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They are used(用来)for jumping. They also have long strong tails(尾巴)used for resting on. Kangaroos’ front legs are much shorter, and are almost ___3___ arms. Kangaroos' heads are quit e small, but their ears are ___4___.Mother kangaroos have a pocket at the front. They have ___5___ baby each year. When it is born, the baby kangaroos goes. straight ___6___ its mother's pocket. The baby kangaroos stay there ___7___ six months. The biggest kangaroos stand more than 2 meters ___8___ ,and their legs are so strong that they can ___9___ more than 9 meters. They are very fast, and can travel at more than 50 kilometers an hour. They are very strong, but only ___10___ fruit, leaves and grass.
1. ( )
A. ways B. kinds
C. animals D. colors
2. ( )
A. has B. there are
C. use D. have
3. ( )
A.1ike B. 1ikes
C. have D. big
4. ( )
A. quite small B. quite large
C. very Small D. not big
5. ( )
A. one B. pocket
C. arm D. kangaroos
6. ( )
A. on B. into
C. up D. out
7. ( )
A. in B. for
C. all D. after
8. ( )
A. small B. big
C. long D. tall
9. ( )
A. fly B. run
C. jump D. walk
10. ( )
A. drink B. eat
C. pick D. play with
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实验一:将空白琼脂和含EDTA的琼脂做成帽状,分别套在甲、乙两组玉米胚根的根冠外(示意图如下)。提示:EDTA的作用是去除与其临接部位的 Ca2+。
将胚根水平放置培养一定时间后,观察到甲组胚根向重力(下)生长,乙组胚根水平生长。根据上述实验结果,得出实验结论: 。
实验二:水平放置的胚根弯曲向下生长,与根冠近地侧的Ca2+浓度明显高于远地侧有关。研究表明,根总是朝着Ca 2+浓度高的方向弯曲生长。为验证这一结论,有人设计了下列实验方案。请根据提供的实验材料和用具,写出第二步及以后的实验步骤和实验结果,并回答问题。
(1)实验材料和用具:胚根等长的萌发玉米种子,空白琼脂帽,含EDTA的琼脂帽,上面部分含Ca2+的琼脂帽(水平方向),培养皿等。
(2)实验步骤:
第一步:取若干个培养皿,在每个培养皿中放置适量的萌发玉米种子,按实验一中乙组的方法处理胚根一定时间后,移去根冠外的琼脂帽。然后将培养皿平均分成两组,编号为 A组、B 组。
第二步: 。
第三步: 。
(3)实验结果: 。
(4)科学家进一步证实,根冠中生长素的分布受Ca2+浓度影响,当胚根水平放置时,重力诱导Ca2+向根冠下侧移动,导致近地侧的生长素浓度比远地侧高。请分析胚根的生长素分布与向重力生长的关系: 。 查看习题详情和答案>>
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