Mammals

Despite their size differences, the great blue whale and the pygmy shrew have something in common: they are both members of a warm-blooded, air-breathing class of vertebrate (backboned) animals known as Mammalia, or mammals. In many ways mammals are the most highly developed of all creatures.

The term mammal explains one important way in which creatures in this class are set apart from other animals. It comes from the Latin mamma, which means “breast”. Every female mammal has special glands, mammae that secrete milk. The females of all but the most primitive mamalian species are viviparous. This means they bear their young alive. The уоung are then fed with milk until they have grown enough to get food for themselves.

Hair is a typical mammalian feature. In many whales, however, it exists only in the fetal stages of development. Another basic trait of mammals is their highly developed brains – the most complex known. Particularly well developed is their cerebrum, the part of the brain that controls memory and learning. The mammalian brain enables the young to learn from the experience of their elders. Since the young mammal is dependent on its mother for nourishment, a period of learning is possible. This in turn has brought about a degree of behavioral adaptability unknown in any other group of organisms. Whales, seals, and dogs are among the most intelligent mammals, but monkeys, apes, and humans are the most intelligent of all.

Задание 1. Прочитайте и переведите предложения, в которых описаны характерные особенности млекопитающих.

Задание 2. Задайте вопросы к следующим предложениям, начав их с вопросительного слова в скобках:

1. Mammals are the most highly developed of all creatures. (What animals)

2. The term mammal comes from the Latin “mamma”, which means “breast”. (Where)

3. Since the young mammal is dependent on its mother for nourishment, a period of learning is possible. (Why)

The Importance of Bacteria

Much of our experience with bacteria involves disease. Although some bacteria do cause disease, many kinds of bacteria live on or in the human body and prevent disease. Bacteria play important roles in the environment and in industry. In most cases the bacteria that cause disease are not part of the bacteria that normally inhabit the body. They are picked up from sick people, sick animals, contaminated food or water, or other external sources. Bacterial disease also can occur after surgery, an accident, or some other event that weakens the immune system.

When the immune system is not functioning properly, bacteria that usually are harmless can overwhelm the body and cause disease. These organisms are called opportunistic because they cause disease only when an opportunity is presented. For example, cuts or injuries to the skin and protective layers of the body enable normally friendly bacteria to enter the bloodstream or other sterile parts of the body and cause infection. Surgery may enable bacteria from one part of the body to reach another, where they cause infection. A weakened immune system may be unable to prevent the rapid multiplication of bacteria and other microorganisms.

Opportunistic infections became more important in the late 20th century because of diseases such as acquired immunodeficiency syndrome (AIDS), a viral disease that ravages the immune system. Some dramatic infectious diseases result from exposure to bacteria that are not part of our normal bacterial community. Cholera, one of the world's deadliest diseases today, is caused by the bacterium Vibrio cholerae. Cholera is spread in water and food contaminated with the bacteria, and by people who have the disease. After entering the body, the cholera bacteria grow in the intestines, often along the surface of the intestinal wall, where they secrete a toxin (poison). This toxin causes massive loss of fluid from the gut, and an infected person can die of dehydration (fluid loss) unless the lost fluids, and the salts they contain, are replaced.

Задание 1. Ответьте на вопросы:

1. Do all bacteria cause disease?

2. Where do bacteria play important roles?

3. In what cases can bacterial disease occur?

4. Can bacteria that are usually harmless cause disease?

5. Why do opportunistic infections become more important in the late 20^th century?

Задание 2. Из списка болезней выберите те, о которых идет речь в тексте:

tuberculosis, cholera, pneumonia, acquired immunodeficiency syndrome, anthrax.

Задание 3. Опишите течение холеры, используя текст и следующие глаголы: to be caused, to be spread, to grow, to secrete, to cause, to die.

Тексты для чтения

по английскому языку

для студентов 1 курса

факультета заочного обучения

по специальности «Зоотехния»

The Theory of Natural Selection

In the 1800s, Charles Darwin, a British naturalist, developed the theory of natural selection in his book “On the Origin of Species by Means of Natural Selection”. Darwin had the opportunity to travel around the world as the naturalist on a British survey ship. Wherever Dar­win visited, he saw a large number of different kinds of plants and animals and noted how well they were adapted to their particular situations.

He determined that there were several factors that could interact together to allow for natural selection:

4. Individuals within a species showed variation; some of the variations were very useful and others were not. For example, individual animals that are part of the same species show different colour variations. Some colours make the animal more conspicuous while others are less conspicuous.

5. Organisms within a species typically produce many more offspring than can survive. This means that here is not enough suitable habitat for all of the offspring to grow to maturity. A pair of rabbits may have three to four litters of offspring each sum­mer with several young in each litter.

6. Because of the excess number of individuals, there is a struggle for survival. Individuals within the population must compete with each other for food, space, mates, or other requirements that are in limited supply.

Great horned owls and other large owls typically produce two young at a time, but if food is in short supply, the larger of the two young will get the majority of the food.

4. Because of variation among individuals, some would have a greater chance of surviving and reproducing than others. The competition for resources often results in the less fit individuals dying; therefore, they do not get a chance to reproduce themselves. Even if they do not die, they may mature more slowly and not be able to repro­duce as many times as the more fit members of the species.

5. As time passes and each generation is subjected to the same kind of process, there will be an increase in the percentage of individuals showing the favorable variations and a decrease in those having unfavorable variations. The species will become better adapted to its environment.

Задание 1. Закончите предложения:

1. Charles Darwin developed the theory of ….

2. Individuals within a species showed ….

3. Organisms within a species typically produce ….

4. Individuals within the population must compete with each other for ….

5. The competition for resources often results in ….

Задание 2. Прочитайте примеры естественного отбора из текста.