1、 1托福阅读真题集锦（六）PASSAGE 11Plants are subject to attack and infection by a remarkable variety of symbiotic species and have evolved a diverse array of mechanisms designed to frustrate the potential colonists. These can be divided into preformed or passive defense mechanisms and inducible or active syste
2、ms.Passive plant defense comprises physical and chemical barriers that prevent entry of pathogens,such as bacteria, or render tissues unpalatable or toxic to the invader. The external surfaces of plants, in addition to being covered by an epidermis and a waxy cuticle, often carry spiky hairs known a
3、s trichomes, which either prevent feeding by insects or may even puncture and kill insect larvae. Other trichomes are sticky and glandular and effectively trap and immobilize insects.If the physical barriers of the plant are breached, then preformed chemicals may inhibit or kill the intruder, and pl
4、ant tissues contain a diverse array of toxic or potentially toxic substances, such as resins, tannins, glycosides, and alkaloids, many of which are highly effective deterrents to insects that feed on plants. The success of the Colorado beetle in infesting potatoes, for example,seems to be correlated
5、 with its high tolerance to alkaloids that normally repel potential pests. Other possible chemical defenses, while not directly toxic to the parasite, may inhibit some essential step in the establishment of a parasitic relationship. For example, glycoproteins in plant cell walls may inactivate enzym
6、es that degrade cell walls. These enzymes are often produced by bacteria and fungi.Active plant defense mechanisms are comparable to the immune system of vertebrate animals,although the cellular and molecular bases are fundamentally different. Both, however, are triggered in reaction to intrusion, i
7、mplying that the host has some means of 2recognizing the presence of a foreign organism. The most dramatic example of an inducible plant defense reaction is the hypersensitive response. In the hypersensitive response, cells undergo rapid necrosis that is, they become diseased and die after being pen
8、etrated by a parasite; the parasite itself subsequently ceases togrow and is therefore restricted to one or a few cells around the entry site.Several theories have been put forward to explain the basis of hypersensitive resistance.1. What does the passage mainly discuss?(A) The success of parasites
9、in resisting plant defense mechanisms(B) Theories on active plant defense mechanisms(C) How plant defense mechanisms function(D) How the immune system of animals and the defense mechanisms of plants differ2. The phrase “subject to“ in line 1 is closest in meaning to(A) susceptible to(B) classified b
10、y(C) attractive to(D) strengthened by3. The word “puncture“ in line 8 is closest in meaning to(A) pierce(B) pinch(C) surround(D) cover .4. The word “which“ in line 12 refers to(A) tissues(B) substances(C) barriers(D) insects5. Which of the following substances does the author mention as NOT necessar
11、ily being toxic to the Colorado beetle?(A) resins(B) tannins(C) glycosides(D) alkaloids6. Why does the author mention “glycoproteins“ in line 17?3(A) to compare plant defense mechanisms to the immune system of animals(B) to introduce the discussion of active defense mechanisms in plants(C) to illust
12、rate how chemicals function in plant defense(D) to emphasize the importance of physical barriers in plant defense7. The word “dramatic“ in line 23 could best be replaced by(A) striking(B) accurate(C) consistent(D) appealing8. Where in the passage does the author describe an active plant-defense reac
13、tion?(A) Lines 1-3(B) Lines 4-6(C) Lines 13-15(D) Lines 24-279. The passage most probably continues with a discussion of theories on(A) the basis of passive plant defense(B) how chemicals inhibit a parasitic relationship.(C) how plants produce toxic chemicals(D) the principles of the hypersensitive
14、response.PASSAGE 12Among the species of seabirds that use the windswept cliffs of the Atlantic coast of Canada in the summer to mate, lay eggs, and rear their young are common murres, Atlantic puffins,black-legged kittiwakes, and northern gannets. Of all the birds on these cliffs, the black-legged k
15、ittiwake gull is the best suited for nesting on narrow ledges. Although its nesting habits are similar to those of gulls that nest on flat ground, there are a number of important differences related to the cliff-nesting habit.The advantage of nesting on cliffs is the immunity it gives from foxes, wh
16、ich cannot scale the sheer rocks, and from ravens and other 4species of gulls, which have difficulty in landing on narrow ledges to steal eggs. This immunity has been followed by a relaxation of the defenses, and kittiwakes do not react to predators nearly as fiercely as do ground-nesting gulls. A c
17、olony of Bonapartes gulls responds to the appearance of a predatory herring gull by flying up as a group with a clamor of alarm calls, followed by concerted mobbing, but kittiwakes simply ignore herring gulls, since they pose little threat to nests on cliffs. Neither do kittiwakes attempt to conceal
18、 their nest. Most gulls keep the nest area clear of droppings, and remove empty eggshells after the chicks have hatched, so that the location of the nest is not given away. Kittiwakes defecate over the edge of the nest, which keeps it clean, but this practice, as well as their tendency to leave the
19、nest littered with eggshells, makes its location very conspicuous.On the other hand, nesting on a narrow ledge has its own peculiar problems, and kittiwake behavior has become adapted to overcome them. The female kittiwake sits when mating, whereas other gulls stand, so the pair will not overbalance
20、 and fall off the ledge. The nest is a deep cup,made of mud or seaweed, to hold the eggs safely, compared with the shallow scrape of other gulls,and the chicks are remarkably immobile until fully grown. They do not run from their nests when approached, and if they should come near to the cliff edge,
21、 they instinctively turn back.1. What aspect of the kittiwake gull does the passage mainly discuss?(A) Its defensive behavior(B) It interactions with other gull species(C) Its nesting habits(D) Its physical difference from other gull species2. The word “rear“ in line 2 is closest in meaning to(A) vi
22、sit(B) watch(C) reverse(D) raise3. The word “scale“ in line 8 is closest in meaning to(A) climb5(B) avoid(C) approach(D) measure4. The word “immunity“ in line 9 is closest in meaning to(A) distance(B) transition(C) protection(D) reminder5. Why is it difficult for ravens to steal the kittiwakes eggs?
23、(A) The kittiwakes can see the ravens approaching the nest.(B) The ravens cannot land on the narrow ledges where kittiwakes nest.(C) The kittiwakes eggs are too big for the ravens to carry.(D) The female kittiwakes rarely leave the nest.6. The author mentions that eggshells litter around the nests o
24、f kittiwakes in order to(A) demonstrate that kittiwakes are not concerned about predators(B) prove how busy kittiwakes are in caring for their offspring(C) show a similarity to other types of gulls(D) illustrate kittiwakes lack of concern for their chicks7. According to the passage , it can be infer
25、red that which of the following birds conceal their nest?(A) Bonapartes gulls(B) Atlantic puffins(C) Kittiwake gulls(D) Northern gannets8. The word “it“ in line 17 refers to(A) location(B) edge(C) nest(D) practice9. The word “conspicuous“ in line 18 is closest in meaning to(A) disordered(B) suspicious(C) noticeable(D) appealing10. The phrase “On the other hand“ in line 19 is closest in meaning to6(A) therefore(B) however(C) for example(D) by no means答案： PASSAGE 11 CAABD CADDPASSAGE 12 CDACB AACCB
