Inheritance

Introduction

Read the following passage and listen to the story about Gregor Mendel’s life. Find six false facts in the story you hear.

An original text in Student’s Book:

Before settling down as a monk in the monastery of St. Thomas in Brünn (now Brno, in the Czech Republic), Gregor Mendel tried his hand at several pursuits, including health care and teaching. To earn his teaching certificate, Mendel attended the University of Vienna for 2 years, where he studied botany and mathematics, among other subjects. This training proved crucial to his later experiments, which were the foundation for the modern science of genetics. At St. Thomas in the mid-1800s, Mendel carried out both his monastic duties and a groundbreaking series of experiments on inheritance in the common edible pea. Although Mendel worked without knowledge of genes or chromosomes, we can more easily follow his experiments after a brief look at some modern genetic concepts.

Six false facts are given in bold:

Before settling down as a monk in the monastery of St. Thomas in Brünn, (now Brno, in the Czech Republic), Gregor Mendel tried his hand at several pursuits, including teaching health care. To earn his medical certificate, Mendel attended the University of Vienna for 2 years, where he studied botany and mathematics only. This training proved very important to his later experiments, which were the foundation for the modern science of genetics. At St. Thomas in the mid-1700s, Mendel carried out both his monastic duties and broke ground in a series of experiments on inheritance in the common edible pea. Although Mendel knew little about genes or chromosomes, we can more easily follow his experiments after a brief look at some modern genetic concepts.

Unit 9

Fungi

Introduction

How do fungi affect humans? Listen to the text and answer the question.

Edible mushrooms are the most obvious fungal contribution to human welfare, but fungi have many other, less visible but more important impacts as well. Many of these impacts are positive, and some fungal benefits extend far beyond mere gastronomic concerns. For example, as decomposers, fungi make an incalculable contribution to ecosystems. The extracellular digestive activities of many fungi liberate nutrients such as carbon, nitrogen, and phosphorus compounds and minerals that can be used by plants. If fungi and bacteria were suddenly to disappear, the consequences would be disastrous. Nutrients would remain locked in the bodies of dead plants and animals, the recycling of nutrients would grind to a halt, soil fertility would rapidly decline, and waste and organic debris would accumulate. In short, ecosystems would collapse.

Although the health of ecosystems depends on the relentless nature of fungal feeding, penetrating fungal filaments can have adverse consequences as well. Parasitic fungi, for instance, cause disease. In humans, such fungi cause a range of diseases such as ringworm and athlete’s foot, which infect the skin; valley fever and histoplasmosis, which infect the lungs; and common vaginal yeast infections. Fungi also cause the majority of plant diseases. The fungi that cause chestnut blight and Dutch elm disease have drastically reduced American chestnut and elm tree populations. Fungal parasites also result in billions of dollars in crop losses annually from diseases such as corn smut.

The fungal impact on agriculture is not entirely negative, however. Fungal parasites that attack insects and other arthropod pests can be an important ally in pest control. Farmers who wish to reduce their dependence on toxic and expensive chemical pesticides are increasingly turning to biological methods of pest control, including the application of “fungal pesticides”. Fungal pathogens are currently used to control a variety of pests, including termites, rice weevils, tent caterpillars, aphids, and citrus mites.

Fungi, of course, also make an important contribution to human nutrition. This contribution goes far beyond the obvious use of wild and cultivated mushrooms. Other fungi, such as the rare and prized truffle, are also consumed directly. Of greater importance, however, are the less visible manifestations of fungal activities. In particular, fungi are responsible for making bread rise, for converting grape juice to wine, for the distinctive flavor of many cheeses, and for the bubbles (and alcohol) in beer. Our diets would certainly be a lot duller without the help we get form fungal partners.

Unit 10

The Evolution of Hormones

Introduction

Now listen to the summary of key concepts concerning the endocrine system of the animal body and get ready to retell it.

Summary of Key Concepts

What are the characteristics of animal hormones?

A hormone is a chemical secreted by cells in one part of the body that is transported in the bloodstream to another part of the body, where it affects the activity of specific target cells. Four types of molecules are known to act as hormones: peptides, amino-acid derivatives, steroids, and prostaglandins.

Most hormones act on their target cells in one of two ways: (1) Peptide hormones and amino-acid derivatives bind to receptors on the surface of target cells and activate intracellular second messengers, such as cyclic AMP. The second messengers then alter the metabolism of the cell. (2) Steroid hormones diffuse through the plasma membranes of the target cells and bind with receptor proteins in the cytoplasm. The hormone-receptor complex travels to the nucleus and promotes the transcription of specific genes. Thyroid hormones also penetrate the plasma membrane but diffuse into the nucleus, where they bind to receptors associated with the chromosomes and influence gene transcription.

Hormone action is commonly regulated through negative feedback, a process in which a hormone causes changes that inhibit further secretion of that hormone.

What are the structures and functions of the mammalian endocrine system?

