Mires are wetland ecosystems comprising bogs, marshes, and similarity swampy areas. They provide ideal conditions for the formation of the partially decomposed vegetation known as peat. One aspect of the biology of mires that has long puzzled ecologists is why so many of the plants, particularity the small woody shrub species, appear to be so well adapted to drought. Although some peatlands become dry on their surfaces during particularity hot and dry summers, drought is not usually long lasting, nor is it usually severe. Yet many of the dwarf shrubs of peatlands, especially those in the temperate zone, have small and leathery rolled, evergreen leaves, which are more often associated with the vegetation of dry conditions, such as chaparral and Mediterranean scrub.These structural characteristics associated with drought in plants are termed “xeromorphic”.
In the arctic mires and many northern temperate peatlands, the black crowberry is a common member of the surface vegetation. This low-lying shrub is evergreen and has shiny,almost cylindrical leaves. On close inspection it can be seen that the leaves are actually tightly rolled in upon themselves, leaving only a very narrow,white-colored strip on the lower side where a thin gap leads to the delicate undersurface of the leaf. The upper part of the leaf is glossy with the presence of wax, which protects its surface cells from desiccation （drying up). The Labrador tea has large and leathery, evergreen leaves, which are not tightly rolled (although they do curl inward at their edges) but have dense masses of hair on the leaf undersides that prevent air movement and thus minimize the plant’s evaporation and water loss. The leatherleaf, another woody shrub of peatlands, has quite narrow evergreen leaves whose undersides are covered with small scales that serve a similar purpose of reducing evaporation.
In fact, almost all of the small, woody plants of temperate peatlands exhibit some degree of adaptation to drought, and this type of structure appears, at first sight, most inappropriate for such wet habitats.Plant ecologists and physiologists have developed several theories to account for the phenomenon, and it is entirely probable that a number of different causes lie behind this surprising aspect of mire vegetation. Perhaps the most obvious explanation is that the plants of the high latitude peatlands experience physiological drought, which means that although water may be present in abundance in the environment, it remains unavailable to the plant,which therefore suffers drought. The water is unavailable because of its very low temperature (or even its frozen state) in winter. Some experiments have shown that plants reduce their water uptake when the soil they are grown in is cooled, but this is not universally the case. It could be argued that under cold conditions the transpiration rate (the rate at which the leaves lose water vapor through pores on their surfaces) would be low anyway, so reducing evaporation in winter is not a problem. The idea that physiological drought can account for the xeromorphic characteristics of wetland plants is no longer strongly favored .
An alternative explanation,currently receiving considerable support from experimental work, is that reduced transpiration from leaves can cut down the quantity of toxins absorbed from the wetland soils. The main toxins proposed are iron and manganese. These elements are needed in small quantities by plants but in excess can prove harmful. Both elements are present in mire waters, especially under acid conditions when they become more soluble. The toxicity problem is overcome in part by the diffusion of oxygen from wetland plant roots.Oxygen passes from the atmosphere, through the plant,and leaks from the roots, where it intercepts iron and manganese, forming oxides that precipitate (condense) in the soil and therefore do not enter the plant. A fast rate of transpiration, however, can result in a greater inward movement of these toxins, leading to their accumulation in the leaves and causing death in sensitive species. In one very informative experiment, a sensitive species, bell heather, was sprayed with silicone to prevent transpiration, following which there was less uptake of iron, and the plant survived. So the xeromorphic adaptations of these wetland species may simply be a means of protecting themselves from accumulating unwanted metals in their tissues.
1
Mires are wetland ecosystems comprising bogs, marshes, and similarity swampy areas. They provide ideal conditions for the formation of the partially decomposed vegetation known as peat. One aspect of the biology of mires that has long puzzled ecologists is why so many of the plants, particularity the small woody shrub species, appear to be so well adapted to drought. Although some peatlands become dry on their surfaces during particularity hot and dry summers, drought is not usually long lasting, nor is it usually severe. Yet many of the dwarf shrubs of peatlands, especially those in the temperate zone, have small and leathery rolled, evergreen leaves, which are more often associated with the vegetation of dry conditions, such as chaparral and Mediterranean scrub.These structural characteristics associated with drought in plants are termed “xeromorphic”.
