic disease.
35 Monkeys have been shown to experience a longer than average life span.
36 Monkeys enjoyed a reduced chance of heart disease.
37 Monkeys produced greater quantities of insulin.
Complete the flow-chart below.
Choose NO MORE THAN TWO WORDS from the passage for each answer.
Write your answers in boxes 38-40 on your answer sheet.
How a caloric-restriction mimetic works
Less 38..............is processed
Production of ATP is decreased
Theory 1: Theory 2:
Cells less damaged by disease because Cells focus on 40..............because
fewer 39..............are emitted food is in short supply
关键词：drugs available today/ growing old
定位原文: 第1段第1句“As researchers on aging…”
关键词： eating fewer calories/ extend human life
定位原文: 第1段最后1句“Those findings suggest…”
解题思路: 这些研究结果表明，限制热量的摄取可能也会延缓衰老，延长人类寿命。” scientific evidence与findings是近义词，所以符合题干。
定位原文: 第2段第2句“Few mortals could…”
解题思路: 原文没有提到这个信息，所以是NOT GIVEN。
定位原文: 第3段第2句“… rats fed a low-calorie diet lived…”
解题思路: 被喂食低热量食物的鼠类平均寿命长于自由摄取食物的鼠类”，这里关键是知道free-feeding与ate what they wanted是同义表达。
关键词： less likely / diabetic
定位原文: 第6段第2句“...they have more normal blood…( pointing to a reduced risk for diabetes)” 血糖浓度也比较正常(表示得糖尿病的风险较低)。
解题思路: 这句话阐述的是calorie-restricted animal的情况，也就是calorie- restricted monkeys的情况，所以正确答案是A。
关键词：more chronic disease
定位原文: 第6段第3句“Further, it has recently…”
解题思路: 此外，有关研究最近指出，长期限制热量摄人(将近15年)的恒河猴患慢性病的几率也较低。rhesus monkeys与control monkeys 比较，前者患慢性病几率低，也就是说后者患慢性病几率高。正确答案是B。
关键词：a longer than average lifespan
定位原文: 第6段第4句: “They and other monkeys…” 但想要知道限制热量摄人是否会延长猴类的平均寿命和最大寿命，我们还必须对这些恒河猴以及其他猴类做更长时间的跟踪研究。
解题思路: They 指的是calorie-restricted mon?keys s other monkeys指的就是 control monkeys，原文既然说还需更多研究才能知道它们的寿命是否得到延长，也就是说两类猴都还没有表明寿命得到延长。正确答案是C。
关键词：reduced chance of heart disease
定位原文: 第6段第2句“For example, they have lower blood pressure and triglyceride levels (signifying a decreased likelihood of heart disease )…” 例如，它们的血压与甘油三酸酯含量都比较低(表示得心脏病的可能性较小)。
解题思路: 这句话阐述的是calorie-restricted animal的情况，也就是calorie- restricted monkeys的情况，所以正确答案是A。
关键词：greater quantities of insulin
定位原文: 第5段(就1句话)“..compared with control animals that eat normally, caloric-restricted monkeys have lower body temperatures and levels of the pancreatic hormone insulin.”比起正常饮食的对照组动物，限制热量摄人组猴子的体温和胰岛素浓度都较低。
关键词：production of ATP is decreased
定位原文: 第8段第2句“By limiting food intake, caloric restriction…” 通过限制食物的摄取量，可使进入细胞的葡萄糖降到最低，因此减少ATP的生成量。
解题思路: 通过 minimizes the amount of glucose 和 less … is processed 的同义转换关系很快选出答案应该是glucose。
答案： free radicals
定位原文: 第8段第5句“One possibility relates to the ATP-making…” 其中一种说法与ATP生成过程中自由基的释放有关，人们认为自由基会损伤细胞，因此引起衰老以及像癌症这类与衰老有关的疾病。
解题思路: 根据原文，free radicals促进 cancer之类的disease破坏细胞，所以free radicals越少，被疾病破坏的细胞就越少。即题目中给出的部分：cells less damaged by disease，所以答案为free radicals。
关键词： focus on
定位原文: 第8段最后1句“Another hypothesis suggests…” 另一种假设认为，葡萄糖代谢的降低让细胞以为食物不足(即使事实并非如此)，而促使细胞进人抗衰老的状态，这种状态着重的是维持……
解题思路: emphasize与focus on属于同义表达，scarce与in short supply属于同义表达，所以对应答案为preservation。