Glossary — Biological Classification — Notes

Term	Definition	NEET Context
Phylogenetic	Related to evolutionary history and relationships between organisms	One of Whittaker's 5 criteria for classification
Prokaryote	Cell without a membrane-bound nucleus; DNA is in nucleoid region	Kingdom Monera exclusively
Eukaryote	Cell with a membrane-bound nucleus and membrane-bound organelles	All kingdoms except Monera
Peptidoglycan	Polymer of sugars and amino acids forming bacterial cell walls	Absent in Archaebacteria; present in Eubacteria
Archaebacteria	Ancient bacteria living in extreme environments; no peptidoglycan in cell wall	Methanogens, Halophiles, Thermoacidophiles
Eubacteria	True bacteria; cell wall has peptidoglycan; includes cyanobacteria	Most common bacteria studied in NEET
Cyanobacteria	Photosynthetic prokaryotes (blue-green algae) capable of $N_{2}$ fixation	Monera kingdom; Nostoc, Anabaena
Heterocyst	Thick-walled differentiated cell in cyanobacteria for nitrogen fixation	Found in Nostoc and Anabaena
Mycoplasma	Smallest living cell; no cell wall; causes diseases	Monera kingdom; penicillin-resistant due to no cell wall
Gram staining	Differential staining of bacteria based on cell wall structure	Crystal violet retained by Gram+ve; not by Gram-ve
Frustule	Siliceous ( $SiO_{2}$ ) two-part cell wall of diatoms	Forms diatomaceous earth upon death
Diatomaceous earth	Sedimentary deposits of siliceous frustules of dead diatoms	Used in filtration, polishing, insulation
Dinoflagellate	Unicellular protist with two flagella and cellulose plates	Causes red tides; some bioluminescent
Red tide	Toxic bloom of dinoflagellates (e.g., Gonyaulax) that discolours seawater	Kills marine life, makes shellfish poisonous
Pellicle	Proteinaceous, flexible covering in euglenoids instead of cell wall	Distinguishes Euglena from plants
Mixotrophic	Nutrition mode combining autotrophic (photosynthesis) and heterotrophic (ingestion)	Characteristic of Euglena
Plasmodium	Multinucleate mass (in slime moulds) OR a genus of parasitic protozoan (malaria)	Two different organisms — context matters in NEET
Mycelium	Body of a fungus consisting of a network of thread-like hyphae	Distinguishes fungi from other kingdoms
Hyphae	Thread-like filaments forming mycelium in fungi	Septate (with walls) or coenocytic (without walls)
Coenocytic	Hyphae without cross-walls (septa); multinucleate	Characteristic of Phycomycetes only
Chitin	Structural polysaccharide (N-acetylglucosamine) in fungal cell walls	Distinguishes fungi from plants (cellulose) and animals (absent)
Glycogen	Polysaccharide energy storage in fungi and animals	Fungi store glycogen, NOT starch (NEET trap)
Ascus	Sac-like structure in Ascomycetes containing ascospores	Plural: asci; gives Ascomycetes its name
Basidium	Club-shaped structure in Basidiomycetes bearing basidiospores	Plural: basidia; gives Basidiomycetes its name
Phycobiont	Algal photosynthetic partner in a lichen	Provides organic nutrition to the fungal partner
Mycobiont	Fungal partner in a lichen	Provides water, minerals, and structural support
Capsid	Protein coat surrounding the nucleic acid of a virus	Absent in viroids; viruses must have it
Viroid	Smallest infectious agent — naked circular RNA without protein coat	Discovered by T.O. Diener (1971); plant diseases only
Prion	Infectious protein with no nucleic acid; causes neurodegenerative diseases	Discovered by Stanley Prusiner (1982)
Nitrogenase	Enzyme catalysing conversion of atmospheric $N_{2}$ to $NH_{3}$	Functions only in anaerobic conditions (heterocysts provide this)