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2008-08-05 10:00  来源:     我要纠错 打印 收藏   

Eat to Live

  A meager diet may give you health and long life, but it's not much fun—and it might not even be necessary. We may be able to hang on to most of that youthful vigor even if we don't start to diet until old age.

  Stephen Spindler and his colleagues from the University of California at Riverside have found that some of an elderly mouse's liver genes can be made to behave as they did when the mouse was young simply by limiting its food for four weeks. The genetic rejuvenation won't reverse other damage caused by time for the mouse, but could help its liver metabolize drugs or get rid of toxins.

  Spindler's team fed three mice a normal diet for their whole lives, and fed another three on half-rations. Three more mice were switched from the normal diet to half-feed for a month when they were 34 months old—equivalent to about 70 human years.

  The researchers checked the activity of 11,000 genes from the mouse livers, and found that 46 changed with age in the normally fed mice. The changes were associated with things like inflammation and free radical production—probably bad news for mouse health. In the mice that had dieted all their lives, 27 of those 46 genes continued to behave like young genes. But the most surprising finding was that the mice that only started dieting in old age also benefited from 70 per cent of these gene changes.

  “This is the first indication that thee effects kick in pretty quickly,” says Huber Warner from the National Institute on Aging near Washington, D. C.

  No one yet knows if calorie works in people as it does in mice, bus Spindler is hopeful. “There's attracting and tempting evidence out there that it will work,” he says.

  If it does work in people, there might be good reasons for rejuvenating the liver. As we get older, out bodies are les efficient at metabolizing drugs, for example. A brief period of time of dieting, says Spindler, could be enough to make sure a drug is effective.

  But Spindler isn't sure the trade-off is worth it. “The mice get less disease, they live longer but they're hungry,” he says. “Even seeing what a diet does, it's still hard to go to a restaurant and say: 'I can only eat half of that'.”

  Spindler hopes we soon won't need to diet at all. His company, Life Span Genetics in California, is looking for drugs that have the effects of calorie restriction.

  1. According to the passage, which of the following is NOT true?
  A. Eating less than usual might make us live longer.
  B. If we go on a diet when old, we may keep healthy.
  C. Dieting might not be needed.
  D. We have to begin dieting from childhood.

  2. Why does the author mention an elderly mouse in paragraph 2?
  A. To describe the influence of old age on mice.
  B. To illustrate the effect of meager food on mice.
  C. To tell us how mice's liver genes behave.
  D. To inform us of the process of metabolizing drugs.

  3. What can be inferred about completely normally fed mice mentioned in the passage?
  A. They will not experience free radical production.
  B. They will experience more genetic rejuvenation in their lifetime.
  C. They have more old liver genes to behave like young genes.
  D. They are more likely to suffer from inflammation.

  4.According to the author, which of the following most interested the researchers?
  A. The mice that started dieting in old age.
  B. 27 of those 46 old genes that continued to behave like young genes.
  C. Calorie restriction that works in people.
  D. Dieting that makes sure a drug is effective.

  5.According to the last two paragraphs, Spindler believes that
  A. calorie restriction is very important to young people
  B. seeing the effect of a diet, people will eat less than normal.
  C. dieting is not a go0d method to give us health and a long life.
  D. drugs do not have the effects of calorie restriction.

Single-parent Kids Do Best

  Single mums are better at raising their kids than two parents—at least in the bird world. Mother zebra finches have to work harder and raise fewer chicks on their own, but they also produce more attractive sons who are more likely to get a mate.

  The finding shows that family conflict is as important an evolutionary driving force as ecological factors such as hunting and food supply. With two parents around, there's always a conflict of interests, which can have a detrimental effect on the quality of the offspring.

  In evolutionary terms, the best strategy for any parent in the animal world is to find someone else to care for their offspring, so they can concentrate on breeding again. so it's normal for parents to try to pass the buck to each other. But Ian Hartley from the University of Lancaster and his team wondered how families solve this conflict, and how the conflict itself affects the offspring.

  To find out, they measured how much effort zebra finch parents put into raising their babies. They compared ingle females with pairs, by monitoring the amount of food each parent collected, and removing or adding chicks so that each pair of birds was raising four chicks, and each single mum had two—supposedly the same amount of work.

  But single mums, they found, put in about 25 per cent more effort than females rearing with their mate. To avoid being exploited, mothers with a partner hold back from working too hard if the father is being lazy, and it's the chicks that pay the price. “The offspring suffer some of the cost of this conflict,” says Hartley.

  The cost does not show in any obvious decrease in size or weight, but in how attractive they are to the opposite sex. When the chicks were mature, the researchers tested the “fitness” of the male offspring by offering females their choice of partner. Those males reared by single mums were chosen more often than those from two-parent families.

  Sexual conflict has long been tough to affect the quality of care given to offspring, says zoologist Rebecca Kilner at Cambridge University, who works on conflict of parents in birds. “But the experimental evidence is not great. The breakthrough here is showing it empirically.”

