2. 外语
  3. 　　　 Pheromones are substances that serve as chemical signals between members of the 　　　 same species. They are secreted to t

　　　 Pheromones are substances that serve as chemical signals between members of the 　　　 same species. They are secreted to t

admin2004-12-28  98
问题 　　　     Pheromones are substances that serve as chemical signals between members of the
　　　 same species. They are secreted to the outside of the body and cause other individuals
　　　 of the species to have specific reactions. Pheromones, which are sometimes called
　　　 line "social hormones," affect a group of individuals somewhat like hormones do an individual
(5)     animal. Pheromones are the predominant medium of communication among insects
　　　 (but rarely the sole method). Some species have simple pheromone systems and produce
　　　 only a few pheromones, but others produce many with various functions. Pheromone
　　　 systems are the most complex in some of the so-called social insects, insects that live
　　　 in organized groups.
(10)        Chemical communication differs from that by sight or sound in several ways.
　　　 Transmission is relatively slow (the chemical signals are usually airborne), but the
　　　 signal can be persistent, depending upon the volatility of the chemical, and is sometimes
　　　 effective over a very long range. Localization of the signal is generally poorer than
　　　 localization of a sound or visual stimulus and is usually effected by the animal’s moving
(15)    upwind in response to the stimulus. The ability to modulate a chemical signal is limited,
　　　 compared with communication by visual or acoustic means, but some pheromones may
　　　 convey different meanings and consequently result in different behavioral or physiological
　　　 responses, depending on their concentration or when presented in combination. The
　　　 modulation of chemical signals occurs via the elaboration of the number of exocrine
(20)    glands that produce pheromones. Some species, such as ants, seem to be very articulate
　　　 creatures, but their medium of communication is difficult for humans to study and
　　　 appreciate because of our own olfactory, insensitivity and the technological difficulties
　　　 in detecting and analyzing these pheromones.
　　　     Pheromones play numerous roles in the activities of insects, They may act as alarm
(25)    substances, play a role in individual and group recognition, serve as attractants between
　　　 sexes, mediate the formation of aggregations, identify foraging trails, and be involved in
　　　 caste determination. For example, pheromones involved in caste determination include
　　　 the "queen substance" produced by queen honey bees. Aphids, which are particularly
　　　 vulnerable to predators because of their gregarious habits and sedentary nature, secrete
　　　 an alarm pheromone when attacked that causes nearby aphids to respond by moving away.
选项 A、How insects use pheromones to communicate
B、How pheromones are produced by insects
C、Why analyzing insect pheromones is difficult
D、The different uses of pheromones among various insect species
答案D
解析
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