除病毒外，生物都是由______构成的，它是生物体结构和功能的基本单位．
生物的特征主要有：①生物的生活需要营养；②生物能进行呼吸；③生物能排出身体内产生的废物；④生物能对外界刺激作出反应；⑤生物能生长和繁殖；⑥生物都有遗传和变异的特性；⑦除病毒以外，生物都是由细胞构成的．生物体具有共同的物质基础和结构基础．从化学组成上说，生物体的基本组成物质中都有蛋白质和核酸，其中蛋白质是生命活动的主要承担者，核酸贮存着遗传信息．从结构上说，除病毒外，生物体都是由细胞构成的，细胞是生物体结构和功能的基本单位．
故答案为：细胞．
| 完形填空。 | ||||
| Eight ways to have a good school-life Your schooldays should be some of the best and happiest days of your 1 . How can you get the 2 from them, and ensure you do not 3 this wonderful opportunity (机会) to learn? 1 Be positive (积极) about school! Don't say things are difficult or 4 . Be interested in school-life and your school subjects. Join lots of activities. Be quick to put your hand up. Go round the school with a big smile. 2 Expect to work. School is not a holiday camp. If you are not working, you are not learning, and you are wasting your time at school. Teachers cannot make everything 5 . 3 Keep fit. If you do not eat a good breakfast, you will be thinking about 6 in class. If you go to bed 7 and do not have enough sleep, you will be sleepy in class. Play some sports to keep your body strong. 4 Do today's work today. Do not say you will do things 8 . if you get 9 the class, it is very difficult to get back in front. You cannot finish a race if you rest all the time. 5 Don't be too disappointed if things sometimes go 10 . Everyone fails some tests, loses some matches and has bad days. Friends are not always perfect, and they sometimes say and do 11 things. Don't let small problems seem very big and important. 6 Talk about problems-sometimes they are only the result of misunderstanding. Don't be too embarrassed (窘迫) to ask for help. You are young. No one thinks you can do 12 ! 7 Plan your time. Don't waste life 13 in bed on Saturday morning. Go and play a sport, learn the piano, work on a project, read a book, practice English, or help someone 14 problems. There are always a lot of things to do. 8 Set targets (目标). If your last grade was a D, work for a C. Try to make 15 bit by bit. Think of small targets:"I will speak in class four times this week", "I will finish my project on Wednesday" or "I will get two more marks this week" Follow our advice, and have a happy school-life!
|