Questions 40-50 4 R5 S3 a1 f$ E" E9 Q- F
Pheromones are substances that serve as chemical signals between members of the 0 K% T' I/ R4 w1 J' g. ]
same species. They are secreted to the outside of the body and cause other individuals , }/ Y( L* s, e( Y% p5 t# i
of the species to have specific reactions. Pheromones, which are sometimes called
/ W& }) u8 p& k8 y/ ` Line "social hormones," affect a group of individuals somewhat like hormones do an individual ) z9 j+ g# B! _5 [" a
(5) animal. Pheromones are the predominant medium of communication among insects
. _5 x. w& E O( G (but rarely the sole method). Some species have simple pheromone systems and produce 9 x* H3 Q/ Z- M$ T# V
only a few pheromones, but others produce many with various functions. Pheromone " f# a% D6 D# ]' z8 h7 U/ D
systems are the most complex in some of the so-called social insects, insects that live ; \$ h) h6 T8 Q* g# c {1 I
in organized groups.
+ X. F" S& x: e (10) Chemical communication differs from that by sight or sound in several ways. 2 W% w& \/ w0 d3 m
Transmission is relatively slow (the chemical signals are usually airborne), but the 2 I5 L" K' e& h0 P& Y. K4 Z2 E: s
signal can be persistent, depending upon the volatility of the chemical, and is sometimes
6 C S+ N4 U" j. c effective over a very long range. Localization of the signal is generally poorer than
4 l9 e. c' S; A$ l+ y* k localization of a sound or visual stimulus and is usually effected by the animal’s moving
. D" G" C# v$ | v) h2 V (15) upwind in response to the stimulus. The ability to modulate a chemical signal is limited,
$ m9 I% U1 ^$ C/ C; `* t9 W) q# Z! S compared with communication by visual or acoustic means, but some pheromones may 8 r3 V! T2 I' Q% ]* C) l
convey different meanings and consequently result in different behavioral or physiological 6 \( s# J" w2 f- d2 j' x O
responses, depending on their concentration or when presented in combination. The
/ I. e2 ?- p: @# P9 y7 _ modulation of chemical signals occurs via the elaboration of the number of exocrine 9 W9 }. B; l3 h
(20) glands that produce pheromones. Some species, such as ants, seem to be very articulate
3 m9 D' U% L3 N' v creatures, but their medium of communication is difficult for humans to study and # D# \/ T* W% x: f
appreciate because of our own olfactory, insensitivity and the technological difficulties / ~ [+ ~5 f1 M! V1 x
in detecting and analyzing these pheromones.
$ _6 J& y3 J+ {+ [6 I5 |% x Pheromones play numerous roles in the activities of insects. They may act as alarm ' t' B1 x6 W9 j8 h+ l* @; c5 c
(25) substances, play a role in individual and group recognition, serve as attractants between
) |1 d& i' t; U9 W, | sexes, mediate the formation of aggregations, identify foraging trails, and be involved in
. ?0 l& ^0 G v1 I4 ]4 `0 V, j caste determination. For example, pheromones involved in caste determination include / T2 O% [+ w2 J Q+ D9 [
the "queen substance" produced by queen honey bees. Aphids, which are particularly 3 W/ A: M) d) Y- x. _) J# Q
vulnerable to predators because of their gregarious habits and sedentary nature, secrete 5 X9 C( _9 w) C6 M
an alarm pheromone when attacked that causes nearby aphids to respond by moving away. 1 I/ L! ?, R3 m K- _, d% D
40. What does the passage mainly discuss? 2 v4 k+ z, k* G
(A) How insects use pheromones to communicate
6 s9 `$ e! ?3 k/ B$ S+ C/ f0 n (B) How pheromones are produced by insects ) D) K6 Z+ c9 i" r* S: m! A
(C) Why analyzing insect pheromones is difficult ! U! p ~4 ^& `" A8 g
(D) The different uses of pheromones among various insect species
3 e u1 z0 r& [7 t 41. The word "serve" in line I is closest in meaning to 3 g1 t! Q# a) A! ~7 n8 m
(A) improve + j0 |, O7 I5 ]' [5 C6 Z
(B) function ' m7 v- A! [1 E: `( y
(C) begin
# q: V0 F6 _9 M) ?/ V1 K$ Z (D) rely |
发表于 2012-8-14 22:34:35
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