Groups of microorganisms
Algae are relatively simple organisms. The most primitive types are unicellular. Others are aggregations of similar cells with little or no differentiation in structure or function. Still other algae, such as the large brown kelp, have a complex structure with cell types, specialiged for particular functions. Regardless of size or complexity, algal cells contains chlorophyll and are capable of photosynthesis. Algae are found most commonly in aquatic environments or in damp soil.
Viruses are very small non-cellular pasasites or pathogens of plants, animals and bacteria as well as other protists. They are so small that they can be visualized only by the electron microscope. Viruses can be cultivated only in living cells.
Bacteria are unicellular prokaryotic organisms or simple associations of similar cells. Cell multiplication is usually by binary fission.
Protozoa are unicellular eukaryotic organisms. They are differentiated on the basis of morphological, nutritional and physiological characteristics. Their role in nature is varied but the best known protozoa are the few that cause disease in human beings and animals.
Fungi are eukaryotic lower plants devoid of chlorophyll. They are usually multicellular but are not differentiated into roots, stems and leaves. They range in size and shape from single celled microscopic yeasts to giant multicellular mushrooms and puffballs. We are particularly interested in those organisms commonly called molds, the mildews, the yeasts and the plant pathogens known as rusts. True fungi are composed of filaments and masses of cells which make up the body of the organism known as mycelium. Fungi reproduce by fission by budding or by means of spores borne on fruiting structures that are quite distinctive for certain species.
Microbiologists may specialize in the study of certain groups of microorganisms. Strictly speaking, bacteriology is the study of bacteria, but the term is often used as a synonym for microbiology, Protozoology is the study of protozoa; a special branch of Protozoology called parasitology deals exclusively with the parasitic or disease producing protozoa and other parasitic micro and macroorganisms.
Mycology is the study of fungi such as yeasts and molds. Virology is the science that deals with viruses. Phycology is the study of algae. Further specialization in some aspect of the biology of a particular group of organisms is not uncommon.e.g., Bacterial genetics, algal physiology and bacterial cytology.
Importance of microorganisms
Microorganisms affect the well being of people in a great many ways. As we have already stated, they occur in large numbers in most natural environments and bring about many changes, some desirable and others undesirable. The diversity of their activities ranges from causing diseases in humans, animals and plants to the production and deposition of minerals, the formation of coal and the enhancement of soil fertility.
There are many more species of microorganisms that perform important roles in nature than there are diseases producing species.
Although microorganisms have existed for a long time, their existence was unknown until the invention of the microscope in the 17th century. The year 1674, marks the birth of microbiology when Antony van Leeuwenhoek, a dutch merchant, looked at a drop of lake water through a glass lens which he had ground. He described a variety of microorganisms such as protozoa, algae, yeast and bacteria. He prepared 400 simple microscopes capable of enlarging objects from 50 to 300 times.
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