Question

Birds that are half-asleep—with one brain hemisphere (半球) alert and the other sleeping—control which side of the brain remains awake, according to a new study of sleeping ducks.

Earlier studies have documented half-brain sleep in a wide range of birds. The brain hemispheres take turns sinking into the sleep stage characterized by slow brain waves. The eye controlled by the sleeping hemisphere keeps shut, while the wakeful hemisphere’s eye stays open and alert. Birds also can sleep with both hemispheres resting at once.

Decades of studies of bird groups led researchers to predict extra alertness in the end-of-the-row sleepers which tend to be attacked more easily. Sure enough, the end birds tended to watch carefully on the side away from their companions. Ducks in the inner spots showed no preference for gaze direction.

Also, birds napping at the end of the line depend on single-hemisphere sleep, rather than total relaxation, more often than inner ducks did. Turning 16 birds through the positions in a four-duck row, the researchers found that compared with 12% for birds in inner spots, outer birds half sleep during some 32% of napping time.

“We believe this is the first evidence for an animal behaviorally controlling sleep and wakefulness at the same time in different regions of the brain,” the researchers say.

The results provide the best evidence for a long-standing assumption that single-hemisphere sleep evolved when creatures scanned for enemies. The preference for opening an eye on the lookout side could be widespread, he predicts. He’s seen it in a pair of birds napping side by side in the zoo and in a single pet bird sleeping by a mirror. The mirror-side eye closed as if the reflection were a companion and the other eye stayed open.

Useful as half-sleeping might be, it’s only been found in birds and such water animals as dolphins, whales, and seals. Perhaps keeping one side of the brain awake allows a sleeping animal to surface occasionally to avoid drowning.

Studies of birds may offer unique insights(理解) into sleep. Jerome M. Siegel of the UCLA says he wonders if birds’ half-brain sleep “is just the tip of the iceberg.” He supposes that more examples may turn up when we take a closer look at other species.

1.According to the passage, birds often half sleep because _________________________.

A. they have to watch out for possible attacks

B. their brain hemispheres take turns to rest

C. the two halves of their brain are differently structured

D. they have to constantly keep an eye on their companions

2.What does the underlined word “evolved” mean in paragraph 6?

A. developed         B. changed

C. disappeared       D. helped

3.What is implied about the example of a bird's sleeping in front of a mirror?

A. Birds prefer to sleep in pairs for the sake of their security.

B. An imagined companion gives the bird a sense of security.

C. The phenomenon of birds napping in pairs is widespread.

D. A single pet bird enjoys seeing its own reflection in the mirror.

4.While sleeping, some water animals tend to keep half awake in order to _________________.

A. alert themselves to the approaching enemy

B. surface from water now and then to breathe

C. be sensitive to the ever-changing environment

D. avoid being swept away by rapid currents

5.It can be inferred that _______________________.

A. birds never sleep with both hemispheres resting at once.

B. inner ducks depend on single-hemisphere sleep, rather than total relaxation, as often as birds napping at the end of the line do.

C. it is not the first time for scientists to research on birds’ half-brain sleep

D. birds hardly sleep without a companion

6. By saying “just the tip of the iceberg”, Siegel suggests that _________________________.

A. half-brain sleep has something to do with icy weather

B. the mystery of half-brain sleep is close to being solved

C. most birds living in cold regions tend to be half sleepers

D. half-brain sleep may exist among other species

Answer

1.A

2.A

3.B

4.B

5.C

6.D

【解析】

试题分析:研究表明鸟和我们人类的睡眠不一样。因为鸟的左右两个半脑轮流休息睡眠以保持警戒。研究人员大胆推测，可能还有其他物种的睡眠方式是这样的。

1.A推理判断题。根据第二段的the wakeful hemisphere’s eye stays open and alert可知，鸟儿是要时刻保持警觉，注意有可能的危险。故选A。

2.A词义推测题。根据单词所在的句子的意思可知，从单一睡眠到大脑左右半脑轮流休息以去关注周围可能存在的危险，这是进化而不能简单地说是改变。故选A。

3.B 推理判断题。根据The mirror-side eye closed as if the reflection were a companion and the other eye stayed open.可知，靠近镜子一边的眼睛闭上了，而另一只眼睛一直睁着，说明假想的伴侣给了鸟一些安全感。故选B。

4.B 细节理解题。根据倒数第二段的…to surface occasionally to avoid drowning可知，水里的动物睡觉时把一侧的大脑放在水面是为了防止溺水，选B

5.C 推理判断题。根据第一段的a new study 和第二段的Earlier studies可知，对鸟的这种睡眠方式的研究早有研究。一只鸟会大脑左右半脑轮流休息，一群鸟则有在外侧的警觉性更高，而在里面的则差一些。故排除其他选C。

6.

考点：考查科普类短文阅读。