题干

下列不属于单细胞生物的是(  )

A:狗

B:酵母菌

C:草履虫

D:衣藻

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A

同类题1

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    The insects are important to farmers. When a honeybee lands on a flower in plant, pollen (花粉) sticks to its legs. When the bee lands on another flower, some of the pollen falls off and fertilizes the second plant.

    The act of spreading pollen is responsible for many fruits, vegetables, nuts and other crops. Yet about 30 percent of honeybees in the United States and other areas have died in recent years.

    Mike Leggett is a researcher at the University of Maryland. He wants to learn why so many bees are dying. “The number of colonies (蜂群) that die every winter has been one in three. So on average 30 percent of the colonies have died every winter over the last six winters. And that's a huge number.” His research team examined the pollen that honeybees carried to their homes. They found that the pollen contained high levels of 35 different pesticides (杀虫剂), which are chemicals used to protect plants. “Pesticides are used, and have been used, pretty widely, for centuries, to protect plants from diseases,” says Mr Leggett.

    Keith Oh linger, a farmer and beekeeper in Maryland, has watched many of his bees die every winter. Mr Ohlinger thinks widespread bee death is caused by several things happening at once. But he does not feel sure that pesticides are a part of the problem, “I felt it was the result of a lot of little things. I didn't feel that there was probably one smoking gun. But there's a division (分歧) there, some people feel that it is just one thing.”

    Honeybees are important to agriculture. This makes the search for an answer to their death very important for Mr Leggett's team. As he knows, one in every three bites of food we eat is somehow pollinated by honeybees.

同类题4

阅读下文,回答相关问题。
        去除饮水中可能致命的细菌或许会成为纳米管最早的实际用途之一。
        科研人员已经研制出能让细菌聚结成块的纳米管,随后就可以将菌块从水中滤出,并消灭它们。他们进行的实验很容易用于实践。
        南加州克来姆森大学负责此项研究的孙亚平说,这种纳米管最初或可以用作水净化处理厂的过滤器。他的研究成果发表在最新一期的《化学通讯》杂志上。
        新研制的纳米管能捕捉大肠杆菌O157:H7,即臭名昭著的“汉堡细菌”,被它污染的肉可能置食客于死地。他给纳米管表面覆上一层半乳糖分子,而半乳糖分子能与大肠杆菌表面的受体蛋白粘合。每根纳米管都覆有数以百计的半乳糖分子,因此能一举拿下大量细菌。
        该研究小组还研制了能捕捉污染事物的另一种常见细菌――空肠弯曲杆菌――的纳米管。这种细菌多见于肌肉之中。这一次纳米管的表面富有甘露糖分子,它能与空肠弯曲杆菌表面的受体蛋白粘合。孙说:“我们正在研制富有能捕捉不同细菌的多种配位体‘糖’的纳米管。这是可行的。”
        研究者认为,从理论上说,这种纳米管可以用于将细菌从患者的血液中滤出,不过它们必须首先经过试验,排除任何毒副作用的可能。英国史密斯叔侄公司的彼得·阿诺得说:“将来,类似于这类碳纳米管的交互性生物材料有望选择性地捕捉和消灭致病细菌。”该公司是一家医疗技术公司,正在研制能加快组织修复的生物材料。
        研制临床诊断用的纳米材料的英国奥克斯尼卡公司的凯文·马修斯说,孙的工作是传统无机化学与生物化学相结合的极好例子,二者结合“提供的可能性超越了其中任何一种单独所能提供的可能性。”

                                                                                                                                                            摘自2005年3月12日《参考消息》
       注:“半乳糖”和“甘露糖”是配位体糖的两个具体种类。