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 w
"Symbiotic Relationships" Symbiosis is a close, long-lasting physical relationship between two different species. In other w
admin
2012-01-14
28
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, commensalism, 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, like 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
If the relationship between organisms is one in which one organism benefits while the other is not affected, it is called commensalism. 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. There are many examples of commensal relationships. Orchids often 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 beans, clover, 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 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
Look at the four squares [m] that show where the following sentence could be inserted in the passage. They live on the feathers of birds or the fur of animals. Where could the sentence best be added? Click on a square [■] to insert the sentence in the passage.
选项
A、Square A.
B、Square B.
C、Square C.
D、Square D.
答案
A
解析
Pronoun reference is a transitional device that connects the insert sentence with the previous sentence. "Fleas, lice and some molds and mildews are examples of ectoparasites. They [fleas, lice and some molds] live on the feathers of birds or the fur of animals." Choices B, C, and D are not correct because the pronoun does not refer to endoparasites, which live inside the host and are explained later in the passage.
转载请注明原文地址:https://kaotiyun.com/show/1fyO777K
0
托福(TOEFL)
相关试题推荐
Completethesummaryusingthelistofwords,A-H,below.Writethecorrectletters,A-H,inboxes37-40onyouranswersheet.S
Lookatthefollowingnamesofpeopleororganisations(Questions33-36)andthelistofopinionsbelow.Matcheachnamewithth
Completethesentencesbelow.WriteNOMORETHANTWOWORDSfromthepassageforeachanswer.Writeyouranswersinboxes21-26o
AccordingtoMrSingh,onwhichthingdomanypeoplemakesuperficialobservations?Whatisbecomingmorewidelyavailabletop
Betweenwhattimesistheroadtrafficlightest?airconditioning
Betweenwhattimesistheroadtrafficlightest?mechanicalventilation
Studentsoncourseslastingoverayearareusuallygivenuntil______toleavethecountry.
TheproblemthatConstableGraydescribesis
kitchen本题询问酒店提供的生活服务。录音原文中指出,每一层楼都有一个厨房(kitchen),以供旅客做饭使用(forresidentstocookin)。录音中的residents“居民”与题目中的guests“客人”为同义替换。
Whatdoesthepassagemainlydiscuss?Itcanbeinferredfromthepassagethatbrainsizeisassumedto
随机试题
症见心痛彻背,背痛彻心,持续剧痛,喘不能卧,身寒肢冷,脉象沉紧。治疗宜用
计算机病毒有哪几个生命周期
不属于烘干硬化水玻璃砂型或型芯的烘干硬化方法是()。
下列关于市场跟进战略说法正确的有
A.空腹高血糖B.甘油三酯升高C.消瘦乏力,伤口不易愈合D.反应性低血糖E.餐后高血糖肌肉组织摄取氨基酸能力下降引起
反复发生上腹部疼痛,多发生在夜间或进食后2~3小时,进食后疼痛可缓解。这是下列哪种疾病的重要特征
监管部门通过制定贷款集中度的上限,避免银行将“鸡蛋放在一个篮子里”,目的包括()。
非保险转移是指通过担保、备用信用证等方式将信用风险转移给()。
商业银行应在每一会计季度终了编制本年度个人理财业务报告。个人理财理业务报告应全面反映()等,并附年度报表。
在招聘评估中,成本效用评估主要包括()。(2004年11月三级真题)
最新回复
(
0
)