Waterfalls can act as barriers that pose a number of challenges to plants and animals. There is evidence that waterfalls can so isolate the upper parts of rivers that distinct varieties or even unique species of fish may evolve in the riveron each side of the waterfall. Waterfalls commonly form obstacles to migration but, as the well-known example of salmon testifies, some creatures are able to overcome low waterfalls and rapids. particularly where the descent is broken into separate waterfalls forming a natural staircase. While no fish can swim against falling water, many jump effectively. Atlantic salmon can clear over three meters. To enable it to jump higher, the salmon leaps from the peak of the standing wave that commonly forms near the foot of a waterfall. Here there is an upward component in the turbulence which assists the fish in its leap. To facilitate the movement of fish upstream, fish passes, which are artificial stepped channels bypassing waterfalls, have been built on many rivers, while in some places the waterfalls themselves have been deliberately modified or destroyed for this purpose.
When descending rivers, fish may have no difficulty dealing with waterfalls and rapids, particularly where the drop is small enough for them or their parents to have ascended. Here water acts as a cushion and lessens the effect of the fall, helping prevent damage. Waterfalls can be destructive of aquatic life, however. Some researchers have found that many species of plankton, minute water animals and plants usually living in colonies, are eliminated by waterfalls and rapids. Others have shown that some species can survive the descent of steep rapids and even major waterfalls.
Swimming and jumping are not the only means by which fish can overcome the barriers imposed by rapids and waterfalls. Species with suckers (organs that help an animal cling to a surface) can often ascend wet vertical rock faces beside or beneath falling water in stream courses. Some fish belonging to the large family of gobies have the ability to climb waterfalls in this way. Other fish that have the ability to overcome waterfall barriers include young eels, which make use of wet areas beside the stream to bypass falling water.
While waterfalls often act as barriers to movement and form obstacles in the stream that separate parts of the stream where life can be readily sustained, they provide a habitat to which some species are well adapted. There are plants and other organisms that survive and even flourish in the fast-flowing, turbulent water of waterfalls and rapids. Its waters well supplied with oxygen by numerous falls, the tumbling stream provides an ideal environment for the production of chemical energy by living organisms in the form of plants such as algae, so long as there is adequate sunlight for photosynthesis. Particularly important are the small plants which grow closely attached to other plants, rocks, stones, and dead branches in the stream. These form a dense, slimy surface of algae or mosses. which are the most important photosynthetic organisms in running streams. The highly productive level at which living material is generated is due largely to the rapid current. This prevents the development of a layer of nutrient- and carbon dioxide-depleted water that would otherwise build up around the plants, as they absorb nutrients and use carbon dioxide for photosynthesis. Such a layer would reduce photosynthesis. Within the mass of algae and other plants lives a very rich collection of small animals, such as water mites and insect larvae. Clinging to solid holds in the tumbling flow and in the splash zones of waterfalls, these communities of plants and tiny animals flourish, providing food for the rest of the inhabitants of the stream. Many of the latter, however are unable to live in the fast-moving, turbulent waters of rapids and waterfalls, except for some species that pass through them for short periods on their way to more favorable environments. Indeed, the animals that are commonly found in and around fast-moving streams and waterfalls normally take advantage of any available protection from the powerful currents, finding refuge behind or beneath rocks, or in gentle currents and quiet pools outside the main flow.
1
Waterfalls can act as barriers that pose a number of challenges to plants and animals. There is evidence that waterfalls can so isolate the upper parts of rivers that distinct varieties or even unique species of fish may evolve in the riveron each side of the waterfall. Waterfalls commonly form obstacles to migration but, as the well-known example of salmon testifies, some creatures are able to overcome low waterfalls and rapids. particularly where the descent is broken into separate waterfalls forming a natural staircase. While no fish can swim against falling water, many jump effectively. Atlantic salmon can clear over three meters. To enable it to jump higher, the salmon leaps from the peak of the standing wave that commonly forms near the foot of a waterfall. Here there is an upward component in the turbulence which assists the fish in its leap. To facilitate the movement of fish upstream, fish passes, which are artificial stepped channels bypassing waterfalls, have been built on many rivers, while in some places the waterfalls themselves have been deliberately modified or destroyed for this purpose.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
AAlthough waterfalls often make migration difficult, some animals can overcome low waterfalls.
