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
"Symbiotic Relationships" Symbiosis is a close, long-lasting physical relationship between two different species. In other wo
"Symbiotic Relationships" Symbiosis is a close, long-lasting physical relationship between two different species. In other wo
admin
2018-07-24
106
问题
"Symbiotic Relationships"
Symbiosis is a close, long-lasting physical relationship between two different species. In other words, the two species are usually in physical contact and at least one of them derives some sort of benefit from this contact. There are three different categories of symbiotic relationships: parasitism, commensal-ism, and mutualism.
Parasitism is a relationship in which one organism, known as the parasite, lives in or on another organism, known as the host, from which it derives nourishment. Generally, the parasite is much smaller than the host. Although the host is harmed by the interaction, it is generally not killed immediately by the parasite, and some host individuals may live a long time and be relatively little affected by their parasites. Some parasites are much more destructive than others, however.Newly established parasite-host relationships are likely to be more destructive than those that have a long evolutionary history. With a longstanding interaction between the parasite and the host, the two species generally evolve in such a way that they can accommodate one another. It is not in the parasite’s best interest to kill its host. If it does, it must find another. Likewise, the host evolves defenses against the parasite, often reducing the harm done by the parasite to a level the host can tolerate.
Parasites that live on the surface of their hosts are known as ectoparasites. Fleas, lice, and some molds and mildews are examples of ectoparasites. A Many other parasites, such as tapeworms, malaria parasites, many kinds of bacteria, and some fungi, are called endoparasites because they live inside the bodies of their hosts. B A tapeworm lives in the intestines of its host where it is able to resist being digested and makes use of the nutrients in the intestine. C
Even plants can be parasites. Mistletoe is a flowering plant that is parasitic on trees. It establishes itself on the surface of a tree when a bird transfers the seed to the tree. It then grows down into the water-conducting tissues of the tree and uses the water and minerals it obtains from these tissues to support its own growth. D
Commensalism is a relationship between organisms in which one organism benefits while the other is not affected. It is possible to visualize a parasitic relationship evolving into a commensal one. Since parasites generally evolve to do as little harm to their host as possible and the host is combating the negative effects of the parasite, they might eventually evolve to the point where the host is not harmed at all.
Many examples of commensal relationships exist. Many orchids use trees as a surface upon which to grow. The tree is not harmed or helped, but the orchid needs a surface upon which to establish itself and also benefits by being close to the top of the tree, where it can get more sunlight and rain. Some mosses, ferns, and many vines also make use of the surfaces of trees in this way.
In the ocean, many sharks have a smaller fish known as a remora attached to them. Remoras have a
sucker
on the top of their heads that they can use to attach to the shark. In this way, they can hitchhike a ride as the shark swims along. When the shark feeds, the remora frees itself and obtains small bits of food that the shark misses. Then, the remora reattaches. The shark does not appear to be positively or negatively affected by remoras.
Mutualism is another kind of symbiotic relationship and is actually beneficial to both species involved. In many mutualistic relationships, the relationship is obligatory; the species cannot live without each other. In others, the species can exist separately but are more successful when they are involved in a mutualistic relationship. Some species of Acacia, a thorny tree, provide food in the form of sugar solutions in little structures on their stems. Certain species of ants feed on the solutions and live in the tree, which they will protect from other animals by attacking any animal that begins to feed on the tree. Both organisms benefit; the ants receive food and a place to live, and the tree is protected from animals that would use it as food.
One soil nutrient that is usually a limiting factor for plant growth is nitrogen. Many kinds of plants, such as legumes, beans, clover, Acacia trees, and Alder trees, have bacteria that live in their roots in little
nodules
. The roots form these nodules when they are infected with certain kinds of bacteria. The bacteria do not cause disease but provide the plants with nitrogen-containing molecules that the plants can use for growth. The nitrogen-fixing bacteria benefit from the living site and nutrients that the plants provide, and the plants benefit from the nitrogen they receive.
Glossary
sucker: an adaptation for sucking nourishment or sticking to a surface nodules: growths in the form of knots
An introduction for a short summary of the passage appears below. Complete the summary by selecting the THREE answer choices that mention the most important points in the passage. Some sentences do not belong in the summary because they express ideas that are not included in the passage or are minor points from the passage. This question is worth 2 points.
Symbiosis is a close, continuing physical relationship between two species.
-
-
-
Answer Choices
A Parasitic species will feed on the host species, causing varying degrees of damage to the host as a result of the relationship.
B Orchids benefit from being near the top of a tree where they can be exposed to more sunlight and rain.
C Nodules in the roots of plants supply nitrogen from bacteria, thereby enriching the soil.
D In commensalism, one species will benefit from the relationship, but the other species is not affected by it.
E Certain species form mutualistic relationships in which both species benefit from the physical contact.
F Evolutionary changes in species may allow them to live in close physical contact with little damage to each other.
选项
答案
A, D, E
解析
summarize the passage. Choice B is true, but it is an example of a commensal relationship described in major point D. Choice C refers to a mutualistic relationship developed in major point E. Choice F is mentioned as a minor point in the discussion of parasitic relationships described in major point A.
转载请注明原文地址:https://kaotiyun.com/show/E3fO777K
0
托福(TOEFL)
相关试题推荐
WhatrulesapplytotakingdifferentobjectstotheCentre?Matcheachobjectwiththecorrectrule,A-C.Writethecorrectlett
WhatrulesapplytotakingdifferentobjectstotheCentre?Matcheachobjectwiththecorrectrule,A-C.Writethecorrectlett
WhatrulesapplytotakingdifferentobjectstotheCentre?Matcheachobjectwiththecorrectrule,A-C.Writethecorrectlett
WhatdidPhoebefinddifficultaboutthedifferentresearchtechniquessheused?ChooseFIVEanswersfromtheboxandwritethe
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
Whatadvantagedoesthespeakermentionforeachofthefollowingphysicalactivities?ChooseSIXanswersfromtheboxandwrite
Whatadvantagedoesthespeakermentionforeachofthefollowingphysicalactivities?ChooseSIXanswersfromtheboxandwrite
随机试题
以下哪种肝炎不是经消化道传播的
A.间歇性肉眼血尿B.尿流突然中断C.膀胱刺激症状D.排尿滴沥及会阴疼痛,严重者引起尿潴留结石位于输尿管膀胱壁段常有
引起饮片泛油的原因是
下列除哪一项外,均为蕨类植物粉末的特征
无锡汇海服装进出口公司(230441××××)委托无锡纺织品进出口公司(230491××××)进口全棉印花布一批,经营单位栏应填报“无锡汇海服装进出口公司(230441××××)”
1990年12月19日和1991年7月3日,深圳证券交易所和上海证券交易所先后正式开业。()
背景说明:你是宏远公司的行政秘书高叶,下面是行政经理需要你完成的几项工作任务。便条高叶:公司最近准备更新办公用品与设备,请你说明获得设备使用
上市公司发放股票股利可能导致的结果有()。
在面向对象的语言中,______是程序设计的基本实体。
A、Exerciseonatreadmill.B、ConnectwirelessInternet.C、Workoutonachestpress.D、MakeInternetphonecalls.C①四个选项都是动作,可预测
最新回复
(
0
)