Tuna fish not only swim fast, but they can also cover great distances over short periods of time or during long migrations. At night, tuna are known to cover some 15 kilometers during offshore excursions (possibly for feeding).For swimming at such great speeds and over long distances, the tuna has evolved a muscle structure and circulatory system that athletes can only dream of.
In general, fish move by a series of muscle contractions that begin at the head and progress through the body toward the thruster, the tail. Two types of muscle, white and red, are used in swimming and are arranged along the flanks (sides)of the fish. White muscle contracts quickly and is used for bursts of high-speed swimming. It operates anaerobically (without oxygen),generating lactic acid as a by-product (similar to the lactic acid that can build up in humans after prolonged vigorous exercise and produce fatigue or muscle cramps).Red muscle contracts more slowly, is used for slow, continuous swimming, and operates through an aerobic (with oxygen)metabolic pathway. Because red muscle does not produce lactic acid, it can continue to contract almost indefinitely with the necessary fuel (oxygen and glucose).In most fish, the bulk of the muscle is white, with only a small lateral strip of red. The tuna, however, is equipped with a much larger proportion of red muscle than the average fish. This allows the tuna to cruise at high speeds aerobically, without lactic acid buildup. White muscle is used to generate additional thrust to go from cruising to extremely high speed. To sustain such athletic skill, the tuna requires an efficient means of supplying blood and oxygen to its hard-working muscles and a way of releasing the heat generated during muscle contractions.
Fish, like other animals, need oxygen to respire and to fuel their working muscles. Dissolved oxygen is some 30 times as dilute in the sea as in the air. Fish use their gills to extract oxygen from the water by pumping water in through their mouths, then over and out through the gills. The pumping is done by repetitively opening and closing the mouth, thus sucking or gulping the water in and pushing it past the gills. The tuna’s skull and jaw are rigid to enhance swimming speed, so it cannot physically pump water in. Instead, it breathes by means of ram ventilation As a tuna swims, its mouth stays open and water is literally rammed in and over its extraordinarily large gills. Like some of the other fast-swimming fish, the tuna must constantly move or else it will suffocate.
Tuna and some sharks have evolved a specialized circulatory system that uses excess heat production to stay warm in their often-chilly medium. Fish are typically cold-blooded; their body temperature is regulated by the surrounding water. But the tuna has a special internal heat exchanger made up of intermingling arteries and veins. Cool, oxygen-rich blood flows from the gills to the tissues through arteries and a network of small blood vessels. Running parallel to and intermingling with the arterial network (the vessels carrying blood from the gills to the organs)is the venous system. In the venous system, warm, oxygen-depleted blood is carried from the organs and tissues back to the gills. Because the veins and arteries are intermingling and in close contact, heat is readily transferred from the warm blood in the veins to the cold blood in the arteries. With elegant physiological simplicity, this countercurrent heat exchange uses the tuna’s own internal heat from muscle contractions to warm incoming blood. In most other fish, heat is lost directly from the gills; but in the tuna, there is little heat loss, and by the time the blood reaches the tuna’s interior, it is nearly as warm as the internal body tissues. This exchange is so effective that a tuna’s core temperature has been measured at 10 to 20 degrees Celsius warmer than the surrounding water. Scientists suspect that elevated body temperatures help keep the tuna’s metabolism high for food processing, allow its red muscle to contract more quickly, and may enhance lactic-acid breakdown. Tuna may also be able to partially shut down the heat exchanger if they become too warm, or they may make excursions into deeper, colder water to avoid overheating.
题目：
1
Tuna fish not only swim fast, but they can also cover great distances over short periods of time or during long migrations. At night, tuna are known to cover some 15 kilometers during offshore excursions (possibly for feeding).For swimming at such great speeds and over long distances, the tuna has evolved a muscle structure and circulatory system that athletes can only dream of.
Why does the author discuss tuna’s “offshore excursions”?
