23.3 Groups of Protists

• Various methods are used for transportation by protists.

• There are a variety of mechanisms that protists reproduce by.
• Some people undergo asexual reproduction to produce two daughter cells.
• In protists, the axis of orientation can be used to divide the atom into two parts.
• The true slime molds exhibit multiple fission and divide into many daughter cells.
• Others produce buds that grow to the size of the parent.

• Many protist species can switch from asexual to sexual reproduction when necessary.
• Sexual reproduction is associated with periods when the environment is changing.
• Sexual reproduction may allow the protist to recombine genes and produce new variations of progeny, some of which may be better suited to surviving changes in a new or changing environment.
• The cysts can be resistant to temperature extremes, desiccation, and low pH.
• This strategy allows certain protists to wait out stressors until their environment becomes more favorable for survival or until they are carried to a different environment because cysts exhibit virtually no cellular metabolism.

• Protist life cycles range from simple to elaborate.
• The life cycle of certain protists is complicated by the fact that they have different host species at different stages of development.
• Some protists are unicellular in the haploid form and multicellular in the diploid form.
• Other protists have multicellular stages in both haploid and diploid forms.

• Most protists exist in some type of aquatic environment, including freshwater and marine environments, damp soil, and even snow.
• Several protist species are parasites.
• Some protist species live on dead organisms and contribute to their decay.

• By the end of this section, you will be able to describe representative protist organisms from each of the six recognized supergroups.

• The Kingdom Protista has been disassembled due to the discovery of new genetic relationships among these eukaryotes.

• Protist classification is difficult because of convergent evolution.
• All of the protists as well as animals, plants, and fungi are included in the six "supergroups" that make up the emerging classification scheme.
• All organisms within each supergroup are believed to have evolved from a single common ancestor, meaning that they are most closely related to each other than to organisms outside that group.
• There is no evidence for the monophyly of some groups.
• Each supergroup is a representation of one of the many variations on the cell structure.
• One or more of the defining characters of the cell may have deviated from the "typical" pattern.

• The diagram shows a proposed classification.
• There are six supergroups in the domain Eukarya.
• Multiple kingdoms are within each supergroup.
• The dotted lines suggest evolutionary relationships among the supergroups that are still debated.

• The true evolutionary relationships are still to be determined, and the classification scheme presented here represents just one of several hypotheses.
• As data accumulates, the six supergroups may be modified or replaced.
• When learning about protists, it is a good idea to focus on the similarities and differences of each group, rather than the terminology.

• The hypothesis that all Archaeplastida are descendants of a relationship between a Heterotrophic protist and a cyanobacterium is supported by evidence.
• There are protist members of the group.
• The land plants evolved from the closest relatives of these protists.
• unicellular, multicellular, and colonial forms are included in the red and green algae.
• The most complex of the life cycles is the change of generations, in which both haploid and diploid stages are multicellular.
• Cells that undergo meiosis can produce haploid spores.
• The haploid gametophyte makes gametes by virtue of the growth of the spores.
• The gametes grow into a diploid sporophyte.
• Alternation of generations can be seen in some species of Archaeplastid algae.
• The gametophyte and sporophyte are vastly different in some species.

• The peptidoglycan cell wall of the ancestral cyanobacterial endosymbiont is retained by the grucophytes.

• Redalga, or rhodophytes, are multicellular and range in size from small, unicellular protists to large, multicellular forms.
• There is a second cell wall outside of the inner cell wall.
• Carbohydrates in the wall are the source of agarose and agar.
• The red in the red algae is caused by red photopigments that obscure the green tint of chlorophyll in some species.

• The red algae and the glaucophytes store the same amount of carbohydrates in the cytoplasm as in the plastid.
• Red algae can be found at depths of 260 meters in tropical waters.
• There are red algae in the water.
• The red algae life cycle has two sporophyte phases, with meiosis occurring only in the second one.

