You have learned that dissolved materials always diffuse from where there is more of them to where there is less. Oxygen from the air dissolves in the moisture on the lining of the air sac and diffuses through the lining into the blood. Meanwhile, carbon dioxide diffuses from the blood into the air sac. The blood then flows from the lungs back to the heart, which sends it out to all other parts of the body. Soon after air goes into an air sac, it gives up some of its oxygen and takes in some carbon dioxide from the blood. To keep diffusion going as it should, this carbon dioxide must be gotten rid of. Breathing, which is caused by movements of the chest, forces the used air out of the air sacs in your lungs and brings in fresh air. The breathing muscles are controlled automatically so that you breathe at the proper rate to keep your air sacs supplied with fresh air. Ordinarily, you breathe about twenty-two times a minute. Of course, you breathe faster when you are exercising and slower when you are resting. Fresh air is brought into your lungs when you breathe in, or inhale, while used air is forced out of your lungs when you breathe out, or exhale. 26. In the respiratory process, only one of the following actions takes place: it is_______. A. the diffusion of blood through capillary walls into air sacs B. the diffusion of carbon dioxide through capillary and air sac walls into the blood C. the diffusion of oxygen through the air sac and capillary walls into the blood D. the exchange of nitrogen within air sacs 27. The number of times per minute that you breathe is_______. A. independent of your rate of exercise B. fixed at twenty-two times per minute C. influenced by your age and sex D. controlled automatically by an unspecified body mechanism 28. The process by which carbon dioxide and oxygen are transferred does not depend on A. the presence of nitrogen in the blood B. breathing muscles C. the flow of blood D. the moisture in the air sac linings 29. The authors style in this passage can best be described as---------. A informal and matter of fact B. impersonal C. personal P- matter of fact and formal 30. Which of the following words can replace the word exhale? A. Breathe out. B. Breathe in. C. Diffuse. D. Exchange.
中考英语词汇“美味水果”大聚会
初中英语语法几大基本时态讲与练(3)
中考英语常用词组及句型100例二
中考英语介词知识点精讲大全
初中英语8种时态归纳复习
中考英语考前语法复习
初中英语常用动词习惯用法72例三
how long,how often与how soon的区别
初中英语:since的四种用法
初中英语语法几大基本时态讲与练(5)
中考英语复习词组攻略二
中考英语重点句型43例二
初中英语九大简单基本句型
初中英语语法几大基本时态讲与练(1)
初中英语语法几大基本时态讲与练(2)
英语完型填空老是做不好,如何提高?
初中英语:比较since和for
2014中考英语真题专项练习:连词(40)
中考英语常用词组及句型100例四
初中生容易混淆拼错的英文单词二
中考英语基础练习之动词的时态1
2014中考英语专项练习:补全对话(4)
中考病句题金题精炼及参考答案
中考英语语法:使用比较等级的三点注意
容易误用作及物动词的9个不及物动词
中考英语阅读猜词6大法宝
中考英语完形填空四步法
初中生容易混淆拼错的英文单词三
初中英语语法几大基本时态讲与练(4)
猪流感英语词汇
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |