Bio Lab 6

• Protist taxonomy is in constant flux, with little consensus on the classification of tens of thousands of species.
• Molecular studies of DNA and protein have provided data to organize the taxonomic mess of protists.
• Protists are being split into several kingdoms due to evidence showing some are more closely related to plants, animals, or fungi than to other protists.
• Any organism with eukaryotic cells that is not an animal, plant, or fungus is classified as a protist.
• Protists can be heterotrophic, autotrophic, or mixotrophic.
• Most protists are unicellular eukaryotes, but some are colonial or multicellular.
• Many protists have powered locomotion using undulipodia (cilia or flagella).
• Some protists reproduce asexually, while others reproduce sexually.
• Eukaryotes can be categorized into four supergroups: Excavata, SAR Clade, Archaeplastida, and Unikonta.

Excavata

• United by highly modified mitochondria.
• Some have an "excavated" groove on one side of the cell body.
• Includes diplomonads, parabasalids, and euglenozoans.

SAR Clade

• Named after three large clades: Stramenopila, Alveolata, and Rhizaria.
• Includes all modes of eukaryote nutrition.

Archaeplastida

• Includes red and green algae, and Kingdom Plantae.
• Protists in Archaeplastida are key photosynthetic species that form the base of the food chain in many aquatic communities.

Unikonta

• Includes slime molds, amoebas, choanoflagellates, Kingdom Animalia, and Kingdom Fungi.

Introduction to Examples of the Supergroups

• Excavata lack conventional mitochondria, possessing unusual organelles initially mistaken as absent.
• Excavata flagellum are distinct from other groups.
• Many Excavata possess a slot-like feeding groove.

Diplomonads

• Have unique mitochondria called mitosomes that support anaerobic metabolism.
• Giardia intestinalis (= lamblia) is a common parasite that causes diarrhea and has dispersal (trophozoites) and dormant (cysts) stages.

Parabasalids

• Possess modified mitochondria called hydrogenosomes that produce hydrogen gas.
• Trichomonas vaginalis causes Trichomoniasis, the most common protozoan disease in the industrial world, with 180 million new cases each year.

Euglenozoans

• Diverse group including free-living, parasitic, photosynthetic, and heterotrophic forms.
• Euglena is a common free-living photosynthetic form.
• Trypanosoma is a blood parasite that causes sleeping sickness.

The "SAR" Clade

• Proposed based on whole-genome sequence analysis.
• Stramenopiles, alveolates, and rhizarians form a monophyletic supergroup.

The Stramenopiles Clade

• Includes important photosynthetic organisms.
• Characterized by numerous short, hair-like structures along their flagellum.

Diatoms

• Have secreted silicate shells (frustules).
• Exclusively aquatic and very abundant.
• Responsible for up to 25% of all carbon fixation.
• Major source of atmospheric oxygen.
• Silicaceous shells form thick layers on the sea bottom, transforming into diatomaceous earth.
• Diatomaceous earth is used as an abrasive and in water filtration systems.
• Two main morphologies: centrales (spherical or disk-shaped) and pennales (elongate).

Golden Algae and Brown Algae

• Primarily unicellular organisms that are major contributors to photosynthesis in freshwater habitats.
• Golden algae have high levels of carotenoids in their plastids.
• Some are facultative heterotrophs, consuming organic carbon when light levels are low.
• Kelps and brown algae are the giants of the chromalveolates.
• Macrocystis can be over 50 meters long and form kelp forests.
• Kelp forests provide nursery grounds, feeding areas, and refuge for many marine species.
• Brown algae's color is due to fucoxanthin and chlorophyll c.
• Holdfast anchors the organism, stipe provides buoyancy, and blades facilitate photosynthesis.
• Floatation bladders keep the blades at the ocean surface to maximize photosynthesis.
• Brown algae exhibit alternation of generations with diploid sporophyte and haploid gametophyte stages.
• Macrocystis is a key algae in kelp forests off the West Coast.
• Ectocarpus is a filamentous brown alga.
• Sargassum is a floating seaweed made famous by the Sargasso Sea.
• Fucus is a brown algae common off the California coast.

The Alveolates Clade

• Characterized by membrane-bound sacs (alveoli) under the plasma membrane that may play a role in osmoregulation.
• Includes dinoflagellates, apicomplexans, and ciliates.
• Also includes Paramecium.