Hormones are produced by endocrine glands, which are clusters of cells embedded within a network of capillaries. Hormones are secreted into the extracellular fluid and diffuse into the capillaries. The major endocrine glands of the human body are the hypothalamus – pituitary complex, the thyroid and parathyroid glands, the pancreas, the sex organs, and the adrenal glands. Prostaglandins, unlike other hormones, are not secreted by discrete glands but are synthesized and released by many cells of the body. Other endocrine organs include the pineal gland, thymus, kidneys, heart, and the stomach and small intestine.

Unit 11

The Immune Response

Introduction

What are the key characteristics of the immune response? Listen to the text and say whether the following sentences are true or false.

Phagocytic cells, natural killer cells, the inflammatory response, and fever are all nonspecific defenses; their role is to prevent or overcome any microbial invasion of the body. Unfortunately, however, these nonspecific defenses are not impregnable. When they fail to do the job, the body mounts a highly specific immune response directed against the particular organism that has successfully invaded the body.

The essential features of the immune response to infection were recognized more than 2000 years ago by the Greek historian Thucydides. He observed that occasionally someone would contract a disease, recover, and never catch that particular disease again – the person had become immune. With rare exceptions, however, immunity to one disease confers no protection against other diseases. Thus, the immune system attacks one type of microbe, overcomes it, and provides future protection against that microbe but no others. This is why we refer to the immune response as a specific defense against invasion.

The immune system consists of about 2 trillion lymphocytes, a kind of white blood cell. Lymphocytes are distributed throughout the body in the blood and lymph, though many are clustered in specific organs, particularly the thymus, lymph nodes, and spleen. The immune response arises from interactions among the various types of lymphocytes and the molecules that they produce. The theatre of the immune response has a large cast of characters and is difficult to follow without a program. The table below provides a brief overview of the major actors and their roles.

The key actors in the immune response are two types of lymphocytes, called B cells and T cells. Like all white blood cells, B lymphocytes and T lymphocytes arise from precursor cells in the bone marrow. Some of these lymphocyte precursors are released into the bloodstream and come to rest in the thymus, where they complete their differentiation into T (for thymus) cells. In contrast, B cells differentiate in the bone marrow itself. The two cell types play quite different roles in the immune response, but immune responses produced by both B cells and T cells consist of the same three fundamental steps: (1) recognizing the invader, (2) launching a successful attack to overcome the invader, and (3) retaining a memory of the invader to ward off future infections.

1 The Greek physician Thucydides recognized the essential features of the immune response to the infection more than 2000 years ago. F: physician

2 Immunity to one disease always confers no protection against other diseases. F: always

3 We refer to the immune response as a specific defense against invasion. T

4 Lymphocytes are distributed throughout the body in the blood. F: and lymph

5 T cells and B cells play similar roles in the immune response. F: similar

Unit 12

Animal Behaviour

Introduction

I. Listen to the text and determine differences of innate and learned behaviour.

Although all animal behaviour is influenced by both genetic and environmental factors, it can be useful to distinguish between behaviours whose development is not highly dependent on external factor and behaviours that require more extensive environmental stimuli in order to develop behaviours in the first category are sometimes designated as innate and can be performed properly the first time an animal encounters the appropriate stimulus. Innate behaviours include kineses, in which animals orient by varying the speed of essentially random movements, stopping when they encounter favorable conditions. In contrast, taxes are directed movements toward or away from specific stimuli. A fixed action pattern is a complex innate behaviour elicited by a specific stimulus called a releaser. Learning can in some cases modify the releasers for fixed action patterns.

Behaviour that changes in response to input from an animal’s social and physical environment is said to be learned. Learning is especially adaptive in environments that are changing and unpredictable, and learning can modify innate behaviour to make it more appropriate.

Among the diverse array of learning methods are imprinting, habituation, conditioning, trial and error, and insight. Imprinting is a special kind of learning that occurs during a limited sensitive period early in life. This form of simple learning typically involves attachment between parent and offspring or learning the features of a future mate.

Habituation is the decline in response to a harmless stimulus that is repeated frequently. It commonly modifies innate escape responses or defensive responses.

During classical conditioning, an animal learns to make a reflexive response, such as withdrawal or salivation, to a stimulus that did not originally elicit that response. During operant conditioning, an animal learns to make a new response, such as pressing a button, to obtain a reward or to avoid punishment.

Trial-and-error learning can modify innate behaviour or can produce new behaviour as a result of rewards and punishments provided by the environment.

Insight, the most complex form of learning, can be considered a form of mental trial-and-error learning. An animal showing insight makes a new and adaptive response to an unfamiliar situation.

Although the distinction between innate and learned behaviour is conceptually useful, the distinction is not sharp in naturally occurring behaviours. In virtually all behaviours, learning and instinct interact to produce adaptive behaviour. Certain types of learning, such as imprinting, occur instinctively, during a rigidly defined time span. Instinctive responses are typically modified by experience. Learning allows animals to modify these innate responses so that they occur only with appropriate stimuli.