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Protist Evolution

It is thought that protists were once prokaryotes that had other prokaryotes living inside of them.

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Are You Going To Eat That?
Teacher Contributed

Are You Going To Eat That?

Microbe species Paramecium cadatum

Student Exploration

Are You Sure You're Related?

Protista has been called a "garbage" grouping. Historically, this is because "Protista" is where all organisms were placed which didn't fit into other categories. If an organism wasn't quite a plant, it was a protist. If an organism wasn't quite an animal, it was a protist. A very pragmatic solution to the intriguing problem of how living organisms relate to each other. But while science may create categories like this out of necessity, that doesn't mean the issue is closed. Advances in molecular biology have made it possible to look at these creatures at a new level, a genetic level, and with this increased insight, relationships within the group protista and between the protista and other groups are gaining clarity. What does this all mean? Within the coming decades protista will be split into new groups so that the groupings reflect shared characteristics between organisms, rather than a lack of characteristics with other organisms. So why study protista? Well, the organisms exist even if we don't fully understand their relationships to other organisms, and they certainly have something to teach us about the diversity and nature of life.


Now that you have a sense of the beauty and diversity of these organisms, find out more about the question of where scientists believe the Eukarya and the Protista came from.


So there you have some information on the endosymbiotic theory. But how often did this occur? Well, that is something scientists still argue over, but stay tuned. Thanks to molecular biology, the answer to that question may not be far off.

Extension Investigation

Use the resources below to answer the following questions:

  1. Are all protists single-celled? Are all protists eukaryotes? What led to these organisms being grouped together?
  2. What effect did the accumulation of oxygen (O2) have on the organisms living on Earth? How is it believed they responded?
  3. What benefit could an anaerobic bacteria gain by engulfing an aerobic bacteria? What would the oxygen (O2) levels of the habitat where this occurred have to be for this to be a viable explanation?
  4. Which organelle do you think first arose, the chloroplast or the mitochondria? Think carefully and give specific examples to defend your choice?
  5. Do you find the fact that mitochondria and chloroplasts have their own DNA a compelling argument that they were once independent organisms? Why or why not? Can you think of an alternative explanation for this situation?

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