  More surprising, says Kilner, is Hartley's statement that conflict may be a strong influence on the evolution of behaviour, clutch size and even appearance. “People have not really made that link,” says Hartley. A female's reproductive strategy is usually thought to be affected by hunting and food supply. Kilner says conflict of parents should now be taken into account as well.

  1. With which of the following statements would the author probably agree?
  A. Single mums produce stronger sons.
  B. Single mums do not produce daughters.
  C. Two-parent families produce less attractive children.
  D. Two-parent families produce more beautiful offspring.

  2.According to the passage, in what way does family conflict affect the quality of the offspring?
  A. The young males get less care.
  B. The young females will decrease in weight.
  C. The offspring will become lazy fathers or mothers in the future.
  D. the offspring will not get mature easily.

  3.What is the relationship between paragraph 4 and paragraph 5?
  A. Cause and effect.
  B. Experiment and result.
  C. Problem and solution.
  D. topic and comment.

  4. According to Hartley, which of the following is NOT influenced by sexual conflict?
  A. The evolution of the offspring's behaviour.
  B. The look of the offspring's faces.
  C. the number of eggs produced by one offspring at a time.
  D. The offspring's body size.

  5.According to the passage, people believe that a female's reproductive strategy is influenced by
  A. an evolutionary driving force.
  B. a conflict of interests.
  C. ecological factors.
  D. the quality of the offspring.

Food Fright

  Experiments under way in several labs aim to create beneficial types of genetically modified (GM) foods, including starchier potatoes and caffeine-free coffee beans. Genetic engineers are even trying to transfer genes from a cold-water fish to make a frost-resistant tomato.

  A low-sugar GM strawberry now in the works might one day allow people with health problems such as diabetes to enjoy the little delicious red fruits again. GM beans and grains supercharged with protein might help people at risk of developing kwashiorkor, Kwashiorkor, a disease caused by severe lack of protein, is common in parts of the world where there are severe food shortages.

  Commenting on GM foods, Jonathon Jones, a British researcher, said: “The future benefits will be enormous, and the best is yet to come.”

  To some people, GM foods are no different from unmodified foods. “A tomato is a tomato,” said Brian Sansoni, an American food manufacturer.

  Critics of GM foods challenge Sansoni's opinion. They worry about the harm that GM crops might do to people, other animals, and plants.

  In a recent lab study conducted at Cornell University, scientists tested pollen made by Bt corn, which makes up one-fourth of the U. S. corn crop. The scientist sprinkled the pollen onto milkweed, a plant that makes a milky juice and is the only known food source of the monarch butterfly caterpillar. Within four days of munching on the milkweed leaves, almost half of a test group of caterpillars had died. “Monarchs are considered to be a flagship species for conservation, ”said Cornell researcher Linda Raynor. “This is a warning bell.”

  Some insects that are not killed by GM foods might find themselves made stronger. How so? The insecticides used to protect most of today's crops are sprayed on the crops when needed and decay quickly in the environment. But GM plants produce a continuous level of insecticide. Insect species feeding on those crops may develop resistance to the plants and could do so in a hurry, say the critics. Insects may also develop a resistance to the insecticide Bt.

  At the forum on GM food held last year in Canada. GM crops that have been made resistant to the herbicide might crossbreed with wild plants, creating “superweeds” that could take over whole fields.

  So where do you stand? Should GM foods be banned in the United States, as they are in parts of Europe? Or do their benefits outweigh any of the risks they might carry?

  1. Paragraphs 1, 2 & 3 tries to give the idea that
  A. GM foods may bring about great benefits to humans.
  B. we cannot recognize the benefits of GM foods too early.
  C. GM foods may have both benefits and harm.
  D. GM foods are particularly good to the kwashiorkor patients.

  2. Why is the case of the pollen-sprayed milkweed cited in Paragraph 6?
  A. It is cited to show GM foods can kill insects effectively.
  B. It is cited to show GM foods contain more protein.
  C. It is cited to show GM foods also have a dark side.
  D. It is cited to show GM foods may harm crops.

  3. What happens to those insects when not killed by the spray of insecticide?
  A. They may lose their ability to produce offspring.
  B. They may have a higher ability to adapt to the environment.
  C. They move to other fields free from insecticide.
  D. They never eat again those plants containing insecticide.

  4. Which of the following statements concerning banning GM foods is true according to the passage?
  A. Underdeveloped countries have banned GM foods.
  B. Both Europe and the U. S. have banned GM foods.
  C. Most European countries have not banned GM foods.
  D. The United States has not banned GM foods.

  5. What is the writer's attitude to GM foods?
  A. We cannot tell from the passage.
  B. He thinks their benefits outweigh their risks.
  C. He thinks their risks outweigh their benefits.
  D. He thinks their benefits and risks are balanced.

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