老托福閱讀真題及答案：passage11

1、老托福閱讀真題及答案： 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 system

2、s. 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

3、as 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 chemicalsmay 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 correlate

5、d 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 enzy

6、mes 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,

7、 implying that the host has some means of recognizing 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 pe

8、netrated by a parasite; the parasite itself subsequently ceases to grow 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 parasite

9、s in resisting plant defense mechanisms(B) Theories on active plant defense mechanisms(C) How plant defense mechanisms functiondiffer(D) Howthe immune system of animals and the defense mechanisms of plants2. The phrase subject to in line 1 is closest in meaning to(A) susceptible to(B) classified by(

10、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 NOTnecessarily bei

11、ng toxic to the Colorado beetle(A) resins(B) tannins(C) glycosides(D) alkaloids6. Why does the author mention glycoproteins in line 17(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 illustrate how che

12、micals 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 reaction(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) th