问题 解答题

曲线图能更直观地反映某些科学规律.

(1)如图若反映人体的酶的催化效率随温度变化的曲线(横坐标为温度,纵坐标为酶的催化效率),则曲线中最高点所对应的温度为______℃左右.

(2)此曲线图还能大致反映______.

A.在“草→鹿→狼”食物链中,大量捕杀狼以后的一定时期内,鹿的数量变化

B.氯化钡溶液巾不断加入稀硫酸,产生沉淀物质量的变化

C.通电导体发热的功率随电流的变化.

答案

(1)消化酶的活性受受温度、pH等因素的影响;各种酶在最适温度范围内,酶活性最强,消化酶的最适温度在37℃左右,当温度过低或过高时,酶的活性受到抑制,当温度达到60~80℃时,大部分酶被破坏,发生不可逆变性;当温度接近100℃时,酶的催化作用完全丧失,所以,人在发烧时,不想吃东西.曲线图中的最高点是消化酶发挥作用的最适温度,因此应在37℃左右.

(2):A、在“草→鹿→狼”这条食物链中,大量捕杀狼以后,鹿因失去天敌而大量繁殖,数量会迅速升高,但当增加到一定数量后,鹿会因食物不足而发生生存斗争,会导致一部分鹿死去,因此数量又会减少;故符合曲线图的变化.

B、氯化钡溶液中不断加人稀硫酸,产生沉淀物硫酸钡的质量也会不断增加,直至反应结束,因此不符合曲线图的变化.

C、通电导体发热的功率随电流的增大而增大,随电流的减少而减少,因此不符合曲线图的变化.

故选:A

故答案为:(1)37

(2)A

单项选择题 B型题
阅读理解

阅读理解

     BUKHANNON, West Virginia- Two rescue teams slowly moved along a two-mile path in Monday

night to the site of a coal mine explosion that trapped 13 miners, who had not been heard from since the

early morning accident.

     Meanwhile, at a nearby church, more than 250 family members and friends gathered, waiting for

updates(最新报道) on the rescuers' progress.

     The miners were trapped at about 6:30 a.m. and many families weren't informed of the accident until

about 10 a.m.-more than three hours after it happened. "It's very upsetting, but you've got to be patient, I

guess," said John Helms, whose brother, Terry, was trapped in the mine.

     The trapped miners were about 260 feet underground and about 10000 feet from the Sago Mine's

entrance, said Roger Nicholson, general counsel from International Coal Group.

     At a late night news conference, Nicholson said one team had advanced about 4800 feet in the four

hours since entering the mine just before 6 p.m. Another team entered the mine about 30 minutes later.

     He said the crew was very experienced, with some members having worked underground for 30 to 35

years. The miners were equipped with about one hour of breathable oxygen each. The company has not

released the names of the miner.

     The teams test the air about every 500 feet, and have to disconnect (remove) the power to the phones

they use to communicate with the surface before doing that. "We don't want to be energizing anything if it's

in an atmosphere with burnable gases," Kips said.

     The cause of the explosion was not immediately known. High level of carbon monoxide were detected

shortly after the explosion, which delayed rescue efforts, but those levels have since subsided(减退),

authorities said.

1. According to the passage, we can infer that _____.      

A. all the miners who were trapped underground were still alive

B. communication with the trapped miners was cut off

C. the two rescue teams entered the mine at the same time

D. the rescue started as soon as the accident happened

2. If the first team advanced at an average speed, they could dig about _____ per hour.

A. 1000 feet                          

B. 2400 feet

C. 1200 feet                          

D. 4800 feet

3. Where can the passage be seen?

A. In a magazine.                      

B. In a newspaper.

C. In a science book.                  

D. In an advertisement.