BSalmon can overcome waterfalls, but they can only do so when the descent forms a natural staircase.
CIf descents can be broken into separate waterfalls, they will form a natural staircase for creatures to use for migration.
DAs the well-known example of salmon testifies, waterfalls commonly form obstacles to migration.
2
Waterfalls can act as barriers that pose a number of challenges to plants and animals. There is evidence that waterfalls can so isolate the upper parts of rivers that distinct varieties or even unique species of fish may evolve in the riveron each side of the waterfall. Waterfalls commonly form obstacles to migration but, as the well-known example of salmon testifies, some creatures are able to overcome low waterfalls and rapids. particularly where the descent is broken into separate waterfalls forming a natural staircase. While no fish can swim against falling water, many jump effectively. Atlantic salmon can clear over three meters. To enable it to jump higher, the salmon leaps from the peak of the standing wave that commonly forms near the foot of a waterfall. Here there is an upward component in the turbulence which assists the fish in its leap. To facilitate the movement of fish upstream, fish passes, which are artificial stepped channels bypassing waterfalls, have been built on many rivers, while in some places the waterfalls themselves have been deliberately modified or destroyed for this purpose.
According to paragraph 1, which of the following techniques do salmon use to overcome barriers in streams?
AThey cause waves in the water that facilitate their movement upstream
BThey destroy barriers in some places and bypass waterfalls in others
CThey take advantage of turbulence at the bottom of waterfalls to increase the height of their leaps
DThey use their ability to swim upward through the water of waterfalls.
3
When descending rivers, fish may have no difficulty dealing with waterfalls and rapids, particularly where the drop is small enough for them or their parents to have ascended. Here water acts as a cushion and lessens the effect of the fall, helping prevent damage. Waterfalls can be destructive of aquatic life, however. Some researchers have found that many species of plankton, minute water animals and plants usually living in colonies, are eliminated by waterfalls and rapids. Others have shown that some species can survive the descent of steep rapids and even major waterfalls.
The word “Others” in the passage refers to
Aother waterfalls and rapids
Bother colonies
Cother minute animals and plants
Dother researchers
4
According to paragraph 3, how do some fish belonging to the family of gobies overcome barriers imposed by waterfalls?
AThey use suckers to climb rocks.
BThey use their swimming and jumping ability to go up falling water.
CThey use a special organ to attach to fish that can swim or jump up waterfalls.
DThey push rocks into vertical structures beside and beneath falling water.
5
While waterfalls often act as barriers to movement and form obstacles in the stream that separate parts of the stream where life can be readily sustained, they provide a habitat to which some species are well adapted. There are plants and other organisms that survive and even flourish in the fast-flowing, turbulent water of waterfalls and rapids. Its waters well supplied with oxygen by numerous falls, the tumbling stream provides an ideal environment for the production of chemical energy by living organisms in the form of plants such as algae, so long as there is adequate sunlight for photosynthesis. Particularly important are the small plants which grow closely attached to other plants, rocks, stones, and dead branches in the stream. These form a dense, slimy surface of algae or mosses. which are the most important photosynthetic organisms in running streams. The highly productive level at which living material is generated is due largely to the rapid current. This prevents the development of a layer of nutrient- and carbon dioxide-depleted water that would otherwise build up around the plants, as they absorb nutrients and use carbon dioxide for photosynthesis. Such a layer would reduce photosynthesis. Within the mass of algae and other plants lives a very rich collection of small animals, such as water mites and insect larvae. Clinging to solid holds in the tumbling flow and in the splash zones of waterfalls, these communities of plants and tiny animals flourish, providing food for the rest of the inhabitants of the stream. Many of the latter, however are unable to live in the fast-moving, turbulent waters of rapids and waterfalls, except for some species that pass through them for short periods on their way to more favorable environments. Indeed, the animals that are commonly found in and around fast-moving streams and waterfalls normally take advantage of any available protection from the powerful currents, finding refuge behind or beneath rocks, or in gentle currents and quiet pools outside the main flow.
