题目内容
Winter is the toughest season for grasses and flowers to survive in desert.
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Sleep Lets Brain File Memories
To sleep. Perchance to file？ Findings published online this week by the proceedings of the National Academy of Sciences further support the theory that the brain organizes and stows memories formed during the day while the rest of the body is catching zzz's.
Gyorgy Buzsaki of Rutgers University and his colleagues analyzed the brain waves of sleeping rats and mice. Specifically, they examined the electrical activity emanating(散发) from the somato-sensory (耳、目、口等以外的) neocortex (新大脑皮层) (an area that processes sensory information) and the hippocampus(海马), which is a center for learning and memory. The scientists found that oscillations in brain waves from the two regions appear to be intertwined. So-called sleep spindles (bursts of activity from the neocortex) were followed tens of milliseconds later by beats in the hippocampus known as ripples. The team posits that this interplay between the two brain regions is a key step in memory consolidation.
A second study, also published online this week by the proceedings of the National Academy of Sciences, links age-associated memory decline to high glucose levels.
Previous research had shown that individuals with diabetes(糖尿病，多尿症) suffer from increased memory problems. In the new work, Antonio Convit of New York University School of Medicine and his collaborators studied 30 people whose average age was 69 to investigate whether sugar levels, which tend to increase with age, affect memory in healthy people as well. The scientists administered recall tests, brain scans (细看，审视，浏览，扫描) and glucose tolerance tests, which measure how quickly sugar is absorbed from the blood by the body's tissues. Subjects with the poorest memory recollection, the team discovered, also displayed the poorest glucose tolerance. In addition, their brain scans showed more hippocampus shrinkage than those of subjects better able to absorb blood sugar.
"Our study suggests that this impairment (损害、损伤) may contribute to the memory deficits (赤字、不足额) that occur as people age. " Convit says. "And it raises the intriguing possibility that improving glucose tolerance could reverse some age-associated problems in cognition. " Exercise and weight control can help keep glucose levels in check(阻止、制止), so there may be one more reason to go to the gym.
Which of the following statements is nearest in meaning to the sentence "To sleep. Perchance to file？"
A．to confrontB．confrontedC．confrontingD．being confronted
Plants in Desert
Only special plants can survive the terrible climate of a desert, for these are regions where the annual range of the soil temperature can be over 75℃. Furthermore, during the summer there are few clouds in the sky to protect plants from the sun's ray. Another problem is the fact that there are frequently strong winds which drive small, sharp particles of sand into the plants, tearing and damaging them. The most difficult problem for all forms of plant life, however, is the fact that the entire annual rainfall occurs during a few days or weeks in spring.
Grasses and flowers in desert survive from one year to the next by existing through the long, hot, dry season in the form. of seeds. These seeds remain inactive unless the right amount of rain falls. If no rain falls, or if insufficient rain falls, they wait until the next year, or even still the next. Another factor that helps these plants to survive is the fact that their life cycles are short. By the time that the water from the spring rains disappears—just a few weeks after it falls—such plants no longer need any.
The perennials have special features which enable them to survive as plants for several years. Thus, nearly all desert perennials have extensive root systems below ground and a small shoot system above ground. The large root network enables the plant to absorb as much water as possible in a short time. The small shoot system, on the other hand, considerably limits water loss by evaporation.
Another feature of many desert perennials is that after the rainy season they lose their leaves in preparation for the long, dry season, just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season. Then, in next rainy season, they come fully alive once more, and grow new branches, leaves and flowers, just as the grasses and flowers in desert do.
Ordinary plants are unable to survive in the desert mainly because of the changeable weather.
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