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提问人：网友Dume2021
发布时间：2022-01-07
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真核生物的mRNA合成由RNA聚合酶Ⅱ催化完成。（)
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更多“真核生物的mRNA合成由RNA聚合酶Ⅱ催化完成。()”相关的问题
第4题
下列关于mRNA的描述哪项是错误的（）
A、原核细胞的mRNA在翻译开始前需加多聚A尾巴
B、在原核细胞的许多mRNA携带着几个多肽链的结构信息
C、真核细胞转录生成的mRNA经常被“加工”
D、真核细胞mRNA在5′端携带有特殊的“帽子”结构
E、真核细胞mRNA是由RNA聚合酶Ⅱ催化合成的
第5题
真核生物的转录特点是（）
A、需要σ因子辨认起始点
B、发生在细胞质内，因为转录产物主要供蛋白质合成用
C、RNA聚合酶催化转录，还需要多种蛋白因子
D、mRNA因作为蛋白质合成模板，所以寿命最长
E、真核生物主要RNA有5种，所以RNA聚合酶也有5种
第6题
Organic agriculture is a relatively untapped resource for feeding the Earth's population，especially inthe face of climate change and other global challenges. That's the conclusion I reached in reviewing40 years of science comparing the long-term prospects of organic and conventional farming.
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The review study,"Organic Agriculture in the 21st Century,”is featured as the cover story for theFebruary issue of the journal Nature Plants. It is the first to compare organic and conventional agricultureacross the main goals of sustainability identified by the National Academy of Sciences: productivity,economics，and environment.
Critics have long argued that organic agriculture is inefficient，requiring more land to yield the sameamount of food. It's true that organic farming produces lower yields，averaging 10 to 20 percent less thanconventional. Advocates contend that the environmental advantages of organic agriculture far outweighthe lower yields，and that increasing research and breeding resources for organic systems would reduce theyield gap.Sometimes excluded from these arguments is the fact that we already produce enough food tomore than feed the world's 7.4 billion people but do not provide adequate access to all individuals
In some cases，organic yields can be higher than conventional. For example，in severe droughtconditions，which are expected to increase with climate change in many areas，organic farms can produceas good，if not better，yields because of the higher water-holding capacity of organically farmed soils.
What science does tell us is that mainstream conventional farming systems have provided growingsupplies of food and other products but often at the expense of other sustainability goals.
Conventional agriculture may produce more food，but it often comes at a cost to the environment.Biodiversity loss，environmental degradation，and severe impacts on ecosystem services have not onlyaccompanied conventional farming systems but have often extended well beyond their field boundaries.With organic agriculture，environmental costs tend to be lower and the benefits greater.
Overall，organic farms tend to store more soil carbon，have better soil quality， and reduce soil erosioncompared to their conventional counterparts. Organic agriculture also creates less soil and water pollutionand lower greenhouse gas emissions. And it's more energy-efficient because it doesn't rely on syntheticfertilizers or pesticides.
Organic agriculture is also associated with greater biodiversity of plants，animals，insects andmicroorganisms as well as genetic diversity. Biodiversity increases the services that nature provides andimproves the ability of farming systems to adapt to changing conditions.
Despite lower yields，organic agriculture is more profitable for farmers because consumers are willingto pay more.Higher prices，called price premiums，can be justified as a way to compensate farmers forproviding ecosystem services and avoiding environmental damage or external costs.
51. What do we learn from the conclusion of the author's review study?
A)More resources should be tapped for feeding the world's population.
B)Organic farming may be exploited to solve the global food problem.
C)The long-term prospects of organic farming are yet to be explored.
D) Organic farming is at least as promising as conventional farming.
52. What is the critics' argument against organic farming?
A)It cannot meet the need for food.
B) It cannot increase farm yields.
C )It is not really practical.
D) It is not that productive.
53. What does the author think should be taken into account in arguing about organic farming?
A)Growth in world population.
B)Deterioration in soil fertility.
C) Inequality in food distribution.
D)Advance in farming technology.
54. What does science tell us about conventional farming?
A) It will not be able to meet global food demand.
B)It is not conducive to sustainable development.
C) It will eventually give way to organic farming.
D) It is going mainstream throughout the world.
55. Why does the author think higher prices of organic farm produce are justifiable?
A)They give farmers going organic a big competitive edge.
B)They motivate farmers to upgrade farming technology.
C) Organic farming costs more than conventional farming.
D)Organic farming does long-term good to the ecosystem.