• The green algae is abundant.
• The green algae exhibit has the same structure as the land plants.
• Carbohydrates are stored in the plastid in both plants and green algae.
• The group of protists shared a common ancestor with land plants.
• The chlorophytes and charophytes are related to the green algae.
• The charophytes are related to land plants in many ways.
• Spirogyra is a charophyte.
• The presence of charophytes in wet habitats signals a healthy environment.

• The chlorophytes have a wide range of form and function.
• plankton is a common component of chlorophytes.
• The protist of chlamydomonas is a unicellular chlorophyte with a pear-shaped morphology and two anterior flagella that guide it toward light.
• There are more complex chlorophyte species that have haploid gametes.

• One of the few examples of a colonial organism is the chlorophyte Volvox, which behaves in some ways like a collection of individual cells, but in other ways like the specialized cells of a multicellular organisms.
• Each Volvox colony contains up to 60,000 cells, each with two flagella, and is composed of a hollow, spherical matrix.
• Individual cells in a Volvox colony move in a coordinated fashion.
• Basic cell specialization can be seen in the example of a few cells reproducing to create daughter colonies.
• The daughter colonies are produced with their flagella on the inside and have to evert as they are released.

• There is a green alga in this group.
• The colony consists of cells immersed in a matrix and intertwined with each other via hair-like extensions.
• Some chlorophytes are large, multinucleate, single cells.
• The foliage of the species can reach lengths of 3 meters.
• The cells of cauliflower species do not complete cytokinesis, remaining as massive and elaborate single cells.

• A chlorophyte consisting of a single cell contains thousands of nuclei.

• There is a question about how a single cell can make such shapes.

• Look at the video to see the green alga.

• The Amoebozoa include species with single cells, species with large multinucleated cells, and species that have multicellular phases.
• Amoebozoan cells exhibit pseudopods that are similar to tubes or flat lobes.

• The pseudopods project outward from anywhere on the cell surface.
• The entire cell is then moved by the protist.
• This type of motion is similar to the cytoplasmic streaming used in the Archaeplastida, and is also used by other protists as a means of locomotion or as a method to distribute nutrients and oxygen.
• The Amoebozoa have both free-living and parasites.

• The naked amoebae and the shelled amoebae are the same species.
• The multinucleate amoebae Pelomyxa is 10 times the size of Amoeba proteus, which is 500 um in diameter.
• Although it has hundreds of nuclei, Pelomyxa has lost its main source of energy, the mitochondria.
• In other protist groups, the secondary loss or modification of mitochondria is a feature.

• Amoebae are seen under a microscope.
• The isolates would be classified as amoebozoans.

• The slime mold, a subset of the amoebozoans, is thought to be the result of convergent evolution.
• During times of stress, some slime molds develop into fruiting bodies similar to fungi.

• The life cycles of the slime molds are categorized into plasmodial or cellular types.
• The large, multinucleate cells that make up the plismodial slime mold move along the surface like a blob of slime during their feeding stage.
• Food particles are deposited into the mold as it moves.
• The plasmodium has the ability to form fruiting bodies during times of stress.
• Haploid spores can be spread through the air or water and can potentially land in more favorable environments.
• If this happens, the cells can combine with each other to form a diploid slime mold, which is the end of the life cycle.

• The life cycle of a plasmodial mold is shown.
• The plasmodium is a single-celled, multinucleate mass.

• The cells that make up the cellular slime mold are independent amoeboid cells.
• When food is low, cells aggregate into a mass of cells that behave as a single unit.
• Some cells in the slug contribute to drying up and dying in the process.
• The asexual fruiting body is made up of cells atop the stalks.
• If they land in a moist environment, the plasmodial slime mold can grow.

• There are several stages in the life cycle of Dictyostelium discoideum, including aggregated cells, mobile slugs and their transformation into fruiting bodies.

• This video shows the formation of a fruiting body by a mold.

