Life in an Estuary
An estuary is the wide part of a river where it flows into the sea. It is affected by both marine influences(tides, waves, and the influx of saline water) and riverine influences (flows of fresh water and sediment) and is therefore not a perfectly stable environment. As a result, an estuary contains fewer resident species than the nearby marine or freshwater ecosystems, resulting in less competition for food and space. Because there is less competition, many estuarine species tend to be generalists that is,they are able to consume a variety of foods, depending on what is available. Species that can tolerate the salinity and temperature changes in estuaries can exploit the area’s high productivity grow rapidly, and multiply into enormous populations.
Many marine animals have body fluids that contain about the same concentration of salts as seawater and that are essentially isosmotic to the surrounding water; that is, the pressure of their body fluids is equal to the pressure of the seawater, and they neither gain nor lose water Because the marine environment remains relatively constant, they do not have a problem maintaining water balance. Animals that live in estuaries, however, must have some physiological mechanism for dealing with the varying salinity; otherwise, their tissues and cells would absorb water and lose salts as they encountered an environment with lower salinity than the sea. Thus, estuarine animals are either osmoconformers, which survive by having tissues and cells that tolerate the loss of salts through dilution, or osmoregulators, which maintain an optimal salt concentration in their tissues regardless of the salt content of their environment.
Animals such as jellyfish are unable to actively adjust the amount of water in their tissues. When their environment becomes less saline, their body fluid gains water and loses ions until it is isosmotic to the surroundings. These organisms are examples of osmoconformers. The ability of osmoconformers to inhabit estuaries is limited by their tolerance for changes in their body fluid.in contrast to osmoconformers, osmoregulators employ a variety of strategies to maintain a constant salt concentration in their bodies. Osmoregulators that live in estuarine waters concentrate salts in their body fluids when the concentration of salts in the surrounding water decreases. For instance some crabs and fish regulate their salt content in less-saline water by actively absorbing salt ions through the gills to compensate for salt ions lost from their body. This helps them to maintain a relatively constant body fluid. Some animals can either concentrate salts when their environment is less saline or excrete salts when the environment is extremely salty. The latter are generally animals that live partly on land or in areas such as salt marshes and mangrove swamps that occasionally receive large amounts of rain. Other animals, such as the blue crab, are osmorcgulators at lower environmental salinity and osmoconformers at higher environmental salinity. Many fish species are osmoregulators that can adjust to both high-salt and low-salt environments.
Some estuarine organisms wall themselves off from their external environment to decrease water and salt exchange with their surroundings. Many estuarine animals have body surfaces that are less permeable than those of purely marine forms. This decreased permeability can be the result of increased amounts of calcium in the exoskeleton (outer skeleton) or increased numbers of mucous glands in the skin.
In addition to changes in salinity, the problem of remaining stationary in a changing environment affects the distribution of organisms in estuaries. The more or less constant movement of water in an estuary makes it difficult for some organisms to remain stationary long enough to feed and carry on other vital functions. Because of this, survival favors organisms that are benthic – those that live at the bottom .Marine plants and algae in estuaries have substantial root systems, or holdfasts, to prevent moving water from pulling them up and carrying them out to sea. Animals live attached to the bottom, either in the available spaces around other sedentary animals and plants or buried in the small crevices between sediment particles.
1.An estuary is the wide part of a river where it flows into the sea. It is affected by both marine influences(tides, waves, and the influx of saline water) and riverine influences (flows of fresh water and sediment) and is therefore not a perfectly stable environment. As a result, an estuary contains fewer resident species than the nearby marine or freshwater ecosystems, resulting in less competition for food and space. Because there is less competition, many estuarine species tend to be generalists that is,they are able to consume a variety of foods, depending on what is available. Species that can tolerate the salinity and temperature changes in estuaries can exploit the area’s high productivity grow rapidly, and multiply into enormous populations.
The word”exploit”in the passage is closest in meaning to
Vocabulary Questions词汇题
Atake advantage of
Badd to
Crestore
DTransform
2.An estuary is the wide part of a river where it flows into the sea. It is affected by both marine influences(tides, waves, and the influx of saline water) and riverine influences (flows of fresh water and sediment) and is therefore not a perfectly stable environment. As a result, an estuary contains fewer resident species than the nearby marine or freshwater ecosystems, resulting in less competition for food and space. Because there is less competition, many estuarine species tend to be generalists that is,they are able to consume a variety of foods, depending on what is available. Species that can tolerate the salinity and temperature changes in estuaries can exploit the area’s high productivity grow rapidly, and multiply into enormous populations.
