Biological Classification – Class 11 Biology (Chapter 2)

Vocabulary flashcards covering key terms and definitions from the Class 11 Biology chapter on Biological Classification.

Biological Classification

Scientific arrangement of organisms into hierarchical groups based on similarities and differences.

Artificial System of Classification

Grouping organisms using only one or a few superficial morphological traits (e.g., Aristotle’s system).

Natural System of Classification

Classifies organisms by considering many characters to reveal natural relationships (e.g., Bentham & Hooker).

Phylogenetic System of Classification

Arranges organisms according to evolutionary relationships (e.g., Engler & Prantl, Hutchinson).

Two-Kingdom System

Linnaeus’s scheme separating life into Plantae and Animalia mainly by presence or absence of a cell wall.

Three-Kingdom System

Haeckel’s addition of Protista for unicellular, undifferentiated organisms.

Five-Kingdom System

R.H. Whittaker’s kingdoms: Monera, Protista, Fungi, Plantae, Animalia, reflecting cell type, level of organization and nutrition.

Kingdom Monera

Includes all prokaryotes such as bacteria, cyanobacteria, mycoplasma; cells lack a true nucleus and membrane-bound organelles.

Archaebacteria

Primitive prokaryotes with unique cell wall (no peptidoglycan) living in extreme habitats; includes halophiles, thermoacidophiles, methanogens.

Eubacteria

‘True’ bacteria with rigid cell walls; may be autotrophic or heterotrophic and often possess flagella.

Cyanobacteria

Gram-positive photosynthetic eubacteria (blue-green algae) containing chlorophyll a; some have heterocysts for nitrogen fixation.

Chemosynthetic Bacteria

Oxidize inorganic substances like ammonia or nitrite to obtain energy, recycling elements such as nitrogen and sulphur.

Coccus

Spherical-shaped bacterial form.

Bacillus

Rod-shaped bacterial morphology.

Spirillum

Spiral or coiled bacterial shape.

Vibrio

Comma-shaped bacterium.

Mycoplasma (PPLO)

Smallest free-living prokaryotes lacking cell wall; can survive anaerobically and cause diseases in plants and animals.

Kingdom Protista

Unicellular or colonial eukaryotes (e.g., algae-like, protozoans) with diverse nutrition and predominantly aquatic habitat.

Chrysophytes

Group containing diatoms and desmids; possess silica cell walls and are major oceanic producers.

Diatomaceous Earth

Heaps of indestructible silica cell walls of dead diatoms used in polishing and filtration.

Dinoflagellates

Unicellular, biflagellate photosynthetic protists; blooms of some species cause ‘red tide’ (e.g., Gonyaulax).

Red Tide

Discoloration of seawater due to explosive growth of pigmented dinoflagellates producing toxins.

Euglenoids

Flexible, pellicle-bearing flagellates (e.g., Euglena) that are photosynthetic in light and heterotrophic in darkness.

Slime Moulds

Saprophytic protists forming multinucleate plasmodium that yields spore-bearing fruiting bodies.

Plasmodium (Slime Mould)

A multinucleate, creeping mass formed by slime moulds under favourable conditions.

Protozoans

Heterotrophic protists regarded as primitive animals; include amoeboids, flagellates, ciliates, sporozoans.

Amoeboids

Protozoans moving by pseudopodia (e.g., Amoeba, Entamoeba).

Flagellated Protozoans

Free-living or parasitic protozoans possessing flagella (e.g., Trypanosoma).

Ciliated Protozoans

Aquatic protozoans covered with cilia used for locomotion and feeding (e.g., Paramecium).

Sporozoans

Protozoans with infectious spore-like stage; lack locomotory organelles (e.g., Plasmodium—malaria parasite).

Kingdom Fungi

Achlorophyllous, heterotrophic, chitinous-walled eukaryotes storing glycogen; reproduce via spores and sexual cycles of plasmogamy, karyogamy, and meiosis.

Phycomycetes

Aquatic or damp-habitat fungi with aseptate coenocytic mycelium; reproduce by zoospores or aplanospores (e.g., Rhizopus).

Ascomycetes (Sac Fungi)

Septate fungi producing sexual ascospores in ascocarps; asexual spores are conidia (e.g., Neurospora, Aspergillus).

Basidiomycetes (Club Fungi)

Septate fungi forming basidiospores on basidia within basidiocarps; asexual spores absent (e.g., Agaricus, Puccinia).

Deuteromycetes (Fungi Imperfecti)

Fungi with only vegetative and asexual phases known; many are saprophytes or parasites (e.g., Alternaria).

Kingdom Plantae

Multicellular, chlorophyll-bearing eukaryotes with alternation of generations; includes algae, bryophytes, pteridophytes, gymnosperms, angiosperms.

Kingdom Animalia

Multicellular, heterotrophic eukaryotes lacking cell walls; store glycogen/fat; reproduce sexually with embryonic development.

Virus

Non-cellular infectious agent with protein coat and DNA or RNA; crystalline outside host but replicates inside living cells.

Bacteriophage

Virus that infects and replicates within bacteria.

Viroid

Infectious, free, circular RNA molecule lacking protein coat; causes potato spindle tuber disease (discovered by T.O. Diener).

Lichen

Symbiotic association between fungus (mycobiont) and alga (phycobiont); indicators of unpolluted air.

D.J. Ivanowsky

Scientist who first recognized viruses while studying tobacco mosaic disease.

Heterocyst

Specialized nitrogen-fixing cell found in some cyanobacteria such as Nostoc and Anabaena.

Halophiles

Archaebacteria thriving in extremely salty environments.

Thermoacidophiles

Archaebacteria inhabiting hot, acidic environments like hot springs.

Methanogens

Archaebacteria producing methane; live in anaerobic habitats such as ruminant guts and biogas digesters.