chapter 28 protists. most eukaryotes are single-celled organisms protist is the informal name of...
TRANSCRIPT
Chapter 28Protists
Most Eukaryotes are Single-celled Organisms
Protist is the informal name of the group of mostly unicellular eukaryotes
Eukaryotic cells have organelles; more complex than prokaryotic cells
Most protists are unicellular, but there are some colonial and multicellular species
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Eukaryotic systematics have caused the classification of protists to change significantly
Protists exhibit more structural and functional diversity than any other group of eukaryotes
Protists, the most nutritionally diverse of all eukaryotes, include
Photoautotrophs, which contain chloroplasts
Heterotrophs, which absorb organic molecules or ingest larger food particles
Mixotrophs, which combine photosynthesis and heterotrophic nutrition
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Some protists reproduce asexually, while others reproduce sexually, or by the sexual processes of meiosis and fertilization
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Endosymbiosis in Eukaryotic Evolution There is now considerable evidence that
much protist diversity has its origins in endosymbiosis
Endosymbiosis is the process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then organelle in the host cell
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Five Supergroups of Eukaryotes Our understanding of the relationships
among protist groups continues to change rapidly
One hypothesis divides all eukaryotes (including protists) into five supergroups
1. Excavata
2. Chromalveolata
3. Rhizaria
4. Archaeplastida
5. Unikonta© 2011 Pearson Education, Inc.
Protists Roles in Ecological Communities
Protists are found in diverse aquatic environments
Protists often play the role of symbiont or producer
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Symbiotic Protists Some protist symbionts benefit their hosts
Dinoflagellates nourish coral polyps that build reefs
Wood-digesting protists digest cellulose in the gut of termites
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Some protists are parasiticPlasmodium causes malariaPfiesteria shumwayae is a dinoflagellate
that causes fish killsPhytophthora ramorum causes sudden
oak death
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Photosynthetic Protists Many protists are important producers that
obtain energy from the sun In aquatic environments, photosynthetic
protists and prokaryotes are the main producers
In aquatic environments, photosynthetic protists are limited by nutrients
These populations can explode when limiting nutrients are added
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Biomass of photosynthetic protists has declined as sea surface temperature has increased
If sea surface temperature continues to warm due to global warming, this could have large effects on
Marine ecosystemsFishery yieldsThe global carbon cycle
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