托福阅读真题练习：植物生长的文本+真题+答案

2017年11月06日14:53 来源：小站整理: 参与（0）阅读（16414）

摘要：托福阅读真题哪里有?大家平时备考托福阅读考试的时候都用的是哪些真题呢?除了官方真题Official的托福阅读真题以外，大家进行托福阅读的练习大多数可能都是根据老托资料或者是课外资料来练习了。那么到哪里去找到托福阅读真题来进行练习呢?

托福阅读如何进行备考?除了大量的托福词汇储备以外，大家可能最需要的就是托福阅读真题的练习。那么除了官方真题Official你还有哪些托福阅读真题进行练习呢?今天小编就为大家整理了托福阅读真题100篇：植物生长的文本、题目以及答案，希望可以帮助到大家。

托福阅读100篇真题练习汇总：http://toefl.zhan.com/tfziliao63739.html

托福阅读文本：

Plants 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 systems.

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 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 chemicals may inhibit or kill the intruder, and plant 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 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 enzymes 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, 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 penetrated 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.

托福阅读题目：

1. What does the passage mainly discuss?

(A) The success of parasites in resisting plant defense mechanisms

(B) Theories on active plant defense mechanisms

(D) How the immune system of animals and the defense mechanisms of plants differ

2. The phrase "subject to" in line 1 is closest in meaning to

(A) susceptible to

(B) classified by

(D) strengthened by

3. The word "puncture" in line 8 is closest in meaning to

(A) pierce