Protists: With the three-domain system, Protists, which was one kingdom is broken down into other kingdoms. We’ll call it a Super Kingdom.
Characteristic of Protists:
1) Unicellular or simple colonial. 2) Eukaryotic.
3) May have diverse nutritive modes including photosynthesis, ingestion and absorption. These are also called mixotrophs.
4) May reproduce sexually or asexually.
5) May have motility by eukaryotic cilia or undulipodia or by other means (pseudopods) or may be non-motile.
The different types of Protists:
Note: We realize that the taxonomy of protists undergoes constant revision since it is a polyphyletic taxon and the evolutionary relationships are uncertain. The following taxonomy is one that is a combination of taxonomies from the following textbooks: Wallace, King and Sanders (1981); Arms and Camps (1987); Curtis and Barnes (1989); Campbell (1993); Campbell, Reece and Mitchell (1999); and Campbell and Reece (2002).
Super Kingdom: Protista
Kingdom: Diplomonadida Phylum: Diplomonads Kingdom: Parabasala
Phylum: Trichomonads Kingdom: Euglenozoa
Phylum: Euglenoids Phylum: Kinetoplastids Kingdom: Alveolata:
Phylum: Dinoflagellates Phylum: Apicomplexa Phylum: Ciliates Kingdom: Stramenophila
Phylum: Oomycota
Phylum: Chrysophyta (Golden Algae) Phylum: Bacillariophyta (Diatoms) Phylum: Phaeophyta
Kingdom: Rhodophyta Phylum: Rhodophyta Kingdom: Chlorophyta
Phylum: Chlorophyta Kingdom: Mycetozoa
Phylum: Myxogastridia Phylum: Dictyostelida Kingdom: Unknown
Phylum: Actinopoda Phylum: Formaminiferan
Protists:
Kingdom Diplomonadida and Parabasala:
These kingdoms contain heterotrophic flagellates. Some are free-living, others are parasitic, and still others are symbionts. The parasitic form often has complex lifecycles involving two hosts. The symbionts are found in the guts of termites and wood roaches; these flagellates engulf and digest the wood eaten by their insect hosts. They lack mitochondria. Giardia, an example of a Diplomonadida, are found in lakes and reservoirs causes diarrhea, cramps, fatigue and loss of weight.
An example of a parabasalid is trichomanas vaginalis. This is a common inhabitant of the human vagina. It can infect and proliferate in the vagina killing the beneficial bacteria. This protist can even be found in the male urethra, but without symptoms, which means that this protist can be transmitted sexually.
Kingdom Euglenozoa:
Most members of this group live in fresh water, and are abundant in polluted habitats. These protists have two flagella, one for locomotion, and the other specialized to help detect light. Euglenophytes lack cell walls but have elastic, transparent pellicles made of protein just beneath their plasma membrane. They contain chlorophyll a and b and carotenoids.
Euglenonoids reproduce asexually through binary fission.
Euglenas can either be autotrophic or heterotrophic (mixotrophic). For example, euglenas raised in the dark lose their green color and become heterotrophs, ingesting food through a gullet. Kinetoplastids have a single, large, mitochondrion. They are symbiotic and parasitic. They can change the molecular structure of their coats often, which prevents attacks from the host immune system.
A parasitic genus Trypanosoma, which live in the blood of vertebrates, mainly mammals, causes many diseases including sleeping sickness and Chaga's disease (a disease in which the protists damages the heart and other organs). Nagana is a trypanosome disease, which kills cattle. These diseases are transmitted by blood sucking insects.
Kingdom Alveolata: Dinoflagellates
These are commonly known as dinoflagellates because of their two undulipodia. Most dinoflagellates are photosynthetic, possessing chlorophyll a and c and carotenoids; some are heterotrophic. Dinoflagellates store their food in the form of starch and are abundant in warm oceans. Ancient dinoflagellates formed large oil deposits.
