论文部分内容阅读
讲授根对水分的吸收时,首先要讲清细胞吸水原理。这个实验可以由学生动手做,改教材中的“挖洞”为“切块”,效果较好。具体做法如下:课前三天应准备好新鲜萝卜、饱和食盐水、清水、100或150ml的烧杯2只、小刀等。取萝卜切成截面为2×4厘米左右的四棱柱体,长度略高于烧杯,将此萝卜块从中央纵切一刀,但不能完全劈开。取两只大小相同的烧杯,分別装入饱和食盐水和清水,其水量为烧杯高度的2/3—3/4。把两烧杯排放在一起并调整水量,使两烧杯液面相平,划出水面高度记号。把剖开的萝卜块卡进两个烧杯中,使其中的一边浸入饱和食盐液中,一边浸在清水中(图1)。结
To teach root absorption of moisture, we must first clarify the principle of cell water absorption. This experiment can be done by students, to change the teaching of “digging holes” as “cut”, the effect is better. Specific practices are as follows: three days before class should be prepared fresh radish, salt water, water, 100 or 150ml beaker 2, a knife and so on. Take radish cut into sections of about 2 × 4 cm quadrangular prism, the length slightly higher than the beaker, the radish block longitudinal cut a knife, but can not be completely split. Take two beakers of the same size, filled with saturated salt water and fresh water, respectively, and the amount of water is 2/3 - 3/4 of the height of the beaker. Discharge the beakers together and adjust the amount of water so that the two beakers are level and draw a mark of water’s height. Snap cut carrot pieces into two beakers, so that one of them is immersed in fresh water while immersed in saturated salt solution (Figure 1). Knot