问题 解答题

为探究细菌对植物遗体有何影响,我们活动小组的同学们分别提出了三种实验方案.三种方案的共同点是:将同一种树的落叶分成甲乙两组.实验过程中滴加蒸馏水,使树叶保持潮湿.

方案一:将甲组放在无菌条件下,乙组放在自然条件下(暴露在空气中);方案二:将甲组灭菌后放在无菌条件下,乙组放在自然条件下;方案三:将甲乙两组都进行灭菌处理,甲组放在无菌条件下,乙组接种细菌后放在无菌条件下.

请回答问题,再评价实验方案:

(1)甲乙两组为什么要用相同的树叶?______.

(2)为什么要使树叶保持潮湿?______.

(3)请评价以上哪个实验方案更能说明问题,并说出理由.______.

答案

(1)因为这个实验方案的目的是研究细菌对植物遗体的分解作用,所以在设置对照组时,要控制其他可能影响实验结果的条件.即除了有无细菌的条件不同外,其他条件都应该相同,因此甲乙两组要用相同的树叶.

(2)由于细菌适宜生活在潮湿的环境中.因此实验过程中滴加蒸馏水,使树叶保持潮湿.不可以用自来水来代替,因为自来水中含有细菌,对实验结果有影响.

(3)方案三更能说明问题.因为实验前对照组与实验组所处的条件完全相同(都进行灭菌处理);而实验后,除单一变量(接种与不接种)外,对照组与实验组又处于相同的条件下(无菌的条件).可见,只有方案三排除了所有影响实验的干扰.因此,与方案一和方案二比较,方案三的实验结果更有说服力.

故答案为:(1)为了保证除实验变量外的其他条件都相同;(2)细菌适宜生活在潮湿的环境中;(3)方案三,方案除实验变量外,其他条件完全相同.

阅读理解

阅读理解。

    Have you ever heard of the saying, "If you want a friend, be one." 

    What does it mean? There are many different things that you can do to make friends. You may find out

what they are if you watch someone make friends. Here is how one new teacher made friends with the

students in her class on the first day of the school. When the bell rang, the teacher smiled at all the students.

Then she said, "Good morning. How nice it is to have all of you in my class this year! I want to know each

of you very much. I am sure we will enjoy working together." The teacher smiled, used a pleasant voice,

and acted in a friendly way. She told the students her name and wrote it on the blackboard. Then she told

them something she liked to do and hoped to do with them during the year. The students knew that she liked

many of the same things they liked. Everyone felt that she meant what she said. Each of them wanted to

know her better and be her friend. Then she let the students tell something about themselves. So they felt

that the teacher knew them. 

     Could you make friends as the teacher did? How do you know and like your classmates? One way is to

find out more about them. During the break you can talk to them. You may ask them their names and the

names of the schools they went to last year. They want to know about you, too. You may tell them about

your interests or your holiday experiences. It is often easy to be friends with people who have the same

interests and play the same games. As you talk, the others may be thinking, "I like to do the same things you

do. It should be fun to be friends with you." Remember! Just talking together in a friendly way is one good

way to make friends.

1. Which do you think is the best title for this passage? [ ]

A. Making Friends

B. How to Talk to Others

C. A Talk in Class

D. With the Teacher in Class

2. How did the teacher get the students to feel that she would be a good friend? [ ]

A. She laughed at each boy and girl and told them many things she knew.

B. She told the students many things she liked to do.

C. She laughed and made the students only to know her well in a friendly way.

D. She talked and acted in a friendly way to let the students know she really wanted to be friends with them.

3. If you want to make friends with others, you should ______.[ ]

A. tell others as many things you like as possible during the break

B. try your best to show what you can do for them in class

C. talk with them to find out more about them in a friendly way

D. ask them to have dinner with you and play games with you after class

4. "Everyone felt that she meant what she said" means that ______.[ ]

A. every student in her class felt that she really liked them

B. everyone in her class understood what the teacher said

C. all the students thought it was nothing telling them these

D. everybody felt tired when they heard what the teacher said

选择题