The majority of dinoflagellates reproduce asexually through binary fission.
groove, and the other projecting along the length of the cell. Some are naked, and others are covered with a cellulose armor. Several species are bioluminescent.
Some dinoflagellates produce a nerve poison that can kill humans and fish. During population explosions of Gonyaulax (a dinoflagellate), shellfish that have eaten large quantities of this organism become unfit for human consumption. Since Gonyaulax contains a red pigment, the population explosion may color the water red, a warning signal of 'red tide.'
Pfiesteria is also a dinoflagellate that can be photosynthetic one moment and heterotrophic the next.
Kingdom Alveolata: Phylum Apicomplexa (Sporozoa):
All of the sporozoans are parasitic with complicated lifecycles. Some have gametes that are flagellated and others have gametes with psuedopods. Most feed by absorbing small organic molecules from their hosts.
The sporozoan Toxoplasma may be the most common human parasite. It causes the disease Toxoplasmosis, whose symptoms may be so slight that they go unnoticed, and is sometimes diagnosed as a form of arthritis.
Human malaria is caused by a sporozoan, Plasmodium. These malaria parasites require two different hosts to complete the lifecycle: humans and the female Anopheles mosquito, which transmits the disease from one person to another.
Kingdom Alveolata: Phylum Ciliophora:
The ciliates are heterotrophic protists with cilia either all over the body or in specialized areas on the cell surface. The body wall contains trichocysts, thread-like organelles that can be
discharged to the outside. Some trichocysts have barbed tips, and some eject poison. Trichocysts can be used as anchors, for defense, or to capture prey.
Most ciliates prey on bacteria, small animals or other protists. Specialized cilia around the mouth region sweep food into a gullet. The food enters a vacuole, and is then digested by a lysosome containing digestive enzymes. The products are absorbed and the undigested materials are discharged. A contractile vacuole discharges excess water.
Ciliates also have a micronucleus, which contain one copy of the complete genome, and a large macronucleus, containing up to 500 times more DNA than the micronucleus. The micronucleus is involved in sexual reproduction and heredity; the macronucleus controls growth, metabolism, and asexual reproduction.
Paramecium is the most familiar of the freshwater ciliates.
Kingdom: Mycetozoa: Phylum Myxogastridia: Plasmodium Slime Mold
chitin as in fungi. Because of these traits, the following slime molds and relatives are classified as protists.
Slime mold life cycle:
The slime mold starts as a slimy mass, a plasmodium that looks like a huge ameba. This is a giant cell that is multinucleated (coenocytic) cell that phagocytizes organic matter. The plasmodium seeks moist habitats.
During unfavorable conditions, the slime mold seeks drier areas. The drying mass will produce sporangia (round bodies on top of slender vertical props). Cells in each sporangium then undergo a number of meiotic divisions, producing haploid spores. These spores can be carried to new places by winds. If the spore lands on a moist spot, it begins to divide and form an ameboid growth, myxameba. In some species-- the spore will form flagellated sperm cells called swarm cells, which can swim.
The myxameba or the swarm cells fuse together to form a diploid cell. These undergo numerous mitotic divisions, producing a plasmodium again.
Two types of organisms are commonly called water molds; but because they have flagellated cells, they are actually protists.
Kingdom Stramenophila: Phylum Bacillariophyta: Diatoms:
Most of diatoms are photosynthetic. These protists are found in the sea, freshwater and in wet spots on rocks, plants or wood.
Diatoms contain chlorophylls a and c and an accessory pigment fucoxanthin, which gives the organism its yellow-brown color. They store much of their excess food as oil and are important in the formation of petroleum deposits.
Diatoms are similar to golden algae in pigmentation and storage of food. However, the diatoms have a rigid cell wall impregnated with pectin and silica glass (SiO2). Often the cell wall is
strikingly patterned. The siliceous walls of diatoms are quite resistant to decay and have accumulated on the ocean floor in enormous numbers. Where the sea floor has been raised by geological activity, the deposits (diatomaceous earth) may be mined for commercial uses as fine abrasives in silver polishes and toothpaste and as packing in air and water filters.