According to paragraph 1, estuarine species tend to be generalists because
Factual Information Questions事实信息题
Athey can eat both marine and freshwater species
Bthey need to grow rapidly and multiply while food is available
Cfewer species compete for food in estuaries than in the sea or rivers
Dlarger variety of food is available in estuaries than in the sea
3.Many marine animals have body fluids that contain about the same concentration of salts as seawater and that are essentially isosmotic to the surrounding water; that is, the pressure of their body fluids is equal to the pressure of the seawater, and they neither gain nor lose water Because the marine environment remains relatively constant, they do not have a problem maintaining water balance. Animals that live in estuaries, however, must have some physiological mechanism for dealing with the varying salinity; otherwise, their tissues and cells would absorb water and lose salts as they encountered an environment with lower salinity than the sea. Thus, estuarine animals are either osmoconformers, which survive by having tissues and cells that tolerate the loss of salts through dilution, or osmoregulators, which maintain an optimal salt concentration in their tissues regardless of the salt content of their environment.
According to paragraph 2, all of the following are true about many animals living in seawater EXCEPT:
Negative Factual Information Questions否定事实信息题
ATheir body fluids contain the same proportion of salt and water as the sea.
BThey lose water from their bodies into the sea and gain salt from the seawater.
CThey are easily able to keep the water content of their body fluids in balance.
DTheir body fluids have a pressure equal to the pressure of seawater.
4.Many marine animals have body fluids that contain about the same concentration of salts as seawater and that are essentially isosmotic to the surrounding water; that is, the pressure of their body fluids is equal to the pressure of the seawater, and they neither gain nor lose water Because the marine environment remains relatively constant, they do not have a problem maintaining water balance. Animals that live in estuaries, however, must have some physiological mechanism for dealing with the varying salinity; otherwise, their tissues and cells would absorb water and lose salts as they encountered an environment with lower salinity than the sea. Thus, estuarine animals are either osmoconformers, which survive by having tissues and cells that tolerate the loss of salts through dilution, or osmoregulators, which maintain an optimal salt concentration in their tissues regardless of the salt content of their environment.
According to paragraph 2, osmoconformers are able to live in estuaries by
Factual Information Questions事实信息题
Ahaving tissues that keep the same salt level even when the salt content of the environment changes
Bdiscarding excessive amounts of water in their bodies
Cchoosing estuarine locations where the salt content remains constant
Dhaving tissues that are able to function even when their salt level decreases
5.Animals such as jellyfish are unable to actively adjust the amount of water in their tissues. When their environment becomes less saline, their body fluid gains water and loses ions until it is isosmotic to the surroundings. These organisms are examples of osmoconformers. The ability of osmoconformers to inhabit estuaries is limited by their tolerance for changes in their body fluid.in contrast to osmoconformers, osmoregulators employ a variety of strategies to maintain a constant salt concentration in their bodies. Osmoregulators that live in estuarine waters concentrate salts in their body fluids when the concentration of salts in the surrounding water decreases. For instance some crabs and fish regulate their salt content in less-saline water by actively absorbing salt ions through the gills to compensate for salt ions lost from their body. This helps them to maintain a relatively constant body fluid. Some animals can either concentrate salts when their environment is less saline or excrete salts when the environment is extremely salty. The latter are generally animals that live partly on land or in areas such as salt marshes and mangrove swamps that occasionally receive large amounts of rain. Other animals, such as the blue crab, are osmorcgulators at lower environmental salinity and osmoconformers at higher environmental salinity. Many fish species are osmoregulators that can adjust to both high-salt and low-salt environments.
Why does the author mention “the blue crab” in the passage?
