TF阅读真题第874篇Diving for Food by Birds

Diving for Food by Birds

 

 

Seabirds are physiologically adapted to dive underwater for food, a strategy that necessarily poses problems. An obvious problem is that when underwater, the bird cannot breathe and must rely on its accumulated oxygen stores. Diving adaptations have been most extensively studied in emperor penguins, which can remain underwater for twenty or more minutes. During the first five minutes or so, an emperor penguin’s body processes continue to function as they do when the animal is breathing air, with lactate building in the muscles as the bird expends oxygen from them. After about five minutes, however, lactate begins apparing in the blood, at which point the penguin shifts to anaerobic metabolism-cell function without oxygen-in which nonessential organs are shut down and blood is sent only to selected tissues. Another key adaptation to diving is a reduction in heart rate underwater. Detected via attached electrocardiogram recorders, the heart rate of a resting emperor penguin is around 70 beats per minute. This value roughly doubles to around 140 beats per minute immediately before the dive. If the dive is long, heart rate drops off dramatically and may reach as low as three beats per minute. Just before the penguin surfaces, the rate accelerates. It can be around 200 beats per minute when the penguin surfaces and can breathe once more to replenish its oxygen stores.

Remembering that even in tropical areas, the water temperature below 200 meters is probably no higher than 5°C, a further physiological problem faced by seabirds underwater is potentially that of cold. Penguins and auks have tight plumage (feathers) that retains air close to the skin. This assists heat retention, albeit by creating buoyancy (tendency to float) that hinders the downward dive. The situation is different in cormorants and shags. Their plumage is notoriously wettable. Think of the classic pose of a perched cormorant hanging out its wings to dry after a spell of swimming. If the water has reached the skin, the cormorant will have lost more heat than another seabird whose skin remains dry.

In fact, the paradox is more apparent than real. The great cormorant is one of the most widespread of all seabirds. Its breeding range extends from Australia via Southeast Asia to Europe and Greenland. Whether in northern France or Greenland, it requires less food per day than other seabirds of comparable weight. The birds are evidently not leaking heat and do not need to take in extra food. How they retain heat became evident when European researchers looked at the plumage more closely. All four subspecies studied, living in sub-Arctic to subtropical climes, retained an insulating air layer in their plumage, which was, however, much thinner than for other species of diving birds. Detailed examination of the plumage showed that each cormorant body feather has a loose, instantaneously wet, outer section and a highly waterproof inner portion.  

Because of air trapped in the plumage, plus that in the lungs and air sacs (lung extensions), seabirds are positively buoyant when first submerging. Their natural tendency is to float back upward. Therefore they have to work hard to reach greater depths. As the birds reach those greater depths, the air compresses and eventually a depth is reached where they are neutrally buoyant, that is, they will neither sink nor rise. This depth depends on the quantity of air in the lungs and air sacs at submergence; the more air to be compressed, the greater the depth of neutral buoyancy. In fact, penguins anticipating diving deeper take in more air before submerging, which then allows a longer dive and increases the depth at which they are neutrally buoyant. Therefore, rather neatly, there is a close correlation between diving depth and duration.  

Having, in ornithologist Rory Wilson’s evocative descriptions, pedaled downward, the bird faces an ascent that is relatively easy. This is simply because the compressed air expands at shallower depths, increasing positive buoyancy and serving to thrust the bird upward at an ever-faster speed. For example, Magellanic penguins beginning their ascent from 50 meters initially ascend at a little more than half a meter per second. When they have reached 20 meters, the ascent rate has topped a meter per second.

 

 

 

 

 

1

Seabirds are physiologically adapted to dive underwater for food, a strategy that necessarily poses problems. An obvious problem is that when underwater, the bird cannot breathe and must rely on its accumulated oxygen stores. Diving adaptations have been most extensively studied in emperor penguins, which can remain underwater for twenty or more minutes. During the first five minutes or so, an emperor penguin’s body processes continue to function as they do when the animal is breathing air, with lactate building in the muscles as the bird expends oxygen from them. After about five minutes, however, lactate begins apparing in the blood, at which point the penguin shifts to anaerobic metabolism-cell function without oxygen-in which nonessential organs are shut down and blood is sent only to selected tissues. Another key adaptation to diving is a reduction in heart rate underwater. Detected via attached electrocardiogram recorders, the heart rate of a resting emperor penguin is around 70 beats per minute. This value roughly doubles to around 140 beats per minute immediately before the dive. If the dive is long, heart rate drops off dramatically and may reach as low as three beats per minute. Just before the penguin surfaces, the rate accelerates. It can be around 200 beats per minute when the penguin surfaces and can breathe once more to replenish its oxygen stores.

