Questions 40-50 $ G$ ^4 s( b# y2 Y _/ k0 G
Pheromones are substances that serve as chemical signals between members of the 0 R. P) x; X+ |& ?# J5 @- k4 k# g
same species. They are secreted to the outside of the body and cause other individuals
' s& a9 v8 D% R0 |1 x) l of the species to have specific reactions. Pheromones, which are sometimes called 6 K9 a4 G/ c- b6 H# R: H$ B
Line "social hormones," affect a group of individuals somewhat like hormones do an individual
' Z4 d4 }( h7 g3 {# ~. Y (5) animal. Pheromones are the predominant medium of communication among insects
E, [, _/ ^3 ?" [ (but rarely the sole method). Some species have simple pheromone systems and produce ) f- c8 w2 x x# d
only a few pheromones, but others produce many with various functions. Pheromone
( x# \8 S$ H/ c: _3 v systems are the most complex in some of the so-called social insects, insects that live / O# T, [1 a9 n9 g% c' _
in organized groups. 5 @' {7 [' L' E4 ]$ G
(10) Chemical communication differs from that by sight or sound in several ways. " _/ ?; `; J0 i9 T0 M* k- m
Transmission is relatively slow (the chemical signals are usually airborne), but the
- ]2 f* u% u7 @1 y* n signal can be persistent, depending upon the volatility of the chemical, and is sometimes
0 c% C' F O* ^" I, ` effective over a very long range. Localization of the signal is generally poorer than ; i) C+ m, ~& j" i$ ^9 y
localization of a sound or visual stimulus and is usually effected by the animal’s moving 2 |1 t4 r2 |3 z1 U3 V6 |. g3 X
(15) upwind in response to the stimulus. The ability to modulate a chemical signal is limited, ) ^& M9 @; W- u* y- [. m5 q9 O% n; O' Q
compared with communication by visual or acoustic means, but some pheromones may 7 l! V( F6 u) h* w) Y% w9 e3 P
convey different meanings and consequently result in different behavioral or physiological " C6 e4 L8 |: `2 R- s& W
responses, depending on their concentration or when presented in combination. The ! ?. P+ K* b2 w! i! V/ R" t
modulation of chemical signals occurs via the elaboration of the number of exocrine
# V: |7 _5 ~) a5 C! w (20) glands that produce pheromones. Some species, such as ants, seem to be very articulate
8 s$ g8 z& h' s3 D/ r+ D2 s creatures, but their medium of communication is difficult for humans to study and / m6 {6 t: }- a' z
appreciate because of our own olfactory, insensitivity and the technological difficulties : h& n" ^' h0 K- b4 |* G
in detecting and analyzing these pheromones.
* ~. Y: n! { S4 F9 g' f9 C Pheromones play numerous roles in the activities of insects. They may act as alarm
- U7 z' x7 J' y& n2 d% c" q (25) substances, play a role in individual and group recognition, serve as attractants between 4 f7 t3 V( P' _! ~- N% e. n- f
sexes, mediate the formation of aggregations, identify foraging trails, and be involved in 2 ~% K5 N6 n. Z
caste determination. For example, pheromones involved in caste determination include / c6 L0 i4 K2 {3 S5 ]# I
the "queen substance" produced by queen honey bees. Aphids, which are particularly
i `2 k9 H" Z/ [, m/ | vulnerable to predators because of their gregarious habits and sedentary nature, secrete ( U, W- k8 d. m5 a
an alarm pheromone when attacked that causes nearby aphids to respond by moving away.
' ?5 M0 G. e8 O3 v( P 40. What does the passage mainly discuss? 6 m1 Z. z+ V3 z4 k
(A) How insects use pheromones to communicate 3 W1 a5 i+ F. j0 r: n9 g
(B) How pheromones are produced by insects ) W7 j* C! m5 k8 t
(C) Why analyzing insect pheromones is difficult % ?+ D; q( `+ i7 `: e0 {
(D) The different uses of pheromones among various insect species $ \7 A2 _$ x& b6 l
41. The word "serve" in line I is closest in meaning to
! o# J% F9 U, s8 Q5 ~: ~ (A) improve {) S% V T# `0 r
(B) function + u; P6 _. y+ f# N
(C) begin 7 k( b1 Q* N) o; b/ r
(D) rely |
发表于 2012-8-14 22:34:35
楼主