Questions 40-50
+ l6 e9 l2 n' v. F7 z Pheromones are substances that serve as chemical signals between members of the 2 j7 m0 p4 P& c, f. R5 J
same species. They are secreted to the outside of the body and cause other individuals
2 W. w/ b4 J, n" K( M+ D* [/ H! v) B of the species to have specific reactions. Pheromones, which are sometimes called $ F4 j. `. u& g/ o) N) ^% W) y& b
Line "social hormones," affect a group of individuals somewhat like hormones do an individual
, h( o% g( i3 t" I8 S (5) animal. Pheromones are the predominant medium of communication among insects % s7 N9 B( t: k' {# ^2 H; c9 d
(but rarely the sole method). Some species have simple pheromone systems and produce
+ e1 D7 z; }; s" `# k only a few pheromones, but others produce many with various functions. Pheromone ) r# ~& m$ B6 B5 q- \- y
systems are the most complex in some of the so-called social insects, insects that live
9 ?" n; T0 ~8 P# t) A7 P4 R in organized groups.
+ S R: Y4 X& Q; Q( J, r (10) Chemical communication differs from that by sight or sound in several ways. ) P F. B# Z. b' M" X: h* S
Transmission is relatively slow (the chemical signals are usually airborne), but the - S9 M l! Q J' N
signal can be persistent, depending upon the volatility of the chemical, and is sometimes
6 T2 `6 Y/ e" X9 q U/ w6 B* I9 ` effective over a very long range. Localization of the signal is generally poorer than
$ I- r/ b, `+ ~3 t% s localization of a sound or visual stimulus and is usually effected by the animal’s moving 2 u; s5 q5 C5 k) Z: N
(15) upwind in response to the stimulus. The ability to modulate a chemical signal is limited,
6 ?0 P$ }+ B9 Q8 I1 v) I compared with communication by visual or acoustic means, but some pheromones may 4 k2 Z" Y9 @ o7 J, Z2 |" L
convey different meanings and consequently result in different behavioral or physiological
- z4 G9 d8 R% [) l2 j0 k responses, depending on their concentration or when presented in combination. The 2 A0 l9 {$ Q* A, Q
modulation of chemical signals occurs via the elaboration of the number of exocrine 3 L& O! q( y8 W* w& w3 c4 s
(20) glands that produce pheromones. Some species, such as ants, seem to be very articulate
% y( f2 J/ { ] creatures, but their medium of communication is difficult for humans to study and 2 K. A6 c' r) Z
appreciate because of our own olfactory, insensitivity and the technological difficulties 6 {6 b( Z, ^. z' }3 g
in detecting and analyzing these pheromones. 9 X9 J$ N y2 D
Pheromones play numerous roles in the activities of insects. They may act as alarm
+ p3 @& R9 P6 c% K (25) substances, play a role in individual and group recognition, serve as attractants between
* p* f; E- h( B/ X/ W sexes, mediate the formation of aggregations, identify foraging trails, and be involved in 7 M& t& T, e0 S$ ~' L6 t
caste determination. For example, pheromones involved in caste determination include 3 O' |8 E: X9 r) i3 B
the "queen substance" produced by queen honey bees. Aphids, which are particularly
0 m/ F: F( n% f! E+ ] vulnerable to predators because of their gregarious habits and sedentary nature, secrete 3 d4 @2 c. @- h, a
an alarm pheromone when attacked that causes nearby aphids to respond by moving away.
/ r0 W8 v! T2 W, P! q" W( `5 @* n 40. What does the passage mainly discuss?
6 `8 a" f& {4 F0 K (A) How insects use pheromones to communicate
1 t# |7 Y, E$ B9 @" j (B) How pheromones are produced by insects
- S4 j/ W. O' J# b (C) Why analyzing insect pheromones is difficult 3 ]9 }. D- z6 i
(D) The different uses of pheromones among various insect species
& j9 P7 \' J: ^ 41. The word "serve" in line I is closest in meaning to
; L2 {& E9 y; k$ |+ F w6 C (A) improve
" O3 U( v! r9 G" K% r! O (B) function $ }) _3 h0 U8 X
(C) begin " Y9 R/ n7 R; H W/ K. J
(D) rely |
发表于 2012-8-14 22:34:35
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