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
58
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
The word actually in the passage is closest in meaning to
选项
A、frequently
B、initially
C、really
D、usually
答案
C
解析
In this passage, really is a synonym for "actually."
转载请注明原文地址:https://kaotiyun.com/show/n3fO777K
0
托福(TOEFL)
相关试题推荐
WhatrulesapplytotakingdifferentobjectstotheCentre?Matcheachobjectwiththecorrectrule,A-C.Writethecorrectlett
WhatrulesapplytotakingdifferentobjectstotheCentre?Matcheachobjectwiththecorrectrule,A-C.Writethecorrectlett
WhatdidPhoebefinddifficultaboutthedifferentresearchtechniquessheused?ChooseFIVEanswersfromtheboxandwritethe
WhatdidPhoebefinddifficultaboutthedifferentresearchtechniquessheused?ChooseFIVEanswersfromtheboxandwritethe
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
Whatadvantagedoesthespeakermentionforeachofthefollowingphysicalactivities?ChooseSIXanswersfromtheboxandwrite
随机试题
贫困地区(areaunderpoverty)
心悸的实证应予以
A甲状腺B肾上腺髓质C肾上腺皮质束状带D肾上腺皮质网状带E肾上腺皮质球状带醛固酮来自
《药品管理法实施条例》规定,医疗机构要购进药品,必须具备
A.被称为完全固定桥B.一端的固位体为固定连接,另一端的固位体为活动连接的固定桥C.仅一端有固位体,桥体与固位体之间为固定连接的固定桥D.以各种骨内种植体作为固定桥的支持和固位端制成的固定桥E.可以自行摘戴的固定桥半固定桥
建制镇属于宪法和土地管理法所说的城市范畴,也属于其所说的农村和城市郊区的范畴。()
下列关于含水层渗透系数K与含水层介质粒径d和不同水质之间关系的说法中,正确的是()。
当收购被收购企业的全部股权时,如果被收购企业丧失法人资格,且收购企业对收购价款与被收购企业可确指资产之间产生的差额进行会计处理。则下列各项中,属于对此进行会计处理的科目是()。
假设有一个“图书订单表”,其字段分别为书名、单价和数量,若以此表为数据源创建一个窗体,在窗体中设置一个计算订购总金额的文本框,那么“控件来源”属性值为【】。
第二产业/工业
最新回复
(
0
)