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Архитектура Аудит Военная наука Иностранные языки Медицина Металлургия Метрология Образование Политология Производство Психология Стандартизация Технологии |
Animals need help. Earth is in danger. ⇐ ПредыдущаяСтр 9 из 9
People have lived on our planet for many years. They lived and live on different continents, in different countries. People depend on their planet, on the sun, on animals and plants around them. People must take care of Earth. Our ecology becomes worse and worse with every new day. Many species of animals and birds are disappearing nowadays. People destruct wildlife, cut down trees to make furniture. They forget that people can’t live without trees and plants, because they fill air with oxygen. And, of course, great problems are population and animals destruction. The main reason of pollution is rubbish. Most of our rubbish goes to big holes in the ground, called ‘dumps’. But dumps are very dangerous for our life ‘cause they are full of rats, which can carry infections away from dumps. Another way to get rid of rubbish is to burn it. But the fires make poisons, which go into the air and pollute it. But pollution isn’t the only actual problem. Every day a big number of animals dissapeares. People kill animals for different aims: e.g. people hunt whales for their meat and oil; elephants for their tusks, crocodiles for their leather and so on. And also animals are used for medical experiments. The most wide – speared from such animals are monkeys. Modern life is bad for animals, birds, fish. The air isn’t fresh and the water isn’t pure. They don’t have good meal and facilities for the life. You can find their names in the Red Book. Of course, people can’t stay indifferent to these problems. There are a lot of special organizations, which try to save our nature. The most known are: The Royal Society for the prevention of cruelty to animals (The RSPCA), the World Wildlife Fund (WWF) and Greenpeace. The RSPCA tries to protect animals from bad use. It operates big nation campaigns aimed at lost pets, circus animals. The WWF rescued several species of animals, mammals as well as birds. These organization also helped to create more than 250 National parks. Greenpeace began its work 20 years ago from saving whales. And now Greenpeace is a world-famous organization, which saves plants, animals and people. These organization, want to rescue animals, to help them to survive and to save jungle rain forests, which are in danger of destruction. And they also help animals ‘cause many of them have already gone as they have nowhere to live. Their homes, the trees, have disappeared. We must save wild animals. And we must find the right way to save land, people and animals. We must lake care of nature, because we are part of it. Read the text and say whether these statements are true or false. Then suggest a title to the story and discuss it with your group. Use your dictionary to help you. 1. The first doglike creature could climb trees. 2. Miacis was also the progenitor of goat. 3. The ancestor of today's wild dogs first appeared about 30 million years ago. 4. Jackals are close relatives to domestic dogs. 5. Dogs could live only in warm places. 6. Dogs helped man only to hunt wild animals. 7. There are a lot of different kinds of dogs nowadays. 8. Some dogs have very thick fur to protect them from cold.
The dog's story begins in the lush forests of some 50 million years ago with a small, tree-climbing creature, Miacis. This undoglike patriarh was also the progenitor of both bear and raccoon. From him evolved a carnivore we call Hesperocyon. Though Hesperocyon's long body and short legs little resembled the dog's, he had developed many doglike characteristics. Some 25 to 30 million years ago two larger, shorter-tailed, distinctly doglike forms named Temnocyon and Cynodesmus made their appearance on the open plains. Both evolved from Hesperocyon. Temnocyon is considered the ancestor of today's wild dogs of India, Africa, and Brazil. Cynodesmus became the ancestor of our modern wolves, coyotes, jackals, foxes, and domestic dogs. Though wolves and dogs sprang from a common ancestor, the former maintained their wildness and ferocity; the latter became tractable and domestic. Man unconsciously shaped the dog he wanted. At first he kept only those most useful in the hunt. When he domesticated sheep and cattle, to guard them he chose the dog which could fight off predators. Everywhere man went, dog went too, thus becoming the most widely distributed of four-footed animals. The dog adapted to every climate and every use. The great variety we see in our dogs today once served a practical purpose. The Dachshund's body was bred sausage-shaped so he could wriggle into the badger's don; the tuft of hair on the brow of the vermin-killing Scottio served to keep dirt out of his eyes when he, too, went to earth. The sled dog's fur coat and plumed tail functioned as sleeping bag and muffler. Hunting dogs became specialist: long-legged Deerhounds, keen-nosed Bloodhound, burly Mastiff. Through centuries the dog's life was not an easy one. For a long time man considered it as an efficient tool of the hunt, as burglar insurance, a shepherd, pulling power for a cart. The sports, which made dogs fight against bulls, bears, horses, even lions, and the spectacle of dog fighting dog to death wrote dark chapters