• There is a single flagellum in flagellated cells of the group.
• The flagella of other protists are anterior and their movement pulls the cells along.
• The animal-like choanoflagellates are part of the opisthokonts and are believed to be a descendant of sponges.
• There are unicellular and colonial forms of choanoflagellates.
• The apical flagellum is surrounded by a contractile collar.
• The collar is used to collect and filterbacteria.
• The collar cells of sponges show a feeding mechanism similar to that of choanoflagellates.

• There are at least one form of the Mesomycetozoa that can kill humans.
• Their life cycles are not understood.
• These organisms appear to be related to animals.

• They were grouped with other protists based on their appearance.

• The previous supergroups are all the products of primary endosymbiontic events, and are what would be considered "typical" in an introductory biology book.
• Some of the members of the next three super groups were derived from secondary endosymbiosis.
• There are some interesting variations in nuclear structure.

• The Rhizaria supergroup includes many of the amoebas with thin threadlike, needle-like or root-like pseudopods.
• The body of the cell is composed of calcium carbonate, Silicon, or strontium salts.
• Rhizarians have roles in both carbon and nitrogen cycles.
• Carbon dioxide is locked away from the atmosphere when rhizarians die and their tests sink into deep water.
• The process by which carbon is transported deep into the ocean is referred to as the biological carbon pump, because carbon is "pumped" to the ocean depths where it is not accessible to the atmosphere as carbon dioxide.
• Lower atmospheric carbon dioxide levels are maintained by the biological carbon pump.
• Foraminiferans are the only eukaryotes that are known to participate in the nitrogen cycle by denitrification.

• It has a chambered calcium carbonate shell.

• Foraminiferans, or forams, are unicellular protists, ranging from 20 micrometers to several centimeters in length, and occasionally resembling tiny snails.
• The forams can harvest for nutrition from the test house.
• The forams can move, feed, and gather additional building materials when the forams extend through the pores.
• Sand or other particles are associated with forams.
• Changes in global weather patterns and pollution are indicators of foraminiferans.

• The pseudopods are supported by microtubules and they function to catch food particles.
• The shells of dead radiolarians can be found on the ocean floor.
• Radiolarians are very common in the fossil record.

• The shell was imaged using a scanning electron microscope.

• Both naked and shelled forms are included in the cercozoa.
• The Chlorarachniophytes have acquired chloroplasts.

• Vampyrellids or "vampire amoebae," as their name suggests, obtain their nutrition by sucking out the contents of other cells.

• This rhizarian is mixotrophic, and can obtain both food and water by using its network of pseudopods.

• Current evidence suggests that species classified as chromalveolates are derived from a common ancestor that was engulfed in a red cell.
• The ancestor of chromalveolates is thought to have come from a secondary event.
• Some chromalveolates have lost red alga-derived plastid genes.
• The working group that is subject to change should be considered a hypothesis-based working group.

• Significant disease agents in animals and plants are included in chlorveolates.
• There are two types of chromalveolates, alveolates and stramenopiles.

• The alveolates are derived from a common ancestor according to a large body of data.
• The alveolates are named for the sac beneath the cell.
• The function of the alveolus is unknown, but it may be involved in osmoregulation.
• The alveolates are further categorized into some of the better known protists.

• Heterotrophic, mixotrophic, and photosynthetic dinoflagellates can be found.
• A red alga gave rise to the chloroplast of photosynthetic dinoflagellates.
• Many dinoflagellates are encased in plates.
• Two flagella fit into the grooves between the plates, with one extending longitudinally and the other encircling the dinoflagellate.

• The shape of the dinoflagellates is great.
• There are two flagella that fit in the grooves between the plates.
• The spinning motion is caused by the movement of the two flagella.

• The dinoflagellates have a nuclear variant.
• The chromosomes in the dinosaur are very small and do not have typical histones.
• In dinoflagellates, the chromosomes are separated from the nucleus without the breakdown of the nuclear envelope.

• Large numbers of marine dinoflagellates (billions or trillions of cells per wave) can emit light and cause an entire breaking wave to twinkle or take on a brilliant blue color.
• During the summer months, population explosions of marine dinoflagellates can tint the ocean with a muddy red color.
• The red tide is caused by the abundant red pigments in dinoflagellate plastids.
• The dinoflagellate species can kill fish, birds, and marine mammals.
• Humans who eat protists may become poisoned.

