Biological Diversity: Prokaryotes, Protists, Land Plants, Seed Plants, and Fungi

Comprehensive vocabulary flashcards covering the evolutionary relationships, structures, ecological roles, and critical innovations across prokaryotes (Bacteria and Archaea), protists, land plants, seed plants (Gymnosperms and Angiosperms), and fungi.

Archaea

A domain of unicellular prokaryotes characterized by ether-linked membrane lipids and nuclear/cytoplasmic features shared with Eukarya, including histones and ribosomal proteins.

Ether Linkages

Chemical bonds found in the membrane lipids of Archaea that confer greater resistance to heat and other extreme environmental conditions compared to ester linkages.

Extremophile

An organism that thrives in physically or geochemically extreme environments, such as high-temperature acidic hot springs or high-salinity lakes.

Halophile

An extremophile that thrives in environments with exceptionally high salt concentrations.

Cyanobacteria

Photosynthetic bacteria that are the only prokaryotes capable of generating oxygen ($O_2$) as a byproduct of photosynthesis; evolutionary ancestors of eukaryotic plastids.

Prochlorococcus

A genus of marine cyanobacteria responsible for producing at least $20\%$ of Earth's atmospheric oxygen.

Nitrogen Fixation

The biological process in which nitrogen-fixing bacteria use the enzyme nitrogenase to convert atmospheric nitrogen ($N_2$) into ammonium ($NH_4^+$).

Nitrifying Bacteria

Chemoautotrophic soil bacteria that oxidize ammonia or ammonium ($NH_3 / NH_4^+$) into nitrites ($NO_2^-$) and subsequently into nitrates ($NO_3^-$).

Horizontal Gene Transfer

The non-vertical transfer of genetic material between distinct organisms, a process that has affected approximately $80\%$ of all prokaryotic genes over evolutionary history.

Transformation

A mechanism of horizontal gene transfer wherein a bacterial or archaeal cell takes up naked exogenous DNA released into the environment from disintegrated cells.

Transduction

A mechanism of horizontal gene transfer in prokaryotes mediated by a viral vector (bacteriophage) carrying host DNA from a donor cell to a recipient cell.

Conjugation

A mechanism of genetic transfer involving direct physical contact between a donor and a recipient cell via a sex pilus.

Gram-Positive Bacteria

Bacteria possessing a thick peptidoglycan cell wall that retains crystal violet stain (appearing purple) and is sensitive to penicillin.

Gram-Negative Bacteria

Bacteria with a thin peptidoglycan cell wall surrounded by an outer membrane that does not retain crystal violet and exhibits resistance to penicillin.

Photoautotroph

An organism that utilizes light as its energy source and carbon dioxide ($CO_2$) as its sole carbon source, exemplified by Cyanobacteria.

Chemoautotroph

An organism that obtains energy by oxidizing inorganic compounds and fixes carbon from carbon dioxide ($CO_2$), exemplified by Sulfolobus.

Photoheterotroph

An organism that harnesses light energy for ATP synthesis but must obtain carbon from pre-formed organic compounds, exemplified by Chloroflexi.

Chemoheterotroph

An organism that requires organic molecules for both its energy source and its carbon source.

Obligate Aerobe

An organism that strictly requires oxygen ($O_2$) for cellular respiration and survival.

Facultative Aerobe

An organism capable of utilizing oxygen when available, but able to switch to anaerobic metabolism when oxygen is absent.

Obligate Anaerobe

An organism that cannot tolerate molecular oxygen and is poisoned by its presence.

Aerotolerant Anaerobe

An anaerobic organism that does not utilize oxygen for metabolic reactions but is not poisoned or harmed by its presence.

Syntrophy

A mutualistic association in which two or more microbial species live in close proximity and cross-feed essential nutrients to one another.

Human Gut Enterotypes

Three broad ecological classifications of the human gut microbiome: Enterotype 1 (Bacteroides, high protein/fat diets), Enterotype 2 (Prevotella, high-fiber/plant diets), and Enterotype 3 (Ruminococcus, mucin and complex carbohydrate degradation).

Protist

Any eukaryotic organism that is not classified as a land plant, true animal, or true fungus; protists form a paraphyletic group and are most abundant in moist habitats.

Plankton

Microscopic or weakly swimming aquatic organisms drifting in water columns, divided into photoautotrophic phytoplankton and heterotrophic zooplankton.

Stramenopiles

A major clade of the SAR supergroup characterized by distinctive straw-like flagellar hairs; includes diatoms, golden algae, and brown algae.

