单选题
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 free 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】[解析] 本题考查主旨大意。根据第一段内容可知，文章讲述的是对isolated roots的研究；根据文章第二段第一句“The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants.”可知，对isolated roots的研究提供了shoots and roots之间的关系。所以，答案是A。
单选题
The underlined word "themselves" in Paragraph 1 refers to ______.
【正确答案】
A
【答案解析】[解析] 本题考查细节理解。根据文章第一段第一句“About fifty years ago, plant physiologists set out to grow roots by themselves in solutions in laboratory flasks.”可知，themselves在这里指plant physiologists。所以，答案是A。
单选题
The scientists found what the isolated roots need is ______.
【正确答案】
B
【答案解析】[解析] 本题考查细节理解。根据文章第一段第三句“They required sugar and the usual minerals and vitamins.”可知，isolated roots需要的是sugar, minerals和vitamins。所以，答案是B。
单选题
Roots have the ability to ______.
【正确答案】
A
【答案解析】[解析] 本题考查细节理解。根据文章第一段第六句“Roots are capable of making their own proteins and other organic compounds.”可知，本题答案是A。
单选题
According to the passage, what is ATP?
【正确答案】
C
【答案解析】[解析] 本题考查细节理解。根据第一段倒数第二句“The process of respiration uses sugar to make the high energy compound ATP”可知，ATP是一种高能量化合物。所以，答案是C。
单选题
The underlined word "intact" in Paragraph 2 is closest in meaning to ______.
【正确答案】
C
【答案解析】[解析] 本题考查词义理解。解题点在于第二段第一句“The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants.”句意为：对于分离出的根所做的研究提供了对完整植物中根和芽的关系的理解。intact“完整的”；mature“成熟的”；wild“野生的”；whole“整体的”；tiny“微小的”。比较可知，答案是C。
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】[解析] 本题考查词义理解。根据文章第二段第四句“This comes in handy for the growth of buds in the early spring when leaves are not yet functioning.”可知，这对于芽在早春的生长很是必要，在那时叶还没有起作用。所以comes in handy应表“必要”，unavoidable“不可避免的”；predictable“可预测的”；necessary“必要的”；successful“成功的”。比较可知，答案是C。
单选题
It can be inferred from me passage that, in the early spring, the buds of plants ______.
【正确答案】
D
【答案解析】[解析] 本题考查推理判断。根据第二段第三、四句“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.”可知，根能为芽提供有机氮，这对于芽在早春的生长很是必要，因为叶在那时还没有起作用。由此可知，早春时，植物的芽是从根处获得有机化合物的。所以，答案是D。
单选题
Which of the following best describes the organization of the passage?