题目

任务型阅读     Maybe Snoopy is the coolest dog in the world; maybe Snoopy is one of the greatest kids on two legs. He is a happy-go-luck(逍遥自在的)dog everyone loves.     Snoopy is the pet of Charlie Brown, whose name Snoopy could never remember. For Snoopy, his master is just “that round-headed kid” who brings him his meals.     Snoopy never speaks, but he can make himself understood by using facial expressions(面部表情)and thought balloons(思想泡泡).    ①In Snoopy’s little head, he is everything but a dog. Since 1960s, Snoopy has been standing on two某实验小组为了探究细胞膜的通透性，将小鼠肝细胞在体外培养一段时间后，检测培养液中的氨基酸．葡萄糖和尿素含量，发现它们的含量发生了明显变化（如下图）。请回答问题。    （1）由图可知，随培养时间延长，培养液中葡萄糖和氨基酸含量________，尿素含量________。由于在原培养液中没有尿素，推测其是________的产物。    （2）培养液中的氨基酸进入细胞后，其主要作用是_____________________________；被吸收的葡萄糖主要通过________作用，为细胞提供__________。    （3）转氨酶是肝细胞内参与氨基酸分解与合成的一类酶，正常情况下这类酶不会排出胞外，若在细胞培养液中检测到该类酶，可能的原因是_____________________。    （4）由（1）和（3）可初步判断，细胞膜对物质的转运具有__________________的特性。