图甲表示胚芽鞘受到单侧光的照射,图乙表示不同浓度生长素溶液对胚芽鞘切段生长的影响,如果图甲中b处的生长素浓度为m,则a处的生长素浓度x的范围值为( )。
- A.n<x<i
- B.m<x<n
- C.m<x<i
- D.x>i
正确答案及解析
正确答案
解析
甲图为胚芽鞘,给予右侧单侧光照射,在单侧光的作用下,胚芽鞘尖端的生长素发生横向运输,所以a侧生长素浓度高于b侧;乙图表示不同浓度生长素溶液切去尖端的胚芽鞘生长的影响,i浓度之前的浓度都是促进生长;i浓度既不促进,也不抑制;i浓度之后的浓度都起抑制作用。在单侧光的作用下,生长素向背光侧横向运输,导致向光侧生长素浓度小于背光一侧,所以x>m。根据向光性导致胚芽鞘向光弯曲生长则a侧的生长速度大于b侧,则a侧的生长素浓度应小于n即x
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