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问题 单项选择题

组成细胞膜的主要成分是（）

A.脂质、蛋白质、糖类

B.糖脂、糖蛋白

C.脂质、蛋白质、无机盐

D.脂质、蛋白质、核酸

答案

参考答案：A

解析：细胞膜主要由脂质、蛋白质和少量糖类组成，脂质中磷脂最丰富，功能越复杂的细胞膜，蛋白质种类和数量越多；细胞膜基本支架是磷脂双分子层。所以组成细胞膜的主要成分是脂质、蛋白质、糖类。故选A。考点：细胞的结构和功能点评：本题难度一般，要求学生识记细胞的结构和功能的相关知识，考查学生对组成细胞膜的主要成分的理解。

单项选择题

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 withorganic 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.

What is the main topic of the passage

A．The relationship between a plant’s roots and its shoots.

B．What can be learned by growing roots in isolation.

C．How plants can be grown without roots.

D．What elements are necessary for the growth of plants.
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单项选择题

脾破裂手术处理通常采用

A．脾破裂缝合修补术

B．脾部分切除术

C．脾移植术

D．脾切除术

E．大网膜填塞止血术
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