Microorganism

Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell (unicellular), cell clusters, or multicellular relatively complex organisms. The study of microorganisms is called microbiology.
Classification and structure
Microorganisms can be found almost anywhere in the taxonomic organization of life on the planet. Bacteria and archaea are almost always microscopic, while a number of eukaryotes are also microscopic, including most protists, some fungi, as well as some animals and plants. Viruses are generally regarded as not living and therefore are not microbes, although the field of microbiology also encompasses the study of viruses.
What is a microbe?
A microbe – another word for a microorganism – is a tiny individual living thing that is way too
small to be seen by the human eye alone. The only way this tiny organism can be seen is by using
a microscope. This is why microbes are often called “microscopic organisms.”
Bacteria

Almost all bacteria are invisible to the naked eye, with a few extremely rare exceptions, such as Thiomargarita namibiensis. They lack membrane-bound organelles, and can function and reproduce as individual cells, but often aggregate in multicellular colonies.[31] Their genome is usually a single loop of DNA, although they can also harbor small pieces of DNA called plasmids. These plasmids can be transferred between cells through bacterial conjugation. Bacteria are surrounded by a cell wall, which provides strength and rigidity to their cells. They reproduce by binary fission or sometimes by budding, but do not undergo sexual reproduction. Some species form extraordinarily resilient spores, but for bacteria this is a mechanism for survival, not reproduction. Under optimal conditions bacteria can grow extremely rapidly and can double as quickly as every 10 minutes.
Properties of Bacteria
• prokaryotic (no membrane-enclosed nucleus)
• no mitochondria or chloroplasts
• a single...