题目

请回答下列有关细胞和分子生物学技术的问题： （1） DNA粗提取的实验原理是：DNA在不同浓度的NaCl溶液中的溶解度不同，在mol/L的NaCl溶液中的最低；鉴定DNA所用的试剂是，沸水浴加热呈色；实验中使用酒精的目的是；实验过程中两次用到蒸馏水，第一次目的是使成熟的鸡血红细胞涨破释放出DNA，第二次目的是。 （2） PCR技术的中文全称是，在操作过程中需要添加引物，它的化学本质是。反应过程中控制不同温度的意义是不同的： 90℃以上11．最近你和你的同学就"中学生目前存在的问题"展开了讨论． 现在请你以此为话题，参照表内提供的信息，写一篇短文．ProblemsCauses      Advice1．argue with parents-------- have a talk with parents，understand each other2．can't sleep wellbefore exams  anxious about grades--------3．feel lonely---------------注意：1．开头部分已写好，你只需接着写．2．所写内容必须包括表格中的信息，和你所补全的信息．3．词数：不少于80个．Recently I've had a discussion with my classmates about our problems．Some of my classmates say they often argue with their parents．That is because their parents always ask them to study and they feel they have no free time to d o what they like．If they have a talk with their parents，the y can understand each other．Some say they can't sleep well before exams because they are anxious about the grades．They should take a long walk to relax before going to bed．Some also say they feel lonely because they don't know how to make friends．As the only kid in the family，students should ta ke part in some after-school activities and learn to communicate with others．．