问题 问答题 简答题

C3途径可分为哪三个阶段?各阶段的作用是什么?C4植物与CAM植物在碳代谢途径上有何异同点?

答案

参考答案:

C3途径可分为羧化、还原、再生3个阶段。

(1)羧化阶段指进入叶绿体的CO2与受体RuBP结合,生成PGA的过程。

(2)还原阶段指利用同化力将3-磷酸甘油酸还原为甘油醛-3-磷酸的反应过程。

(3)再生阶段甘油醛-3-磷酸重新形成核酮糖-1,5-二磷酸的过程。

CAM植物与C4植物固定与还原CO2的途径基本相同,二者都是由C4途径固定CO2,C3途径还原CO2,都由PEP羧化酶固定空气中的CO2,由Rubisco羧化C4二羧酸脱羧释放的CO2,二者的差别在于:C4植物是在同一时间(白天)和不同的空间(叶肉细胞和维管束鞘细胞)完成CO2固定(C4途径)和还原(C3途径)两个过程;而CAM植物则是在不同时间(黑夜和白天)和同一空间(叶肉细胞)完成上述两个过程的。

阅读理解

People believe that climbing can do good to health. Where can you learn the skill of climbing then? If you think that you have to go to the mountains to learn how to climb, you’re wrong. Many Americans are learning to climb in city gyms(体育馆). Here, people are learning on climbing. The climbing wall goes straight up and small holding places for hands and feet.

How do people climb the wall? To climb, you need special shoes and (保护带) around your chest to hold you. There are ropes(绳索)tied to your. The ropes hold you in place so that you don’t fall. A beginner’s wall is usually about 15 feet high, and you climb straight up. There are small pieces of metal that stick out for you to stand on and hold on to. Sometimes it’s easy to see the new piece of metal. Sometimes, it’s not. The most difficult is your fear. It’s normal for humans to be afraid of falling, so it’s difficult not to feel fear. But when you move away from the wall, and the ropes hold you, and you begin to feel safe. You move slowly until you reach the top.

Climbing attracts people because it’s good exercise for almost everyone. You use your whole body, especially your arms and legs. This sport gives your body a complete workout. When you climb, both your mind and your body can become stronger.

小题1:What can we infer from the passage?

A.People are fairly interested in climbing nowadays.

B.It is impossible to build up one’s body by climbing.

C.People can only learn the skill of climbing outdoors.

D.It is always easy to see holding places in climbing.小题2:The most difficult thing to do in wall climbing is _______.

A.to tie ropes to your

B.to control your fear

C.to move away from the wall

D.to climb straight up小题3:The word “workout” underlined in the last paragraph most probably means _________.

A.settlement

B.exercise

C.excitement

D.tiredness小题4:Why does the author write this passage?

A.To tell people where to find gyms.

B.To prove the basic need for climbing

C.To encourage people to climb mountains.

D.introduce the sport of wall climbing

单项选择题 A1型题