Protist Design by Owen Borville October 29, 2024 Biology
Protists are classified as eukaryotes that are not land plants, animals, or fungi.
Evolutionists refer to the protist group of organisms as a paraphyletic group, because it does not contain all of its "claimed descendents of its common ancestor." Protists lineages are currently being debated and are not fully known, which gives uncertainty into the evolutionist model.
Most protists are microscopic, unicellular organisms that are abundant in soil, freshwater, brackish, and marine environments. In addition, protists are common in digestive tracts of animals and in the vascular tissues of plants.
Protists can be microscopic in size or up to several meters, and can be unicellular or multicellular.
Characteristics of Protists: Cells with nuclei surrounded by a nuclear envelope with nuclear pores. Mitochondria. A cytoskeleton of microtubules and microfilaments for structure and motility. Flagella and cilia for motility. Chromosomes organized by histone proteins. Mitosis for nuclear cell division. Sexual reproduction. Cell walls.
Evolutionists claim endosymbiosis or endosymbiotic theory to explain the origin of eukaryotes as one prokaryotic cell engulfing another prokaryotic cell to produce a eukaryotic cell. Evolutionists claim similarities between mitochondria and chloroplasts and free-living bacteria are substantial, including their own DNA and ribosomes. One cell is the host cell and the other cell(s) are engulfed into the host cell, according to the theory. Some of the engulfed cells produce new organelles in the host cell, also according to the theory, but this has yet to be fully explained. There is a lack of clear fossil evidence of a transition from prokaryotes to eukaryotes, however. Also, the method of gene transfer between each cell is unclear (host to engulfed cells). Mitochondrial (eukaryotic) DNA differences with bacterial (prokaryotic) DNA are substantial. Explaining the benefit of the symbiotic relationship to the host cell has not been fully explained. Variations in the shape of mitochondrial DNA have yet to be explained (circular to linear). Therefore, endosymbiosis lineage theory has not been fully explained and the intelligent design is apparent.
Some eukaryotes have organelles known as plastids, some of which allow the process of photosynthesis to occur in the organism. When plastids perform photosynthesis, they are rich in the pigment chlorophyll and other pigments that help obtain energy from light. Photosynthetic plastids are called chloroplasts. Evolutionists claim that plastids have an endosymbiotic origin, but this has not been fully explained.
Characteristics of Protists
Protists are very diverse in characteristics as there are thousands of claimed species of protists, but there are several common features of protists. Some protists live as colonies as free-living cells or as a multicellular organism. Some protists are very large single cells of various shapes less than a micrometer in size to three meters or even hectacres. Protist cells can live inside animal-like cell membranes or plant-like cell walls. Some protists are encased in glassy-silicate based shells or wound with pellicles of interlocking protein strips.
Protist metabolism can be aerobic or anerobic. Photosynthetic protists are photoautotrophs. Other protists are heterotrophic and consume other organisms for food. Phagocytosis is a process where protists injest organic particles. The phagolysosome organelle in the protist breaks down the organic particles of food into smaller molecules with digestive enzymes that can be used by the protist. Some protists are both photoautotrophic and heterotrophic.
Most protists are motile, but mobility features vary in protists. Some protists have one or more flagella that they use to move. Other protists are covered with tiny rows of cilia that help movement. Other protists have cytoplasmic extensions called pseudopods that help them move. Some protists can move toward or away from light with light-sensing organelles that direct the protist in a certain direction toward or away (taxis).
Protist reproduction can vary with mechanisms. Most protists reproduce with asexual binary fission to produce two daughter cells. Sexual reproduction, involving meiosis and fertilization, is common among protists, and many protist species can switch from asexual to sexual reproduction when necessary.
A protist cyst is a dormant, protective stage in the life cycle of a protist, which is a single-celled organism, where it encloses itself within a thick cell wall to survive unfavorable environmental conditions like lack of nutrients, extreme temperatures, or desiccation; essentially acting as a resting stage with low metabolic activity until conditions improve, allowing the protist to re-activate and resume normal functions when favorable conditions return. The protist cyst stage represents the intellgent design in protist organisms.
Protist life cycles can also vary from simple to complex and can contain multiple stages. Some protists are unicellular in the haploid form (one set of chromosomes) and multicellular in the diploid form (two sets of chromosomes). Other protists have multicellular stages in both haploid and diploid forms, or alternation of generations.