Dinoflagellates

• Unicellular protists with two flagella (longitudinal and transverse).
• Marine organisms, many of which are photosynthetic.
• Cell surface is covered in cellulose plates forming a theca.
• Capable of bioluminescence.
• Can cause red tides, producing neurotoxins like saxitoxin that can kill fish and concentrate in shellfish.
• Ceratium is an example of a dinoflagellate that has recently contributed to problematic algal blooms.

Apicomplexans

• Largely parasitic group of flagellates.
• Plasmodium causes malaria, infecting 300 million and resulting in 1 to 1.5 million deaths annually.
• Spreads via sporozoites and loses flagella in its final life stages.

Ciliates

• Large and varied group of protists.
• Most are predators of bacteria or small protists.
• Possess cilia covering the cell or in bands.
• Heterotrophic, feeding on bacteria, algal cells, or protozoans.
• Paramecium is a well-known microorganism in this group.

The Rhizarian Clade

• Amoeba-like unicellular organisms that move and feed with pseudopodia.
• Secrete a protective shell of calcium carbonate or silica.
• Dominated by Foraminifera and Radiolaria.

Foraminifera

• Secrete a porous carbonate shell.
• Threadlike pseudopods extend through pores for feeding and gas exchange.
• Most species are known only as fossils.
• Paleo climatologists use foram data to determine climate conditions during prehistoric times.

Radiolarians

• Marine silica-shelled organisms.
• Pseudopodia, supported by axopodia, project from the shell for capturing food and aiding in floatation.
• Dead remains are a component of marine ooze.

Supergroup Archaeplastida

• Monophyletic super group consisting of red and green algae, and land plants.
• Likely share a common ancestor that engulfed a cyanobacterium.
• Cyanobacterium evolved into the Archaeplastida chloroplast.

The Red Algae (Phylum Rhodophyta)

• Includes edible nori.
• Red color due to phycoerythrin, which absorbs blue light and reflects red.
• Lack flagella on their gametes.
• 6000 species have been described.
• Corallina algae secretes a calcium carbonate shell.

The Green Algae (Phyla Chlorophyta and Charophyta)

• Chlorophyte algae are closely related to plants.
• Share characteristics with plants: cellulose and pectin cell walls, starch storage, and chlorophyll types a and b.
• Charophyta is most closely related to plants based on sperm cell and cell division similarities.
• Spirogyra is an example of a Charophyte.
• Chlorophytes range from unicellular to multicellular and includes many colonial species.
• Ulva is a large, thin green algae called sea lettuce.
• Spirogyra has a spiral arrangement of chloroplasts.
• Chlamydomonas is a unicellular green algae with 2 flagella.
• Gonium is a colonial Chlamydomonas-type cell.
• Volvox is a colonial Chlamydomonas-type cell with daughter colonies inside.

Supergroup Unikonta

• Diverse group including amoebozoans, animals, and fungi.
• Ameobozoans move with cytoplasmic streaming, projecting pseudopods.

The Amoebozoans Clade

• Many are free-living, including Ameoba.
• Entamoebas are parasitic.
• Slime molds are included within the Amoebazoa.
• Plasmodial slime molds (Phylum Myxogastria) are enormous single cells with thousands of nuclei formed when individual flagellated cells fuse their cytoplasm.
• Cellular slime molds (Phyla Dictyostelida and the Acrasida) spend most of their lives as separate single-celled amoeboid protists, aggregate into a large mass of amoeboid cells upon chemical signal release.
• Slime molds form sporangia (clusters of spores) for dispersal.
• They live in moist terrestrial habitats.

Experiment: Phototaxis Demonstration with Photosynthetic Protists

• Taxis is movement in relation to an environmental gradient.
• Phototaxis is the reaction to a light gradient.
• Positive phototaxis is movement toward a light source; negative phototaxis is movement away from it.

Observation: Working with pond water cultures

• Pond water contains diverse protists.
• Methyl cellulose slows down motile protists for observation.

Explore protist taxonomy, its constant flux, and classification challenges. Molecular studies help organize protists, leading to their division into multiple kingdoms. Discover the four eukaryotic supergroups: Excavata, SAR Clade, Archaeplastida, and Unikonta, and their unique characteristics.