问题 单项选择题

下列哪种情况下酶促反应速度恒定

A.最适温度时

B.最适pH时

C.底物浓度足够大时

D.样品量足够大时

E.加入酶的激动剂

答案

参考答案:C

解析:本题考查底物浓度对反应速度的影响,如果加大底物浓度,反应速度不再增加,表现为。级反应。此时,无论底物浓度增加多大,反应速度也不再增加,说明酶已被底物所饱和。

阅读理解

阅读理解。

                                                           How to Become Fit?

     Healthy eating habit along with regular exercise is the only way to become fit. If you have the correct

number of calories and exercise regularly, you will lose weight, keep fit, and feel great, too.

     During your teenage years, it is important to give your body the energy it needs. If you skip (跳过) meals,

you won't get enough calories, and then you will feel tired. By the way, calorie is just another word for energy.

About 50% of your calories should come from rice, bread, vegetables and fruit. You also need to drink a lot of

water, 6 to 8 glasses a day. Water helps keep your system clean. Drinking enough water will make your skin

better and make you healthy.

     Exercise is something that can help to make you look good, feel good and be healthy. Experts suggest that

teenagers spend at least 30 minutes exercising, five times a week. That is easy to do! You can walk or ride

your bike to school, and do sports at school. However, teenagers often give up sports, saying they have no

time left after their studies. In fact, doing exercise can help them sleep better at night and increase their ability

to focus on their study.

    If you follow the suggestions above, you will look and feel much better and become fit.

1. What's the main idea of this passage?

A. How to eat food.

B. How to exercise.

C. How to lose weight.

D. How to keep fit.

2. The underlined word "calories" means _______ in this passage.

A. 营养

B. 能量

C. 强壮

D. 锻炼

3. Teenagers spend at least _______ minutes exercising a week according to this passage.

A. 150

B. 50

C. 30

D. 5

4. If you _______, you will become fit.

A. exercise regularly

B. drink lots of water

C. eat rice, bread, vegetables and fruit

D. have a healthy eating habit along with regular exercise

5. Why do teenagers give up sports in school according to this passage? Because they _______.

A. are lazy

B. feel great

C. are busy with their studies

D. don't like sports

解答题