A virus is a small infectious microorganism that exists as a particle rather than a complete cell that is not capable of reproducing outside of a host cell. A virus only reproduces inside of other living cells in other organisms.
Viruses
A virus or a prion.
A prion is a small infectious particle that contains a misfolded protein. These contain no DNA or RNA. These cause Creutzfeldt-Jakob disease, Scrapie in sheep and Kuru. These are deadly and progressive nerve wasting diseases.A plant pathologist discovered an infectious RNA particle smaller than a virus that causes diseases in plants. He called it a viroid. Millions each year are lost by these viroids. These contain only RNA.These two are the smallest infectious particles. They are not called microorganisms because they are not alive any more than viruses are.
A virus
Pathogen.
Prion
BECAUSE MOST INFECTIOUS BACTERIA ARE OF THIS SIZE BECAUSE MOST INFECTIOUS BACTERIA ARE OF THIS SIZE
When a cell engulfs a particle, it is called phagocytosis. Certain white blood cells phagocytize and digest infectious particles like bacteria to kill them.
This allows rapid and sensitive detection of antibodies that are markers of such diseases, as infectious mononucleosis and rheumatoid arthritis
A plant pathologist discovered an infectious RNA particle smaller than a virus that causes diseases in plants. He called it a viroid. Millions each year are lost by these viroids. These contain only RNA.
Atoms are NOT the smallest particle- they are the smallest COMPLETE particle. In an atomic reaction, the atoms are broken apart, and release energy.
They are called Prion. This is the definition I fount at wordnetweb.princeton.edu/perl/webwn: "an infectious protein particle similar to a virus but lacking nucleic acid; thought to be the agent responsible for scrapie and other degenerative diseases of the nervous system".