问题 单项选择题

用纸层析法分离叶绿体中的色素,四种色素扩散速度最快和最慢的分别是()

A.叶绿素a;胡萝卜素

B.叶绿素b;胡萝卜素

C.胡萝卜素;叶绿素a

D.胡萝卜素;叶绿素b

答案

参考答案:D

解析:

色素在层析液中的溶解度不同,在滤纸条上的扩散速度快慢也不同,溶解度越大扩散速度越快,反之越慢。在滤纸条上,色素带从上至下,依次为胡萝卜素、叶黄素、叶绿素a、叶绿素b,所以胡萝卜素扩散速度最快,叶绿素b扩散速度最慢。

考点:考查叶绿素提取和分离实验结果。

选择题
阅读理解

阅读理解。

     I've loved my mother's desk since I was just tall enough to see above the top of it as Mother sat

doing letters. Standing by her chair, looking at the ink bottle, pens, and white paper, I decided that the

act of writing must be the most wonderful thing in the world.

     Years later, during her final illness, Mother kept different things for my sister and brother. "But the

desk," she'd said again, "is for Elizabeth. "

      I never saw her anger, never saw her cry. I knew she loved me; she showed it in action. But as a

young girl, I wanted heart-to-heart talks between mother and daughter.

      They never happened. And a gulf opened between us. I was too "emotional (另动感情的) ".  But

she lived "on the surface".

     As years passed, I had my own family, I loved my mother and thanked her for our happy family. I

wrote to her in careful words and asked her to let me know in any way she chose that she did forgive

(原谅) me.

     I posted the letter and waited for her answer. None came.

     My hope turned to disappointment, then little interest, finally, peace. It seemed that nothing happened.

I couldn't be sure that the letter had even got to Mother. I only knew I had written it, and I could stop

trying to make her into someone she was not.

     Now the present of her desk told me, as she'd never been able to, that she was pleased that writing

was my chosen work. I cleaned the desk carefully and found some papers inside-a photo of my father

and a one-page letter, folded (折叠) and refolded many times.

     Give me the answer, my letter asks, in any way you choose. Mother, you always chose the act that

speaks louder than words.

1. The writer began to love her mother's desk _____

A. after Mother died

B. before she became a writer

C. when she was a child 

D. when Mother gave it to her

2. The passage shows that _____  

A. Mother was cold on the surface but kind in her heart to her daughter

B. Mother was too serious about everything her daughter had done

C. Mother cared much about her daughter in words

D. Mother wrote to her daughter in careful words

3. The word "gulf" in the passage means _____ 

A. deep understanding between the old and the young

B. different ideas between the mother and the daughter

C. free talks between mother and daughter

D. part of the sea going far in land

4. What did Mother do with her daughter's letter asking for forgiveness? 

A. She had never received the letter.

B. For years, she often talked about the letter.

C.  She didn't forgive her daughter at all in all her life.

D. She read the letter again and again till she died.

5. What's the best title of the passage? 

A. My Letter to Mother

B. Mother and Children

C. My Mother's Desk

D. Talks Between Mother and Me