Protists 1: Classification and Ecological Roles Flashcards
Whittaker’s Five Kingdom System included the Kingdom Protista
Defining characteristic: Eukaryotes that did not fit into the Plant, Animal, or
Fungus kingdoms
Diversity
o Size and complexity
Most protists are unicellular, although some are colonial or multicellular
Examples
o Unicellular: Euglena
o Colonial: Dinobryon
o Multicellular: Kelp
Single-celled protists are considered the simplest eukaryotes, but at the cellular
level, many are among the most complex and elaborate of all cells
Include the same eukaryotic organelles we have discussed
Include some unique organelles not found in most other eukaryotes
Diversity
o Nutrition
Some are photoautotrophs and have chloroplasts
Some are heterotrophs, absorbing organic molecules or ingesting larger food
particles
Others are mixotrophs, using both photosynthesis and heterotrophic nutrition
Diversity
o Reproduction
Some only reproduce asexually (binary fission)
Some only reproduce sexually (gametes)
Some have extremely complex life cycles that involve multiple forms of the
organism, some of which reproduce sexually and others asexually (Example:
Plasmodium sp. -> Malaria)
Ecological roles
o Most protists are aquatic and are found almost anywhere there is water
Oceans
Fresh water
Damp soil
Wet leaf litter
Ecological roles
o Some are producers
Photosynthetic protists are THE main producers in aquatic communities
Photosynthetic protists account for approximately 30% of the total
photosynthesis that takes place on earth
o Photosynthetic protists: 30%
o Land plants: 50%
o Photosynthetic prokaryotes (e.g. cyanobacteria): 20%
Include
o Diatoms
o Dinoflagellates
o Algae
Ecological roles
o Some are decomposers
Help to recycle organic and inorganic matter
Ecological roles
o Some are symbionts
Wood-digesting protists in the guts of termites and ruminants
Coral reefs
Photosynthetic dinoflagellates -> carbon
Coral polyps (animals) -> structure
Ecological roles
o Some are parasites
Examples:
Plasmodium sp. (Malaria)
Trichomonas vaginalis (Trichomoniasis [STD])
Giardia lamblia (Giardiasis [“Beaver Fever”])
Trypanosoma brucei (African Sleeping Sickness)
Chryptosporidium parvum (Cryptosporidiosis)
Toxoplasma gondii (Toxoplasmosis)
Eukaryotic Evolutionary History
o Our understanding of eukaryotic evolutionary history has been in flux in recent years
o There is much we don’t know about the evolutionary path of the eukaryotic groups in
existence today
The current hypothesis places all eukaryotes into four major groups (“Supergroups”)
Exavata
“SAR Clade
Archaeplastida
Unkonta
Excavata
Diplomonads
Parabasalids
Euglenozoans
“SAR’ clade
Stramenopiles
o Diatoms
o Brown algae
Alveolates
o Dinoflagellates
o Apicomplexans
o Ciliates
Rhizarians
o Forams
o Cercozoans
Archaeplastida
Red algae
Green algae
Land plants
Unkonta
Amoebozoans
o Gymnamoebas
o Slime molds
Opisthokonts
o Nucleariids
o Fungi
o Choanoflagellates
o Animals
Supergroups
o Excavata
Excavata refers to a conspicuous feeding groove that appears to have been
“excavated” from one side
Many lack “classical” mitochondria, but have modified mitochondria or
mitochondrial remnants that show they all originally had them
Supergroups
o Excavata
[] Mitosomes
o Only recently discovered
o Remnants of mitochondria
o Same general structure
o No Krebs Cycle, No ETS
o Activity: maturation of Fe-S proteins
Supergroups
o Excavata
[] Hydrogensomes
o Same general structure as mitochondria
o Function to produce ATP anaerobically
o Produce hydrogen gas as byproduct