The word “ideal” in the passage is closest in meaning to
Abasic
Bperfect
Cnecessary
Dvarious
2
Mires are wetland ecosystems comprising bogs, marshes, and similarity swampy areas. They provide ideal conditions for the formation of the partially decomposed vegetation known as peat. One aspect of the biology of mires that has long puzzled ecologists is why so many of the plants, particularity the small woody shrub species, appear to be so well adapted to drought. Although some peatlands become dry on their surfaces during particularity hot and dry summers, drought is not usually long lasting, nor is it usually severe. Yet many of the dwarf shrubs of peatlands, especially those in the temperate zone, have small and leathery rolled, evergreen leaves, which are more often associated with the vegetation of dry conditions, such as chaparral and Mediterranean scrub.These structural characteristics associated with drought in plants are termed “xeromorphic”.
According to paragraph 1,which of the following is true about many plants that grow in peatlands?
AThey do much better in temperate climates than in other climates.
BThey are mostly small woody shrub species.
CThey have characteristics associated with dry conditions.
DThey are particularity at risk during hot and dry summers.
3
In the arctic mires and many northern temperate peatlands, the black crowberry is a common member of the surface vegetation. This low-lying shrub is evergreen and has shiny,almost cylindrical leaves. On close inspection it can be seen that the leaves are actually tightly rolled in upon themselves, leaving only a very narrow,white-colored strip on the lower side where a thin gap leads to the delicate undersurface of the leaf. The upper part of the leaf is glossy with the presence of wax, which protects its surface cells from desiccation （drying up). The Labrador tea has large and leathery, evergreen leaves, which are not tightly rolled (although they do curl inward at their edges) but have dense masses of hair on the leaf undersides that prevent air movement and thus minimize the plant’s evaporation and water loss. The leatherleaf, another woody shrub of peatlands, has quite narrow evergreen leaves whose undersides are covered with small scales that serve a similar purpose of reducing evaporation.
According to paragraph 2, all of the following statements about the black crowberry are true EXCEPT:
AIt grows very close to the ground.
BIt grows commonly on the surface in many northern temperate peatlands.
CIt has wax on the upper part of its leaves to prevent cells from becoming dry.
DIt has leaves with completely white undersides.
4
In the arctic mires and many northern temperate peatlands, the black crowberry is a common member of the surface vegetation. This low-lying shrub is evergreen and has shiny,almost cylindrical leaves. On close inspection it can be seen that the leaves are actually tightly rolled in upon themselves, leaving only a very narrow,white-colored strip on the lower side where a thin gap leads to the delicate undersurface of the leaf. The upper part of the leaf is glossy with the presence of wax, which protects its surface cells from desiccation （drying up). The Labrador tea has large and leathery, evergreen leaves, which are not tightly rolled (although they do curl inward at their edges) but have dense masses of hair on the leaf undersides that prevent air movement and thus minimize the plant’s evaporation and water loss. The leatherleaf, another woody shrub of peatlands, has quite narrow evergreen leaves whose undersides are covered with small scales that serve a similar purpose of reducing evaporation.
Paragraph 2 supports which of the following about evaporation in peatland plants?
AIt occurs more rapidly when there is air movement.
BIt occurs more slowly in the black crowberry than in the leatherleaf.
CIt is greatest in plants that have leaves with a glossy surface.
DIt occurs more slowly in plants with narrow leaves than those with large leaves.
5
In fact, almost all of the small, woody plants of temperate peatlands exhibit some degree of adaptation to drought, and this type of structure appears, at first sight, most inappropriate for such wet habitats.Plant ecologists and physiologists have developed several theories to account for the phenomenon, and it is entirely probable that a number of different causes lie behind this surprising aspect of mire vegetation. Perhaps the most obvious explanation is that the plants of the high latitude peatlands experience physiological drought, which means that although water may be present in abundance in the environment, it remains unavailable to the plant,which therefore suffers drought. The water is unavailable because of its very low temperature (or even its frozen state) in winter. Some experiments have shown that plants reduce their water uptake when the soil they are grown in is cooled, but this is not universally the case. It could be argued that under cold conditions the transpiration rate (the rate at which the leaves lose water vapor through pores on their surfaces) would be low anyway, so reducing evaporation in winter is not a problem. The idea that physiological drought can account for the xeromorphic characteristics of wetland plants is no longer strongly favored .
The word “inappropriate” in the passage is closest in meaning to
Aunimportant
Bunsafe
Cunsuitable
Dunusual
6
In fact, almost all of the small, woody plants of temperate peatlands exhibit some degree of adaptation to drought, and this type of structure appears, at first sight, most inappropriate for such wet habitats.Plant ecologists and physiologists have developed several theories to account for the phenomenon, and it is entirely probable that a number of different causes lie behind this surprising aspect of mire vegetation. Perhaps the most obvious explanation is that the plants of the high latitude peatlands experience physiological drought, which means that although water may be present in abundance in the environment, it remains unavailable to the plant,which therefore suffers drought. The water is unavailable because of its very low temperature (or even its frozen state) in winter. Some experiments have shown that plants reduce their water uptake when the soil they are grown in is cooled, but this is not universally the case. It could be argued that under cold conditions the transpiration rate (the rate at which the leaves lose water vapor through pores on their surfaces) would be low anyway, so reducing evaporation in winter is not a problem. The idea that physiological drought can account for the xeromorphic characteristics of wetland plants is no longer strongly favored .
