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
A、To describe ways pests can damage plants B、To examine the life cycle of caterpillars C、To explain how com plants develop D、To
A、To describe ways pests can damage plants B、To examine the life cycle of caterpillars C、To explain how com plants develop D、To
admin
2005-01-30
86
问题
Today, we are going to talk about a special way some plants respond to being invaded by pests. The plants react by emitting a chemical signal, which acts like a call for help. Let’s take corn plants for example. Sometimes, caterpillars chew on the corn leaves. When the caterpillar saliva mixes with the chew portion of a leave, the plant releases a chemical scream that attracts wasps. The wasps respond to the signal by flying to the chewed on leave, and laying their eggs on the caterpillars. The caterpillars die in the next few days as the wasp offspring nourish themselves by feeding of them. Thus the corn plant prevents all its leaves from being eaten by the caterpillars. This chemical scream is specific. It’s only released after the plant has detected the caterpillar saliva. A plant that is cut by in the other means does not give off the same signal, nor doesn’t undamaged plants. This also explains how a wasp can find a caterpillar in a huge field of corn. Soybean, cotton and probably many other plants use similar type of defense against pests. By enhancing this natural response in plants, researchers might reduce, some day even eliminate, the need for chemical pesticide, which can cause ecological damage. For example, scientists might breed plants for this screaming trait, or they might transplant specific genes to increase the release of the chemical signals.
选项
A、To describe ways pests can damage plants
B、To examine the life cycle of caterpillars
C、To explain how com plants develop
D、To describe how a natural pesticide works
答案
D
解析
What’s the main purpose of the talk?
转载请注明原文地址:https://kaotiyun.com/show/T9yO777K
0
托福(TOEFL)
相关试题推荐
MorseCodeMorsecodeisbeingreplacedbyanewsatellite-basedsystemforsendingdistresscallsatsea.Itsdotsanddashesh
Matchthenaturalphenomenonwiththecorrectdeterminedfactor.Writethecorrectletter,A-F,inboxes19-21onyouranswersh
Howdidthestudentgettheuniversityprospectus?HowmanystudentswenttoworkineitherSingaporeorBruneithisyear?
Studentsoncourseslastingoverayearareusuallygivenuntil______toleavethecountry.
Completethenotesbelow.WriteONEWORDAND/ORANUMBERforeachanswer.DRIVINGSCHOOLExampleAnswerLookingfordrivingless
Thebankingsystemsoftheworldhavemanysimilarities,______theyalspdiffer,sometimesinquitematerialrespects.
A、Thesuitisoutofstyle.B、Thesuitismoreappropriatefortheoccasion.C、Thewomanlooksbetterinbluethaninblack.D、T
A、RecentlydiscoveredmanuscriptsB、SimilaritiesamongreligionsC、MethodsofanalyzingancientmanuscriptsD、Howancientmanusc
A、Hewantstogetajobinasmallercompany.B、He’slookingforwardtoworkingontheWestCoast.C、Hehopestokeepworkingwh
A、Children.B、Historicalscenes.C、Well-knownpeople.D、Landscapes.CWhatwillbethesubjectofthepicturesattheexhibit?
随机试题
某公司2011年1~6月月初员工人数(单位:人)分别为200,240,220,200,260,210,则该公司2011年上半年的平均职工人数为()
入汤剂宜先煎的药物是
在下列结构中,实现肺换气的主要部位是
连结“肺主呼吸”和“心主血脉”的中心环节是
在Word中,可直接插入的图形文件只有.bmp一种。()
镗铣类加工中心与数控铣(镗)床的主要区别是什么?
根据有关规定,下列各项中,属于无效民事行为的有()。
将一张幻灯片上的所有内容全部选定的命令快捷键是(56)。
L"Universestvasteetilest______depenserquelavieexisteailleursquesurTerre.
MemoTo:AllDivisionEmployeesFrom:ThomasSunDate:October12,2006Subject:AmeetingonworkshopformatAsyouknow,
最新回复
(
0
)