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
59
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.
The passage most probably continues with a discussion of theories on ______.
选项
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 response
答案
D
解析
文章最后一段讲到,“Several theories have been put forward to explain the basis of hypersensitive resistance.”,因此答案是D。
转载请注明原文地址:https://kaotiyun.com/show/CKTO777K
0
研究生英语学位课统考(GET)
相关试题推荐
PersonalcomputersandtheInternetgivepeoplenewchoicesabouthowtospendtheirtime.Somemayusethisfreedomtosharele
MostpeoplewhodevelopedLymedisease,atick-borninfectionthat’sendemicinpartsoftheNortheastandMidwest,areeasilyc
Planningisaveryimportantactivityinourlivesyetreallysophisticated.Itcangivepleasure,evenexcitement,【C1】______ca
Planningisaveryimportantactivityinourlivesyetreallysophisticated.Itcangivepleasure,evenexcitement,【C1】______ca
ThedevelopmentandwidespreaduseofcomputertechnologyandtheInternethavetransformedhowwecommunicate,howwecommunica
Themajorityofsuccessfulseniormanagersdonotcloselyfollowtheclassicalrationalmodeloffirstclarifyinggoals,assessi
Writeacompositionofatleast250wordsbasedonthetopic"Trust".Yourwritingshouldincludethefollowinginformation.1.当
Some23millionadditionalU.S.residentsareexpectedtobecomemoreregularusersoftheU.S.healthcaresysteminthenext
Forsometimepastithasbeenwidelyacceptedthatbabies—andothercreatures—learntodothingsbecausecertainactsleadto
随机试题
依我国著作权法,将老舍的作品“茶馆”翻译成藏文在国内出版,属于()
《脉经》的作者是
A.0.25GyB.0.5GyC.0.6~1GyD.1.5~3GyE.3.5~6Gy全部骨髓的吸收剂量的阈值剂量为
中东某公司与其招聘的中国籍人杨光签订了劳动合同,合同规定有关劳动争议应适用中东某国法律。依中国的相关规定,下列哪一选项是正确的?()
根据《公路工程抗震规范》,在发展断裂及其邻近地段进行路线、桥位和隧址的布设时,不正确的是()。
编制项目合同编码的基础是()。
根据行政许可法律制度的规定,下列关于行政许可期限或者费用制度的表述中,正确的有()。
生活的真谛是必须()。
首开人类师范教育先河的国家是美国。()
Wheneveryouseetheoldfilm,evenone【M1】______madetenyearsbefore,youcannothelpbeing
最新回复
(
0
)