问题 选择题

“墙脚数枝梅,凌寒独自开。遥知不是雪,为有暗香来。”(王安石《梅花》)诗人在远处就能闻到淡淡的梅花香味的原因是(      )

A.分子很小

B.分子可以再分

C.分子之间存在间隙

D.分子在不断运动

答案

答案:D

题目分析:根据微粒的性质分析,诗人在远处就能闻到淡淡的梅花香味,是因为含有香味的分子在不断的运动,最后运动到诗人的鼻腔中去了,故选D。

点评:利用分子与原子的性质分析和解决问题,就是指利用分子与原子的“质量小,体积小,总是在不停的运动,彼此之间有间隔;同种分子(或原子)性质相同,不同种分子(或原子)性质不同”的性质,以及它们的概念和本质区别等,来分析、解决实际问题。

单项选择题
问答题

There’s a human liver sitting in a lab dish in Madison, Wis. Also a heart, a brain and every bone in the human body even though the contents of the dish are a few cells too small to be seen without a microscope. But these are stem cells, the most immature human cells ever discovered, taken from embryos before they had decided upon their career path in the body. (46) If scientists could only figure out how to give them just the right kick in just the right direction, each could become a liver, a heart, a brain or a bone. (47) When a team from the University of Wisconsin announced their discovery, doctors around the world looked forward to a new era of medicine one without organ-donor shortages or the tissues-rejection problems that bedevil transplant patients today.

Doctors also saw obstacles, though. One of them was a U. S. Congress skittish about research on stem cells taken from unwanted human embryos and aborted fetuses. Indeed, 70 lawmakers asked in a firmly worded letter that the Federal Government ban all such work.

Yet the era of "grow your own" organs is already upon us, as researchers have sidestepped the stem cell controversy by making clever use of ordinary cells. Today a machinist in Massachusetts is using his own cells to grow a new thumb after he lost part of his chest wall in an accident. A teenager born without half of his chest wall is growing a new cage of bone and cartilage within his chest cavity. Scientists announced that bladders, grown from bladder cells in a lab, have been implanted in dogs and are working. Meanwhile, patches of skin, the first "tissue-engineered" organ to be approved by the U. S. Food and Drug Administration, are healing sores and skin ulcers on hundreds of patients across the U. S.

How have scientists managed to do all this without those protean stem cells Part of the answer is smart engineering. (48) Using materials such as polymers with pores no wider than a toothbrush bristle, researchers have learned to sculpt scaffolds in shapes into which cells can settle. The other part of the answer is just plain cell biology. (49) Scientists have discovered that they don’t have to teach old cells new tricks; given the right framework and the right nutrients, cells will organize themselves into real tissues as the scaffolds dissolve. "I’m a great believer in the cells. They’re not just lying there, looking stupidly at each other," says Francois Auger, an infectious disease specialist and builder of artificial blood vessels at Laval University in Quebec City. "They will do the work for you if you treat them right."

Replacement hearts—or even replacement heart parts—are at least a decade off, estimates Kiki Hellman, who monitors tissue-engineering efforts for the FDA. "Any problem that requires lots of cell types ’talking’ to one another is really hard," she notes. Bone and cartilage efforts are much closer to fruition, and could be ready for human trials within two years. (50) And what of those magical stem cells that can grow into any organ you happen to need—if the law and biologists’ knowledge permit "Using them," says Sefton, "is really the Holy Grail.

(47) When a team from the University of Wisconsin announced their discovery, doctors around the world looked forward to a new era of medicine one without organ-donor shortages or the tissues-rejection problems that bedevil transplant patients today.