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Protists (The "SAR" clade is a highly diverse group of protists…
Protists
The "SAR" clade is a highly diverse group of protists define by DNA similarities
The large, diverse supergroup known as the "SAR" clade is proposed based on recent whole-genome analyses
The stramenopiles include several important photosynthetic groups, all characterized by hairlike projections on a flagellum
Diatoms are a major component of marine and freshwater phytoplankton; unique boxlike silica walls protect these unicellular protists
The color of golden algae results from yellow and brown carotenoids. The mostly marine, multicellular brown algae are the largest and most complex algae
Nearly all apicomplexans are animal parasites, and most have complex life cycles that often include sexual and asexual stages and several host species
Dinoflagellates make up a proportion of marine and freshwater phytoplankton
Ciliates are characterized by the cilia they use to move and feed. Small micronuclei are exchanged in a process called conjugation, which results in genetic variation
The third subgroup of the SAR clade is the rhizarians. Amoebas, which move and feed with their cellular extensions called pseudopodia, are spread across many eukaryotic taxa
Excavates include protists with modified mitochondria and protists with unique flagella
The supergroup Excavata was originally based on morphological studies of the cytoskeleton adn an "excavated" feeding groove found in some members
The mitosomes of diplomonads lack functional electron transport chains
The reduced mitochondria of parabsalids are called hydrogenenosomes and harvest energy anaerobically, releasing H2
The diverse clade of euglenozoans includes predatory heterotrophs, autotrophs, and pathogenic parasites, all of which have a spiral or crystalline rod inside their flagella
A single large mitchondrion containing a mass of DNA called a kinetoplast is characteristic of the group called kinetoplastids
The euglenids are characterized by one or two flagella that emerge from one end of the cell
Most eukaryotes are single-celled organisms
Nutritionally, protists can be photoautotrophs, heterotrophs, or mixotrophs, which are both photosynthetic and heterotrophic
Much evidence indicates that mitochondria evolved through endosymbiosis, originating from an endosymbiotic alpha proteobacteria that had been engulfed by a host cell from an archaeal lineage
This lineage of cells eventually gave rise to two lineages of algae: red algae and green algae
In several instances of secondary endosymbiosis, a red or green algae was engulfed by a heterotrophic eukaryote, leading to new protist lineages
Red algae and green algae are the closest relatives of land plants
Archaeplastida is a monophyletic group that includes red algae, green algae, and land plants
The photosynthetic pigment phycoerythrin produces the color of red algae and allows them to absorb those wavelengths of light that penetrate into deep water
The chloroplasts of green algae resemble those of land plants, and molecular and cytological evidence indicates that green algae and plants are closely related
Unikonts include protists that are closely related to fungi and animals
The fourth supergroup Unikonta includes animals, fungi, and some protists
Slime molds, tubulinids, and entamoebas are grouped as amoebozoans, a clade that includes many species of amoeba with lobe- or tube- shaped pseudopodia
Of the protists in the clade opisthokonts, nucleariids are more closely related to fungi, and choanoflagellates are more closely related to animals
Protists play key roles in ecological communities
Many protists are producers. Most aquatic food webs are based on photosynthetic protists and prokaryotes
Dinoflagellates are important photosynthetic symbionts in coral. Some protists are destructive parasites of plants and animals