About fifty years ago, plant
physiologists set out to grow roots by themselves in solutions in laboratory
flasks. The scientists found that the nutrition of isolated roots was quite
simple. They required sugar and the usual minerals and vitamins. However, they
did not require organic nitrogen compounds. These roots got along fine on
mineral inorganic nitrogen. Roots are capable of making their own proteins and
other organic compounds. These activities by roots require energy, of course.
The process of respiration uses sugar to make the high energy compound ATP,
which drives the biochemical reactions. Respiration also requires oxygen. Highly
active roots require a good deal of oxygen. The study of
isolated roots has provided an understanding of the relationship between shoots
and roots in intact plants. The leaves of the shoots provide the roots with
sugar and vitamins, and the roots provide the shoots with water and minerals. In
addition, roots can provide the shoots with organic nitrogen compounds. This
comes in handy for the growth of buds in the early spring when leaves are not
yet functioning. Once leaves begin photosynthesizing, they produce protein, but
only mature leaves can "export" protein to the rest of the plant in the form of
amino acids.
单选题
What is the main topic of the passage?
【正确答案】
A
【答案解析】[分析] 主旨题型。
见本文主旨句，第二段第一句：The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants．(第一段谈的是the study of isolated roots；第二段谈的是the relationship between shoots and roots)：因此选项A应为答案。
单选题
The underlined word "themselves" in Paragraph 1 refers to ______.
【正确答案】
A
【答案解析】[分析] 细节题型。
见第一段第一句：About fifty years ago，plant physiologists set out to grow roots by themselves．in solutions in laboratory flasks．这里指plant physiologists自己培育根用作物：因此themselves在此应为正确选项。
单选题
The scientists found what the isolated roots need is ______.
【正确答案】
B
【答案解析】[分析] 细节题型。
见第一段第三句：They required sugar and the usual minerals and vitamins．所以选项B是答案。
单选题
Roots have the ability to ______.
【正确答案】
A
【答案解析】[分析] 细节题型。
见第一段第六句：Roots are capable of making their own proteins and other organic compounds．所以选项A是答案。
单选题
According to the passage, what is ATP?
【正确答案】
C
【答案解析】[分析] 推断题型。
第一段提到(块)根需要sugar and the usual minerals and vitamins，但不需要 organic nitrogen compounds，因(块)根可自造所需的蛋白质和其它organic compounds；这里反复提到的organic compounds应包括the high energy compound ATP(见第一段倒数第二句)；因此可推断出选项C(一种化合物)为答案。
单选题
The underlined word "intact" in Paragraph 2 is closest in meaning to ______.
单选题
The use of the phrase "comes in handy" underlined in Paragraph 2 indicates that the process is ______.
【正确答案】
C
【答案解析】[分析] 词义题型。
见第二段第四句：This comes in handy for the growth of buds in the early spring when leaves are not yet functioning．这对于芽(蓓蕾)在早春的生长很是必要，因为叶在那时还没有起作用。所以comes in handy应表“必要”，所以选项 C为答案。
单选题
It can be inferred from the passage that, in the early spring, the buds of plants ______.