• The bioluminescence can be seen from the New Jersey coast.

• There is a structure called an apical complemodified secondary.
• The genomes of dinoflagellate chloroplasts and apicoplast are similar.
• The apical complex is used for entry and infections.
• All apicomplexans are parasites.
• The group includes the pathogen that causes Malaria in humans.
• Multiple hosts and stages of sexual and asexual reproduction are involved in the apicomplexan life cycles.

• The apical complex they have enables them to cause harm.
• ciliates can coordinate their movements and eat food by beating their cilia.
• Some ciliates have structures that are similar to paddles, funnels, or fins.
• Ciliates have a pellicle that provides protection without compromising agility.
• Protists in the Paramecium organize their cilia into a plate-like primitive mouth, which is used to capture and digestbacteria.
• Food captured in the oral grooves enters a food vacuole.
• There is a specific region on the cell that contains exocytic vesicles that expel waste particles.
• Without multicellularity, iliates exhibit considerable structural complexity.

• Paramecium has a primitive mouth that allows it to eat and excrete waste.

• Excess water can be released through contractile vacuoles.
• The organisms are able to move.

• The contractile vacuole of Paramecium expels water to keep the cell balanced.

• There are two nuclei in Paramecium, a macronucleus and a micronucleus.
• The micronucleus is an essential part of sexual reproduction, but its genes are not transcribed.
• The macronucleus is the nucleus which is transcribed.

• The macronucleus divides amitotically, and thus becomes genetically unbalanced over a period of successive cell replications.
• Paramecium is one of the ciliates that reproduce sexually.
• The process begins when two different types of Paramecium make physical contact and join with a bridge.
• Two haploid micronuclei are created when one of the three degenerates in each cell.
• The cells move away from each other.
• A completely novel diploid pre-micronucleus are generated by the fusion of the haploid micronuclei.
• The original macronucleus is destroyed when this pre-micronucleus undergoes three rounds of mitosis.
• Four of the eight pre-micronuclei become full-fledged micronuclei, while the other four perform multiple rounds of DNA replication.
• Hundreds of smaller chromosomes are formed by severely edited copies of the micronuclear chromosomes.
• The macronucleus differentiates the smaller chromosomes.
• Four new Paramecia are produced from each original conjugative cell after two cycles of cell division.

• The cells have a macronucleus and a micronucleus.

• The macronuclei are derived from a plant.

• Sexual reproduction can cause meiosis and meosis.

• The stramenopiles is a subgroup of the chromalveolates.

• The red alga is the source of these algae.
• A textured flagellum is the identifying feature of this group.
• There is an additional flagellum that does not have hair-like projections.

• There is a single hairy flagellum and a secondary smooth flagellum in this stramenopile cell.

• The diatoms are unicellular protists that cover themselves in intricately patterned, glassy cell walls composed of Silicon dioxide in a matrix of organic particles.
• The protists are part of the freshwater and marine plankton.
• Most species of diatoms reproduce asexually.
• By expelling a stream of mucopolysaccharides from the raphe, the diatom can attach to surfaces or propel itself in one direction.

• There are a lot of diatoms live among annual sea ice in McMurdo Sound.

• There are 2 to 200 um diatoms.

• diatom populations bloom to numbers greater than can be consumed by aquatic organisms The excess diatoms are not easily reached by saprobes that feed on dead organisms on the sea floor.
• The carbon dioxide that the diatoms had consumed and incorporated into their cells is not returned to the atmosphere.
• Along with other protists, diatoms help maintain a balanced carbon cycle.

• Golden algae are unicellular and can form large colonies.
• Their gold color is a result of their extensive use of the group of carotenoids, which are yellow or orange in color.

• A major part of the plankton community are golden algae, which are found in both freshwater and marine environments.

