Mire Biology

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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