Just about every living organism on Earth can be placed in one of two classes: prokaryotes and eukaryotes. A prokaryote is a cell without a nucleus and eukaryotes are cells that contain nuclei. There's one quick test to distinguish prokaryotes from eukaryotes: if you can see a single organism, it's a eukaryote. All prokaryotes are single-celled organisms. Some eukaryotes are also single-celled organisms, but every multi-celled organism is eukaryotic.
Features of Prokaryotes
Prokaryotes have a semi-rigid cell wall and a flexible membrane that encloses their cytoplasm, the medium that supports the processes of life. They contain one or more loops of DNA within the cytoplasm and protein manufacturing regions called ribosomes. They may have rudimentary internal membranes, but the environment within the cell is essentially uniform. That is, the cytoplasm contains a certain level of salinity, pH and chemical distribution, and all the processes of the cell occur in that environment.
Features of Eukaryotes
The primary distinguishing feature of eukaryotes is the existence of an internal membrane separating the DNA from the remainder of the cytoplasm. The DNA in eukaryotes is generally organized in one or more long chains called chromosomes. Eukaryotes also contain several other internal membranes that create distinct subcellular environments. Each of these internal compartments, called organelles, is able to optimize the conditions for a specific process, which means eukaryotes are generally more efficient than prokaryotes.
Examples of Prokaryotes
Prokaryotes are all single-celled organisms, most of which you know of as bacteria. For example, the famous (or infamous) Escherichia coli bacterium is a prokaryote, as is the streptococcus bacterium responsible for strep throat. The Streptomyces soil bacteria, from which the antibiotic streptomycin is derived, is also a prokaryotic organism. The entire subclass of archaea are also prokaryotes, mostly remarkable because of their ability to thrive in very harsh environments. An example of archaea is the Sulfolobus acidocaldarius archeobacterium that lives in extremely acidic mud pots in geothermally active areas.
Examples of Eukaryotes
Just about every organism you're familiar with is a eukaryote. Single celled organisms like yeast, paramecia and amoebae are all eukaryotes. Grass, potatoes, and pine trees are all eukaryotes, as are algae, mushrooms, and tapeworms. And, of course, moles, fruit flies, and you are also examples of eukaryotes.
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