Alveolates

A major clade of the SAR supergroup distinguished by the presence of flattened, membrane-bound vesicles (alveoli) arranged in a continuous layer beneath the cell periphery.

Dinoflagellates

Alveolate protists typically equipped with two flagella and cellulose plates; known for causing toxic red tide blooms and acting as symbiotic mutualists (zooxanthellae) in reef corals.

Rhizarians

A eukaryotic clade within the SAR group characterized by having thin, hair-like filose pseudopodia; includes Radiolaria and Foraminifera.

Primary Endosymbiosis

The evolutionary process wherein an ancestral heterotrophic eukaryotic host phagocytosed an intact cyanobacterium without digesting it, giving rise to plastids with two bounding membranes.

Secondary Endosymbiosis

The endosymbiotic engulfment of a photosynthetic eukaryotic cell (such as a red or green alga) by a heterotrophic eukaryote, resulting in plastids surrounded by three or four membranes.

Phycoerythrin

A red accessory pigment found in red algae (phylum Rhodophyta) that absorbs blue-green light, allowing photosynthesis at greater ocean depths.

Gametic Life Cycle

A sexual life cycle where all multicellular or vegetative cells are diploid ($2n$) and the only haploid ($n$) cells produced are gametes; exemplified by diatoms.

Zygotic Life Cycle

A sexual life cycle where the single-celled zygote is the only diploid ($2n$) entity, promptly undergoing meiosis to produce haploid ($n$) progeny; common among unicellular protists.

Charophytes

A group of freshwater green streptophyte algae identified as the closest living relatives of modern land plants.

Apical Meristem

Localized growing regions containing undifferentiated, actively dividing cells located at the tips of plant roots and shoots that generate complex 3D tissues.

Sporic Life Cycle (Alternation of Generations)

A life cycle exhibited by land plants and multicellular seaweeds that alternates between a multicellular haploid ($n$) gametophyte and a multicellular diploid ($2n$) sporophyte.

Sporangia

Multicellular reproductive organs situated on the sporophyte wherein diploid sporocytes undergo meiotic division to generate haploid spores.

Sporopollenin

A durable, chemically resistant biopolymer embedded in the walls of plant spores and pollen grains that shields them against desiccation and decay.

Gametangia

Multicellular reproductive structures in plants that produce gametes by mitosis; comprises female archegonia and male antheridia.

Cuticle

A waxy coating secreted by epidermal cells onto outer surfaces of land plants that minimizes water loss and offers defense against pathogens.

Stomata

Specialized surface pores bordered by guard cells that open and close to facilitate photosynthetic gas exchange while limiting transpirational water loss.

Bryophytes

Non-vascular land plants comprising liverworts, hornworts, and mosses; characterized by a dominant gametophyte generation, lack of specialized conducting vascular tissue, and dependence on water for fertilization.

Xylem

A specialized vascular tissue composed of empty, non-living water-conducting cells reinforced with lignin that conveys water and dissolved minerals from roots to shoots.

Phloem

A living vascular conducting tissue that transports watery solutions of photosynthetic sugars and organic compounds throughout the plant body via the pressure-flow mechanism.

Lignin

A rigid, cross-linked structural polymer that impregnates secondary cell walls of tracheids and vessels, enabling plants to stand upright against gravity.

Transpiration-Cohesion-Tension Mechanism

The physiological model explaining how water ascends through xylem: leaf water evaporation (transpiration) establishes negative pressure (tension), pulling cohesive water molecules upward.

Microphylls

Small leaves equipped with a single unbranched vascular strand; unique to the seedless vascular plant phylum Lycophyta.

Megaphylls

True leaves with a branched network of vascular veins (euphylls), found in monilophytes (ferns) and seed plants.

Monilophytes

A clade of seedless vascular plants consisting of ferns, horsetails, and whisk ferns; possesses megaphylls and a dominant, independent sporophyte generation.

Heterospory

The production of two distinct spore sizes within a single plant: microspores that develop into male gametophytes, and megaspores that develop into female gametophytes.

Pollen Grain

A highly reduced, desiccation-resistant male gametophyte of seed plants enclosed within a protective sporopollenin-rich wall.

Ovule

A structure inside seed plant megasporangia consisting of an integument, megasporangium tissue, and a megaspore that develops into a seed following fertilization.

Seed

A reproductive dispersal unit consisting of an embryonic sporophyte surrounded by stored nutritive tissue and enclosed inside a tough, protective seed coat.