Kingdom Stramenophila: Phylum Chrysophyta: Golden Algae
Golden Algae is named for its color—yellow (xanthophyll) and brown (carotene). The cells are biflagellated. They live in freshwater and marine environments. They can extend pseudopods to ingest food particles and bacteria, they can absorb dissolved organic molecules, or they can photosynthesize. Golden algae are usually unicellular, but they can also be colonial.
Kingdom Stramenophila: Phylum Oomycota: Egg Molds
(sperm) and female (egg). However, all of these gametes are nonmotile and have no flagella.
Asexual cycle: Water molds produce sporangia, which produce flagellated zoospores, with two flagella. Swimming zoospores emerge and swim about in search of a food source. When food is available, they form cysts, which germinate into diploid hyphae to form new colonies.
Swimming zoospores are not gametes because they are diploid and never fuse with another cell. They only grow asexually.
Sexual cycle: Begins with the growth of unusually thick hyphae, which produce haploid egg cells in spherical structures called oogonia (gametangia). Haploid male gametes, produced in male gametangia, reach the egg by way of hyphae. Notice that the male gametes do not swim. The male hyphae grow near the oogonium and send branches all over the spherical body. Inside these branches are sperm producing cells. The sperm penetrates the oogonium and fertilizes the egg.
Most terrestrial water molds are saprobes that live off dead organic matter. Some are parasitic and pathogenic, for example, downy mildews and blights. The organism responsible for the potato famine blight is a water mold, Phytophtoroa infestans. It grows on moist leaves and absorbs the nutrients of the leaf.
Kingdom Stramenophila: Phylum Phaeophyta: Brown Algae
There are about 1500 named species. They are distinguished by their characteristic brown pigment, fucoxanthin. Brown algae store their carbohydrates as laminarin and mannitol. They have flagellated sperm; some female reproductive cells are also flagellated. Brown algae only live in the ocean, especially in cold costal water. They come in all shapes and sizes. e.g. Necrocystis or kelp can be 30 m (100 ft) tall. Macrocystis is another giant kelp that has highly specialized tissues and organs, which include:
Holdfasts: anchors the algae to the bottom
Stipes: stem like supporting structures with trumpet hyphae. This demonstrates parallel evolution with conducting tissue of higher plants. Blades: structures that resemble leaves.
Bladders: spherical and hollow, help keep the Photosynthetic cells near the surface.
Thallus: refers to the seaweed body that contains the above structures.
Laminaria (Brown Algae) Life Cycle:
The Brown algae life cycle shows us alternation of generations.
In the brown algae, a zygote grows into a SPOROPHYTE through mitosis. All sporophytes are diploid, and they produce SPORES. The haploid spores are produced through meiosis. Once the spores land on the ocean floor, they grow (through mitosis) into either a male or female brown alga. These organisms are HAPLOID because they have half the diploid number of
see brown algae at the beach, you are looking at the sporophyte (2n) generation. The antheridia and oogonia are very small and you probably will not see them without a microscope.
The generations alternate between the diploid and haploid stages. The diploid stage
(sporophyte), alternates with the haploid stage (oogonium and antheridium). With sex, there are two events (when the gametes fuse): Plasmogamy: fusion of the two cytoplasms and
Karyogamy: fusion of the two haploid nuclei (if the nuclei don’t fuse, they form a dikaryon cell with two haploid nuclei. They act as a diploid, but they are not a true diploid.). Usually these two events occur at the same time, however, as we will see in the Kingdom Fungi, the events can occur at separate times.
Kingdom Rhodophyta: Red Algae
There are 4,000 species of seaweed and a few freshwater species.
