Kingdom - Protista
Protistans are a collection of the simplest eukaryotic organisms. Both single-celled and
multicelled forms are included. One way to define the kingdom is to point out that it is not
prokaryotic. Its members have a nucleus, mitochondria, ER, mitotic apparatus, and more than one
chromosome. They have proteins associated with DNA; use microtubules in a cytoskeleton, spindle
apparatus, and cilia and flagella; may contain chloroplasts; and may divide by mitosis and meiosis.
The Theory of Endosymbiosis was
developed by Lynn Margulis. She proposed that mitochondria and chloroplasts are the descendents of
free-living prokaryotic organisms. Prokaryotes were engulfed by early eukaryotes and became
permanent internal symbionts (a cooperative relationship between two organisms).
Some protistans resemble members of other kingdoms (fungi for example) but are not of sufficient
complexity to be released from their assigned kingdom the Protista.
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