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  3. Bacteria are microscopic organisms which live on the surface of objects. They are one of the most ancient living things, which e

Bacteria are microscopic organisms which live on the surface of objects. They are one of the most ancient living things, which e

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问题     Bacteria are microscopic organisms which live on the surface of objects. They are one of the most ancient living things, which exist on this planet for nearly 4,000 million years. Do you know the size of bacteria? It can only be measured in microns. Maybe you have not a standard in your mind how long a micron is. One micron is a thousandth of a millimeter, which equals about the diameter of a pinhead. Therefore, even if we enlarged the rounded bacterium a thousand times, it would only be the size of a pinhead. We barely see bacteria by a magnification an ordinary microscope of 100 times, even if we try, we cannot make out anything of their structure. There are normally millions of them together, for they can multiply really fast.
    Scientists have found that some bacteria have attached to wavy-looking "hairs" called flagella. The flagella rotate, pushing the bacteria through the water. Others can glide along over surfaces by some little-understood mechanism. Bacteria are so small that they are influenced by the movements of the chemical molecules around them. They are active all the time. Even the bacteria without flagella often bound about in the water. They are pushed here and there, colliding with the watery molecules.
    Bacteria cannot be detected because they don’t produce bad odor or change the color or texture of the food. Therefore, when people eat the food with many bacteria, they are likely to get hepatitis A, acute gastroenteritis and a host of other illnesses. Many households have refrigerators to prevent from bacteria. Of course, freezing food slows or stops the growth of bacteria, however, when food is thawed, the bacteria will become reactivated. Bacteria can not be totally destroyed before the food is thoroughly cooked. We need to know that not all bacteria are in connection with illness. Just some bacteria can cause disease. They are called pathogenic bacteria. Fortunately our immune system can protect us from them.
    Bacteria are prokaryotes ( single cells that do not contain a nucleus). It may seem weird to classify organisms according to such details, but with or without a nucleus is not trivial at all. The division between prokaryotes and eukaryotes (all organisms with a nucleus inside their cells) is of extreme importance in biology, and is the result of a major evolutionary breakthrough. Visit our program tomorrow if you want to know more, thank you.
Which statement is not true about flagella?
选项 A、Flagella are part of bacteria.
B、Flagella help bacteria to move.
C、Flagella are always going round and round.
D、Flagella are like waves.
答案A
解析 根据第二段第一句中“some bacteria have attached to wavy-looking ’hairs’ called flagella”可见，细菌是附着在鞭毛上的，鞭 毛并不是细菌内部的组成部分，A项不符合文意。根据该句中“wavy-looking hairs”可见鞭毛的外表呈波浪状，D项正确。根据第二段第 二句“The flagella rotate, pushing the bacteria through the water.”可见，鞭毛可以推动细菌在水中行进，B项正确。根据该句的前半句可知，鞭毛的运动方式是旋转式的，C项正确。故正确答案为A选项。
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