The word “dense” in the passage is closest in meaning to
Asmooth
Bthick
Csoft
Dfast-growing
6
While waterfalls often act as barriers to movement and form obstacles in the stream that separate parts of the stream where life can be readily sustained, they provide a habitat to which some species are well adapted. There are plants and other organisms that survive and even flourish in the fast-flowing, turbulent water of waterfalls and rapids. Its waters well supplied with oxygen by numerous falls, the tumbling stream provides an ideal environment for the production of chemical energy by living organisms in the form of plants such as algae, so long as there is adequate sunlight for photosynthesis. Particularly important are the small plants which grow closely attached to other plants, rocks, stones, and dead branches in the stream. These form a dense, slimy surface of algae or mosses. which are the most important photosynthetic organisms in running streams. The highly productive level at which living material is generated is due largely to the rapid current. This prevents the development of a layer of nutrient- and carbon dioxide-depleted water that would otherwise build up around the plants, as they absorb nutrients and use carbon dioxide for photosynthesis. Such a layer would reduce photosynthesis. Within the mass of algae and other plants lives a very rich collection of small animals, such as water mites and insect larvae. Clinging to solid holds in the tumbling flow and in the splash zones of waterfalls, these communities of plants and tiny animals flourish, providing food for the rest of the inhabitants of the stream. Many of the latter, however are unable to live in the fast-moving, turbulent waters of rapids and waterfalls, except for some species that pass through them for short periods on their way to more favorable environments. Indeed, the animals that are commonly found in and around fast-moving streams and waterfalls normally take advantage of any available protection from the powerful currents, finding refuge behind or beneath rocks, or in gentle currents and quiet pools outside the main flow.
Why does the author include the information that the development of a certain layer of water “would reduce photosynthesis”?
ATo identify a factor that causes currents to flow more rapidly
BTo illustrate the effects of small animals that sometimes live within algae and other plants
CTo help explain how the rapid current in waterfalls contributes to the productive generation of living material
DTo explain the steps in the process by which plants obtain nutrients from photosynthesis
7
While waterfalls often act as barriers to movement and form obstacles in the stream that separate parts of the stream where life can be readily sustained, they provide a habitat to which some species are well adapted. There are plants and other organisms that survive and even flourish in the fast-flowing, turbulent water of waterfalls and rapids. Its waters well supplied with oxygen by numerous falls, the tumbling stream provides an ideal environment for the production of chemical energy by living organisms in the form of plants such as algae, so long as there is adequate sunlight for photosynthesis. Particularly important are the small plants which grow closely attached to other plants, rocks, stones, and dead branches in the stream. These form a dense, slimy surface of algae or mosses. which are the most important photosynthetic organisms in running streams. The highly productive level at which living material is generated is due largely to the rapid current. This prevents the development of a layer of nutrient- and carbon dioxide-depleted water that would otherwise build up around the plants, as they absorb nutrients and use carbon dioxide for photosynthesis. Such a layer would reduce photosynthesis. Within the mass of algae and other plants lives a very rich collection of small animals, such as water mites and insect larvae. Clinging to solid holds in the tumbling flow and in the splash zones of waterfalls, these communities of plants and tiny animals flourish, providing food for the rest of the inhabitants of the stream. Many of the latter, however are unable to live in the fast-moving, turbulent waters of rapids and waterfalls, except for some species that pass through them for short periods on their way to more favorable environments. Indeed, the animals that are commonly found in and around fast-moving streams and waterfalls normally take advantage of any available protection from the powerful currents, finding refuge behind or beneath rocks, or in gentle currents and quiet pools outside the main flow.
According to paragraph 4, which of the following is true of the surface of algae and mosses that forms around various objects in streams?
AIt forms an obstacle to the production of chemical energy through photosynthesis
BIt prevents plants, rocks, stones, and dead branches from building up in the water.
CIt is not found in waterfalls because of the fast-flowing, turbulent water there.