• The seaweeds are primarily marine, multicellular organisms.
• Giant kelps are brown in color.
• Some brown algae have evolved tissues that look like plants, with root-like holdfasts, stemlike stipes, and leaf-like blades that are capable of photosynthesis.
• The stipes of giant kelps can be up to 60 meters in length.
• Brown algae have a variety of life cycles.
• Multicellular gametophytes are produced by haploid gametes that combine to produce diploid organisms that then become multicellular organisms with a different structure from the haploid form.

• The life cycles of several species of brown algae have evolved in which both the haploid and diploid forms are multicellular.
• The structure of the gametophyte is different.

• There are 1n zoospores in the sporangia.

• The 2n plant is the sporophyte.

• The water molds, oomycetes, were named after them because of their resemblance to a fungus, but the data shows that they are not related to any other organisms.
• The oomycetes are characterized by a cell wall and a network of filaments.
• Many oomycetes have two flagella, one hairy and one smooth.
• The oomycetes have many parasites and saprobes.
• Most of the oomycetes are aquatic.
• The Irish potato famine of the 19th century was caused by the plant pathogen Phytophthora infestans.

• Many of the protist species classified into the supergroup Excavata are asymmetrical, single-celled organisms.
• Heterotrophic predator, photosynthetic species, and parasites are included in this supergroup.
• The diplomonads, parabasalids, and euglenozoans are its subgroup.
• There is a variety of modified mitochondria in the group.
• Many of the euglenozoans are free-living, but most are parasites.

• Giardia lamblia is one of the parasites included in the Excavata.
• These protists were thought to have no mitochondria.
• Although they are essentially nonfunctional as respiratory organelles, the Mitochondrial remnant organelles, called mitosomes, do function in iron and sulfur metabolism.
• Alternative pathways, such as glycolysis, can be used to generate energy.
• Each cell has two different haploid nuclei.
• There are four pairs of flagella that lie between the two nuclei.

• Giardia lamblia is a waterborne protist that causes severe diarrhea when eaten.

• The parabasal apparatus is a subgroup of Excavata that consists of a Golgi complex.
• An axostyle is a bundle of fibers that runs the length of the cell.
• Parabasalids move with flagella and rippling, and these and other modifications may assist locomotion.
• The parabasalids exhibit modified mitochondria.
• These structures are called hydrogenosomes because they produce hydrogen gas as a byproduct.

• 180 million cases of trichomoniasis, a sexually transmitted disease in humans, are reported each year.
• Women who are exposed to this protist may become more susceptible to secondary infections with the human immunodeficiency virus and may be more likely to develop cancer.
• Pre-term delivery is an increased risk for pregnant women with T. vaginalis.

• The guts and rumen of ruminant animals are some of the most complex of the parabasalids.

• These organisms can digest a substance called cellulose.
• They have multiple flagella arranged in complex patterns and some recruit spirochetes that attach to their surface to act as accessory locomotor structures.

• There are parasites, mixotrophs, autotrophs, and Heterotrophs in size from 10 to 500 um.
• Euglenoids move through their aquatic habitats using two long flagella that guide them toward light sources.
• Euglena is a mixotrophic species that can only use light for photosynthesis.
• In the dark, the cells of Euglena are unable to function, and instead take up organic nutrition from their environment.
• The pellicle of Euglena is made of bands of proteins.
• Euglena has exceptional flexibility because the bands spiral around the cell.

• The human parasites, Trypanosoma brucei, is a subgroup of Euglenozoa.
• The subgroup is named after the kinetoplast, a large modified Mitochondrion.
• The subgroup includes several parasites, collectively called trypanosomes, which cause devastating human diseases andinfecting insect species during a portion of their life cycle.
• After a tsetse fly bites a human or other mammal, it develops a disease in the gut.
• When the tsetse fly consumes another blood meal, the parasites travel to the salivary glands of the insect to be transmitted to another human or mammal.
• African sleeping sickness can be fatal if left unattended since it leads to progressive decline of the function of the central nervous system.