题干

某兴趣小组拟用组织培养繁殖一种名贵花卉,其技术路线为“取材→消毒→愈伤组织培养→出芽→生根→移栽”.下列有关叙述,错误的是(    )

A:消毒的原则是既杀死材料表面的微生物,又减少消毒剂对细胞的伤害

B:在愈伤组织中加入适宜浓度的PEG,可诱导细胞发生融合

C:出芽是细胞再分化的结果,受基因选择性表达的调控

D:生根时,培养基通常应含α﹣萘乙酸等生长素类调节剂

上一题 下一题 0.0难度 选择题 更新时间:2017-08-15 12:03:02

答案(点此获取答案解析)

B

同类题3

完形填空

    The four famous rock stars were due to arrive at any moment and a large crowd of young people had gathered at the airport to welcome them.The police found it difficult to keep the crowd under1after the plane landed and the performers appeared.They smiled and waved2at everybody.Dressed in pink shirts and light blue trousers,and with their long hair and their musical instruments3their shoulders,the four young men looked very much4.

    In spite of the large number of policemen5,it was clear that the group would not be able to get to their waiting car6.Word had got out that they had written a new song which would be7when they performed at the grand hall that evening.They were now8with crying of “Play something! Play your new song!”

    Even the police looked9when the young men unfolded their instruments and prepared to do one of their numbers as the10for getting out of the airport.The crowd settled down and listened to the first11of the new song. As soon as it was over,there was a great burst of applause and then everyone started12and shouting like crazy. Several young women fainted and had to be carried away by the13unit which was standing by.Greedy for more, the crowd14a repeat performance.Once again the performers gave in,but when the crowd requested still another song,the group cheerfully but firmly15.

    Now closely surrounded by the police,they put away their16and stared towards their car which was some distance away.The crowd pushed forward,but the policemen,17arm in arm,prevented anyone from getting through. It took the singers a long time to reach their18.Finally,however,they got in and were just about to drive away when a young woman,who had19to get past the police,jumped onto the roof of the car.She shouted loudly as two policemen20her away and the car began moving slowly through the cheering crowd.

同类题4

阅读短文,回答问题.

逆温现象

      太阳短波辐射能穿过大气层到达地球表面,一部分被地球吸收,一部分被反射回太空去.地球吸收太阳短波辐射能后,地球变暖,温度升高.它一方面以长波形式向大气辐射热量,一方面又以对流、传导方式把热量传送给大气.

       一般情况下,大气温度随着高度增加而下降.在数千米以下,总是低层大气温度高,高层大气温度低.大气层容易发生上下翻滚,可将近地面层的污染物向高空乃至远方输散,从而使城市空气污染程度减轻.可是在某些天气条件下,地面上空的大气结构会出现气温随高度增加而升高的反常现象,从而导致大气层层次结构稳定,气象学家称之为“逆温杉,发生逆温现象的大气层称为“逆温层乃.它像一层厚厚的被子罩在我们城乡上空,上下层空气减少了流动,近地面层大气污染物“无路可走“,越积越多,空气污染势必加重.

       导致逆温现象的原因有多种.在我国冬季,当寒流袭击过后,地面受冷气团控制,容易出现逆温现象.白天日照不足,地面增温缓慢,还会使逆温维持.夏天,海水温度较低,也会形成逆温.空气污染中毒事件大都与逆温有关.如果连续出现几天逆温,空气污染物就会大量积累,易发生空气污染中毒事件.可以说,逆温现象是雾霾形成的帮凶.

      这种逆温现象还会使物体反射的光,在冷暖更迭的逆温层中传播时发生扭曲,产生蜃景.据研究推测,当年的泰坦尼克号从温暖的暖流区驶入寒冷的拉布拉多洋流区,就处于一个逆温层中.事故发生前,观察员没有及时发现冰山,是因为平静的海面把实际地平线和错误的地平线之间的区域遮掩了起来,使冰山得以潜影遁形.在冰山大概只有一英里远的时候,泰坦尼克号的一名望员才拉响了警报,全力倒车(指向前航行的轮船,螺旋桨反转,产生与前进方向相反的推力),但也为时已晚.

       逆温现象也非一无是处,它对遏制沙尘天气,以及农业生产都有有利的一面.