2016年9月10日雅思阅读真题+题目+答案：Undersea Movement

2016年9月10日雅思阅读真题+题目+答案：Undersea Movement

A

The underwater world holds many challenges. The most basic of these is movement. The density of water makes it difficult for animals to move. Forward movement is a complex interaction of underwater forces. Additionally, water itself has movement. Strong currents carry incredible power that can easily sweep creatures away. The challenges to aquatic movement result in a variety of swimming methods, used by a wide range of animals. The result is a dazzling underwater ballet.

B

Fish rely on their skeleton, fins, and muscles to move. The primary function of the skeleton is to aid movement of other parts. Their skull acts as a fulcrum and their vertebrae act as levers. The vertebral column consists of a series of vertebrae held together by ligaments, but not so tightly as to prevent slight sideways movement between each pair of vertebrae. The whole spine is, therefore, flexible. The skull is the only truly fixed part of a fish. It does not move in and off itself but acts as a point of stability for other bones. These other bones act as levers that cause movement of the fish’s body.

C

While the bones provide the movement, the muscles supply the power. A typical fish has hundreds of muscles running in all directions around its body. This is why a fish can turn and twist and change directions quickly. The muscles on each side of the spine contract in a series from head to tail and down each side alternately, causing a wave-like movement to pass down the body. Such a movement may be very pronounced in fish such as eels, but hardly perceptible in others, e.g. mackerel. The frequency of the waves varies from about 50/min in the dogfish to 170/min in the mackerel. The sideways and backward thrust of the head and body against the water results in the resistance of the water pushing the fish sideways and forwards in a direction opposed to the thrust. When the corresponding set of muscles on the other side contracts, the fish experiences a similar force from the water on that side. The two sideways forces are equal and opposite unless the fish is making a turn, so they cancel out, leaving the sum of the two forward forces

D

The muscles involved in swimming are of two main types. The bulk of a fish’s body is composed of the so-called white muscle, while the much smaller areas at the roots of the fins and in a strip along the centre of each flank comprise red muscle. The red muscle receives a good supply of blood and contains ampler quantities of fat and glycogen, the storage form of glucose, which is used for most day-to-day swimming movements. In contrast, the white muscle has a poor blood supply and few energy stores, and it is used largely for short-term, fast swimming. It might seem odd that the body of an animal which adapts adapted so efficiently to its environment should be composed almost entirely of a type of muscle it rarely uses. However, this huge auxiliary power pack carried by a fish is of crucial significance if the life of the fish is threatened-by a predator, for instance-because it enables the fish to swim rapidly away from danger.

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Questions 1-6

The Passage has 8 paragraphs A-H.

Which paragraph contains the following information?

Write the appropriate letter, A-H, in boxes 1-6 on your answer sheet.

1 categorizations of fish by swimming speed

2 an example of fish capable of maintaining fast swimming for a long time

3 how fish control stability

4 frequency of the muscle movement of fish

5 a mechanical model of fish skeleton

6 energy storage devices in a fish

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