Vascular Cambium

A cylindrical layer of lateral meristem in woody plants that generates secondary xylem (wood) toward the interior and secondary phloem (inner bark) toward the exterior.

Gymnosperms

Vascular seed plants whose ovules and seeds are borne exposed on modified sporophylls or cone scales rather than enclosed inside an ovary fruit wall.

Coniferophyta

The most species-rich gymnosperm phylum (~600 species); adapted to cold, dry climates with conical forms, needle/scale leaves, thick cuticles, and evergreen habit.

Ginkgophyta

A gymnosperm phylum comprising a single living species (Ginkgo biloba) featuring broad fan-shaped deciduous leaves and distinct male and female trees.

Gnetophyta

A gymnosperm phylum comprising three genera (Gnetum, Ephedra, Welwitschia) that uniquely possess specialized vessel elements in their xylem tissue.

Angiosperms

Flowering plants characterized by seeds enclosed within protective fruits, flowers as specialized reproductive units, double fertilization, and vessel-rich vascular systems.

Double Fertilization

A specialized angiosperm fertilization event wherein one sperm fertilizes the egg to generate a diploid ($2n$) zygote, while a second sperm fuses with two polar nuclei to yield triploid ($3n$) endosperm.

Endosperm

A triploid ($3n$) nutritive seed tissue produced in angiosperms following double fertilization that stockpiles nutrients for the growing embryo.

Fruit

A mature, swollen plant ovary wall (pericarp) that envelops the seeds and aids in protecting them and facilitating animal, wind, or water dispersal.

Coevolution

The reciprocal evolutionary change occurring between two interacting species that exert selective pressures on each other, such as flowering plants and specific animal pollinators.

Pollination Syndrome

A coordinated suite of floral adaptations (such as petal color, floral scent, shape, and nectar depth) matched to the sensory and morphological traits of a specific pollinator.

Secondary Metabolites

Organic molecules synthesized by plants that are not essential for fundamental growth and maintenance, but serve ecological roles such as anti-herbivore defenses, pigments, and scent attractants.

Opisthokonta

The eukaryotic supergroup containing Kingdom Fungi, Kingdom Animalia, and related protist lineages; characterized by shared ancestry, absorptive/ingestive heterotrophy, and glycogen food storage.

Chitin

A tough, nitrogen-containing polysaccharide polymer that constitutes the rigid structural component of fungal cell walls.

Hyphae

Microscopic, tubular, branching filaments that form the basic structural and vegetative units of multicellular fungi.

Mycelium

The diffuse, extensively branched feeding body of a multicellular fungus formed by a dense interconnected network of hyphae.

Fruiting Body

A visible, macroscopic reproductive structure (such as a mushroom) composed of tightly packed dikaryotic hyphae dedicated to producing and shedding spores.

Hyphal Tip Growth

The localized elongation mechanism of fungal hyphae driven by osmotic entry of water (turgor pressure) accompanied by Golgi vesicle transport that secretes digestive enzymes and deposits new chitin.

Plasmogamy

The fusion of the cytoplasm of two compatible haploid fungal hyphae without immediate fusion of their nuclei.

Dikaryotic

A fungal cell, hypha, or mycelium having two genetically compatible but unfused haploid nuclei per cell, denoted as ($n + n$).

Karyogamy

The fusion of two haploid nuclei within a mature dikaryotic fungal cell to form a transient diploid ($2n$) zygotic nucleus prior to meiosis.

Yeast

A general term for any unicellular fungus that primarily reproduces asexually via budding, exemplified by Saccharomyces cerevisiae.

Lichens

Symbiotic mutualistic associations composed of a fungal partner (providing water, carbon dioxide, and minerals) and a photosynthetic partner (green algae and/or cyanobacteria supplying organic sugars and oxygen).

Mycorrhizae

Mutualistic associations established between fungal hyphae and plant root systems, occurring in over $80\%$ of terrestrial plant species to enhance soil mineral and water uptake.

Arbuscules

Intricately branched, tree-like hyphal structures formed by endomycorrhizal fungi inside plant root cortical cells that serve as the main interface for mineral nutrient exchange.

Dermatophytes

Pathogenic parasitic fungi that colonize keratinized epidermal layers in humans, causing conditions such as athlete's foot, ringworm, and dermatomycosis.

Ophiocordyceps unilateralis

An entomopathogenic parasitic fungus known as the zombie ant fungus that manipulates the behavioral patterns of its host before erupting from its body to disperse spores.