首页
登录
职称英语
Lichens To be certain, a lichen is not the mo
Lichens To be certain, a lichen is not the mo
游客
2024-01-04
71
管理
问题
Lichens
To be certain, a lichen is not the most conspicuous of plants. Lichens grow in unassuming fashion on rocks, logs and other exposed surfaces in a wide range of habitats around the world. To the untrained eye they look like little more than crusty patches that, at first glance, might easily be mistaken for a discoloration of the surface. Even if the average person should happen to notice the lichen’s presence and correctly identify it as some form of life, he is unlikely to go much further in contemplating it. Though almost totally ignored by the layperson, for the botanist, lichens are one of the most fascinating of all plants, and one of the most intensely studied.
They are the subject of so much scientific scrutiny primarily because a lichen is not just one plant. It is, in fact, a composite organism made up of fungus and algae living together in a close association that is, presumably, beneficial to both. When these two very different plants combine, the result is a unique and very long-lived composite organism that appears, at least on a macroscopic scale, to be a unitary plant. It is an organism that bears no resemblance to either of its constituents when they are observed individually. The separate fungal and alga) elements can be recognized only when the body of the plant, called a thallus because there are no stems or roots, is sectioned and examined under a microscope. When viewed this way, the fungus component dominates the picture, as it accounts for nine tenths of the total body mass of the lichen. But, entrapped within it, clearly visible as dark spots, are the algae cells. Essentially, nothing is known of how an amorphous mass of fungi and algae come together to form a highly differentiated, structurally stable body.
Despite all the scientific scrutiny lichens have received, it is still not entirely certain what each member gains from the association. Some researchers have speculated that the fungi join in the relationship because they are able to consume the algae cells as they die and therefore are guaranteed a food supply. It is well-known that the chlorophyll-containing algae cells produce food by means of photosynthesis. There may be some mechanism, still unknown to us, through which this energy source is utilized by the fungus. Fungus possesses no chlorophyll of its own. How or even whether the algae benefit from this association is still less certain, though we can easily imagine that they gain mechanical protection from the elements by being tightly enveloped in the structural fibers of the fungus body. They should also benefit from retention of water between the fibers.
The hardiness of lichens has made them what botanists term "pioneer plants". This refers to their ability to colonize habitats where other plants do not exist. They are common on barren rocky surfaces, where the lack of soil precludes the establishment of most other kinds of plant life. They can even be found in places as hostile and extreme as the interior of the Antarctic continent. Although they are most often associated with far northern or southern environments, they have been found living in sun baked desert soils that are otherwise devoid of life. The most highly specialized lichens are the endolithic species of the Antarctic, which as the name indicates, live inside rocks, forming more or less continuous tissue structures between the rock crystals.
As remarkable in their robustness as lichens are, there is one kind of an environment which they are generally unable to tolerate. Habitats that are heavily affected by pollution axe noticeably devoid of lichens. These organisms are especially susceptible to sulfur dioxide poisoning and they absorb and accumulate other toxins as well; both air and waterborne. This heightened sensitivity arises from the fact that lichens have no means of ridding their tissues of these substances. It is thought that the pollutants accumulate and destroy the chlorophyll in the algae cells, thus disrupting the relationship with the fungus. This particular characteristic makes lichens an especially good indicator of environmental health. Surveys currently indicate that lichens are completely absent from urban centers with populations of 100,000 or more. [br] According to the passage, how might the fungus benefit from its association with algae?
选项
A、he algae help provide it with necessary moisture.
B、It consumes nutrients produced by algae.
C、It is made less visible because of the algae’s green color.
D、The algae provide structural support.
答案
B
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3334397.html
相关试题推荐
Lichens.probablythehardiestofallplants,livewherevirtuallynoth
Calciumis(essential)for(blood)clotting,fortheactionof(certain)enzymes,
LichensTobecertain,alichenisnotthemo
LichensTobecertain,alichenisnotthemo
LichensTobecertain,alichenisnotthemo
LichensTobecertain,alichenisnotthemo
LichensTobecertain,alichenisnotthemo
LichensTobecertain,alichenisnotthemo
Scientistshaveknownforsometimethatcertainplants,calledhyperaccumu-
ControversyaboutCausingEmotionP1:Thefactthatwereacttocertainexperien
随机试题
Iamwritingtoapologizefor______(没有提前打电话取消会议).notcallinginadvance/ahead
某企业有生产部和销售部,生产部负责生产产品并送入仓库,销售部从仓库取出产品销售。
下列不属于证券公司发行与承销业务市场准入管理方面法律法规的是()。A.《证券公
川芎茶调散中,善治少阳、太阳、阳明经头痛的药是A.川芎、荆芥、防风 B.川芎、
从今年起,国家对农村低收入人口全面实施扶贫政策。对该政策理解不正确的是()。A
股份有限公司经理的职权不包括()。A.拟订公司管理机构设置方案 B.制定公司的
因持有股票而享有的配股权,从配股除权日到配股确认日的估值方法,表述正确的有()。
“黑马”一词其实是从英语舶来的,原指体育界一鸣惊人的后起之秀,后指实力难测的竞争
一住店客人未付房钱即想离开旅馆去车站。旅馆服务员揪住他不让走,并打报警电话。客人
下列关于施工现场照明用电的说法,正确的是( )。A.比较潮湿的场所,电源电压不
最新回复
(
0
)