WSC: PHYS 0106: Earth History Timeline: First Eukaryotes

html> WSC: PHYS 0106: Earth History Timeline: First Eukaryotes

	Westfield State College PHYS 0106 (Spring, 2001) Earth History Timeline
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First Eukaryotes
Writer/Researcher: Jessica Millot
Editor: Lynn Sniatkowski
Web Page Builder: Jessica Millot

An eukaryote is a single or mult-cellular organism whose cells contain a nucleus and other oragnelles, such as ribosomes and mitochondria (see picture below). The word means "true nuclei." The cells are more complex than prokaryotic cells, allowing eukaryotes to perform more actions than their ancestors. The DNA of an eukaryote is inside the nucleus, which is kept enclosed inside the cell apart from the cytoplasm. Eukaryotic cells replicate through mitosis. The earliest eukaryotes derived from their single-celled predecessors, prokaryotes, mostly bacteria that lack a nucleus, between 1.4 and 1.6 billion years ago, or perhaps even earlier.

Eukaryotic Cell These first eukaryotes were members of the kingdom Protista. Today the Plant Kingdom, as well as the Fungi and Animal Kingdoms, are also composed entirelt of eukaryotes. The first eukaryotes were single-celled, as are all protists. These organisms then evolved into multi-cellular creatures with organs. The primitive protists were very diverse and included forms of amoebas, diatoms, and dinoflagellates. Most protists fall into one of three categories: plant-like, animal-like, or fungi-like.

Endosymbiosis played a major role in the evolution of the earliest eukaryotes. Symbiosis (see example below) is the conditions between two or more organisms, usually mutually benefiting each. It is believed that the first eukaryotes were developed because of some form of this. The very first forms of mitochondria and chloroplasts were some type of bacteria that probably invaded the very first eukaryotes and then evolved into the cell because they were favorable. There is also speculation that the development of eukaryotes from prokaryotes had something to do with the oxygen in the atmosphere. The protists pelobionta has a cell without mitochondria and is able to survive without much oxygen, a condition that early eukaryotes would have had to survive in.

Symbiosis - A bacteria (notice arrow) invading a flagellate (to the right) protist.
Figures from: Patterson, David J. and Sogin, Mitchell L. (See link below.)

REFERENCES
- Microsoft Corporation (2001). Microsoft Encarta. Retrieved from the World Wide Web February 15, 2001.

- Patterson, David J. and Sogin, Mitchell L. (2001). Eukaryotes. Retrieved from the World Wide Web February 15, 2001.

- The University of California Musuem of Paleontology, Berkeley, and the Regents of the University of California (2001). Introduction to the Eukaryota. Retrieved from the World Wide Web February 15, 2001.