Understanding Kingdom Protista

Kingdom Protista

• Protists are eukaryotic microbes and were the first to develop a true nucleus.
• This kingdom possesses vast ecological diversity of approximately 65,000 to 200,000 species.
• Examples of protists include amoebas, paramecium, and diatoms.
• Any organism that does not fit into other kingdoms is placed into the Protista kingdom.
• Some protist species are large enough to be seen with the naked eye.

Characteristics of Protists

• Eukaryotic organisms
• Most are unicellular, but some are simple multicellular organisms.
• Some reproduce asexually via binary fission, multiple fission, or mitosis.
• Some reproduce sexually via meiosis.
• Most live in aquatic environments, damp areas like moist soil, or within other organisms.
• Protists include fungi, plants, and animals.

Protist Classification

• Protists are their own kingdom.
• Protists can be divided into three groups: plant-like protists, fungi-like protists, and animal-like protists.

Unicellular Protist Groups

• Animal-like protists are also known as protozoans and include amoebas, ciliates, and flagellates.
• Plant-like protists include euglenoids, diatoms, and dinoflagellates.
• Fungus-like protists include slime molds and water molds.
• Animal-like protists consume other organisms, and some are parasitic.
• Plant-like protists make their own food via photosynthesis and may consume organisms when light is unavailable. Some are symbionts.
• Fungus-like protists absorb nutrients from other living or dead organisms. Some consume organisms and some water molds are parasites.

Animal-like Protists

• Animal-like protists are often called protozoa.
• Heterotrophic organisms.
• Unicellular organisms.
• Often have contractile vacuoles that remove excess water.
• Live in aquatic environments, and may be predators or decomposers, or may form symbiotic relationships within other organisms such as parasitism, mutualism, or commensalism.
• Classified by their movement.

Cercozoans: Amoeba

• Cercozoans are found in moist soil and water, including human-made pipelines, and within organisms.
• Heterotrophic organisms.
• Move using pseudopods, also known as "fake feet," which are extensions of cytoplasm that are used to ingest food.
• Unique cell organelles include a cytoplasm, plasma membrane, and nucleus; typically lack cilia and flagella.

Brain-eating Amoeba

• Naegleria fowleri
• Found in warm lakes, ponds, untreated swimming pools, hot springs, aquariums, and moist soil.
• Consume bacteria but can feed on brain tissue when infecting humans.
• Infection typically occurs through the nose during water sports such as diving or water skiing.
• Symptoms include headache, fever, stiff neck, loss of appetite, vomiting, seizures, and coma.

Ciliates: Paramecium

• Ciliates live in bodies of water, mostly stagnant water, and within other organisms.
• Heterotrophic organisms.
• Use cilia for locomotion and particle manipulation.
• Unique organelles include oral groove and gullet; cilia move nutrients into the gullet. Have two nuclei, macro and micro.
• The macronucleus provides the nuclear RNA for vegetative growth
• Mating cells exchange haploid micronuclei and a new macronucleus develops from a new diploid micronucleus, therefore micronuclei are involved in sexual reproduction.

Flagellates

• Inhabit aquatic environments, snow, and multicellular organisms, existing in mutualistic or parasitic relationships.
• Heterotrophic organisms.
• Use one or more flagella for mobility.
• Feature an elongated body and flagella.

Sporozoans

• Mostly parasitic
• Heterotrophic
• Reproduce via binary fission and alternate between sexual and asexual reproduction.
• Move without flagella, cilia, or pseudopods.
• Parasitic lifecycle that occurs within two different host species, and have a spore-like stage.

Plant-like Protists

• Commonly called algae.
• Chloroplasts allow for photosynthesis, primarily autotrophic but some are mixotrophic.
• Accessory pigments give a variety of colors like red and green.
• Reproduce asexually, most common, and sexually.
• Live in moist environments such as ponds.

Diatoms

• Diatoms produce a lot of oxygen through photosynthesis from 20-50% generated.
• Made of silica
• Dead diatoms shells make up a significant portion of the ocean floor which is up to 800 meters in some places.
• Cell walls coated in silica in shoebox style
• Important food source of aquatic organisms.

Diatoms: Phylum Chrysophyta

• The most abundant type of phytoplankton lives in aquatic environments and are unicellular.
• Diatoms are autotrophic.
• They reproduce through mitosis in asexual reproduction, and meiosis for sexual reproduction.
• Are free-floating.
• Their cell walls are coated in silica in a shoebox style.
• Reproduce mostly by asexual mitosis but under unfavorable conditions will reproduce by meiosis.

Dinoflagellates

• Phytoplankton that inhabits aquatic environments
• Autotrophic organisms.
• Flagella allows them to spin.
• Have two flagella positioned 90° or perpendicular to one another.
• Pigments give distinctive colors.
• Rapid reproduction in time of optimal conditions and abundant nutrients gives rise to algae blooms, causing either death or increased toxicity to marine life.
• Mutualism while living within coral gives the coral their color; when reefs warm, coral expels dinoflagellates.

Euglenoids

• Found in shallow water.
• Autotrophic, but some can switch to heterotrophic when needed.
• Move via flagellum.
• Stigma (photoreceptor) allows flagellum to position the protist towards the light, or away from light.

Algae

• Most are aquatic but some are terrestrial and can be found on moist soil, trees, and rocks.
• Most are unicellular however some are multicellular, except for some brown algae which are multicellular.
• Autotrophic organisms.
• Reproduction via Mitosis (asexual) or Meiosis (sexual).
• Float, or are attached to objects within water or on land.
• Differ from vascular plants by lacking true roots, stems, and leaves.
• Algae include Phylum Chlorophyta (green algae), Phylum Phaeophyta (brown algae), Phylum Rhodophyta (red algae), Phylum Chrysophyta (golden algae).

Fungus-like Protists

• Resemble fungi in appearance and lifestyle, but differ from true fungi at the cellular level, such as the cell wall.
• Reproduce with spore
• Heterotrophs that feed on bacteria and rotting material, such as water mold & slime mould
• Dog Vomit Slime mold

Plasmodial Slime Molds

• Start as individual amoeboid cell but will join to form a multi-nucleate mass having only one cellular membrane called a plasmodium.
• This plasmodium moves over dead to decaying material looking for bacteria to engulf or digest.
• When plasmodium runs out of food it will produce fruiting structures called Sporangia, which has diploid nuclei that goes under meiosis, producing spores for aerial dispersal.
• Dispersal by spores makes it fungi-like and once landed will germinate into haploid cells two flagella.

Cellular Slime Molds

• Rarely can be visible to the naked eye.
• Have one nuclei in each at times.
• Individuals may join to form a pseudoplasmodium.