Biological Classification – Key Vocabulary

Flashcards cover essential vocabulary terms and definitions from the lecture on biological classification, spanning historical systems, kingdom features, major groups of organisms, and acellular agents.

Aristotle’s Classification

An early system that separated organisms into plants (trees, shrubs, herbs) and animals (with or without red blood) using simple morphology.

Linnaeus’ Two-Kingdom System

18th-century division of all life into Kingdom Plantae and Kingdom Animalia, without distinguishing prokaryotes from eukaryotes.

Whittaker’s Five-Kingdom System

1969 scheme dividing life into Monera, Protista, Fungi, Plantae and Animalia based on cell type, body organisation, nutrition, reproduction and phylogeny.

Three-Domain System

A later proposal that splits Monera into Domains Archaea and Bacteria and groups all eukaryotes in Domain Eukarya, yielding six kingdoms.

Kingdom Monera

Prokaryotic kingdom comprising bacteria and cyanobacteria, characterised by naked DNA, no nuclear membrane and diverse metabolism.

Archaebacteria

Ancient bacteria with unique cell-wall chemistry that inhabit extreme environments such as hot springs, salty lakes and marshes.

Halophiles

Salt-loving archaebacteria that thrive in highly saline habitats.

Thermoacidophiles

Archaebacteria adapted to hot, acidic conditions, e.g., hot springs.

Methanogens

Archaebacteria in ruminant guts that produce methane gas during anaerobic respiration.

Eubacteria

‘True’ bacteria with peptidoglycan cell walls; include autotrophs, heterotrophs and cyanobacteria.

Cyanobacteria

Photosynthetic eubacteria (blue-green algae) possessing chlorophyll a; often form water blooms and some fix nitrogen in heterocysts.

Chemosynthetic Autotrophic Bacteria

Bacteria that obtain energy by oxidising inorganic substances like NH₃, nitrites or sulphur compounds.

Heterotrophic Bacteria

Bacteria that obtain organic carbon from other organisms; include decomposers and many pathogens.

Mycoplasma

The smallest, wall-less bacteria capable of surviving without oxygen; many are animal or plant pathogens.

Kingdom Protista

Eukaryotic, mostly unicellular kingdom including algae-like, protozoan and mould-like organisms; forms a link to plants, animals and fungi.

Chrysophytes

Protistan group of diatoms and desmids with siliceous cell walls; major ocean producers and contributors to diatomaceous earth.

Diatomaceous Earth

Silica-rich sediment formed from indestructible diatom cell walls; used in polishing and filtration.

Dinoflagellates

Mostly marine, cellulose-plated protists with two flagella; rapid blooms of red species like Gonyaulax cause red tides.

Euglenoids

Freshwater protists (e.g., Euglena) with protein pellicle; photosynthetic in light but heterotrophic in darkness.

Slime Moulds

Saprophytic protists forming multinucleate plasmodia that produce resistant spores during unfavourable conditions.

Protozoa

Heterotrophic, unicellular protists classified into amoeboid, flagellated, ciliated and sporozoan groups.

Amoeboid Protozoans

Protozoa that move using pseudopodia, e.g., Amoeba; some are parasites like Entamoeba.

Flagellated Protozoans

Protozoa possessing flagella; include Trypanosoma, the agent of sleeping sickness.

Ciliated Protozoans

Actively swimming protozoa with rows of cilia and a gullet, e.g., Paramoecium.

Sporozoans

Protozoa with an infectious spore-like stage; Plasmodium causes malaria.

Kingdom Fungi

Eukaryotic, heterotrophic kingdom with chitinous cell walls; body of hyphae and mycelium; reproduces via spores.

Coenocytic Hyphae

Multinucleate, non-septate fungal filaments.

Dikaryon

Fungal stage (n+n) with two haploid nuclei per cell preceding karyogamy in ascomycetes and basidiomycetes.

Phycomycetes

Aquatic or parasitic fungi with coenocytic mycelium and asexual zoospores; includes Mucor and Rhizopus.

Ascomycetes

‘Sac fungi’ producing endogenous ascospores in asci; examples include Penicillium, Aspergillus, yeast and morels.

Basidiomycetes

Fungi forming basidiospores on basidia; includes mushrooms (Agaricus), rusts (Puccinia) and smuts (Ustilago).

Deuteromycetes

'Imperfect fungi' known only by asexual conidia; many are decomposers or pathogens, e.g., Alternaria.

Lichens

Symbiotic association of a fungus (mycobiont) with an alga or cyanobacterium (phycobiont); excellent pollution indicators.

Kingdom Plantae

Multicellular, cellulose-walled, photosynthetic eukaryotes exhibiting alternation of generations; includes algae to angiosperms.

Alternation of Generations

Plant life cycle with alternating haploid (gametophyte) and diploid (sporophyte) phases.

Kingdom Animalia

Multicellular, heterotrophic eukaryotes lacking cell walls; nutrition holozoic and development via embryogenesis.

Virus

Acellular nucleoprotein particle with DNA or RNA encased in a protein capsid; obligate intracellular parasite.

Capsid

Protein coat of a virus composed of repeating capsomeres that protect the nucleic acid.

Bacteriophage

Virus that infects bacteria; typically has double-stranded DNA and a head-tail structure.

Viroid

Small, circular, low-molecular-weight RNA molecule without a protein coat; causes diseases like potato spindle tuber.

Prion

Infectious, abnormally folded protein causing neurodegenerative diseases such as mad cow disease and CJD.

Red Tide

Discoloration of seawater caused by explosive blooms of toxin-producing red dinoflagellates.

Heterocyst

Specialised nitrogen-fixing cell in some filamentous cyanobacteria like Nostoc and Anabaena.

Diatoms

Silica-walled, photosynthetic protists forming major phytoplankton; key members of chrysophytes.

Pellicle

Flexible protein layer replacing the cell wall in euglenoids, allowing shape change.

Conidium

Asexual, non-motile fungal spore produced exogenously on conidiophores, characteristic of ascomycetes and deuteromycetes.