Rhetorical Purpose Questions修辞目的题
ATo contrast estuarine species with species that cannot tolerate changing levels of salt in water
BTo argue that no estuarine species is exclusively either an osmoconformer or an osmoregulator
CTo provide an example of an estuarine species that uses more than one strategy to adjust to salt levels
DTo provide evidence that some estuarine species can live in both the river and the sea
6.Animals such as jellyfish are unable to actively adjust the amount of water in their tissues. When their environment becomes less saline, their body fluid gains water and loses ions until it is isosmotic to the surroundings. These organisms are examples of osmoconformers. The ability of osmoconformers to inhabit estuaries is limited by their tolerance for changes in their body fluid.in contrast to osmoconformers, osmoregulators employ a variety of strategies to maintain a constant salt concentration in their bodies. Osmoregulators that live in estuarine waters concentrate salts in their body fluids when the concentration of salts in the surrounding water decreases. For instance some crabs and fish regulate their salt content in less-saline water by actively absorbing salt ions through the gills to compensate for salt ions lost from their body. This helps them to maintain a relatively constant body fluid. Some animals can either concentrate salts when their environment is less saline or excrete salts when the environment is extremely salty. The latter are generally animals that live partly on land or in areas such as salt marshes and mangrove swamps that occasionally receive large amounts of rain. Other animals, such as the blue crab, are osmorcgulators at lower environmental salinity and osmoconformers at higher environmental salinity. Many fish species are osmoregulators that can adjust to both high-salt and low-salt environments.
According to paragraph 4, all osmoregulators living in estuaries are able to do which TWO of the following?To receive credit. you must select Two answers
Factual Information Questions事实信息题
Select 2 answers
AMove onto land or into areas that receive large amounts of rain.
BKeep salt in their body fluids when there is less salt in the water.
CAbsorb salt ions through their gills to maintain their salt concentration levels.
DBecome osmoconformers whenever the salt level of estuary water changes
7.Some estuarine organisms wall themselves off from their external environment to decrease water and salt exchange with their surroundings. Many estuarine animals have body surfaces that are less permeable than those of purely marine forms. This decreased permeability can be the result of increased amounts of calcium in the exoskeleton (outer skeleton) or increased numbers of mucous glands in the skin.
According to paragraph 5, how are some animals that live in estuaries able to maintain salt in their tissues?
Factual Information Questions事实信息题
AThey take increased amounts of calcium from the environment into their cells.
BThey decrease the area of body surface exposed to the environment.
CThey have outside body surfaces that permit little water and salt exchange.
DThey occupy areas with natural walls that offer protection from estuary water
8.In addition to changes in salinity, the problem of remaining stationary in a changing environment affects the distribution of organisms in estuaries. The more or less constant movement of water in an estuary makes it difficult for some organisms to remain stationary long enough to feed and carry on other vital functions. Because of this, survival favors organisms that are benthic – those that live at the bottom .Marine plants and algae in estuaries have substantial root systems, or holdfasts, to prevent moving water from pulling them up and carrying them out to sea. Animals live attached to the bottom, either in the available spaces around other sedentary animals and plants or buried in the small crevices between sediment particles.
Which of the following can be inferred from paragraph 5 about plants in estuaries?
Inference Questions推理题
APlants that normally live near the surface of the water usually do not inhabit estuaries.
BPlants that are unable to adjust to the salinity of an estuary usually move out to the sea.
CPlants use their root systems to trap animals that move along the bottom of estuaries
DPlants that are not attached by roots to the floor of an estuary are held in place by sediment particles.
9.An estuary is the wide part of a river where it flows into the sea. ⬛ It is affected by both marine influences(tides, waves, and the influx of saline water) and riverine influences (flows of fresh water and sediment) and is therefore not a perfectly stable environment. ⬛ As a result, an estuary contains fewer resident species than the nearby marine or freshwater ecosystems, resulting in less competition for food and space. ⬛ Because there is less competition, many estuarine species tend to be generalists that is,they are able to consume a variety of foods, depending on what is available. Species that can tolerate the salinity and temperature changes in estuaries can exploit the area’s high productivity grow rapidly, and multiply into enormous populations. ⬛
Look at the four squaresthat indicate where the following sentence could be added to the passage
Given their high level of nutrients, estuaries also provide excellent habitats for the young of many species to grow and develop before going out to sea.Insert Text Questions句子插入题
Where would the sentence best fit？Click on a square sentence to the passage.
10.
Relatively few animal species are able to live in an estuary the wide part of a river where freshwater and saltwater mix.
Prose Summary Questions概要小结题
Select 3 answers
AUnlike sea animals, animals in estuaries have body fluids that contain the same amounts of salt and water as the water around them.
BWhile some animals in estuaries tolerate changes in salinity, others maintain salt concentrations in their bodies either actively or by physical separation.
CPlants and animals in estuaries must be able to tolerate the continuous movement of the water.
DAnimals in estuaries need to develop a means of adjusting to the varying levels of salinity in the water.
ECrabs and fish that lose salt through their gills often need to move out of estuaries into areas like marshes or swamps.
FBenthic animals in estuaries adjust to the constant water movement by regularly shifting their location from the surface of the water to the bottom.
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