Almost all protists live in an aquatic environment, including freshwater, marine, wet soil, and snow. Some protists are parasites infecting plants or animals.
Classification of protists has been difficult for evolutionists because the proposed lineage is difficult to determine.
Archaeaplastida are photosynthetic organisms, including red and green algae. These are claimed by evolutionists to be the ancestors of land plants, through an endosymbiosis relationship with cyanobacterium. The plastid organelles for photosynthesis are the major feature in the proposed lineage. Colored pigments are found in red and green algae.
Glaucophyte protists are a small group of Archaeplastida unique because their chloroplasts retain remnants of the peptidoglycan cell wall of the ancestral cyanobacterial endosymbiont.
Red algae are mostly multicellular but some are unicellular and lack flagella. These can live in freshwater or tropical marine waters.
Green algae is the most abundant form of algae and have features similar to land plants, such as chloroplast structure. Green algae are divided into chlorophytes and charophytes. Charophytes have many similarities to land plants in morphology and reproductive strategies. Charophytes are found in wet habitats and are beneficial to the environment. Chlorophytes vary in form and function, living in freshwater, damp soil, and plankton. Chlorophytes can be multicellular or can be large single cells.
Amoebozoa can be single celled or multi-cellular. Gymnomoebae or lobose amoebae include the naked and shelled amoebae, whose bodies extend like snails. Proteus amoebae are larger and Pelomyxa amoebae are even larger.
Slime molds are a subset of the amoebozoans that have some morphology like fungi, such as developing into spore-generating fruiting bodies during stress. Plasmodial slime molds are composed of large, multinucleate cells and move along surfaces like an amorphous blob of slime during their feeding stage where food particles are engulfed into the slime mold body. The plasmoidal slime mold life cycle occurs as spores germinate into amoeboid or flagellated forms. Then fertilization of either type by fusion occurs. Then mitosis occurs without cytokinesis results in a mass called a plasmodium. The plasmodium feeds, grows, and produces a sporangium. Meiosis within the sporangium results in haploid spores. The cellular slime molds function as independent amoeboid cells when nutrients are abundant. When food is not abundant, cellular slime molds combine into a mass and act as a single unit. A stalk forms on the mold with haploid spores that are released and can germinate in a moist environment.
Opisthokonta protists has a single flagellum that pushes the organism along. Choanoflagellates are members of opisthokonta have animal-like characteristics, such as microvilli surrounding the flagellum used as a filter and ingestion of bacteria. Mesomycetozoa protists form a small group of parasites of fish and humans, and closely resemble animals.
The Rhizaria supergroup of protists includes many of the amoebas with thin threadlike, needle-like or root-like pseudopodia instead of lobes and many have armor-like body coverings. Rhizaria have roles in the carbon and nitrogen cycles, as they pump carbon to the ocean depths and away from the atmosphere. Rhizarian foraminiferans are the only known eukrayotes to participate in the nitrogen cycle by denitrification.
Foraminiferans, or forams, are unicellular heterotrophic protists, (Rhizarians) ranging from approximately 20 micrometers to several centimeters in length, and occasionally resembling tiny snails. Shells of forams are called tests of calcium carbonate and foram pseudopodia allow movement in marine or freshwater.
Radiolarians are another Rhizarian group and exhibit intricate exteriors of glassy silica with radial or bilateral symmetry. Needle-like pseudopods radiate outward for movement and food capture. The life cycle of the radiolarian ends on the seafloor in an accumulated layer.
Cercozoa are single-celled protists, naked or shelled, and photosynthetic with chloroplasts. They are predators of bacteria and important to the leaf surfaces of plants.
Chromalveolates include very important photosynthetic organisms, such as diatoms, brown algae, and significant disease agents in animals and plants.
Alveolates include the dinoflagellates, apicomplexians, and ciliates. The alveolates are named for the presence of an alveolus, or membrane-enclosed sac, beneath the cell membrane which has an unknown function.
Dinoflagellates exhibit extensive morphological diversity and can be photosynthetic, heterotrophic, or mixotrophic. Many are encased in cellulose armor and have two flagella that fit in grooves between the plates. Some dinoflagellates generate light, called bioluminescence, when they are jarred or stressed. Some dinoflagellate plastids cause a red color in the ocean from a red pigment called red tide. Large amounts of this particular dinoflagellate can be toxic to animals that contact the ocean.
