问题 单项选择题 A1型题

内毒素的主要成分是()。

A.肽聚糖

B.蛋白质

C.脂蛋白

D.核酸

E.脂多糖

答案

参考答案:E

解析:革兰阴性菌的细胞壁除了含有1~2层的肽聚糖结构外,尚有其特殊成分外膜。外膜由脂蛋白、脂质双层和脂多糖三部分组成。由脂质双层向细胞外伸出的是脂多糖(LPS),LPS由脂质A、核心多糖和特异多糖三部分组成,即革兰阴性菌的内毒素。故选E。

阅读理解

Apparently,we are safe neither at home nor in the business office.We use water in both places,but the research shows that chemicals added to our local water supply to kill harmful bacteria can have unwanted side effects.These chemicals can cause potential harm through drinking and in seemingly harmless activities as cleaning one’s house.They are released(set free)from water by daily actions like water running out of tap,spraying from garden pipes,or splashing in dishwashers and washing machines.As the water is moving.these chemicals are released into the air and then breathed in. Once inside our bodies, they start to affect our health.

Does this mean we should stop bathing? No, say the scientists, but we should put all pollution into perspective. Activities at home such as the burning of coal, cooking oil, or even candles release carbon monoxide and particulates such as cigarette ashes which have been proven as harmful to health as working or living near heavy traffic. New tugs, bedding, and even clothing give off that“new smell, ”which is a sure sign of chemicals. In the office, newly applied paint, newly purchased telephones and other telecommunications equipment, and computers release polluting chemicals, too. As offices and homes often have inadequate ventilation (通风), these chemicals can build up to become health problems. Their poisonous effects are only now being slowly recognized.

These facts suggest that, at a minimum, proper airing of newly purchased goods with an obvious chemical smell is a wise warning. Home and office windows should be opened during good weather. Even one’s car needs to be ventilated as well while in the garage.

We need further research to understand better other potential health dangers, too. For example, the effects of overcrowding of schools (carbon dioxide build-up ), the factory work environment ( an endless list of potentially dangerous substances ), and even home heating and cooling (the air conditioner may be our enemies, not our friends) have only recently started to come to light. Until we understand the effects of our new technological environment better, we can only hope that“there is no place like home.”

64.What is the main idea of the first paragraph?

A.The air we breathe in is harmful.

B.The water in everyday use is unsafe.

C.Chemicals are added to the drinking water.

D.Chemicals are released in the running water.

65.In Paragraph 2, the underlined sentence means that       .

A.bathing should be done with caution

B.homes and offices should be aired often

C.any pollution should be taken into consideration

D.we should prevent any pollution from doing harm to us

66.What is the purpose of the passage?

A.To call on us to guard our water.

B.To show us that no place is like home.

C.To make us aware of the pollution around us.

D.To argue that neither homes nor offices are safe.

单项选择题