问题 解答题

为研究甲状腺激素对蝌蚪发育的影响,某同学制定了如下实验方案:

①将两只塑料盆分别标注为“甲“和“乙”.

②在两只塑料盆中分别加入2000ml的新鲜自来水.然后分别放入同种同时孵化的、体长约15mm的蝌蚪各5只.

③甲塑料盆内加入甲状腺激素5mg和新鲜金鱼藻;乙塑料盆内加入甲硫咪唑(甲状腺抑制剂)5mg和新鲜茨藻.

④在甲、乙两只塑料盆中连续投药7天,每天一次,药量相同.每天喂适量食物,每两天换水一次.

⑤每天用小网将蝌蚪捞出放在培养皿中,再将培养皿放在坐标纸上(1mm×1mm)测量蝌蚪体长变化、前后肢生长情况、尾的变化等.连续观察10~20天,把测量的结果记录在实验报告册上.

请据此分析回答:

(1)上述实验方案中有三处明显的错误,请予以指出:

①______

②______

③______

(2)观察到的甲塑料盆内的蝌蚪发育周期明显______,这说明甲状腺激素具有促进______的作用.

答案

(1)一个探究实验中只能有一个实验变量,其他因素均处于相同理想状态,这样便于排除因其他因素的存在而影响、干扰实验结果的可能.方案一中只有一个变量,可证明甲状腺激素具有促进幼年动物个体发育的作用.所以①增加一个缸编号为丙,不加任何激素.②新鲜自来水有氯气不利蝌蚪生长,故饲养蝌蚪不能用新鲜自来水,③放入脸盆的藻类也应相同.

(2)甲状腺激素具有促进新陈代谢和生长发育,提高神经系统的兴奋性.观察到的甲脸盆内的蝌蚪体长变化情况是体长增加较快,尾长变化情况是尾长缩短较快,四肢出现得比较早,发育周期明显缩短,这说明甲状腺激素具有促进幼小动物生长发育的作用.

故答案为:(1)①缺少一个正常的对照组 ②饲养蝌蚪不能用新鲜自来水③放入脸盆的藻类应相同.(2)缩短; 促进幼小动物生长发育

单项选择题
完形填空

It is nice to know what the weather will be like when we plan a trip. Do you know anything about the history of weather? Don’t look at the sky. Don’t look for old weather reports. Looking at the tree rings is more important. Correct weather reports date back only one century, but some trees can provide an exact record of weather even further back.

It is natural that a tree would grow best in a climate with plenty of sunlight and rainfall. It is also expected that little sunlight or rainfall would reduce the growth of a tree. The change from a favorable to an unfavorable climate can be found out by the reading pattern of rings in a tree trunk. To find out the weather of ten years ago, you can count the rings of a tree trunk from the outside to the inside. If the tenth ring is far from the other rings, then it is certain that plenty of sunny and rainy weather occurred. If the rings are close together, then the climate was bad for the tree.

Studying trees is important not only for the history of weather, but also for the history of man. In an area of New Mexico you can find only sand — no trees or people. However, many centuries ago a large population lived there. They left suddenly. Why?

A scientist studied the pattern of the rings of dead trees that had grown there. He made up his mind that the people had to leave because they had cut down all the trees. Trees were necessary to make fires and buildings. So, after the people destroyed the trees, they had to move.

In this example studying tree rings uncovered an exciting fact about the history of man.

小题1:We can find out the weather of five years ago by counting the rings of a tree trunk ____.

A.from the left to the right

B.from the right to the left

C.from the inside to the outside

D.from the outside to the inside小题2:If the ring was far from the others, we can conclude that the weather of that year was ______.

A.bad

B.sunny

C.favorable

D.rainy小题3:By studying the rings of dead trees in an area of New Mexico, the scientist found _______.

A.why the people had to leave

B.where the people had to go

C.what the people had to eat

D.how the people left小题4:The ancient people usually lived where there were plenty of trees mainly because ______.

A.trees provided an exact record of weather for research

B.trees could supply them with fruit and food to live on

C.trees could supply them with shades

D.trees were materials for fires and buildings小题5:By giving the example of an area of New Mexico, the author tries to prove        .

A.trees can’t live in the area without population

B.that studying trees is important for the history of man and weather.

C.what the real relation is between tree rings and the history of man and weather

D.the history of man is important for the history of trees