A large varied group of protists, are named for their use of cilia to move and feed.
Have large macronuclei and small micronuclei.
Micronuclei function during conjugation, a sexual process that produces genetic variation.
Conjugation is separate from reproduction, which generally occurs by binary fission.
Paramecium:
Feeding, waste removal, and water balance via contractile vacuoles, oral groove, cell mouth, cilia, food vacuoles, macronucleus, and micronucleus.
Diatoms
Unicellular algae with a unique two-part, glass-like wall of hydrated silica.
Usually reproduce asexually, and occasionally sexually.
A major component of phytoplankton and are highly diverse.
Fossilized diatom walls compose much of the sediments known as diatomaceous earth.
Golden Algae
Named for their color, which results from yellow and brown carotenoids.
The cells of golden algae are typically biflagellated, with both flagella near one end.
All golden algae are photosynthetic, and some are also heterotrophic.
Most are unicellular, but some are colonial.
Brown Algae
The largest and most complex algae. All are multicellular, and most are marine.
Include many species commonly called “seaweeds.” Giant seaweeds called kelps live in deep parts of the ocean.
Have the most complex multicellular anatomy of all algae.
The algal body is plantlike but lacks true roots, stems, and leaves and is called a thallus.
The rootlike holdfast anchors the stemlike stipe, which in turn supports the leaflike blades.
Alternation of Generations
A variety of life cycles have evolved among the multicellular algae.
The most complex life cycles include an alternation of generations, the alternation of multicellular haploid (gametophyte) and diploid forms (sporophyte).
Heteromorphic generations are structurally different.
Isomorphic generations look similar.
Brown Algae Alternation of Generations.
Oomycetes (Water Molds and Their Relatives)
Include water molds, white rusts, and downy mildews… Fungus-like.
They were once considered fungi based on morphological studies.
Most oomycetes are decomposers or parasites.
They have filaments (hyphae) that facilitate nutrient uptake.
Their ecological impact can be great, as in Phytophthora infestans causing potato blight.
Life Cycle of Oomycetes = Water Mold: Asexual and sexual reproduction.
Rhizarians
Defined by DNA similarities: DNA evidence supports Rhizaria as a monophyletic clade.
Amoebas move and feed by pseudopodia; some but not all belong to the clade Rhizaria.
Rhizarians include forams and radiolarians.
Forams and Radiolarians
Foraminiferans, or forams, are named for porous, generally multichambered shells, called tests. Pseudopodia extend through the pores in the test.
Foram tests in marine sediments form an extensive fossil record.
Radiolarians have tests fused into one delicate piece, made of silica.
Radiolarians use their pseudopodia to engulf microorganisms by phagocytosis.
Red and Green Algae
The closest relatives of land plants
Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont.
The photosynthetic descendants of this ancient protist evolved into red algae and green algae.
Land plants are descended from the green algae.
Archaeplastida is a supergroup used by some scientists and includes red algae, green algae, and land plants.
Red Algae
Reddish in color due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll.
The color varies from greenish-red in shallow water to dark red or almost black in deep water. Red algae are the most abundant large algae in coastal waters of the tropics.
Red algae are usually multicellular; the largest are seaweeds.
Examples: Bonnemaisonia hamifera, Dulse (Palmaria palmata), Nori (Porphyra).
Green Algae
Named for their grass-green chloroplasts.
Plants are descended from the green algae.
The two main groups are chlorophytes and charophyceans.
Most chlorophytes live in fresh water, although many are marine. Other chlorophytes live in damp soil, as symbionts in lichens, or in snow.
Chlorophytes include unicellular, colonial, and multicellular forms.
Examples: Ulva (sea lettuce), Caulerpa.
Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages.
Unikonts
Include protists that are closely related to fungi and animals
The supergroup Unikonta includes animals, fungi, and some protists.
This group includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists)
The root of the eukaryotic tree remains controversial.
Amoebozoans
Amoeba that have lobe- or tube-shaped, rather than threadlike, pseudopodia.
They include gymnamoebas, entamoebas, and slime molds.
Slime Molds
Slime molds, or mycetozoans, were once thought to be fungi. Molecular systematics places slime molds in the clade Amoebozoa.
Many species of plasmodial slime molds are brightly pigmented, usually yellow or orange.
At one point in the life cycle, plasmodial slime molds form a mass called a plasmodium (not to be confused with malarial Plasmodium).
The plasmodium is undivided by membranes and contains many diploid nuclei. It extends pseudopodia through decomposing material, engulfing food by phagocytosis.
Life Cycle of Plasmodial Slime Mold.
Cellular Slime Molds
Form multicellular aggregates in which cells are separated by their membranes.
Cells feed individually, but can aggregate to form a fruiting body.
Dictyostelium discoideum is an experimental model for studying the evolution of multicellularity.
Life Cycle of Cellular Slime Mold: Asexual and sexual reproduction.
Protists in Ecological Relationships
Protists are found in diverse aquatic environments.
Protists often play the role of symbiont or producer.
Some protist symbionts ++ benefit their hosts
Dinoflagellates nourish coral polyps that build reefs.
Hypermastigotes digest cellulose in the gut of termites.
Some protists are parasitic + - symbionts
Plasmodium causes malaria.
Pfesteria shumwayae is a dinoflagellate that causes fish kills… toxic red tides ..
Phytophthora ramorum causes sudden oak death.
Photosynthetic Protists
Many protists are important producers that obtain energy from the sun.
In aquatic environments, photosynthetic protists and prokaryotes are the main producers.
The availability of nutrients can affect the concentration of protists.