According to paragraph 1， an emperor penguin experiences all of the following changes during dives lasting longer than five minutes EXCEPT:

Negative Factual Information Questions否定事实信息题

AThe lactate levels in its blood decrease.

BBody processes not needed stop operating.

CBlood stops flowing to some parts of its body.

DThe heart slows the rate at which it beats.

 

2

Seabirds are physiologically adapted to dive underwater for food, a strategy that necessarily poses problems. An obvious problem is that when underwater, the bird cannot breathe and must rely on its accumulated oxygen stores. Diving adaptations have been most extensively studied in emperor penguins, which can remain underwater for twenty or more minutes. During the first five minutes or so, an emperor penguin’s body processes continue to function as they do when the animal is breathing air, with lactate building in the muscles as the bird expends oxygen from them. After about five minutes, however, lactate begins apparing in the blood, at which point the penguin shifts to anaerobic metabolism-cell function without oxygen-in which nonessential organs are shut down and blood is sent only to selected tissues. Another key adaptation to diving is a reduction in heart rate underwater. Detected via attached electrocardiogram recorders, the heart rate of a resting emperor penguin is around 70 beats per minute. This value roughly doubles to around 140 beats per minute immediately before the dive. If the dive is long, heart rate drops off dramatically and may reach as low as three beats per minute. Just before the penguin surfaces, the rate accelerates. It can be around 200 beats per minute when the penguin surfaces and can breathe once more to replenish its oxygen stores.

According to paragraph 1， emperor penguins’ heart rates are highest when these penguins

Factual Information Questions事实信息题

Aare resting after a short dive

Bare preparing to dive into the water

Cbegin the switch to anaerobic metabolism

Dhave just come back to the surface after a dive

3

Remembering that even in tropical areas, the water temperature below 200 meters is probably no higher than 5°C, a further physiological problem faced by seabirds underwater is potentially that of cold. Penguins and auks have tight plumage (feathers) that retains air close to the skin. This assists heat retention, albeit by creating buoyancy (tendency to float) that hinders the downward dive. The situation is different in cormorants and shags. Their plumage is notoriously wettable. Think of the classic pose of a perched cormorant hanging out its wings to dry after a spell of swimming. If the water has reached the skin, the cormorant will have lost more heat than another seabird whose skin remains dry.

It can be inferred from paragraph 2 that compared with penguins and auks, cormorants and shags

Inference Questions推理题

Again less buoyancy from the air near their skin

Bare better able to hold air close to their skin

Care more likely to remain warm in cold water

Dare more likely to keep their skin dry

 

4

In fact, the paradox is more apparent than real. The great cormorant is one of the most widespread of all seabirds. Its breeding range extends from Australia via Southeast Asia to Europe and Greenland. Whether in northern France or Greenland, it requires less food per day than other seabirds of comparable weight. The birds are evidently not leaking heat and do not need to take in extra food. How they retain heat became evident when European researchers looked at the plumage more closely. All four subspecies studied, living in sub-Arctic to subtropical climes, retained an insulating air layer in their plumage, which was, however, much thinner than for other species of diving birds. Detailed examination of the plumage showed that each cormorant body feather has a loose, instantaneously wet, outer section and a highly waterproof inner portion.  

What is the author’s purpose in including the information that great cormorants require “less food per day than other seabirds of comparable weight”?

Factual Information Questions事实信息题

ATo explain why great cormorants are able to travel long distances around the world

BTo explain why the feathers of great cormorants differ from those of most other diving birds

CTo explain why the insulating layer of great cormorants’ plumage is thinner than that of other diving birds

DTo support the idea that great cormorants do not lose particularly large amounts of heat

 

5

In fact, the paradox is more apparent than real. The great cormorant is one of the most widespread of all seabirds. Its breeding range extends from Australia via Southeast Asia to Europe and Greenland. Whether in northern France or Greenland, it requires less food per day than other seabirds of comparable weight. The birds are evidently not leaking heat and do not need to take in extra food. How they retain heat became evident when European researchers looked at the plumage more closely. All four subspecies studied, living in sub-Arctic to subtropical climes, retained an insulating air layer in their plumage, which was, however, much thinner than for other species of diving birds. Detailed examination of the plumage showed that each cormorant body feather has a loose, instantaneously wet, outer section and a highly waterproof inner portion.  

