Diversity of Life: Protists, Prokaryotes, Evolution, Phylogeny, and Plant Biology

Vocabulary flashcards covering key terms and concepts across protist classification, prokaryote structures and metabolic diversity, evolutionary mechanisms, phylogenetics, and plant anatomy.

Physarum polycephalum

A plasmodial slime mold characterized as a single cell containing many nuclei.

Endosymbiosis Theory

The theory proposing that mitochondria and chloroplasts evolved from prokaryotes that were engulfed by host cells and lived symbiotically within them.

Mutualism

A symbiotic relationship in which both participating species benefit from the interaction.

Parasitism

A symbiotic relationship in which one member benefits while the other member is harmed.

Commensalism

A symbiotic relationship in which one member benefits while the other member is neither harmed nor helped.

Euglenozoans

A protistan clade within Excavata that includes free-living mixotrophs such as Euglena and parasites such as Trypanosoma, which causes African sleeping sickness.

Mixotroph

An organism capable of both photosynthesis and heterotrophic nutrient absorption depending on light availability.

Stramenopiles

A clade within the supergroup SAR whose members possess flagellated cells with hair-like projections at some stage in their life cycle.

Diatoms

Photosynthetic aquatic plankton protected by unique glass-like cell walls composed of silica ($SiO_2$).

Diatomaceous Earth

Sedimentary deposits formed on lake or ocean bottoms from the accumulated silicon dioxide cell walls of deceased diatoms.

Brown Algae

Multicellular, sessile, photosynthetic protists that possess brown accessory pigments alongside chlorophylls.

Alveolates

A clade within the supergroup SAR defined by the presence of membrane-bound sacs (alveoli) directly beneath the plasma membrane.

Dinoflagellates

Aquatic alveolates distinguished by two perpendicular flagella, some of which cause toxic algal blooms or live as coral endosymbionts.

Harmful Algal Bloom (HAB)

A rapid population explosion of algae or dinoflagellates that can produce potent toxins or deplete oxygen to form anoxic dead zones.

Ciliates

Aquatic heterotrophic alveolates covered in cilia used for movement and feeding, containing both a macronucleus and a micronucleus.

Foraminiferans (Forams)

Rhizarians protected by porous, multichambered shells made of calcium carbonate ($CaCO_3$) through which long, slender pseudopodia extend.

Archaeplastida

A major eukaryotic supergroup including red algae, green algae, and land plants, all sharing double-membrane chloroplasts.

Unikonta

A eukaryotic supergroup composed of Amoebozoans and Opisthokonts, whose flagellated cells typically feature a single flagellum.

Amoebozoans

A clade of unikonts that move and feed using broad, lobe-shaped pseudopodia, including slime molds and tubulinids.

Extremophiles

Organisms adapted to survive and thrive under extreme physical or chemical conditions such as high salinity, extreme pH, high pressure, or elevated temperature.

Thermophiles

Extremophilic organisms that thrive in environments with elevated temperatures, such as $90\,^\circ C$ hot springs.

Halophiles

Extremophilic organisms adapted to inhabit highly saline environments.

Microbiome

The complete community of microorganisms—including prokaryotes, fungi, viruses, and protists—along with their genetic material in a specific habitat or host.

Nucleoid

The non-membrane-bound region within a prokaryotic cell where the single, circular chromosome is located.

Plasmids

Small, circular, extrachromosomal DNA molecules found in many prokaryotes that carry auxiliary genes.

Gram-Positive Cell Wall

A bacterial cell wall structure consisting of a thick outer layer of peptidoglycan that retains crystal violet stain.

Gram-Negative Cell Wall

A bacterial cell wall structure consisting of a thin peptidoglycan layer located between the plasma membrane and an outer membrane containing lipopolysaccharides.

Phototroph

An organism that absorbs light energy to synthesize ATP.

Chemotroph

An organism that obtains energy for ATP synthesis by oxidizing chemical compounds.

Autotroph

An organism capable of synthesizing organic building blocks from inorganic carbon sources such as carbon dioxide ($CO_2$) or bicarbonate ($HCO_3^-$).

Heterotroph

An organism that requires organic compounds from other organisms as a carbon source for biomass construction.

Nitrogen Fixation

The biological process of converting inorganic atmospheric nitrogen ($N_2$) into ammonia ($NH_3$) or ammonium ($NH_4^+$).

Heterocysts

Specialized cells in certain filamentous cyanobacteria that carry out nitrogen fixation.

Biofilms

Surface-coating colonies of prokaryotes encased in a protective matrix that can resist antibiotics and host immune defenses.

Chemoautotrophic Hydrothermal-Vent Bacteria

Symbiotic bacteria in hydrothermal-vent worms that oxidize reduced sulfur ($H_2S$) to obtain energy for synthesizing organic molecules from inorganic carbon.

Evolution

A change in the genetic composition or allele frequencies of a population over generations.

Population

A group of individuals belonging to the same species living in the same geographical area at the same time.