Apicomplexan protists are parasitic and cause malaria in humans. Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an apicoplast—with an apical complex membrane.
The ciliates, which include Paramecium and Tetrahymena, are a group of protists 10 to 3,000 micrometers in length that are covered in rows, tufts, or spirals of tiny cilia for movement and food ingestion. The genus Paramecium contains a primitive mouth where food enters a vacuole with digestive enzymes and waste particles are released from the anal pore on the cell membrane. The Paramecium also has contractile vacuoles, where water enters by osmosis and exits by contraction. The Paramecium also has two nuclei in each cell: a macronucleus and micronucleus. The micronucleus genes are not transcribed while the macronucleus genes are transcribed.
Sexual reproduction in the Paramecium: Two different mating types form a cytoplasmic bridge. Meiosis produces four haploid micronuclei, three of which disintegrate. Each remaining micronucleus divides by mitosis. The conjugate pair swaps micronuclei. The haploid micronuclei fuse, forming a diploid micronucleus. The micronucleus undergoes three rounds of mitosis, producing eight micronuclei. The original macronucleus disintegrates, and four of the micronuclei become macronuclei. Two rounds of cell division produce four daughter cells.
The other subgroup of chromalveolates, the stramenopiles, includes photosynthetic marine algae and heterotrophic protists. The identifying feature of this group is the presence of a textured, hairy flagellum. Many stramenopiles also have an additional flagellum that lacks hair-like projections. Members of this subgroup range in size from single-celled diatoms to the massive and multicellular kelp.
The diatoms are unicellular photosynthetic protists that encase themselves in intricately patterned, glassy cell walls composed of silicon dioxide in a matrix of organic particles. These protists are a component of freshwater and marine plankton. Most species of diatoms reproduce asexually, although some instances of sexual reproduction and sporulation also exist. Some diatoms exhibit a slit in their silica shell, called a raphe. By expelling a stream of mucopolysaccharides from the raphe, the diatom can attach to surfaces or propel itself in one direction. Diatoms also help the carbon cycle like other protists by keeping carbon dioxide on the seafloor and away from the atmosphere.
Golden algae are mostly unicellular, but some form colonies. Their color comes from carotenoids, photosynthetic pigments. Golden algae are found in freshwater and marine environments and are important to the plankton community. Brown algae are mostly marine, multicellular organisms, also known as seaweed or kelps. Some kelps extend for 60 meters. Brown algae have a variety of life cycles, including alternation of generations. Laminaria brown algae life cycle involves spores during meiosis that form two gametophytes (haploids), sperm and egg fertilize into a zygote, which later develops a sporophyte (diploid) that produces more spores.
Water molds (oomycetes "egg fungus") have a fungus-like morphology, but are molecularly not closely related to fungi. They have a cellulose-based cell wall and a large network of filaments that allow nutrient intake. Many oomycetes have two different flagella for locomotion. They also have saprobes, white, fluffy growths on dead organisms. Oomycetes are also parasitic and many are aquatic, but some terrestrial.
Excavata are asymmetrical, single-celled organisms with a feeding groove excavated from one side. Diplomonads are small protists with flagella that inhabit the digestive systems of animals. Diplomonads usually have two nuclei, four pairs of flagella, and feed by digestion or absorption. Parabasalids are named for the parabasal apparatus, which consists of a Golgi complex associated with cytoskeletal fibers, including an axostyle that runs the length of the cell. Flagella are also present in the parabasalids, which form symbiotic relationships with animals (parasitic). Euglenozoans includes parasites, heterotrophs, autotrophs, and mixotrophs, ranging in size from 10 to 500 µm. Euglenoids move through their aquatic habitats using two long flagella that guide them toward light sources sensed by a primitive ocular organ called an eyespot. Some subgroups cause diseases in humans (T.brucei).
Protists have a large role in the environment and ecology as food sources for many other organisms. Photosynthetic protists are primary producers of nutrition for many other organisms. About 25 percent of the world's photosynthesis is conducted by photosynthetic protists. Protists can cause diseases in other organisms, animals, plants, and humans as parasites (human pathogens). Protists also work as decomposers to absorb nutrients from dead organic matter and returning inorganic nutrients to the soil and water, allowing for new plant growth and preserves the food chain.