The word “instantaneously”in the passage is closest in meaning to

Vocabulary Questions词汇题

Arelatively

Bgenerally

Cimmediately

Drarely

 

6

In fact, the paradox is more apparent than real. The great cormorant is one of the most widespread of all seabirds. Its breeding range extends from Australia via Southeast Asia to Europe and Greenland. Whether in northern France or Greenland, it requires less food per day than other seabirds of comparable weight. The birds are evidently not leaking heat and do not need to take in extra food. How they retain heat became evident when European researchers looked at the plumage more closely. All four subspecies studied, living in sub-Arctic to subtropical climes, retained an insulating air layer in their plumage, which was, however, much thinner than for other species of diving birds. Detailed examination of the plumage showed that each cormorant body feather has a loose, instantaneously wet, outer section and a highly waterproof inner portion.  

Paragraph 3 suggests that European researchers discovered which of the following about the body feathers of cormorants?

Inference Questions推理题

AThey lose their insulating layer of air when cormorants are underwater.

BThey vary somewhat based on the subspecies and its location.

CThe inner part of these feathers stays wet longer than the outer part does.

DThey are structured in a way that helps cormorants keep body heat in while underwater.

 

7

Because of air trapped in the plumage, plus that in the lungs and air sacs (lung extensions), seabirds are positively buoyant when first submerging. Their natural tendency is to float back upward. Therefore they have to work hard to reach greater depths. As the birds reach those greater depths, the air compresses and eventually a depth is reached where they are neutrally buoyant, that is, they will neither sink nor rise. This depth depends on the quantity of air in the lungs and air sacs at submergence; the more air to be compressed, the greater the depth of neutral buoyancy. In fact, penguins anticipating diving deeper take in more air before submerging, which then allows a longer dive and increases the depth at which they are neutrally buoyant. Therefore, rather neatly, there is a close correlation between diving depth and duration.  

The word “anticipating”in the passage is closest in meaning to

Vocabulary Questions词汇题

Aexpecting

Brelying on

Cused to

Dcapable of

 

8

Because of air trapped in the plumage, plus that in the lungs and air sacs (lung extensions), seabirds are positively buoyant when first submerging. Their natural tendency is to float back upward. Therefore they have to work hard to reach greater depths. As the birds reach those greater depths, the air compresses and eventually a depth is reached where they are neutrally buoyant, that is, they will neither sink nor rise. This depth depends on the quantity of air in the lungs and air sacs at submergence; the more air to be compressed, the greater the depth of neutral buoyancy. In fact, penguins anticipating diving deeper take in more air before submerging, which then allows a longer dive and increases the depth at which they are neutrally buoyant. Therefore, rather neatly, there is a close correlation between diving depth and duration.  

According to paragraph 4， which of the following changes would increase the depth at which a diving seabird becomes neutrally buoyant?

Factual Information Questions事实信息题

AAn increase in the amount of air in the bird’s body

BAn increase in the bird’s effort to move downward

CAn increase in the exchange of air between the bird’s lungs and air sacs.

DA decrease in the amount of time the bird spends underwater

 

9

In fact, the paradox is more apparent than real. The great cormorant is one of the most widespread of all seabirds. Its breeding range extends from Australia via Southeast Asia to Europe and Greenland. Whether in northern France or Greenland, it requires less food per day than other seabirds of comparable weight. The birds are evidently not leaking heat and do not need to take in extra food. [■]How they retain heat became evident when European researchers looked at the plumage more closely. [■]All four subspecies studied, living in sub-Arctic to subtropical climes, retained an insulating air layer in their plumage, which was, however, much thinner than for other species of diving birds. [■]Detailed examination of the plumage showed that each cormorant body feather has a loose, instantaneously wet, outer section and a highly waterproof inner portion.  [■]

Look at the four squaresthat indicate where the following sentence could be added to the passage

Why not?Insert Text Questions句子插入题

Where would the sentence best fit？Click on a square  sentence to the passage.

10

Seabirds dive into the ocean for food.

Prose Summary Questions概要小结题

Select 3 answers

AMost seabirds can remain underwater for about five minutes before their oxygen stores run out, but emperor penguins have extra stores that help them remain underwater longer.

BSome seabirds have an insulating layer of air that protects the skin from getting wet, although the thickness of this layer varies according to species.

CIt is easier for seabirds to ascend than to dive because the air in their lungs and air sacs expands as these birds near the surface, causing the pace of ascent to increase as they go up.

DSome seabirds are able to stay underwater even after their oxygen supply becomes low by changing their heart rate and undergoing other changes within the body.

ESeabirds need large amounts of food in order to replenish their oxygen stores and reheat their bodies after resurfacing from a dive.

FThe need to take in enough air before diving to allow for a dive of long duration competes with the need to achieve neutral buoyancy by releasing air from the lungs.