Because of their color, red algae absorb blue light, which has the greatest penetration in water. Some red algae are black or green. They contain the accessory pigment phycoerythrin from the family of pigments called phycobilins. The pigments of red algae are very similar to those in cyanobacteria. It is believed that the red algae are the result of symbiotic relations between eukaryotic hosts and cyanobacteria (actually, all photosynthetic eukaryotes are the result of symbiosis with cyanobacteria or other algae). Red algal cells, including sperm, contain no flagella or cilia. Nearly all types of red algae are marine, eg. Red seaweeds in the tide pools. Red algae grow on rocky coasts, where they attach firmly to the rocks firmly by structures using holdfasts.
They store food as a starch-like compound called floridan. They also produce another polysaccharide: agar-agar, which is used to thicken soups and prepare a jelly-like medium to grow bacteria. Irish moss, a red alga, is harvested for carrageenan, the thickening agent in ice cream. It is non-caloric and contains no fat. Nori, Japanese seaweed, is also a red alga.
Rhodophyta presents us with a clear picture of alternation of generations. Both haploid and diploid are multicellular forms with thalli (branched bodies) that resemble each other. You can differentiate between the two by inspecting the reproductive structures under a microscope. Neither generation is dominant. The life history of red algae consists of three phases: haploid gametophyte, diploid carposporophyte and diploid tetrasporophyte.
A sperm from a gametophyte (n) lands on and fertilizes the egg in a female gametophyte (n). The diploid carposporophyte forms inside the female gametophyte. The carposporophyte
produces diploid spores, which leave and germinate into diploid tetrasporophyte through mitosis. Meiosis occurs in the tetrasporophyte and produces haploid tetraspores, which germinate into haploid gametophytes (male and female). These structures will produce haploid gametes through mitosis. However, there is no flagella.
Kingdom Chlorophyta: Green Algae
or inhabit damp soil or snow, or occupy cells, body cavities of protists and invertebrates as symbionts. Many unicellular green algae are photosynthetic symbionts in lichens, ciliates and invertebrates. They all contain chlorophyll a and b, and store food as starch. Chlorophyta occur in single-cell flagellated or unflagellated forms, as chains or filaments, as inflated fingers or as delicate flattened blades.
Examples:
1) Volvox (simple colonial). Volvox is composed of identical cells, each one similar to a single Chlamydomonas cell. The structure of Volvox suggests a way that multicellularity could have arisen.
Volvox features:
a) The sphere swims in an organized manner. The flagella in front pull and the flagella in back push.
b) In the sexual phase, some cells differentiate and specialize for reproduction.
c) In the asexual phase, pockets of the sphere depress inwards, and new spheres bud off. However, since the flagella originally point inwards, the cells have to turn themselves inside out within the colony.
2) Ulothrix:
These multicellular organisms have haploid and diploid generations. In the Ulothrix, there is an alternation of generations with the domination of the haploid generation over the diploid
generation. Alternation of generations continues in the evolution of land plants, with the diploid generation becoming increasingly dominant.
Molecular evidence, life history, and morphology suggest that Coleocheate, a green alga (Charales), was the closest relatives of land plants.
These protists were classified as Sarcodines; however, in the three-domain system, they are unclassified.
Phylum Rhizopods: Amebas
The Rhizopods are protists that move and engulf their prey with pseudopodia. Because the ameba (Ameba proteus) is such a familiar creature, Rhizopods are often thought of as naked and amoeboid. Many amebas have shells, and all members of the three other classes in the phylum, foraminiferans, heliozoans, and radiolarians, also have shells. These live in both marine and freshwater environments. They can be parasitic.
Phylum Foraminiferans:
Foraminiferans inhabit the warmer oceans of the world and secrete shells made of calcium carbonate with many holes. It is through these holes that they poke their long thin pseudopodia. The pseudopodia branch and join outside the shell to form a net that traps and digests the
Phylum: Actinopods: Radiolarians and Heliozoans
Radiolarians secrete elaborate outer shells usually made of silica. Like foraminiferans, they extend their pseudopodia through holes in the shell, but they draw their food into their shell for digestion.