Protists are classified as eukaryotes that are not land plants, animals, or fungi.
Evolutionists refer to the protist group of organisms as a paraphyletic group, because it does not contain all of its "claimed descendents of its common ancestor." Protists lineages are currently being debated and are not fully known, which gives uncertainty into the evolutionist model.
Most protists are microscopic, unicellular organisms that are abundant in soil, freshwater, brackish, and marine environments. In addition, protists are common in digestive tracts of animals and in the vascular tissues of plants.
Protists can be microscopic in size or up to several meters, and can be unicellular or multicellular.
Characteristics of Protists: Cells with nuclei surrounded by a nuclear envelope with nuclear pores. Mitochondria. A cytoskeleton of microtubules and microfilaments for structure and motility. Flagella and cilia for motility. Chromosomes organized by histone proteins. Mitosis for nuclear cell division. Sexual reproduction. Cell walls.
Evolutionists claim endosymbiosis or endosymbiotic theory to explain the origin of eukaryotes as one prokaryotic cell engulfing another prokaryotic cell to produce a eukaryotic cell. Evolutionists claim similarities between mitochondria and chloroplasts and free-living bacteria are substantial, including their own DNA and ribosomes. One cell is the host cell and the other cell(s) are engulfed into the host cell, according to the theory. Some of the engulfed cells produce new organelles in the host cell, also according to the theory, but this has yet to be fully explained. There is a lack of clear fossil evidence of a transition from prokaryotes to eukaryotes, however. Also, the method of gene transfer between each cell is unclear (host to engulfed cells). Mitochondrial (eukaryotic) DNA differences with bacterial (prokaryotic) DNA are substantial. Explaining the benefit of the symbiotic relationship to the host cell has not been fully explained. Variations in the shape of mitochondrial DNA have yet to be explained (circular to linear). Therefore, endosymbiosis lineage theory has not been fully explained and the intelligent design is apparent.
Some eukaryotes have organelles known as plastids, some of which allow the process of photosynthesis to occur in the organism. When plastids perform photosynthesis, they are rich in the pigment chlorophyll and other pigments that help obtain energy from light. Photosynthetic plastids are called chloroplasts. Evolutionists claim that plastids have an endosymbiotic origin, but this has not been fully explained.
Characteristics of Protists
Protists are very diverse in characteristics as there are thousands of claimed species of protists, but there are several common features of protists. Some protists live as colonies as free-living cells or as a multicellular organism. Some protists are very large single cells of various shapes less than a micrometer in size to three meters or even hectacres. Protist cells can live inside animal-like cell membranes or plant-like cell walls. Some protists are encased in glassy-silicate based shells or wound with pellicles of interlocking protein strips.
Protist metabolism can be aerobic or anerobic. Photosynthetic protists are photoautotrophs. Other protists are heterotrophic and consume other organisms for food. Phagocytosis is a process where protists injest organic particles. The phagolysosome organelle in the protist breaks down the organic particles of food into smaller molecules with digestive enzymes that can be used by the protist. Some protists are both photoautotrophic and heterotrophic.
Most protists are motile, but mobility features vary in protists. Some protists have one or more flagella that they use to move. Other protists are covered with tiny rows of cilia that help movement. Other protists have cytoplasmic extensions called pseudopods that help them move. Some protists can move toward or away from light with light-sensing organelles that direct the protist in a certain direction toward or away (taxis).
Protist reproduction can vary with mechanisms. Most protists reproduce with asexual binary fission to produce two daughter cells. Sexual reproduction, involving meiosis and fertilization, is common among protists, and many protist species can switch from asexual to sexual reproduction when necessary.
A protist cyst is a dormant, protective stage in the life cycle of a protist, which is a single-celled organism, where it encloses itself within a thick cell wall to survive unfavorable environmental conditions like lack of nutrients, extreme temperatures, or desiccation; essentially acting as a resting stage with low metabolic activity until conditions improve, allowing the protist to re-activate and resume normal functions when favorable conditions return. The protist cyst stage represents the intellgent design in protist organisms.
Protist life cycles can also vary from simple to complex and can contain multiple stages. Some protists are unicellular in the haploid form (one set of chromosomes) and multicellular in the diploid form (two sets of chromosomes). Other protists have multicellular stages in both haploid and diploid forms, or alternation of generations.