According to paragraph 3,people have thought that plants might be unable to make use of the water in mires during at least certain periods because
Athe rate at which they lose water vapor is low
Bthe adaptation to conditions without water has been successful
Cthe water lacks necessary nutrients
Dthe water can become very cold or even frozen
7
An alternative explanation,currently receiving considerable support from experimental work, is that reduced transpiration from leaves can cut down the quantity of toxins absorbed from the wetland soils. The main toxins proposed are iron and manganese. These elements are needed in small quantities by plants but in excess can prove harmful. Both elements are present in mire waters, especially under acid conditions when they become more soluble. The toxicity problem is overcome in part by the diffusion of oxygen from wetland plant roots.Oxygen passes from the atmosphere, through the plant,and leaks from the roots, where it intercepts iron and manganese, forming oxides that precipitate (condense) in the soil and therefore do not enter the plant. A fast rate of transpiration, however, can result in a greater inward movement of these toxins, leading to their accumulation in the leaves and causing death in sensitive species. In one very informative experiment, a sensitive species, bell heather, was sprayed with silicone to prevent transpiration, following which there was less uptake of iron, and the plant survived. So the xeromorphic adaptations of these wetland species may simply be a means of protecting themselves from accumulating unwanted metals in their tissues.
According to paragraph 4,all of the following statements about iron and manganese are true EXCEPT:
AThey accumulate in plant tissues more rapidly when the plant has a higher transpiration rate.
BThey can kill a plant even in relatively small amounts.
CThey can be partly blocked from entering a plant by oxygen leaked from the plant’s root.
DThey become more soluble under acidic conditions.
8
An alternative explanation,currently receiving considerable support from experimental work, is that reduced transpiration from leaves can cut down the quantity of toxins absorbed from the wetland soils. The main toxins proposed are iron and manganese. These elements are needed in small quantities by plants but in excess can prove harmful. Both elements are present in mire waters, especially under acid conditions when they become more soluble. The toxicity problem is overcome in part by the diffusion of oxygen from wetland plant roots.Oxygen passes from the atmosphere, through the plant,and leaks from the roots, where it intercepts iron and manganese, forming oxides that precipitate (condense) in the soil and therefore do not enter the plant. A fast rate of transpiration, however, can result in a greater inward movement of these toxins, leading to their accumulation in the leaves and causing death in sensitive species. In one very informative experiment, a sensitive species, bell heather, was sprayed with silicone to prevent transpiration, following which there was less uptake of iron, and the plant survived. So the xeromorphic adaptations of these wetland species may simply be a means of protecting themselves from accumulating unwanted metals in their tissues.
In paragraph 4, why does the author discuss an experiment in which bell heather was sprayed with silicone?
ATo support the idea that slow transpiration rates protect mire plants against the accumulation of toxic metals
BTo suggest a way of protecting wetland plants from toxins in order to preserve sensitive species
CTo show that silicone can enable even highly sensitive plant species to survive some accumulation of certain toxic metals
DTo explain how toxins needed in small quantities by wetland species can be harmful in excess
9
An alternative explanation,currently receiving considerable support from experimental work, is that reduced transpiration from leaves can cut down the quantity of toxins absorbed from the wetland soils. The main toxins proposed are iron and manganese. These elements are needed in small quantities by plants but in excess can prove harmful. ■ Both elements are present in mire waters, especially under acid conditions when they become more soluble. ■The toxicity problem is overcome in part by the diffusion of oxygen from wetland plant roots. ■ Oxygen passes from the atmosphere, through the plant,and leaks from the roots, where it intercepts iron and manganese, forming oxides that precipitate (condense) in the soil and therefore do not enter the plant. ■ A fast rate of transpiration, however, can result in a greater inward movement of these toxins, leading to their accumulation in the leaves and causing death in sensitive species. In one very informative experiment, a sensitive species, bell heather, was sprayed with silicone to prevent transpiration, following which there was less uptake of iron, and the plant survived. So the xeromorphic adaptations of these wetland species may simply be a means of protecting themselves from accumulating unwanted metals in their tissues.
Look at the four squaresthat indicate where the following sentence could be added to the passage
This poses a threat to wetland plants taking water from the soil.
