题干

某同学设计的渗透装盆实验如图所示(开始时状态),烧杯中盛放有蒸馏水.图中猪膀胱膜允许单糖透过.倒置的长颈漏斗中先装人蔗糖溶液一段时间后再加入蔗糖酶(微量).有关该实验描述正确的是(  )

A:漏斗中液面开始时先上升.加酶后即下降

B:漏斗中液面先上升,加酶后继续上升.然后下降.最后保持内外液面基本相平

C:漏斗中液面先上升,加酶后继续上升,然后保持一定的液面差不变

D:加酶后在烧杯中可检侧出的有机物仅有葡萄糖

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答案(点此获取答案解析)

B

同类题3

阅读下列短文,根据短文内容选择最佳答案。

                                                                           C

    Flying is a fast way to travel. But it is a big headache for some people. They can't help worrying about things like, “Is turbulence (颠簸) a bad thing?” or, “Is it dangerous if we don't change our mobile phones to flight mode (飞行模式)?” British newspaper Daily Mail spoke to some experts to answer these questions. They also tell us other interesting things about flying.

    Is turbulence dangerous?

    It's scary and uncomfortable. But it is not something you really need to worry about.

    Turbulence is caused when two groups of air hit one another at different speeds. Wind, thunderstorms (暴风雨) and being close to mountains can be reasons for this.

    You may feel like turbulence is dangerous, but it won't crash (坠毁) your plane. “Even in extremely rough air (扰动气流), the wings (机翼) are not going to break off,” explained Patrick Smith, an airline pilot, who is also an air travel blogger and author of Ask The Pilot. com.

    Why are plane windows round?

    Round windows are for passenger safety.

    As the airplane flies higher and higher, the outside atmospheric pressure (气压) gets lower and lower. During the flight, the pressure inside the plane becomes greater than the pressure outside.

    When this happens, square windows can break. That's because having different pressures inside and outside puts pressure on the corners of square windows. But rounded corners can spread the pressure through the window.

    What happens when a phone isn't on flight mode?

    Some passengers believe mobile phones and tablets need to be turned off because they could bring the plane down. However, this is not true.

    If you don't change your phone to flight mode, pilots and air traffic controllers may hear unpleasant sounds in their headphones. It also influences radio communications. So it's still best to put it on flight mode.