Prokaryotes are the most numerous organisms on Earth today. They
lived on Earth by themselves for over 1 billion years-before any other
organism. They have the ability to live in habitats that are cold, hot, salty,
acidic, and alkaline. No wonder they thrived in the harsh conditions of early
Earth! Prokaryotes are typically around 1-5 micrometers in diameter, but some
vary in size. Because they are so small, it is very easy for them to live just
about anywhere. It is said that there are more prokaryotes found in a person’s
mouth than the number of humans that have ever lived on Earth! That’s pretty
gross if you think about it, right? We all know there is a vast amount of cells
in our body. Well, guess what? The number of prokaryotes living ON your body is
about 10 times more than the number of cells INSIDE your body! There are two
domains of prokaryotes which are bacteria and archaea. The most common domain
is bacteria of course because we know the many ways that they can help or harm
us. Most bacteria are beneficial to us, but some can be deadly and cause
sickness. So no matter where you go, prokaryotes will always be there with you!
Source: Class Notes:Chapter 16-The Origin and Evolution of Microbial Life: Prokaryotes and Protists
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