问题 选择题

通过实验,你发现下列物质能通过透析袋的是(  )

A.淀粉

B.蛋白质

C.脂肪

D.葡萄糖

答案

当血液流经肾小球时,肾小球对血液具有过滤作用,红细胞和大分子的蛋白质不能过滤到肾小囊腔中,而血透机的血液透析原理和肾小球对血液的过滤作用相似,血液与透析液可通过分隔该两种液体的半透膜,通常是将半透膜制成袋状,将生物大分子样品溶液置入袋内,将此透析袋浸入水或缓冲液中,样品溶液中的大分子量的生物大分子被截留在袋内,而小分子物质不断扩散透析到袋外,直到袋内外两边的浓度达到平衡为止.保留在透析袋内未透析出的样品溶液称为“保留液”,袋(膜)外的溶液称为“渗出液”或“透析液”.透析袋具有选择透过性,只能让小分子的物质,如葡萄糖、维生素、无机盐、尿素透过,而不能让大分子的物质如淀粉、蛋白质、脂肪以及血细胞等透过.

故选D

阅读理解

阅读理解

       Experts say that students usually need eight to ten hours' sleep at night , but more Chinese students

do not get enough sleep. Some Chinese parents are usually glad to see their children studying late. They

will think their children work very hard. But not all parents are happy about this. Once a mother told us

that every morning her 10-year-old boy put up one finger with his eyes still closed ,begging(央求) for

one more minute to sleep . Like thousands of student "early birds" in China, he has to get up before six

every morning.

       A report shows that a good night's sleep , students seem to be weaker than they should be. Many

students have fallen asleep during class at one time or another. Too much homework is not the only reason why students stay up late . Some watch TV or play the computer games late into the night.

       Experts have ever said that students should develop good study habits. So some clever students

never study late, they are able to work well in class.

1. The 10-year-old boy begged for one more minute to sleep because_____.

A. he didn't have enough sleep  

B. it wasn't time for him to get up

C. he didn't want to go to school

D. he wanted his mother to wake him up

2. In this passage "early birds" means persons who ______.

A. get up early  

B. get up late    

C. sleep less    

D. don't want to sleep

3. From the passage we know if students don't get enough sleep, they may ______.

A. become too weak to sleep  

B. not work well in class

C. go to bed early        

D. be weak in English

4. "Stay up late "here means _____.

A. study late                   

B. watch TV late

C. not go to bed until late        

D. stay outside

5. According to the passage , which of the following is right ?

A. If you want to study better, you must work hard

B. Sleeping less means working hard

C. Some clever students can work well in class because they have good study habits.

D. Students don't have enough sleep only because they have a lot of homework to do.

单项选择题