题目

    We have known for a long time that flowers of different plants open and close at different time of day. Yet no one really understands why flowers open and close like this at particular times. It is not as simple as we might think, as new experiments have shown. In one experiment, flowers were kept in darkness. We might expect that the flowers, without any information about the time of the day, did not open as they usually do. In fact, they continued to open at their usual time. This shows that they have some mysterious (神秘的) way of knowing the time.      Their sense of17．如图为维持内环境稳态的部分结构示意图．请据图回答问题：（1）人在进食时，食物刺激产生的兴奋通过迷走神经引起脾液分泌胰液的反射属非条件反射，在此过程中，兴奋在迷走神经纤维上的传导方向是单向性（填“单向”或“双向”）；当该处迷走神经刚产生兴奋时，其膜内的Na+浓度变化是变多．（2）英国科学家斯他林和贝利斯还研究发现，小肠黏膜产生促胰液素也能引起胰腺分泌胰液，该调节方式与迷走神经促进胰腰分泌胰液的方式不同之处有：反应速度比较较缓慢、作用范围比较较广泛、作用时间比较长等．