2012雅思阅读模拟练习 1-5文章+题目+答案解析

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

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

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

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

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

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

13. But Horsfield stresses that that’s different from a proof of Turin’s idea. “So far things look plausible， but we need proper experimental verification. We’re