问题 单项选择题

饥饿时肝酮体生成增多,为减少酮中毒的可能,应主要补充的物质是

A.葡萄糖

B.必需脂肪酸

C.亮氨酸

D.丙氨酸

E.ATP

答案

参考答案:A

解析:[考点] 酮体生成和利用及糖、脂、蛋白质代谢联系[分析] 饥饿时酮体生成过多而酮体氧化不畅。酮体氧化需先转变为乙酰乙,酰CoA后,再硫解生成乙酰CoA,后者进入三羧酸循环彻底氧化。饥饿时机体不能进食,而储存的肝糖原已耗竭,糖代谢减弱,三羧酸循环中间产物供应不足,造成酮体氧化受阻,因而应主要补充葡萄糖,使糖代谢加强,三羧酸循环中间产物充足,大量乙酰 CoA被氧化供能,这样既增加酮体的去路,也减少酮体的来源,故应选A。此时补充脂肪酸会增加酮体生成。亮氨酸是生酮氨基酸,补充也将增加酮体生成。丙氨酸需脱氨基转变为丙酮酸,后者可羧化成三羧酸循环中间产物——草酰乙酸,从而加速三羧酸循环运转,但综合评价不如补充葡萄糖好。

阅读理解

You may have seen a lot of frogs, but if you haven't, you must have heard about frogs. However, have you heard about a frog that can kill a person?

These small brightly colored amphibians (两栖动物) live in the tropical  rain forests of Central and South America. They are best known for their ability to kill persons even though they are no more than 2 inches long. If we touch their poisonous skin without proper protection (such as gloves), we may die! For animals of this size that can be so deadly, they are certainly one of the world's most poisonous animals! Who are they? They are poison arrow frogs or, simply, poison frogs.

Poison frogs acquired their name from the Indians. The Indians catch and kill many of these frogs before hanging them upside down over a campfire. As the frogs get hot, the poison drips out of their skin. The Indians collect the poisonous liquid in a bottle and dip(蘸) the tips of their arrows into the bottle. Once the tips are dried, they are ready to be used for their arrows for hunting.

There are about 170 different types of poison arrow frogs in the world. Though most species have bright markings, either in stripes or patches, on their black bodies, some just wear noticeable single-colored coats. Their shocking skin colors-usually in yellow, red, green, blue or orange-serve as a warning sign to other animals. The sign simply says,” Stay away or pay with your life!” They certainly do not bluff.

小题1:We can infer that the Indians may kill poison frogs in order to______.

A.treat diseases

B.avoid being bitten

C.hunt animals

D.eat their meat小题2:According to the passage,  poison frogs______.

A can grow to several meters long                   B. like to change colors on the back

C. have bright-colored skin or markings            D. are on the edge of dying out

小题3:Which of the following best explains the last sentence of the passage?

A.Poison frogs don't want to kill others.

B.Poison frogs do not just scare others.

C.Poison frogs want to stop others from coming near.

D.Poison frogs just pretend to be dangerous animals.

单项选择题