Almost all protists live in an aquatic environment, including freshwater, marine, wet soil, and snow. Some protists are parasites infecting plants or animals.
Classification of protists has been difficult for evolutionists because the proposed lineage is difficult to determine.
Archaeaplastida are photosynthetic organisms, including red and green algae. These are claimed by evolutionists to be the ancestors of land plants, through an endosymbiosis relationship with cyanobacterium. The plastid organelles for photosynthesis are the major feature in the proposed lineage. Colored pigments are found in red and green algae.
Glaucophyte protists are a small group of Archaeplastida unique because their chloroplasts retain remnants of the peptidoglycan cell wall of the ancestral cyanobacterial endosymbiont.
Red algae are mostly multicellular but some are unicellular and lack flagella. These can live in freshwater or tropical marine waters.
Green algae is the most abundant form of algae and have features similar to land plants, such as chloroplast structure. Green algae are divided into chlorophytes and charophytes. Charophytes have many similarities to land plants in morphology and reproductive strategies. Charophytes are found in wet habitats and are beneficial to the environment. Chlorophytes vary in form and function, living in freshwater, damp soil, and plankton. Chlorophytes can be multicellular or can be large single cells.
Amoebozoa can be single celled or multi-cellular. Gymnomoebae or lobose amoebae include the naked and shelled amoebae, whose bodies extend like snails. Proteus amoebae are larger and Pelomyxa amoebae are even larger.
Slime molds are a subset of the amoebozoans that have some morphology like fungi, such as developing into spore-generating fruiting bodies during stress. Plasmodial slime molds are composed of large, multinucleate cells and move along surfaces like an amorphous blob of slime during their feeding stage where food particles are engulfed into the slime mold body. The plasmoidal slime mold life cycle occurs as spores germinate into amoeboid or flagellated forms. Then fertilization of either type by fusion occurs. Then mitosis occurs without cytokinesis results in a mass called a plasmodium. The plasmodium feeds, grows, and produces a sporangium. Meiosis within the sporangium results in haploid spores. The cellular slime molds function as independent amoeboid cells when nutrients are abundant. When food is not abundant, cellular slime molds combine into a mass and act as a single unit. A stalk forms on the mold with haploid spores that are released and can germinate in a moist environment.
Opisthokonta protists has a single flagellum that pushes the organism along. Choanoflagellates are members of opisthokonta have animal-like characteristics, such as microvilli surrounding the flagellum used as a filter and ingestion of bacteria. Mesomycetozoa protists form a small group of parasites of fish and humans, and closely resemble animals.
The Rhizaria supergroup of protists includes many of the amoebas with thin threadlike, needle-like or root-like pseudopodia instead of lobes and many have armor-like body coverings. Rhizaria have roles in the carbon and nitrogen cycles, as they pump carbon to the ocean depths and away from the atmosphere. Rhizarian foraminiferans are the only known eukrayotes to participate in the nitrogen cycle by denitrification.
Foraminiferans, or forams, are unicellular heterotrophic protists, (Rhizarians) ranging from approximately 20 micrometers to several centimeters in length, and occasionally resembling tiny snails. Shells of forams are called tests of calcium carbonate and foram pseudopodia allow movement in marine or freshwater.
Radiolarians are another Rhizarian group and exhibit intricate exteriors of glassy silica with radial or bilateral symmetry. Needle-like pseudopods radiate outward for movement and food capture. The life cycle of the radiolarian ends on the seafloor in an accumulated layer.
Cercozoa are single-celled protists, naked or shelled, and photosynthetic with chloroplasts. They are predators of bacteria and important to the leaf surfaces of plants.
Chromalveolates include very important photosynthetic organisms, such as diatoms, brown algae, and significant disease agents in animals and plants.
Alveolates include the dinoflagellates, apicomplexians, and ciliates. The alveolates are named for the presence of an alveolus, or membrane-enclosed sac, beneath the cell membrane which has an unknown function.
Dinoflagellates exhibit extensive morphological diversity and can be photosynthetic, heterotrophic, or mixotrophic. Many are encased in cellulose armor and have two flagella that fit in grooves between the plates. Some dinoflagellates generate light, called bioluminescence, when they are jarred or stressed. Some dinoflagellate plastids cause a red color in the ocean from a red pigment called red tide. Large amounts of this particular dinoflagellate can be toxic to animals that contact the ocean.
