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• The theory of endosymbiosis, accepted by almost all biologists, proposes that mitochondria and chloroplasts were once aerobic eubacteria that were engulfed by ancestral eukaryotes.
• There is some suggestion that centrioles may also have an endosymbiotic origin.
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1. What kind of bacteria most likely gave rise to the chloroplasts in the eukaryotic cells of plants and some algae?
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• The kingdom Protista consists of predominantly unicellular phyla, together with three phyla that include large numbers of multicellular organisms.
• The catch-all kingdom Protista includes all eukaryotic
organisms except animals, plants, and fungi.
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2. Why is the kingdom Protista said to be an artificial group? How is this different from the other kingdoms?
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• The largest of the five groups are the unicellular, amoeboid protists that includes the rhizopads, the radiolarians, and the forams.
• Dinoflagellates (phylum Dinoflagellata) are a major phylum of primarily unicellular organisms that have unique chromosomes and a very unusual form of mitosis.
• Euglenoids (phylum Euglenophyta) have chloroplasts that are similar to those found in green algae and plants.
• Diatoms (phylum Chrysophyta) are unicellular, photosynthetic protists with opaline silica shells.
• Brown algae (phylum Phaeophyta) are multicellular, marine protists, some reaching 100 meters in length. The kelps contribute greatly to the productivity of the coastal sea areas.
• The zoomastigotes (phylum Sarcomastigophora) are a group of heterotrophic, mostly unicellular protists that includes Trypanosoma.
• There are about 8000 named species of ciliates (phylum Ciliophora); these protists have a very complex morphology with numerous cilia.
• The malarial parasite, Plasmodium, is a member of the phylum Apicomplexa. Carried by mosquitoes, it multiplies rapidly in the liver of humans and other primates and brings about the cyclical fevers characteristic of malaria by releasing toxins into the bloodstream of its host.
• The groups Oomycota and Acrasiomycota are considered
to be fungus-like protists.
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3. Why is mitosis in dinoflagellates unique? What are zooxanthellae?
4. What determines whether a collection of individuals is truly multicellular?
5. What unique characteristic differentiates the members of Ciliophora from other protists? What is the function of two vacuoles exhibited by most members of Ciliophora?
6. Why has it been so difficult to produce a vaccine for trypanosome-caused diseases?
7. What differentiates the oomycetes from the kingdom Fungi, in which they were previously placed? What is the feeding strategy of this phylum? Why are these organisms generally considered harmful?
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