Protista
Domain: Eukarya
Description: Organisms of the Kingdom Protista have varied characteristics. They are mainly unicellular, with colonial and multicellular variants. Their mode of nutrition is highly diverse as well, ranging from photoautotrophs to heterotrophs to mixotrophs (a combination of the first two). Their reproductive cycles can be either sexual or asexual, depending on the type of protist. Their flagella and pseudopodia allow them to be motile, while also serving as unique morphological features. While protists seem to be the most simple of eukaryotes, they are highly complex at a cellular level and command a large portion of the phylogenetic tree. |
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Divergent Event: Modern day protists probably arrived from humble beginnings. Due to infoldings of the plasma membrane of ancestral prokaryotes, the development of the endomembrane system and the nucleus came into being. The resulting organism engulfed an aerobic heterotrophic prokaryote, which would become the mitochondria. The resulting ancestral heterotrophic eukaryote would again display endosymbiosis, this time engulfing a cyanobacteria. The cyanobacteria evolved into plastids, giving rise to photosynthetic protists, algae. Red and green algae have also undergone a secondary endosymbiosis, this time being taken in by the vacuoles of heterotrophic eukaryotes. This then gave rise to many of the protists we today.
Body Plan: Most protists are just unicellular (Like amoebas), with flagella, cilia and pseudopodia for movement. Some are colonial (Volvox) and some are multicellular (Brown algae). Protists have subcellular organelles like the nucleus, golgi apparatus and lysosomes. They also have unique organelles like a contractile vacuole which pumps out excess water from the cell.
Metabolism: Heterotrophic protists include the supergroup Rhizaria which trap prey with their pseudopodia while photoautotrophic protists like algae use their chloroplasts. The heterotrophic protists obtain their organic molecules from the prey they consume while photosynthesis allows photoautotrophic protists to make their own sugars. Either way, both types use their mitochondria (or modified mitrochondrias called mitosomes) which perform cellular respiration, resulting in the creation of ATP.
Digestion: Heterotrophic protists have an intracellular digestion system. The pseudopodia traps the prey and the protist then performs phagocytosis, engulfing the prey in a food vacuole. Lysosomes then release hydrolytic enzymes into the food vacoule, breaking the prey into small compounds for the protist to use.
Nervous: Protists do not have a nervous system.
Circulatory: Due to their high surface area to volume ration and semi-permeable membrane, protists can simply rely on passive and active transport to move substances around.
Respiratory: Protists do not have a respiratory system.
Reproductive: Some protists reproduce sexually and asexually like Ciliates. Ciliates have a macronuclei and micronuclei. They exchange the haploid micronuclei via conjugation, which results in genetic diversity. Ciliates can also perform binary fission for asexual reproduction. Multicellular protists like brown algae perform alternation of generations, in which multicellular haploid and diploid forms exist.
Click on the following link to learn about the phyla within Protista:
Body Plan: Most protists are just unicellular (Like amoebas), with flagella, cilia and pseudopodia for movement. Some are colonial (Volvox) and some are multicellular (Brown algae). Protists have subcellular organelles like the nucleus, golgi apparatus and lysosomes. They also have unique organelles like a contractile vacuole which pumps out excess water from the cell.
Metabolism: Heterotrophic protists include the supergroup Rhizaria which trap prey with their pseudopodia while photoautotrophic protists like algae use their chloroplasts. The heterotrophic protists obtain their organic molecules from the prey they consume while photosynthesis allows photoautotrophic protists to make their own sugars. Either way, both types use their mitochondria (or modified mitrochondrias called mitosomes) which perform cellular respiration, resulting in the creation of ATP.
Digestion: Heterotrophic protists have an intracellular digestion system. The pseudopodia traps the prey and the protist then performs phagocytosis, engulfing the prey in a food vacuole. Lysosomes then release hydrolytic enzymes into the food vacoule, breaking the prey into small compounds for the protist to use.
Nervous: Protists do not have a nervous system.
Circulatory: Due to their high surface area to volume ration and semi-permeable membrane, protists can simply rely on passive and active transport to move substances around.
Respiratory: Protists do not have a respiratory system.
Reproductive: Some protists reproduce sexually and asexually like Ciliates. Ciliates have a macronuclei and micronuclei. They exchange the haploid micronuclei via conjugation, which results in genetic diversity. Ciliates can also perform binary fission for asexual reproduction. Multicellular protists like brown algae perform alternation of generations, in which multicellular haploid and diploid forms exist.
Click on the following link to learn about the phyla within Protista: