Definition of Microorganisms on earth and man as a cell

A Microorganisms also spelled micro-organism, micro organism or Microorganisms or microbe is a microscopic organisms that comprise either a single cell (unicellular)  cell cluster, or multicellular relatively complex organisms. They are indeed, organisms or forms of life requiring magnification with the aid of a microscopic to see and resolve their structures.

 Microorganisms are very diverse ;they include bacteria, fungi, algea, and protozoa ;microscopic plant (green algea) ; and animal such as rotifers and planarians. Some microbiologist also include viruses, but others consider these as nonliving. Most Microorganisms are unicellular (single-celled), but this is not universal, since some multicellular organisms are microscopic, while some unicellular proist and bacteria, like thiomargarita Namibiensis, are microscopic and visible to the naked eye.

Indeed, the word "microscoorganisms"  is general terms that becomes more understandable if it is divided into its principal types as previously mentioned which are predominantly unicellular microbes.  Viruses are also include, although they cannot live or reproduce on their own. They are particles, not cells, they consist of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), but no both. Viruses invade living cells- bacteria, algea, fungi, protozoa, plants, and animals(including humans) and use their host metabolic and genetic machinery to produce thousands of new virus particle. Some virus can transform normal cell to cancer cells. Rickettsias and chlamydiae are very small cell that can grow and multiply only inside other living cells.

 Although bacteria, actiomycetes, yeasts, and molds are cell that must be magnified in order to see them, when cultured on solid media that allow their growth and multiplication, they form visible colonies consisting of millions of cells.

The study of Microorganisms is called microbiology, a subject that began with Anton Van leeuwenhoeks's discovery of Microorganisms in 1675, using a microscopic of his own design. Microorganisms live in all parts of the biosphere where there is liquid water, including soil, hot springs, on ocean floor, high in the atmosphere and deep inside rock within the earth's crust.

Microorganisms are critical to nutrient recycling in ecosystem as they act as decomposers. As some Microorganisms can fix nitrogen, they are vital part of the nitrogen cycle and recent studies indicate that airborne microbes may play a role in precipitation and weather.

Microbes are also exploited by scientists in biotechnology, both in traditional food and beverage preparation, and in modern technologies based on genetic engineering however, pathogenic microbes are harmful, since they invade and grow within other organisims causing diseases that kills human, other animal and plant.

MICROBIAL EVOLUTION
single-celled Microorganisms were the first form of life to develop on earth, approximately 3-4 billion years ago so, for most of the history of life on earth the only form of life were Microorganisms. Fossil microbes have also been found in rocks 3.3 to 3.5billion years old since then, microorganisms have had the principal task of recycling organic matter In the environment. As such they are absolutely essential to the health of the earth. Without them, the earth would be a gigantic, permanent waste dump.

Microorganisms are responsible for recycling the huge masses or organic matter synthesized by plant as life on earth evolved. Furthermore, micro organism -  the cynabacteria or their DNA in the chloroplast of the plant cells - were the source of most of free oxygen in the early atmosphere. They also oxidize ammonia (the universal end product of protein metabolism)  to nitrate, which is the only nitrogen source used by plant and is therefore essential for production of our plant foods.

Microorganisms are also responsible for cellouse hydrolysis in the runmens (first stomach compartments)  of cattle, facilitating the production of animal protein for human consumption. And, in recent times, Microorganisms have been the source of antibiotics that have enabled the cure of numerous diseases.

Blue-green algea (cyanobacteria) are prokaryotes (that is their cell have no distinct nucleus). They are very independent nutritionally since they can carry out photosynthesis using chlorophyll. Thus they can synthesize sugars for energy from carbon dioxide using solar radiation. They also release oxygen. They can respire aerobically and can fix nitrogen, generating amino acid and protein. They require only water, nitrogen gas oxygen carbon dioxide, some minerals and sunlight. The evidence is that they were on earth 3.2billion years ago. The cyanobacteria are among the earliest Microorganisms and very important even today.

Green algea are eukaryotes (that is, their cells have a distinct nucleus). They evolved about one billion years ago. They contain chlorophylls a and b, which enables them to convert carbon dioxide, through radiation, to sugar and to polymerize sugar to starches, hemicelluloses, and cellulose some of our most important source of food energy.

Green algea are still major source of food in the oceans green algea were likely the life forms that evolved into plants which first lived primarily in the oceans but moved to the land about 450 million years ago about the same time as the amphibians and the first land animal evolved. It is believed that the first mammals evolved about 150 millions years later, along with insects and reptiles, which were dominant. Another 150million years later, dinosaurs and first birds evolved, along with the first flowering plants. During the entire period from, 3.6 billion years ago, microorganisms were consuming and recycling the organic matter from themselves and other forms of life as they lived and died.

For several billion years, bacteria, algea, and other Microorganisms serves food for other microbes and for higher animals as they evolved. When plant evolved in the oceans and then subsequently moved to land ; they become major sources of food for other forms of life, including Microorganisms, animals and eventually humans.

Most Microorganisms reproduce rapidly, but slow when the environment is cold and microbes such as bacteria can also freely exchange genes by conjuction, transformation and transduction between widely-divergent species. This horizontal gene transfer, coupled with a high mutation rate and many other means of gene variation, allows Microorganisms to swiftly evolve (Via natural selection) to survive on new environment and respond to environmental stresses. An example of this is the evolution of specialized nylon-eating bacteria, it's also been studied in experimental evolution. This rapid evolution is important in medicine, as it has led to the recent development of super-bugs—pathogenic bacteria that at resistant to morden antibiotics.