DIt supports other living organisms in the stream by providing the greatest source of photosynthesis.
8
While waterfalls often act as barriers to movement and form obstacles in the stream that separate parts of the stream where life can be readily sustained, they provide a habitat to which some species are well adapted. There are plants and other organisms that survive and even flourish in the fast-flowing, turbulent water of waterfalls and rapids. Its waters well supplied with oxygen by numerous falls, the tumbling stream provides an ideal environment for the production of chemical energy by living organisms in the form of plants such as algae, so long as there is adequate sunlight for photosynthesis. Particularly important are the small plants which grow closely attached to other plants, rocks, stones, and dead branches in the stream. These form a dense, slimy surface of algae or mosses. which are the most important photosynthetic organisms in running streams. The highly productive level at which living material is generated is due largely to the rapid current. This prevents the development of a layer of nutrient- and carbon dioxide-depleted water that would otherwise build up around the plants, as they absorb nutrients and use carbon dioxide for photosynthesis. Such a layer would reduce photosynthesis. Within the mass of algae and other plants lives a very rich collection of small animals, such as water mites and insect larvae. Clinging to solid holds in the tumbling flow and in the splash zones of waterfalls, these communities of plants and tiny animals flourish, providing food for the rest of the inhabitants of the stream. Many of the latter, however are unable to live in the fast-moving, turbulent waters of rapids and waterfalls, except for some species that pass through them for short periods on their way to more favorable environments. Indeed, the animals that are commonly found in and around fast-moving streams and waterfalls normally take advantage of any available protection from the powerful currents, finding refuge behind or beneath rocks, or in gentle currents and quiet pools outside the main flow.
Paragraph 4 supports which of the following statements about the animals that eat water mites and insect larvae?
AThey inhabit the stream but do not spend much time in the rapids or waterfalls themselves.
BThey cling to objects that are inside waterfalls or in the splash zones surrounding waterfalls.
CThey help prevent the development of layers of nutrient- and carbon dioxide-depleted water
DThey prefer fast-moving, turbulent waters.
9
Waterfalls can act as barriers that pose a number of challenges to plants and animals. ■There is evidence that waterfalls can so isolate the upper parts of rivers that distinct varieties or even unique species of fish may evolve in the riveron each side of the waterfall. ■Waterfalls commonly form obstacles to migration but, as the well-known example of salmon testifies, some creatures are able to overcome low waterfalls and rapids. particularly where the descent is broken into separate waterfalls forming a natural staircase. ■While no fish can swim against falling water, many jump effectively. ■Atlantic salmon can clear over three meters. To enable it to jump higher, the salmon leaps from the peak of the standing wave that commonly forms near the foot of a waterfall. Here there is an upward component in the turbulence which assists the fish in its leap. To facilitate the movement of fish upstream, fish passes, which are artificial stepped channels bypassing waterfalls, have been built on many rivers, while in some places the waterfalls themselves have been deliberately modified or destroyed for this purpose.
Look at the four squaresthat indicate where the following sentence could be added to the passage
For instance, varieties of one species of fish living in streams above and below waterfalls on the island of Trinidad have been found to differ in growth and reproductive rates.
Where would the sentence best fit？Click on a square sentence to the passage.
10
Waterfalls and rapids have important effects on life in rivers.
AWaterfalls often act to isolate parts of a stream, preventing species from migrating upstream and destroying organisms passing through them downstream.
BFish can often easily descend waterfalls, especially small waterfalls, and some species of fish have developed ways of moving up waterfalls.
CSlimy masses of algae that grow in waterfall environments generally ad to the development of layers of nutrient- and carbon dioxide-depleted water.
DThe modification and destruction of streams and waterfalls has led to the destruction of many species of aquatic life and reduced Atlantic salmon populations.
EIf sunlight is present, the waterfall environment provides good conditions for photosynthesis and is thus favorable for species that can live in turbulent water.
FThe animals that are able to live in the fast-moving, turbulent waters of rapids and waterfalls are generally large animals, while small animals tend to stay in quiet pools outside the main flow.
