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CHAPTER 21 PROKARYOTES AND VIRUSES Microorganisms consist of organisms that are too small to be seen clearly without a microscope. These microorganisms include: -prokaryotes, which range in size from 0.2-1.0 micrometers in diameter. and -unicellular eukaryotic organisms of the kingdom Protista that are in the 10-100 micrometer range. (See fig 21.1) How big (or small) is a micrometer? 1/1,000,000 of a meter. But just how small is that? The period at the end of this sentence is about 1 millimeter (1000 micrometers) in diameter. There are groups of biological entities that are even smaller than bacteria. These groups are, VIRUSES, VIROIDS, AND PRIONS -some are things pathogens that can make organisms sick. -these are not organisms, because they don’t have all the requirements for being alive. They are however derived from organisms. THE PROKARYOTIC DOMAINS The organisms that make up the two prokaryotic domains ( Bacteria and Archaea ) were the first organisms to arise on earth (about 3.5 billion years ago).
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While only about 5000 prokaryotic species have been described, there may be as many as 100-1000 times that number. Bacteria have evolved to live in almost every possible environmental condition found on Earth including some very extreme conditions. While the range of conditions that the domains bacteria and archaea can in live in is large, the conditions a single species requires may be very specific. In order for these domains to be able to occupy so many different ecological niches, they have had to develop the ability to use many different energy sources. Some autotrophic prokaryotes, like cyanobacteria , are photoautotrophic and obtain their energy from sunlight via photosynthesis. Other prokaryotic species are chemoautotrophs which derive their energy from inorganic chemicals ( chemosynthesis ). There are also heterotrophic bacteria that must have an organic food source for either their energy or their carbon source. The two domains are similar in many respects (See table 21.1):
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This note was uploaded on 04/25/2008 for the course V 011 taught by Professor Staff during the Spring '06 term at NYU.

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