ATo identify a consequence of tuna’s way of feeding
BTo suggest that tuna can be as fast and strong as some human athletes are
CTo support the claim that tuna cover longer distances at night than during the day
DTo emphasize the great distances that tuna’s muscles and circulatory system allow them to swim
2
In general, fish move by a series of muscle contractions that begin at the head and progress through the body toward the thruster, the tail. Two types of muscle, white and red, are used in swimming and are arranged along the flanks (sides)of the fish. White muscle contracts quickly and is used for bursts of high-speed swimming. It operates anaerobically (without oxygen),generating lactic acid as a by-product (similar to the lactic acid that can build up in humans after prolonged vigorous exercise and produce fatigue or muscle cramps).Red muscle contracts more slowly, is used for slow, continuous swimming, and operates through an aerobic (with oxygen)metabolic pathway. Because red muscle does not produce lactic acid, it can continue to contract almost indefinitely with the necessary fuel (oxygen and glucose).In most fish, the bulk of the muscle is white, with only a small lateral strip of red. The tuna, however, is equipped with a much larger proportion of red muscle than the average fish. This allows the tuna to cruise at high speeds aerobically, without lactic acid buildup. White muscle is used to generate additional thrust to go from cruising to extremely high speed. To sustain such athletic skill, the tuna requires an efficient means of supplying blood and oxygen to its hard-working muscles and a way of releasing the heat generated during muscle contractions.
Paragraph 2 suggests that most fish generally move by
Acontracting muscle at the head more rapidly than muscle at the tail
Bmoving their thruster from side to side
Cusing a high proportion of red muscle
Dswimming in rapid bursts
3
In general, fish move by a series of muscle contractions that begin at the head and progress through the body toward the thruster, the tail. Two types of muscle, white and red, are used in swimming and are arranged along the flanks (sides)of the fish. White muscle contracts quickly and is used for bursts of high-speed swimming. It operates anaerobically (without oxygen),generating lactic acid as a by-product (similar to the lactic acid that can build up in humans after prolonged vigorous exercise and produce fatigue or muscle cramps).Red muscle contracts more slowly, is used for slow, continuous swimming, and operates through an aerobic (with oxygen)metabolic pathway. Because red muscle does not produce lactic acid, it can continue to contract almost indefinitely with the necessary fuel (oxygen and glucose).In most fish, the bulk of the muscle is white, with only a small lateral strip of red. The tuna, however, is equipped with a much larger proportion of red muscle than the average fish. This allows the tuna to cruise at high speeds aerobically, without lactic acid buildup. White muscle is used to generate additional thrust to go from cruising to extremely high speed. To sustain such athletic skill, the tuna requires an efficient means of supplying blood and oxygen to its hard-working muscles and a way of releasing the heat generated during muscle contractions.
According to paragraph 2,white muscle and red muscle differ in all of the following ways EXCEPT
Athe rate at which they contract
Bthe part of the fish’s body where they are located
Cthe type of fuel they need to function
Dthe amount of lactic acid they produce
4
Fish, like other animals, need oxygen to respire and to fuel their working muscles. Dissolved oxygen is some 30 times as dilute in the sea as in the air. Fish use their gills to extract oxygen from the water by pumping water in through their mouths, then over and out through the gills. The pumping is done by repetitively opening and closing the mouth, thus sucking or gulping the water in and pushing it past the gills. The tuna’s skull and jaw are rigid to enhance swimming speed, so it cannot physically pump water in. Instead, it breathes by means of ram ventilation As a tuna swims, its mouth stays open and water is literally rammed in and over its extraordinarily large gills. Like some of the other fast-swimming fish, the tuna must constantly move or else it will suffocate.
The word“rigid”in the passage is closest in meaning to
Asmall
Bsharp
Cstiff
Dsmooth
5
Fish, like other animals, need oxygen to respire and to fuel their working muscles. Dissolved oxygen is some 30 times as dilute in the sea as in the air. Fish use their gills to extract oxygen from the water by pumping water in through their mouths, then over and out through the gills. The pumping is done by repetitively opening and closing the mouth, thus sucking or gulping the water in and pushing it past the gills. The tuna’s skull and jaw are rigid to enhance swimming speed, so it cannot physically pump water in. Instead, it breathes by means of ram ventilation As a tuna swims, its mouth stays open and water is literally rammed in and over its extraordinarily large gills. Like some of the other fast-swimming fish, the tuna must constantly move or else it will suffocate.
According to paragraph 3,which of the following does NOT correctly describe the respiration process in tuna?
ATuna breathe through a method known as ram ventilation.
BTuna pump water over the gills by opening and closing the mouth.
CTuna have extremely large gills for breathing.
DTuna can only breathe if they are in motion.