Allele

An alternative form or variant sequence of a specific gene.

Natural Selection

The evolutionary mechanism by which individuals possessing specific inherited traits survive and reproduce at higher rates than individuals lacking those traits.

Evolutionary Fitness

The relative reproductive success of an individual measured by its ability to produce viable offspring that survive to reproduce.

Adaptation

A heritable trait that enhances an individual's survival and reproductive success in a specific environment.

Genetic Drift

A mechanism of evolution causing random fluctuations in allele frequencies within a population due to chance events.

Gene Flow

The movement and incorporation of alleles into or out of a population resulting from the migration of fertile individuals or gametes.

Binomial Nomenclature

The system of naming organisms using a unique, two-part italicized scientific name consisting of the Genus and species epithet.

Taxonomy

The biological discipline concerned with naming, describing, and classifying organisms into hierarchical groups.

Systematics

The branch of biology focused on classifying organisms and determining their evolutionary relationships.

Phylogeny

The evolutionary history and pattern of descent of a group of organisms.

Sister Taxa

Groups of organisms that share an immediate common ancestor not shared by any other group on a phylogenetic tree.

Branch Point (Node)

A point on a phylogenetic tree representing the divergence of two or more evolutionary lineages from a single common ancestor.

Anatomy of a Phylogenetic Tree

The structural components of a tree diagram illustrating lineages through time (branches), ancestral nodes, tips (taxa), root, and outgroup.

Polytomy

A node on a phylogenetic tree depicting an ancestral branch splitting into three or more descendant lineages, reflecting unresolved evolutionary relationships.

Synapomorphy

A shared, derived trait present in an ancestral species and all its descendants that defines a monophyletic group.

Monophyletic Group (Clade)

An evolutionary lineage consisting of an ancestral species and all of its descendants.

Paraphyletic Group

A taxonomic grouping that includes an ancestral species and some, but not all, of its descendants.

Polyphyletic Group

A grouping that includes organisms with similar traits derived via convergent evolution rather than from a shared common ancestor.

Principle of Maximum Parsimony

The concept that the preferred phylogenetic tree is the one that minimizes the total number of required evolutionary changes.

Homoplasy

A similar trait shared by different species due to convergent evolution rather than common ancestry.

Shoot System

The aboveground plant structures—comprising stems, leaves, and buds—that harvest light energy and carbon dioxide ($CO_2$).

Root System

The belowground plant organ system that anchors the plant and absorbs water and dissolved mineral nutrients from the soil.

Rhizome

A modified horizontal underground shoot that produces new vertical shoots from axillary buds.

Stolon

A modified horizontal aboveground shoot ("runner") that grows along the soil surface to enable asexual reproduction.

Tuber

An enlarged portion of a rhizome or stolon specialized for nutrient storage, featuring clusters of axillary buds.

Cuticle

A waxy coating secreted by epidermal cells on leaves and stems that reduces water loss.

Guard Cells

Specialized epidermal cells surrounding stomatal pores that regulate gas exchange and water loss by opening and closing the pores.

Trichomes

Hairlike outgrowths of shoot epidermal tissue that deter herbivores, reflect solar light, or reduce moisture loss.

Parenchyma

Ground tissue cells responsible for photosynthesis in leaves (mesophyll) and nutrient storage in roots and stems.

Collenchyma

Elongated ground tissue cells with unevenly thickened primary walls that provide flexible structural support to growing shoots.

Sclerenchyma

Rigid plant cells with thick, secondary cell walls containing lignin that provide structural support to non-growing tissues.

Xylem

Vascular tissue responsible for unidirectional transport of water and dissolved minerals from roots upward to shoots.

Tracheids

Long, slender xylem cells reinforced with secondary walls containing lignin that conduct water and are dead at maturity.

Vessel Elements

Shorter, wider xylem cells with perforated ends that conduct water efficiently, found mainly in angiosperms and dead at maturity.

Phloem

Vascular tissue that transports sugars, amino acids, and hormones bidirectionally throughout the plant body.

Sieve Tube Cells

Elongated conducting cells of phloem that lack nuclei and major organelles at maturity, facilitating sugar transport.

Companion Cells

Nucleated phloem cells linked to sieve tube elements via plasmodesmata that provide metabolic support and load sugars.

Apical Meristems

Populations of undifferentiated cells at shoot and root tips responsible for primary growth, increasing plant length.

Secondary Growth

The pattern of growth in woody plants that increases the circumference or width of stems and roots via lateral meristems.

Vascular Cambium

A lateral meristem that produces secondary xylem (wood) toward the interior and secondary phloem toward the exterior.

Cork Cambium

A lateral meristem that produces protective cork cells toward the outside to replace the epidermis during secondary growth.

Bark

All plant tissues located exterior to the vascular cambium, including secondary phloem, cork cambium, and cork.

Wood

Accumulated secondary xylem produced internally by the vascular cambium in woody stems and roots.