in man's attitude to his " best friend". The 19th century brought changes in canine status. As emphasis on the hunt declined, the dog's role as companion became more important What is a breed? The classic definition of a " breed" is usually stated as a variation of this statement. Animals that, through selection and breeding, have come to resemble one another and pass those traits uniformly to their offspring. Unfortunately this definition leaves some unanswered questions. For example, when is a crossbred animal considered a composite breed and when do we stop thinking about them as composites? Perhaps this definition from The Genetics of Populations by Jay L. Lush helps explain why a good definition of " breed" is elusive. A breed is a group of domestic animals, termed such by common consent of the breeders, ... a term which arose among breeders of livestock, created one might say, for their own use, and no one is warranted in assigning to this word a scientific definition and in calling the breeders wrong when they deviate from the formulated definition. It is their word and the breeders` common usage is what we must accept as the correct definition. As you can see from Dr. Lush's definition it is at least in part the perception of the breeders and the livestock industry which decides when a group of individuals constitutes a " breed". The development of the breeds takes different routes also. In some breeds you can see the amount of change that can occur as the result of selection for a small number of traits. As an example, Holstein cattle have been selected primarily for milk production and are the highest milk producing cattle in the world. Other breeds have traits that result from natural selection pressure based upon the environment in which they were developed. An example of this might be the N'dama cattle from west Africa. These animals have, through the centuries, developed a resistance to trypanosomiasis or sleeping sickness spread by the tse-tse fly, which is fatal to most other breeds of cattle. The veterinary profession The education and training of a veterinarian requires him to study the basic preclinical disciplines of anatomy, histology, physiology, pharmacology, microbiology (including bacteriology, virology, and parasitology), and pathology. The clinical subjects of study can be broadly divided into internal medicine, surgery, preventive medicine, and clinical practice. Internal medicine includes the diagnosis and treatment of diseases as they affect animals. Preventive medicine and public health concern the broader aspects of disease prevention and control, especially of those diseases transmissible between animals and humans or affecting human welfare. Surgery includes wound treatment, fracture repair, the excision of body parts, and the related techniques of radiology, anesthesiology, obstetrics, treatment of lameness, and so on. In most veterinary schools, a clinic is operated to enable students to observe and assist with actual cases of disease or other conditions requiring attention. In both medical and surgical treatment, the same techniques are used as in medical practice on humans. Many veterinarians specialize either in the care of small animals, i.e., pets, or in the care of livestock. A few veterinarians specialize in the care of wild animals held in zoos. To qualify for membership in the veterinary profession in most countries of the world, candidates must complete an educational program of from four to six years of work at the university level, after which they must obtain a license to practice from some duly constituted authority. In many countries the degree of doctor of veterinary medicine (D.V.M.) is awarded after successful completion of such formalized course of study. Veterinary associations exist in practically all countries, their purpose being to advance the standards and improve the services of the profession.
A drop of blood Do you know that we have between 250 and 300 million red cells in each drop of blood? As for the white cells there are only about 350 to 500 thousand of them in a drop of your blood so long as you are in good health. But suppose you get an infection - appendicitis, for example. Almost immediately the number of white cells begins to increase until you may have as many as a million and a half in a drop of blood. The disease germs produce certain chemicals in the body. These chemicals make the white cells divide, so that each white cell produces two new cells. The chemicals also stimulate the movement of the white cells toward the place where the germs are causing the infection. Then, when a white cell is close to a germ, it is further stimulated to change its shape. It wraps the germ up. The germ is now inside the white cell, which then proceeds to digest it. So we can say that the white cells really eat up disease germs. Our blood also has proteins in it. And it has a lot of little cells called platelets, which contain a special chemical. Ordinarily, of course, this chemical stays inside the platelets. But, suppose, you cut your finger. The blood comes to the surface of the wound and the platelets break down. The chemical is released and it starts to affect the gelatin – like protein in the blood, building a network of fibres. Soon the network is big enough to form a jelly-like stopper for the wound. We say that the blood has clotted and the wound stoops bleeding.