6
Tuna and some sharks have evolved a specialized circulatory system that uses excess heat production to stay warm in their often-chilly medium. Fish are typically cold-blooded; their body temperature is regulated by the surrounding water. But the tuna has a special internal heat exchanger made up of intermingling arteries and veins. Cool, oxygen-rich blood flows from the gills to the tissues through arteries and a network of small blood vessels. Running parallel to and intermingling with the arterial network (the vessels carrying blood from the gills to the organs)is the venous system. In the venous system, warm, oxygen-depleted blood is carried from the organs and tissues back to the gills. Because the veins and arteries are intermingling and in close contact, heat is readily transferred from the warm blood in the veins to the cold blood in the arteries. With elegant physiological simplicity, this countercurrent heat exchange uses the tuna’s own internal heat from muscle contractions to warm incoming blood. In most other fish, heat is lost directly from the gills; but in the tuna, there is little heat loss, and by the time the blood reaches the tuna’s interior, it is nearly as warm as the internal body tissues. This exchange is so effective that a tuna’s core temperature has been measured at 10 to 20 degrees Celsius warmer than the surrounding water. Scientists suspect that elevated body temperatures help keep the tuna’s metabolism high for food processing, allow its red muscle to contract more quickly, and may enhance lactic-acid breakdown. Tuna may also be able to partially shut down the heat exchanger if they become too warm, or they may make excursions into deeper, colder water to avoid overheating.
Which of the following can be inferred from paragraph 4 about the circulatory system of most fish?
AThe circulatory system of most fish is highly efficient at elevating body temperature.
BThe circulatory system of most fish is not efficient at getting rid of excess heat.
CThe veins and arteries of most fish do not intermingle much.
DThe blood of most fish is generally warmer than the surrounding tissues.
7
Tuna and some sharks have evolved a specialized circulatory system that uses excess heat production to stay warm in their often-chilly medium. Fish are typically cold-blooded; their body temperature is regulated by the surrounding water. But the tuna has a special internal heat exchanger made up of intermingling arteries and veins. Cool, oxygen-rich blood flows from the gills to the tissues through arteries and a network of small blood vessels. Running parallel to and intermingling with the arterial network (the vessels carrying blood from the gills to the organs)is the venous system. In the venous system, warm, oxygen-depleted blood is carried from the organs and tissues back to the gills. Because the veins and arteries are intermingling and in close contact, heat is readily transferred from the warm blood in the veins to the cold blood in the arteries. With elegant physiological simplicity, this countercurrent heat exchange uses the tuna’s own internal heat from muscle contractions to warm incoming blood. In most other fish, heat is lost directly from the gills; but in the tuna, there is little heat loss, and by the time the blood reaches the tuna’s interior, it is nearly as warm as the internal body tissues. This exchange is so effective that a tuna’s core temperature has been measured at 10 to 20 degrees Celsius warmer than the surrounding water. Scientists suspect that elevated body temperatures help keep the tuna’s metabolism high for food processing, allow its red muscle to contract more quickly, and may enhance lactic-acid breakdown. Tuna may also be able to partially shut down the heat exchanger if they become too warm, or they may make excursions into deeper, colder water to avoid overheating.
According to paragraph 4,the tuna’s internal heat exchanger works by
Akeeping incoming blood close to the organs and tissues
Bslowing the rate at which oxygen is lost from the blood
Cusing heat from the veins to warm incoming blood
Dslowing muscle contractions when the blood becomes too cold
8
Tuna and some sharks have evolved a specialized circulatory system that uses excess heat production to stay warm in their often-chilly medium. Fish are typically cold-blooded; their body temperature is regulated by the surrounding water. But the tuna has a special internal heat exchanger made up of intermingling arteries and veins. Cool, oxygen-rich blood flows from the gills to the tissues through arteries and a network of small blood vessels. Running parallel to and intermingling with the arterial network (the vessels carrying blood from the gills to the organs)is the venous system. In the venous system, warm, oxygen-depleted blood is carried from the organs and tissues back to the gills. Because the veins and arteries are intermingling and in close contact, heat is readily transferred from the warm blood in the veins to the cold blood in the arteries. With elegant physiological simplicity, this countercurrent heat exchange uses the tuna’s own internal heat from muscle contractions to warm incoming blood. In most other fish, heat is lost directly from the gills; but in the tuna, there is little heat loss, and by the time the blood reaches the tuna’s interior, it is nearly as warm as the internal body tissues. This exchange is so effective that a tuna’s core temperature has been measured at 10 to 20 degrees Celsius warmer than the surrounding water. Scientists suspect that elevated body temperatures help keep the tuna’s metabolism high for food processing, allow its red muscle to contract more quickly, and may enhance lactic-acid breakdown. Tuna may also be able to partially shut down the heat exchanger if they become too warm, or they may make excursions into deeper, colder water to avoid overheating.
According to paragraph 4,which of the following prevents the tuna from overheating?
AGiving off heat through the gills
BAvoiding deep water
CPartially stopping its heat exchanger
DRemaining in water 10 to 20 degrees Celsius cooler than its core