Where would the sentence best fit？Click on a square sentence to the passage.
10
Ecologists are puzzled by the adaptation of many plants in wetland ecosystems to drought.
APlant ecologists have attributed the adaptation of small,woody shrubs to drought conditions to the fact that some peatlands become dry during particularity hot and dry summers.
BAccording to a theory that was once supported by scientists, the xeromorphic characteristics of wetland plants developed in response to the plants’ reduced ability to take in water in cold conditions.
CCertain metals contained in mire soils can prevent water from reaching the wetland plants’ roots, which results in the need to reduce the rate of evaporation through the leaves.
DThe leaves of many peatland shrubs have several structural characteristics that work to prevent the leaves from drying out and reduce evaporation and water loss.
EA fast rate of transpiration can cause the formation of oxides inside plants,and these substances are particularity toxic to bell heather and some other plant species.
FExperimental evidence suggests that adaptations to drought may reduce the quantity of toxins absorbed from wetland soils,thus preventing dangerous accumulation of these toxins in plant tissues.
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答案：
1B
2C
3D
4A
5 C
6D
7B
8A
9B
10BDF
沼泽是由泥炭地、沼泽和类似的沼泽地区组成的湿地生态系统。它们为部分分解的植被——泥炭的形成提供了理想条件。沼泽生物学的一个长期困扰生态学家的方面是，为什么许多植物，特别是小型木本灌木物种，似乎非常适应干旱。虽然一些泥炭地在特别炎热和干燥的夏季表面会变干，但干旱通常既不持久也不严重。然而，泥炭地的许多侏儒灌木，特别是温带地区的灌木，都有小而皮质的卷曲常绿叶，这种特征更常与干旱条件下的植被，如硬叶灌丛和地中海灌木丛相关。与植物干旱相关的这些结构特征被称为“旱生形态”。
在北极沼泽和许多北部温带泥炭地，黑果越桔是地表植被的常见成员。这种低矮的灌木是常绿的，叶子光滑，几乎呈圆柱形。仔细观察可以看到，叶子实际上是紧紧地卷向内部，只在下侧留下一个非常窄的白色条带，那里有一个细小的缝隙通向叶子的脆弱的下表面。叶子的上部因为蜡的存在而呈光泽，这层蜡保护其表面细胞免于干燥（干涸）。拉布拉多茶的叶子大而皮质，是常绿的，虽然叶子没有紧紧地卷起（虽然它们确实向内卷曲），但其叶子下面有密集的毛发，阻止空气流动，从而最大限度地减少植物的蒸发和水分损失。另一种泥炭地的木本灌木——桤叶藓，其常绿叶片相当狭窄，下面覆盖着小鳞片，起到减少蒸发的类似作用。
事实上，温带泥炭地的几乎所有小型木本植物都表现出某种程度的适应干旱，这种结构在第一眼看来似乎不适合这种湿润的栖息地。植物生态学家和生理学家已经提出了几种理论来解释这一现象，很可能有多种不同的原因在这一令人惊讶的沼泽植被特性背后。最明显的解释是，高纬度泥炭地的植物体验到生理干旱，这意味着尽管环境中的水可能很丰富，但它对植物来说是不可用的，因此植物遭受干旱。水之所以不可用，是因为其温度非常低（或甚至处于冻结状态）在冬季。一些实验表明，当所种植土壤温度降低时，植物会减少水分吸收，但这并非普遍情况。
可以认为，在寒冷条件下，蒸腾率（叶片通过表面孔隙失去水蒸气的速率）本来就低，因此冬季减少蒸发并不是问题。认为生理干旱可以解释湿地植物的旱生特征的观点已不再受到强烈支持。
另一种解释，目前从实验工作中获得了相当多的支持，是减少叶片的蒸腾作用可以减少从湿地土壤中吸收的毒素量。主要提出的毒素是铁和锰。这些元素植物需要少量，但过量则可能有害。这两种元素特别是在酸性条件下，当它们变得更易溶时，在泥炭地水域中存在。通过湿地植物根部的氧气扩散部分解决了毒性问题。氧气从大气中通过植物传递，并从根部泄漏，其中它与铁和锰相遇，形成沉淀在土壤中的氧化物，因此不进入植物。然而，快速的蒸腾速率可能会导致这些毒素的更大内流动，使它们在叶子中积累，导致敏感物种死亡。在一次非常有启发性的实验中，一个敏感物种——石楠花，被喷涂硅胶以阻止蒸腾，之后铁的摄取减少，植物存活下来。因此，这些湿地物种的旱生适应可能仅仅是一种保护自己不在组织中积累不需要的金属的方式。