Cell division and DNA There are three main parts in every human or animal cell. First, it has a thin outside shell called a cell membrane. Inside the cell there is a small, rounded body called the nucleus. Filling the rest of the cell is substance called cytoplasm. Within the nucleus there are threads of material called chromosomes. The chromosomes are important in the process of making new cells. The chromosomes make copies of themselves and then separate. The cell splits into two cells and each contains chromosomes. All attempts to separate the nuclei failed for a long time. Work continued on cells until it was shown that the nucleus alone determined how the plant would grow. Soon it was found that all viruses contain nucleic acid and a protein shell. It was discovered that there are two nucleic acid “brothers” - deoxyribonucleic acid and ribonucleic acid – DNA and RNA. It was learned that a little string of DNA hidden in the nucleus of a cell stores and then sends from one cell to another all the information necessary to create a new living thing. We know that to build even the simplest house requires pages of drawings, details and measurements. How could these little pieces contain plants for a living being? It seemed impossible, but everything indicated that DNA did the job. By 1953 the scientists had discovered much more about DNA. They knew that DNA was a huge molecule. They knew that it contained sugar molecules and phosphate molecules that were joined to each other. In addition to the sugar and phosphates, there were four bases that are called A, G, C and T. There were thousands of these six different pieces, each with its own shape and size, in the DNA molecules. Some scientists tried to build a model of a DNA molecule. They began to build it using wire and many pieces of metal. Each piece of metal represented a piece of the DNA molecule, either a sugar, a phosphate, or one of the bases. The wire was used to hold the metal pieces to each other. They tried many times to fit the pieces together. They found that the pieces would not fit where they places them. Each failure taught them more about the arrangement of molecules within DNA. They realized that only one model would be correct. Finally the pieces began to fit into the right places. The phosphates and sugar molecules formed long curving lines. The four bases were attached to them to form a ladder; the sides of the ladder were made of the sugars and phosphates. The steps of the ladder were the bases – A, G, C and T. But the bases were of different sizes. A and G were bigger, longer; C and T were smaller, shorter. How could there be a ladder with steps of different sizes? They discovered that two bases were required for each step. Each step had to contain one long base and one short base. Even so, there are four possible arrangements of the bases that form these steps. The whole truth then was that all DNA molecules had the same size pieces (sugars, phosphates, and four bases) and all were in the same shape (a curving ladder). Only one thing could change – the order of steps. The DNA was found in the nucleus, the RNA – in both the nucleus and cytoplasm, the substance of the cell outside the nucleus. Experiments showed that RNA moved from nucleus out to the cytoplasm. The DNA contains the direction for making the living material. Within the nucleus, in a way as yet unknown, the DNA passes its protein manufacturing instructions to the RNA. Then the RNA goes out into the cytoplasm to help in the manufacture of the proteins. In the 1955 some RNA was synthesized in a laboratory. One year later some DNA was made.
Proteins Protein molecules are the largest and most complex of all molecules; they may be up to ten million times as heavy as a hydrogen atom and be built of many thousands of atoms – mainly of carbon, hydrogen, oxygen and nitrogen. Proteins are fundamental units of living material; among other compounds of vital importance they include the enzymes, which bring about most of the chemical changes in protoplasm. Proteins are built of units called amino-acids. When a protein is treated with acid it will break up into chains of molecules called peptides and finally into amino-acids. There are about twenty different kinds of amino-acids, the molecules of which vary in size from the molecular weight of 90 to one of about 250. An average protein molecule contains about 500 amino-acid molecules. In order to appreciate the complexity of a protein, we may compare the molecule of a typical carbohydrate (glucose built of 12 atoms), a fat (about 170 atoms), and a protein. The protein lactoglobulin, found in milk, has about 5940 atoms in the molecule. Carbohydrates, fats, and proteins are very important in living material, but the there are many other substances, such as the nucleic acids, vitamins, etc. which play a vital part in living organisms. The human body consists approximately of 65 per cent water, 15 per cent protein, 14 per cent fat, 5 per cent inorganic salts, and about 1 per cent of other materials. Vocabulary: ten million times as heavy as a hydrogen atom – в десять миллионов раз тяжелее, чем атом водорода vital importance – жизненно важный is treated with –зд. обрабатывается in order to appreciate – для того, чтобы оценить carbohydrate – углевод enzymes – энзимы (ферменты)
Importance of zoology Animals play a big part in man’s life. Ages ago primitive people hunted them for meat and hides to make clothing and footwear. Some of the animals were gradually tamed and domesticated. At present they provide us with meat and dairy produce as well as raw materials for making our clothes and footwear. Many of the wild animals are also of use to man. The seas and rivers are full of fish which we eat; in the woods there are fur-bearing animals whose pelts are very valuable; useful birds live everywhere, constantly destroying insects harmful to orchards and crops. Some of the animals, however, are quite harmful. Many insects cause damage to plantations and woods. (Which of them do you know? ) Wolves are known to attack domestic animals. Mice and rats are a grave threat to food stores. Flies and lice spread disease. Persistent struggle must be carried on against them. To protect useful animals, to take proper care of domestic animals, and to combat harmful animals, it is necessary to know all about their habits and constitutions. This is exactly what zoology as a science is interested in. Zoology studies animal life.
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