问题 多项选择题

以紫色洋葱鳞片叶外表皮为实验材料观察植物细胞质壁分离现象,下列叙述正确的是()

A.细胞在发生质壁分离时能观察到紫色中央液泡逐渐缩小

B.质量浓度30%的蔗糖溶液比质量浓度10%的蔗糖溶液,发生质壁分离所需的时间更长

C.滴加清水后,质壁分离的细胞又复原,说明此细胞是活细胞

D.用任何浓度的NaCl溶液代替蔗糖溶液都不能引起细胞质壁分离

答案

参考答案:A, C

解析:细胞在发生质壁分离时由于液泡中水分外流,导致液泡体积缩小,故A正确。质量浓度30%的蔗糖溶液比质量浓度10%的蔗糖溶液,渗透压高,细胞液中的水分更快流出道蔗糖溶液,故发生质壁分离时间更短,故B错。死亡的细胞无法发生质壁分离复原,故C正确。主要是浓度比细胞液病毒大的NaCl溶液都会引起质壁分离,只不过会自动复原,故D错。

完形填空
完形填空。
      Helen was seven years old. One day one of her teeth began to hurt. She     1    in class at school, and her teacher       2    kindly," What's the matter, Helen?"
      "One of my teeth hurts," answered Helen.
      "Tell your mother about        3  ," said the teacher, "and then go to see the dentist. "
      That afternoon Helen told her mother about her tooth, and her mother      4   her to the dentist's a few hours    5   . The dentist looked at the tooth and then said to Helen. "It's very      6          . I'm going to pull it    7   , and then you're going to get a new tooth. It will be as nice as   8    next year. " Then he did it with no trouble.
       The next day Helen's teacher asked her about the tooth. She said to her,  " Does it    ______9     hurt, Helen?"
       "I don't know. You'd better ask the dentist," Helen answered.
       "Why?" the teacher asked.
       "Because the dentist has   10   it," Helen answered
( )l. A. cried    
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( )6. A. hurt      
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( )8. A. the other
( )9. A. much      
( )10.A. kept      
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D. them        
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