The Origin and Diversification of Eukaryotes

Practice flashcards covering the vocabulary and key concepts of eukaryotic evolution and diversification as presented in Chapter 19.

Protists

A convenience term for a monophyletic group of eukaryotes that are not plants, animals, or fungi.

Flexible cell surface

A characteristic that allows for infolding, increased surface area, and endocytosis, which enables eukaryotic cells to be larger than prokaryotes.

Endosymbiosis

A process in which a proteobacterium was incorporated into a cell and evolved into the mitochondrion, and cyanobacteria were incorporated to develop into chloroplasts.

Primary endosymbiosis

An event where a cyanobacterium was engulfed by a larger eukaryotic cell, leading to chloroplasts with two membranes in glaucophytes, red algae, green algae, and land plants.

Secondary endosymbiosis

An event where a eukaryote engulfed a green alga cell, resulting in chloroplasts with three membranes, such as those found in euglenids.

Tertiary endosymbiosis

An event where an organism, such as a dinoflagellate, lost its chloroplast and took up another protist that had already acquired a chloroplast through secondary endosymbiosis.

Alveolates

A group of unicellular eukaryotes characterized by sacs called alveoli just beneath the cell membrane; examples include dinoflagellates, apicomplexans, and ciliates.

Dinoflagellates

Mostly marine photosynthetic primary producers that have two flagella, can cause red tides, and sometimes live as endosymbionts in corals.

Apicomplexans

Obligate parasites, such as Plasmodium, that use an apical complex of organelles at the tip of the cell to invade host tissues.

Ciliates

Heterotrophic eukaryotes that use numerous hairlike cilia for precise locomotion and possess two types of nuclei.

Trichocysts

Defensive organelles found in Paramecium that can explode as sharp darts from the pellicle.

Contractile vacuoles

Organelles in freshwater protists like Paramecium that excrete excess water taken in by osmosis.

Stramenopiles

A clade characterized by rows of tubular hairs on the longer of two flagella; includes diatoms, brown algae, and oomycetes.

Diatoms

Unicellular photosynthetic producers that deposit silica in two-piece cell walls and perform approximately $1/5$ of all carbon fixation on Earth.

Brown algae

Multicellular marine organisms containing the carotenoid fucoxanthin; some varieties like giant kelp reach lengths of up to $60\text{ meters}$.

Oomycetes

Absorptive heterotrophs, such as water molds and downy mildews, that secrete enzymes to digest large food molecules.

Rhizaria

Unicellular, mostly aquatic organisms with long, thin pseudopods, including cercozoans, foraminiferans, and radiolarians.

Foraminiferans

Organisms with external shells of calcium carbonate and branched pseudopods that form a sticky net to catch plankton.

Radiolarians

Marine organisms with radial symmetry and thin, stiff pseudopods reinforced by microtubules that secrete glassy endoskeletons.

Excavates

A diverse group of eukaryotes, some of which lack mitochondria; includes diplomonads, parabasalids, heteroloboseans, euglenids, and kinetoplastids.

Diplomonads

Unicellular organisms that lack mitochondria, an example of which is Giardia lamblia, the cause of the disease giardiasis.

Kinetoplastids

Parasites like trypanosomes that possess two flagella and a mitochondrion containing a kinetoplast with multiple circular DNA molecules.

Amoebozoans

Eukaryotes characterized by an amoeboid body form and lobe-shaped pseudopods, such as loboseans and slime molds.

Plasmodium (coenocyte)

The vegetative state of a plasmodial slime mold, consisting of a mass of cytoplasm with many diploid nuclei and no cell walls.

Myxamoebas

The vegetative state of cellular slime molds, consisting of haploid cells that can aggregate into a slug or pseudoplasmodium when conditions are unfavorable.

Conjugation

A sexual process in Paramecia where two individuals fuse and exchange micronuclei without producing new individuals.

Alternation of generations

A life cycle in which a multicellular diploid spore-producing organism gives rise to a multicellular haploid gamete-producing organism.

Heteromorphic

A condition in alternation of generations where the two generations (haploid and diploid) differ morphologically.

Sporocytes

Specialized cells of a diploid spore-producing organism that divide meiotically to produce four haploid spores.

Phytoplankton

Aquatic primary producers, including diatoms and other protists, that are essential for global photosynthesis.

Coral bleaching

A phenomenon where corals lose or expel their endosymbiotic photosynthetic dinoflagellates, often due to rising temperatures.

Diatomaceous earth

Sedimentary rock composed of the silica cell walls of diatoms, used for insulation, filtration, and as an insecticide.