Apicomplexan protists are parasitic and cause malaria in humans. Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an apicoplast—with an apical complex membrane.
The ciliates, which include Paramecium and Tetrahymena, are a group of protists 10 to 3,000 micrometers in length that are covered in rows, tufts, or spirals of tiny cilia for movement and food ingestion. The genus Paramecium contains a primitive mouth where food enters a vacuole with digestive enzymes and waste particles are released from the anal pore on the cell membrane. The Paramecium also has contractile vacuoles, where water enters by osmosis and exits by contraction. The Paramecium also has two nuclei in each cell: a macronucleus and micronucleus. The micronucleus genes are not transcribed while the macronucleus genes are transcribed.
Sexual reproduction in the Paramecium: Two different mating types form a cytoplasmic bridge. Meiosis produces four haploid micronuclei, three of which disintegrate. Each remaining micronucleus divides by mitosis. The conjugate pair swaps micronuclei. The haploid micronuclei fuse, forming a diploid micronucleus. The micronucleus undergoes three rounds of mitosis, producing eight micronuclei. The original macronucleus disintegrates, and four of the micronuclei become macronuclei. Two rounds of cell division produce four daughter cells.
The other subgroup of chromalveolates, the stramenopiles, includes photosynthetic marine algae and heterotrophic protists. The identifying feature of this group is the presence of a textured, hairy flagellum. Many stramenopiles also have an additional flagellum that lacks hair-like projections. Members of this subgroup range in size from single-celled diatoms to the massive and multicellular kelp.
The diatoms are unicellular photosynthetic protists that encase themselves in intricately patterned, glassy cell walls composed of silicon dioxide in a matrix of organic particles. These protists are a component of freshwater and marine plankton. Most species of diatoms reproduce asexually, although some instances of sexual reproduction and sporulation also exist. Some diatoms exhibit a slit in their silica shell, called a raphe. By expelling a stream of mucopolysaccharides from the raphe, the diatom can attach to surfaces or propel itself in one direction. Diatoms also help the carbon cycle like other protists by keeping carbon dioxide on the seafloor and away from the atmosphere.
Golden algae are mostly unicellular, but some form colonies. Their color comes from carotenoids, photosynthetic pigments. Golden algae are found in freshwater and marine environments and are important to the plankton community. Brown algae are mostly marine, multicellular organisms, also known as seaweed or kelps. Some kelps extend for 60 meters. Brown algae have a variety of life cycles, including alternation of generations. Laminaria brown algae life cycle involves spores during meiosis that form two gametophytes (haploids), sperm and egg fertilize into a zygote, which later develops a sporophyte (diploid) that produces more spores.
Water molds (oomycetes "egg fungus") have a fungus-like morphology, but are molecularly not closely related to fungi. They have a cellulose-based cell wall and a large network of filaments that allow nutrient intake. Many oomycetes have two different flagella for locomotion. They also have saprobes, white, fluffy growths on dead organisms. Oomycetes are also parasitic and many are aquatic, but some terrestrial.
Excavata are asymmetrical, single-celled organisms with a feeding groove excavated from one side. Diplomonads are small protists with flagella that inhabit the digestive systems of animals. Diplomonads usually have two nuclei, four pairs of flagella, and feed by digestion or absorption. Parabasalids are named for the parabasal apparatus, which consists of a Golgi complex associated with cytoskeletal fibers, including an axostyle that runs the length of the cell. Flagella are also present in the parabasalids, which form symbiotic relationships with animals (parasitic). Euglenozoans includes parasites, heterotrophs, autotrophs, and mixotrophs, ranging in size from 10 to 500 µm. Euglenoids move through their aquatic habitats using two long flagella that guide them toward light sources sensed by a primitive ocular organ called an eyespot. Some subgroups cause diseases in humans (T.brucei).
Protists have a large role in the environment and ecology as food sources for many other organisms. Photosynthetic protists are primary producers of nutrition for many other organisms. About 25 percent of the world's photosynthesis is conducted by photosynthetic protists. Protists can cause diseases in other organisms, animals, plants, and humans as parasites (human pathogens). Protists also work as decomposers to absorb nutrients from dead organic matter and returning inorganic nutrients to the soil and water, allowing for new plant growth and preserves the food chain.