Noses have it pretty hard. Boxers fatten them. Doctors rearrange them. People make jokes about their unflattering characteristics. Worst of all, when it comes to smell, no one really understands them.
Despite the nose's conspicuous presence, its workings are subtle. Smell, or olfaction is a chemosense, relying on specialized interactions between chemicals and nerve endings. When a rose, for example, is sniffed, odor molecules are carried by the rising airstream to the top of the nasal cavity, just behind the bridge of the nose, where the tips of the tens of millions of olfactory nerve cells are clustered in the mucous lining. The molecules somehow trigger the nerve endings, which carry the message to the olfactory lobes of the brain. Because smell information then travels to other regions of the brain, the scent of a rose can elicit not only a pleasurable sensation but emotions and memories as well.
Though just how odors stimulate the nerves is unknown, scientists do know that our sense of smell is surprisingly keen, capable of distinguishing up to tens of thousands of chemical odors. The laboratory task of isolating the components of an odor is far from simple. Tobacco smoke, for example, is made up of several thousand different chemicals. Moreover, smell researchers must grapple with the problem of what to call the different odors that the nose detects. People generally refer to smells by their sources of associations. Descriptions such as "like a wet dog" or "like my elementary school" may convey perceptions but are vastly inadequate for labeling the chemistry involved.
To further complicate research, olfaction is connected to other sensations. Besides olfactory nerves, the nasal cavity contains pain-sensitive nerves that perceive sensations such as the kick in ammonia of the burning in chili peppers. Smell also interwines with taste to create flavor. A coffee drinker holding his nose while sipping would taste only the bitter in his brew, for taste receptors generally appear limited to bitter, salty, sour and sweet. The sense of smell is ten thousand times more sensitive than taste and makes subtle distinctions among lemon, chocolate, and many more flavors.
So how does the nose manage this sophisticated discrimination? Lake of evidence hasn't kept scientists from speculating. One idea is that every odor molecule vibrates at its own frequency, creating patterns of disturbance in the air similar to the wave patterns produced by sound. According to this theory, the nerves act as receivers for the unique vibrations of every odor molecule. The scheme requires no direct contact between the molecule and the nerve cell.
Another suggestion is that primary odors, equivalent to the primary color s of vision underlie all smells and are detected by receptor sites on the olfactory nerves. Different combinations of about thirty basic smells, with labels such as malty, minty, and musky, could form an infinite number of odors.
Other scientists think that each smell is its own primary smell. They believe the olfactory nerve endings have specific receptor proteins that bind to each of the chemicals people can sense. This theory, however, calls for thousands of different proteins - none of which has been found.
"The science of smell is so empirical, " says Robert Gesteland, a neurobiologist at Northwestern University, "there's no predictive base for experiments." Unlike the senses of sight, touch, and hearing, olfaction studies have attracted only a small share of scientific interest. That may change. Researchers hope that unraveling the mystery of smell and taste disorders that affect two million Americans. And in the future, with enough known about smell, it might be possible to endow strange, unappealing but nutritious foods with more familiar odors, perhaps expanding the world's food supply. For the moment, however, what the nose knows it isn't revealing.
34.We may conclude from this passage that
(A) our sense of smell is as important as any of our other senses
(B) each smell is its primary smell
(C) olfactory study has become a major research area
(D) there is much more to be learned about the nose
35.According to the passage the only statement which is not true is
(A) doctors use smell research to better understand taste disorders
(B) significant progress has been made in separating the various proteins in the nerve endings
(C) smell researchers have difficulty in labeling different odors
(D) our sense of taste is not nearly as acute as our sense of smell
36.Which of the following sentences from the passage illustrates the need for further research？
(A) Smell also interwines with taste to create flavor.
(B) The molecules somehow trigger the nerve endings, which carry the message to the olfactory lobes of the brain.
(C) The science of smell is so empirical, there's no predictive base for experiments
(D) Smell, or olfaction, is a chemosense, relying on specialized interactions between chemicals and nerve endings
37.In attempting to analyze the intricacies of smell discrimination, some scientists have suggested
I.that odor molecules work in the same way that sound waves do
II.that primary odors, which are inherent in all smells, are communicated to receptor sites on the olfactory nerves
III.that recognition takes place as the molecule stimulates the nerve cell
(A) II only (B) I and II only (C) I and III only (D) I, II, and III
38.The author attempts to lighten this serious biological report by means of
(A) the incongruity of widespread smell research
(B) similes such as "like a wet dog"
(C) the opening and closing statements
(D) the confession of our basic ignorance
39.The comparison of a smell to a person's elementary school was made in order to
(A) illustrate a unique perception
(B) show how imagery may be employed in a lab situation
(C) point out the uselessness of such a description to scientists
(D) personalize a complicated topic
(E) maintain the reader's interest
40.According to the passage, we can find massive quantities of olfactory nerve cells
(A) in every chemosense (B) on the brain lobes
(C) behind the bridge of the nose (D) in special taste receptors
42.The broadest example of a major problem facing smell researchers is contained with
(A) the reference to tabbacco smoke (B) the reference to the rose
(C) the coffee drinker's experience (D) Robert Gesteland's statement
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