Official 42 Set 5

纠错
  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
置顶

Fungi

纠错
  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
What is the lecture mainly about?
  • A. Why fungi cannot grow well in polluted ecosystems

  • B. Why fungi pose a danger to the underground water system

  • C. How to prevent heavy metals from getting into the soil

  • D. How fungi can clean up pollution that is in the soil

显示答案 正确答案: D

我的笔记 编辑笔记

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    NARRATOR:Listen to part of a lecture in an environmental science class.

    FEMALE PROFESSOR:When you try to imagine a fungus, you probably picture a mushroom popping up out of the ground... and think that's it.But a fungus like that... most of it actually lives underground.And fungi in general are often an important active component of the soil.A fungus secretes enzymes into the soil, enzymes that break down ...decompose organic material in the soil... so the fungus can absorb this material and get nutrition.

    But to me what's most interesting about this process is how it may enable fungi to help clean up environmental pollution in the soil...And that's thanks in part to a substance in their cell walls called chitin.

    Now a lot of people think fungi are related to plants, but they're not.Believe it or not, the only other place chitin is found in abundance is in the exoskeletons of insects, crabs, and such!So, in this sense, fungi are more associated with insects than with any plant.Strange, huh?And the chitin in the cell walls of a filamentous fungus...

    [resuming] ...A filament, of course, is a long, threadlike structure-cells joined end to end.Filamentous fungi grow in soil and in decaying vegetation, and, as their name implies, they exist as filaments.And, although regarded as microorganisms, filaments from a single fungus can fan out to occupy many square meters or even several square kilometers of forest floor.Their vast surface area allows them to break down and take in huge amounts of nutrients.But beyond that, the filaments also pull out of the soil a great deal of the [slowly] pollution that might be in there, especially heavy metals.

    And here's where chitin comes in.Like some other substances in fungal cell walls, chitin forms strong chemical bonds to heavy metals in the environment...in a process we call [stress first syllable] adsorption.

    Now don't confuse this with absorption, where a substance is absorbed into a cell, into the interior of a cell.I mean that's happening here too, but adsorption means binding to the outer surface of the cell.And a filamentous fungus can adsorb toxic heavy metals...bind them to the surface of its enormous network of filaments-and thereby detoxify a large soil ecosystem.The heavy metals are still there, but instead of leaching into the water system and contaminating the water underground, large amounts of these metals may remain bound to the chitin...to the cell walls of filamentous fungi in the soil...and thus remain chemically inactive for as long as thirty years-perhaps longer.

    In fact, we can actually use the cell walls of filamentous fungi as a filter, even after the fungi are dead.For example, the pharmaceutical industry grows filamentous fungi in large quantities in the lab.Like, to produce the antibiotic penicillin, the drug company grows the fungus Penicillium.And after the penicillin is extracted, these dead Penicillium filaments...we can use the chitin in their cell walls to make industrial filters to adsorb heavy metals.We can put these filters into waste pipes from industrial processes and use the filters to trap heavy metals, like mercury and zinc.Later, we can chemically extract the heavy metals and reuse the filter over and over.

    Now, going back to the [stress first syllable] absorption of toxic metals into the body of the fungus, let's turn our attention to mushrooms.Like other fungi, mushrooms can absorb large quantities of heavy metals.In fact, they may contain up to two-and-a-half times the concentration of toxic metals found in the soil they grow in.So mushrooms, at least what we see above ground...we can potentially harvest them and then, once and for all, safely dispose of the pollutants contained within them.In fact, to clean up...especially the groundwater system... permanently, harvesting mushrooms is probably the best way to go.For some reason, this hasn't happened yet, as far as I know.But I can easily envision cultivating mushrooms for the sole purpose of detoxifying a large underground ecosystem.

  • 旁白:请听环境科学课上的部分内容。

    教授:当你们试着想象真菌的时候,你们可能会想到蘑菇冒出地面的场景,并且认为这是真菌。但是像那样的真菌......实际上大部分的真菌都生活在地下。而且菌类通常是土壤中重要的活跃成分。真菌会把酶分泌进土壤中,酶会分解土壤中的有机材料,这样真菌就能吸收这种材料得到养分了。

    但是这个过程对我来说最有趣的部分是它能够帮助清理土壤中的环境污染。而这某种程度上要感谢它们细胞壁中一种叫做角素的物质。

    很多人认为菌群和植物有关,但其实不是。信不信由你,唯一能发现丰富的角素的其他地方只有昆虫、螃蟹之类的外骨骼中。就这种意义而言,真菌和昆虫的联系比和任何植物还要紧密。很奇怪,对吧?而丝状真菌的细胞壁中的角素......

    单纤维是一种很长的像线一样的结构,细胞首尾相连。丝状真菌在土壤和腐烂的植物中生长,而且正如它们的名字所指的那样,它们以丝的形式存在。虽然被视作微生物,但是一个单独的真菌的菌丝可以呈扇形散开,占据森林地面上很多平方米或甚至好几平方千米的面积。它们巨大的表面面积允许它们分解并吸收大量的营养物质。不过除此之外,这些菌丝还从土壤中带出了可能存在其中的大量污染物质,尤其是重金属。

    这就是角素的来源。和真菌细胞壁中的一些其他物质一样,在一个我们称为吸附的过程中,角素形成了牢固的化学粘着剂粘结了环境中的重金属。

    不要把这和吸收混淆了,吸收指的是一个物质被吸收进了细胞内,进入了细胞内部。我是说,这个过程也在这里发生,但是吸附指的是黏在细胞的外表面。丝状真菌可以吸附有毒的重金属,把它们黏在它巨大的菌丝网的表面,因此除去了一个大土壤生态系统中的毒素。重金属还是在那儿,不是渗透到水系统中并且污染地下水,而大量的这些金属也许会一直黏着在角素中,在土壤里的丝状真菌的细胞壁上,因此可以保持化学性质稳定长达30年,可能更长时间。

    事实上,我们还可以把丝状真菌的细胞壁用作过滤器,即使在这些真菌死后。举个例子来说,制药行业在实验室中培育了大量的丝状真菌。比如为了制造抗菌的盘尼西林,医药公司会培育盘尼西林菌群。青霉素提取后,这些死青霉菌丝...我们可以用它们细胞壁中的甲壳素来制造工业过滤器来吸附重金属。我们可以把这些过滤器放进工业工序的废物管道中,用这些过滤器困住像汞和锌这样的重金属。稍后我们可以用化学手段提取出重金属,并且一遍又一遍地重复使用这个过滤器。

    现在我们回到把有毒金属吸附进真菌内部,让我们把注意力转向蘑菇。和其他菌类一样,蘑菇可以吸附大量的重金属。事实上,它们可能包含的重金属是在它们生长的土壤中发现的有毒金属的2.5倍。所以蘑菇,至少是我们在地面上看到的那些......我们能把它们采摘下来,然后永久地安全地把包含在其中的污染物处理掉。事实上,为了永久地清洁,尤其是地下水系统,采摘蘑菇可能是最好的方法。据我所知,出于某种原因,这种做法还没有采用。但我能很容易地想象出仅仅为了去除大片地下生态系统中的毒素而种植蘑菇的场景。

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    题型分类:细节题

    题干分析:根据fungi get their food定位

    原文定位:A fungus secretes enzymes into the soil, enzymes that break down …decompose organic material in the soil… so the fungus can absorb this material and get nutrition. 

    选项分析:教授说fungi通过向土壤中分泌enzyme(生化酶)来分解土壤中的有机物质,这样fungi就能吸收分解后的有机营养了,选项B正确。

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