现代教育理论认为:教学过程既是学生在教师的指导下的认知过程,又是能力的发展过程.因此教师要把主要的精力放在为学生创设学习情境,提供信息,引导学生积极思维上,教学难点无疑最能激发学生思维,教师对难点的预设无疑是提高学生的参与意识,从而提高学生的参与度的关键.科学教学中每一课时都有难点,教参中提到的难点范畴 The modern educational theory holds that the teaching process is not only the cognitive process but also the developing process of the ability of the students under the guidance of teachers.Therefore, teachers should focus their efforts on creating learning situations for students, providing information and guiding students’ positive thinking, It is undoubtedly the most difficult point of teaching to inspire students thinking, teachers presupposition of difficulty is undoubtedly improve students’ awareness of participation, thereby enhancing the participation of students the key to science teaching difficult in every class, teaching reference difficulties