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Chapter Seven: The Classification of Unicellular Organisms
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Chapter One discussed the two important classes of unicellular organisms: prokaryotes and eukaryotes. Remember, eukaryotic cells are in general more complex than prokaryotic organisms. Below is the same charts presented in Chapter One, but now you should be familiar with the terms.
| Prokaryote | Eukaryote | |
| cell membrane | yes | yes |
| nucleus | no membranes | surrounded by two membranes |
| endoplasmic reticulum | no | yes |
| Golgi bodies | no | yes |
| mitochondria | no | yes |
| vacuoles | no | yes |
| lysosomes | no | yes |
| ribosomes | yes | yes |
| chromosomes | circular without histones | linear with histones |
Organisms may also be classified by their method of nutrition and requirements for respiration. Those which produce their own food (through photosynthesis, for example) are called autotrophs. Heterotrophs are organisms which must ingest nutrients from the external environment. Cells which require oxygen to perform their nutritional process (whether it be photosynthesis or glycolysis) are called aerobes; those which do not need oxygen are called anaerobes.
Biologists have devised a system of classification for all life on earth based on assigning each organism to one of five large categories called kingdoms. The five kingdoms are Monera (prokaryotic organisms), Protista (single-celled eukaryotes), Fungi, Plantae, and Animalia. Only the first two kingdoms contain unicellular organisms, so we will discuss only those.
Within each kingdom are many additional categories called phyla (one such category is called a phylum). Organisms may be classified using additional subdivisions under the phyla, but for our purposes, we will not require this specificity.
All prokaryotic organisms are part of the kingdom Monera. As we discussed above, these organisms do not have membrane-bound organelles, and their DNA and other structures are chemically different from those in eukaryotic organisms. The kingdom Protista, on the other hand, contains unicellular eukaryotic organisms.
The remainder of this chapter is devoted to discussing each major type of unicellular organism with a special focus on information which may come in handy for the Simulation.
