Researched by Katlin T.
2002-03

• PURPOSE 
• HYPOTHESIS 
• EXPERIMENT DESIGN 
• MATERIALS 
• PROCEDURES 
• RESULTS 
• CONCLUSION 

• RESEARCH REPORT 
• BIBLIOGRAPHY 
• ACKNOWLEDGEMENTS 

• ABOUT THE AUTHOR 

Health is very important to human survival and happiness. The world’s smallest living organisms, bacteria, sometimes can threaten human health. Bacteria are everywhere, inside and outside the human body. Some bacteria make people sick, and in some cases can be fatal.

Bacteria are simple organisms that consist of one cell lacking a nucleus. They are among the smallest living things on earth. Most bacteria measure from 0.2 to 0.3 microns. The diameter can only be seen through a microscope. Scientists classify bacteria as prokaryotes. Bacteria are widespread, present in soil, air, and water, and as parasites on and in other living things.

Bacteria were likely the only form of life on earth for over two billion years. Antony van Leeuwenhoek first observed them in the 17th century. Bacteriology as an applied science began to develop in the 19th century.

Bacteria are amazingly adaptable to varied environmental conditions. They are found in the bodies of all living organisms and on all parts of the earth and ocean depths, Artic ice and glaciers, in hot springs, and even in the stratosphere. The understanding of bacteria and their metabolic processes have been expanded by the discovery of species that can live only deep below the earth’s surface and by species that thrive without sunlight in the high temperature and pressure near hydrothermal vents on the ocean floor. There are more bacteria, as separate individuals, than any other type of organism. There can be as many as 2.5 billion bacteria in one gram of fertile soil.

Bacteria are grouped in a number of different ways. Most bacteria are of one of three typical shapes: rod- shaped (bacillus), round (coccus, e.g., streptococcus), and spiral (spirillum). Another group, vibrios, appears as incomplete spirals. The cytoplasm and plasma membrane of most bacterial cells are surrounded by a cell wall. The further classification of bacteria is based on cell wall characteristics. They can also be characterized by their patterns of growth, such as the chains formed by streptococci. Many bacteria, primarily the bacillus and spiral forms, are motile, swimming about by whip like movements of flagella; other bacteria have rigid rod like protuberances called "pili" that is serve as tethers.

Some bacteria can function only in the presence of oxygen. Others cannot grow in the presence of free oxygen but obtain oxygen from compounds. Facultative anaerobes can grow with or without free oxygen; obligate anaerobes are poisoned by oxygen

Bacteria that cause disease are called pathogens. Among bacterial plant diseases are leaf spot, fire blight and wilts. Animal diseases caused by bacteria include tuberculosis, cholera, syphilis, typhoid fever, and tetanus. Some bacteria attack the tissues directly; others produce poisonous substances called toxins.
Antibodies provide natural defense against harmful bacteria. Certain bacterial diseases, e.g., tetanus, can be prevented by injection of antitoxin or of serum containing antibodies against specific bacterial antigens; immunity to some can be induced by vaccination; and certain specific bacterial parasites are killed by antibiotics.

New strains of more virulent bacterial pathogens, which many   resistant to antibiotics, have appeared in recent years. Many believe this is due to the overuse antibiotics, which are both prescriptions of minor ailments.

Certain types of bacteria live in the intestines of humans and animals. These bacteria help in digestion and in destroying harmful organisms. Intestinal bacteria also produce some vitamins needed to help the human body.

Bacteria in soil and water play a vital role in recycling carbon, nitrogen, sulfur, and other chemical elements used by living things. Many bacteria help decompose dead organisms and animal wastes into chemical elements. Certain kinds of bacteria invert.

Antibiotics are body compounds used to inhibit bacteria growth. In the beginning antibiotic referred only to natural compounds. They are produced by bacteria. Penicillin is the most familiar antibiotic and has been used to fight many infectious diseases including syphilis, gonorrhea, tetanus, and scarlet fever. Another antibiotic, streptomycin, has been used to fight tuberculosis.

Antibiotics are mainly useful for treating infections caused by bacteria. Antibiotics came into general use during the 1940’s. At the time, they were often called "wonder drugs" because they cured as many bacterial diseases that were once fatal.

Some antibiotics are effective against infections caused by fungi and protozoa. Few antibiotics are useful in treating cancer. Antibiotics are also used to treat diseases in animals. The antibiotics support the animal’s growth for reasons that are not entirely understood. Farmers sometimes add small amounts of antibiotics to their livestock feed. This worries some scientists.

Antibiotics are not effective against colds, influenza, or other viral diseases. The effectiveness of antibiotics is limited because both pathogenic microbes and cancer cells can become resistant to them.

Antibiotics fight microbes and cancer cells by interfering with normal cell functions. The interference occurs in one of three ways: prevention of cell wall formation, damage to cell membrane, or disruption of chemical processes.

A lot of antibiotics are regarded among the safest drugs when properly used. Antibiotics can sometimes cause dangerous side affects. The three main dangers are allergic reactions, destruction of helpful microbes, and damage to organs and tissues.

In most cases allergic reactions are mild and produce only a rash of fever. Stern reactions can occur, and even cause death. All antibiotics are able to produce allergic reactions, but such reactions occur most often with penicillin’s. A physician usually asks if the patient has had any allergic reactions to any antibiotics before prescribing it.

A virus is a microscopic organism that lives in a cell of another living thing. Even though viruses are extremely small they are major causes of diseases. Some viruses pass on a disease to human beings. Some diseases are measles, influenza and the common cold.

Viruses are not made up of cells. They lack some of the substances needed to live on their own. To find these substances, a virus must enter a cell of another living thing. It then can use the cell’s materials to live and reproduce.

A basic virus has two basic parts a core of a nucleic acid and an outer coat of protein. The core consists of either deoxyribonucleic acid or ribonucleic acid. The DNA or RNA enables the virus to reproduce after it has entered a cell.

Most viruses reproduce in specific cells of certain organisms. When viruses cause colds reproduce in cells of the human respiratory infection area. Viruses cannot live outside their particular cells. They must be carried into the organism by air currents of some other means, and then transported by body fluids to the cells.

Some different viruses in humans are AIDS, chickenpox, colds, cold sores, hepatitis, a liver disease, influenza, measles, mumps, poliomyelitis, rabies, and yellow fever. The nature of the disease caused by a particular type of virus is determined by which cells and tissues in the body the virus tends to invade.

Virologists study viruses mainly to learn how they cause disease and how to control these organisms. Scientists also use viruses for such purposes as insect control, cell research, and development of vaccine and other drugs.
 

resoults
 

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