2012年雅思考试阅读模拟试题(含答案)

　　Rogue theory of smell gets a boost

　　1. A controversial theory of how we smell,which claims that our fine sense of odour dependson quantum mechanics, has been given the thumbsup by a team of physicists.

　　2. Calculations by researchers at UniversityCollege London (UCL) show that the idea that wesmell odour molecules by sensing their molecularvibrations makes sense in terms of the physicsinvolved.

　　3. That’s still some way from proving that the theory, proposed in the mid-1990s bybiophysicist Luca Turin, is correct. But it should make other scientists take the idea moreseriously.

　　4. "This is a big step forward," says Turin, who has now set up his own perfume companyFlexitral in Virginia. He says that since he published his theory, "it has been ignored rather thancriticized."

　　5. Most scientists have assumed that our sense of smell depends on receptors in the nosedetecting the shape of incoming molecules, which triggers a signal to the brain. This molecular’lock and key’ process is thought to lie behind a wide range of the body’s detection systems:it is how some parts of the immune system recognise invaders, for example, and how thetongue recognizes some tastes.

　　6. But Turin argued that smell doesn’t seem to fit this picture very well. Molecules that lookalmost identical can smell very different — such as alcohols, which smell like spirits, and thiols,which smell like rotten eggs. And molecules with very different structures can smell similar.Most strikingly, some molecules can smell different — to animals, if not necessarily to humans— simply because they contain different isotopes (atoms that are chemically identical but havea different mass).

　　7. Turin’s explanation for these smelly facts invokes the idea that the smell signal inolfactory receptor proteins is triggered not by an odour molecule’s shape, but by itsvibrations, which can enourage an electron to jump between two parts of the receptor in aquantum-mechanical process called tunnelling. This electron movement could initiate thesmell signal being sent to the brain.

　　8. This would explain why isotopes can smell different: their vibration frequencies arechanged if the atoms are heavier. Turin’s mechanism, says Marshall Stoneham of the UCLteam, is more like swipe-card identification than a key fitting a lock.

　　9. Vibration-assisted electron tunnelling can undoubtedly occur — it is used in anexperimental technique for measuring molecular vibrations. "The question is whether this ispossible in the nose," says Stoneham’s colleague, Andrew Horsfield.

　　10. Stoneham says that when he first heard about Turin’s idea, while Turin was himselfbased at UCL, "I didn’t believe it". But, he adds, "because it was an interesting idea, I thought Ishould prove it couldn’t work. I did some simple calculations, and only then began to feel Lucacould be right." Now Stoneham and his co-workers have done the job more thoroughly, in apaper soon to be published in Physical Review Letters.

　　11. The UCL team calculated the rates of electron hopping in a nose receptor that has anodorant molecule bound to it. This rate depends on various properties of the biomolecularsystem that are not known, but the researchers could estimate these parameters based ontypical values for molecules of this sort.

　　12. The key issue is whether the hopping rate with the odorant in place is significantlygreater than that without it. The calculations show that it is — which means that odouridentification in this way seems theoretically possible.

　　13. But Horsfield stresses that that’s different from a proof of Turin’s idea. "So far thingslook plausible, but we need proper experimental verification. We’re beginning to think aboutwhat experiments could be performed."

　　14. Meanwhile, Turin is pressing ahead with his hypothesis. "At Flexitral we have beendesigning odorants exclusively on the basis of their computed vibrations," he says. "Oursuccess rate at odorant discovery is two orders of magnitude better than the competition."At the very least, he is putting his money where his nose is.

　　(668 words Nature)