首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Plants are subject to attach and infection by a remarkable variety of symbiotically species and have evolved a diverse array of
Plants are subject to attach and infection by a remarkable variety of symbiotically species and have evolved a diverse array of
admin
2013-05-29
86
问题
Plants are subject to attach and infection by a remarkable variety of symbiotically 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(病原体), 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(表皮层) and a waxy cuticle, often carry spiky hairs known as trichomes(毛状物), 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 intrude, 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(糖蛋白) 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.
Why does the author mention "glycoproteins" in Line 16?
选项
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 chemicals function in plant defense.
D、To show the advantages of plant defense mechanisms.
答案
C
解析
文中第二段阐明了植物如何通过化学物质抵御外来入侵,举例后使意思更具体。选项C是正确的。
转载请注明原文地址:https://kaotiyun.com/show/tKTO777K
0
研究生英语学位课统考(GET)
相关试题推荐
Ishappinessproportionaltoincome—tothemoneyapersonhas?Isamanwithtworoomsandloavesofbreadhappierthanaman
______theassignmentsareturnedinbeforetheendofthisweek.
Todaybusinesscardsaredistributedbyworkingpeopleofallsocialclasses,illustratingnotonlytheuniquityofcommerciali
Planningisaveryimportantactivityinourlivesyetreallysophisticated.Itcangivepleasure,evenexcitement,【C1】______ca
ThedevelopmentandwidespreaduseofcomputertechnologyandtheInternethavetransformedhowwecommunicate,howwecommunica
Thecar,andtheroadsittravelson,willberevolutionizedinthetwentyfirstcentury.Thekeytotomorrow’s"smartcars"wil
BirdsevolvedduringthegreatreptilianradiationoftheMesozoicera.Amnioticeggsandscalesonthelegsarejusttwoofthe
Susannevertookanycookerycourses;shelearnedcookingby______usefultipsfromTVcookeryprograms.
IwasluckybecauseIhadturnedmybackon______,pursuinginsteadcommon-sensereality.
随机试题
数据库学科的研究领域有数据库管理系统软件的研制、数据库理论和_______。
调节呼吸最重要的体液因素是_______。
下列方剂中含有山茱萸、附子的是
选择注射部位时应避开
下列对合理使用土地补偿费,安置补助费表述正确的是()。
如托运人与承运人之间事先无货运协议或类似性质的任何协议,提单就是双方之间订立的运输合同。当托运人将提单通过背书方式转让给第三者时,提单就是承运人与第三者之间的合同。()
()是决定当代中国命运的关键一招,也是决定我军发展壮大,制胜未来的关键一招。
他们都到海边去了。我为左眼发炎不曾去。我独坐在前廊,偎坐在一张安适的大椅内,袒着胸怀,赤着脚,一头的散发,不时有风来撩拂。清晨的晴爽,不曾消醒我初起时睡态;但梦思却半被晓风吹断。我阖紧眼帘内视,只见一斑斑消残的颜色,一似晚霞的余赭,留恋地胶附在天边。廊前的
1.从2008年2月15日起,《机关事业单位人员带薪年休假实施办法》正式开始实施。办法规定:机关、团体、企业、事业单位、民办非企业单位、有雇工的个体工商户等单位的职工连续工作1年以上的,享受带薪年休假。单位确因工作需要不能安排职工休年假的,经职工本人同意,
卢梭曾说:“一切重大的法律,都不是刻在大理石或铜板上,而是铭记在公民的心上。”请谈谈你对这句话的理解。
最新回复
(
0
)