Microorganisms, microbes and "beasties"
Introduction to microbes (extract from "And You Thought You Were Safe")
What are these little creatures that have such an impact on our world? We cannot see them, so they must be either a myth, or extremely small in size. Well, the latter is true. Microorganisms are organisms so small that we cannot see them with the unaided eye. To see a microorganism we need a viewing system such as a microscope in order to magnify them. Microorganisms are things such as bacteria, fungi, viruses, protozoa and algae.
The term microbe is nearly synonymous with microorganism. The difference being the term microbe is used more for living microorganisms such as bacteria, protozoa and fungi. Didn't we already say that bacteria, fungi and protozoa were microorganisms? You are right, they are. However, did you notice that viruses were not included in the list? Viruses are what we call nonliving. Although viruses are categorised as nonliving, they still cause substantial morbidity (sickness) and mortality (death) through their own mechanisms.
To be categorized as living, an entity has to be able to perform certain criteria such as eating, growth, reproduction and death. Viruses do not grow or eat. They can remain inert for thousands of years in a closed or sealed room (e.g., a tomb), or on a calm surface until disturbed by an air current, sweeping them into the air and enabling them to be inhaled, or even touched by an unsuspecting individual. Depending in the virus, contact with enough of these infectious entities may result in disease or even death in certain circumstances. Instead of undergoing the process of physical growth as compared to humans and other animals, viruses are just produced in an "assembly line" fashion in our cells. Once a virus enters a human cell, the virus uses this cell as its host. Our cells act as "factories" for viruses, allowing them to replicate within the intracellular environment. A virus can "force" a host cell to build thousands of viral copies before the cell is damaged or destroyed. Since a virus forces the cell to replicate or reproduce copies of the original virus, it satisfies the criteria of reproduction. And because a virus is assembled in a host cell, but does not grow in size (once it is assembled, it is what we would define as adult size), viruses do not meet the criteria for growth. Because viruses do meet some of the criteria of living organisms, we categorize them between living and nonliving. However, they are still microorganisms, considering we cannot see them with the unaided eye.
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