Revision: Class 11 >> Biological Classification NEET (UG) Biological Classification

• Earliest system - First scientific classification by Aristotle, based on morphological traits.
• Plants - Divided into Herbs, Shrubs, and Trees.
• Animals - Divided into Enaima (with RBCs) and Anaima (without RBCs).
• Limitation - The system was based only on body structure, ignoring other biological features.

• Two Kingdom - Given by Carolus Linnaeus; divided organisms into Plantae and Animalia; proved insufficient as it couldn't distinguish prokaryotes, eukaryotes, fungi, etc.
• Three Kingdom - Given by Ernst Haeckel; added Protista for unicellular organisms; still lacked distinction between prokaryotes and eukaryotes.
• Four Kingdom - Given by Herbert F. Copeland; introduced Monera (prokaryotes), Protista, Plantae and Animalia; first to recognise prokaryote-eukaryote difference.
• Five Kingdom - Given by R. H. Whittaker (1969); kingdoms - Monera, Protista, Fungi, Plantae, Animalia; based on cell structure, nutrition, reproduction and phylogenetic relationships.
• Six Kingdom - Given by Carl Woese; split Monera into Bacteria and Archaea; recognised archaea as distinct based on genetic and biochemical differences.

• Monera - Primitive, single-celled prokaryotes; includes archaebacteria, cyanobacteria, mycoplasma and eubacteria. e.g. Bacteria, Oscillatoria, Nostoc.
• Protista - Single-celled eukaryotes, mainly aquatic; includes diatoms, golden algae, Euglena, and protozoans; often photosynthetic. e.g. Amoeba, Paramecium, Plasmodium.
• Fungi (Mycota) - Made of thread-like mycelium and hyphae; mostly saprophytes, parasites and symbionts; includes lichens and mycorrhiza. e.g. Aspergillus.
• Plantae (Metaphyta) - Multicellular plants with chlorophyll; includes herbs, shrubs, trees, flowering and non-flowering plants. e.g. Rose plant, Mango tree, Algae, Bryophytes.
• Animalia (Metazoa) - Heterotrophic, multicellular organisms; lack a cell wall; include all types of animals. e.g. Lion, Peacock.

• Meaning - Ancient, primitive microorganisms; also called extremophiles as they survive in extremely harsh conditions like hot springs, volcanoes, salty areas and deep sea.
• Halophiles - Live in extremely salty environments. e.g. salt lakes.
• Thermoacidophiles/Thermophiles - Live in hot water areas like geysers, hydrothermal vents and volcanoes.
• Methanogens - Found in the gut of ruminants and marshy areas; produce methane gas from dung.
• Difference - Archaebacteria are different from regular bacteria and blue-green algae in their structure and biochemistry.

• Meaning - Also known as blue-green algae; contain chlorophyll 'a' and perform photosynthesis; found in marine and terrestrial environments.
• Forms - Can be unicellular, colonial or filamentous; often surrounded by a gelatinous sheath; form algal blooms in polluted water.
• Reproduction - By fragmentation, hormogones (small trichome segments that separate naturally) and akinetes (thick-walled resting spores).
• Nitrogen fixation - Some fix atmospheric nitrogen using specialised cells called heterocysts. e.g. Nostoc, Anabaena.
• Ecological role - Protect against soil erosion and help in the reclamation of saline and alkaline soil.

1. Meaning - All single-celled eukaryotes act as a link between plants, animals and fungi; mostly aquatic; have a nucleus and membrane-bound organelles.

2. Chrysophytes - Includes diatoms and golden algae; cell wall has silica; deposits form Diatomaceous Earth (used in polishing and filtration); chief producers in oceans.

3. Dinoflagellates - Mostly marine, photosynthetic; cell wall of cellulosic plates; have two flagella (one longitudinal, one transverse); rapid multiplication of red dinoflagellates (e.g. Gonyaulax) causes red tides.

4. Euglenoids - Have a pellicle instead of a cell wall; photosynthetic in sunlight but become heterotrophs in its absence. e.g. Euglena.

5. Slime Moulds - Saprophytic; feed on decaying matter; undergo syngamy to form a plasmodium that spreads over several feet.

6. Protozoans - 4 types:

• Amoeboid - move by pseudopodia. e.g. Amoeba, Entamoeba
• Flagellated - have flagella; cause sleeping sickness. e.g. Trypanosoma
• Ciliated - have cilia; have a gullet for feeding. e.g. Paramecium
• Sporozoans - no locomotory organelle; all parasitic. e.g. Plasmodium

1. Meaning - Heterotrophic organisms; body made of thread-like hyphae; network of hyphae = mycelium; cell wall made of chitin; grow in warm and humid places; except yeasts, all are multicellular.

2. Nutrition - Can be saprophytic (feed on dead matter), parasitic or symbiotic (as lichens and mycorrhiza).

3. Reproduction - Asexual by spores (conidia, zoospores, aplanospores); sexual reproduction involves 3 steps - plasmogamy → karyogamy → meiosis; Ascomycetes and Basidiomycetes undergo a dikaryotic stage.

4. 4 Classes of Fungi:

• Phycomycetes - Mycelium aseptate, coenocytic; spores endogenous in sporangium. e.g. Rhizopus, Albugo
• Ascomycetes (Sac fungi) - Asexual spores = conidia; sexual spores = ascospores in ascus. e.g. Aspergillus, Neurospora
• Basidiomycetes - No asexual spores; sexual spores = basidiospores (exogenous). e.g. Agaricus, Ustilago, Puccinia
• Deuteromycetes (Imperfect Fungi) - Sexual form unknown; saprophytic/parasitic. e.g. Alternaria, Colletotrichum

5. Classification basis - Based on morphology, mode of spore formation and fruiting bodies.

6. Important examples - Puccinia (wheat rust), Penicillium (antibiotic), Agaricus (mushroom), Neurospora (genetic research).

1. Meaning- All eukaryotic, chlorophyll-containing organisms; cell wall made of cellulose; mostly autotrophic; some are insectivorous (e.g. Venus fly trap, Bladderwort) or parasitic (e.g. Cuscuta).

2. Members - Includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms.

3. Alternation of generations - Life cycle has two phases - diploid sporophyte and haploid gametophyte - which alternate with each other.

4. Plant groups at a glance:

• Algae - Simple, aquatic, no true roots/stems/leaves. e.g. Seaweed, Green algae
• Bryophytes - Non-vascular, moist environments. e.g. Mosses, Liverworts
• Pteridophytes - Vascular, no seeds, reproduce by spores. e.g. Ferns
• Gymnosperms - Naked seeds in cones, no flowers/fruits. e.g. Pine, Fir
• Angiosperms - Seeds enclosed in fruits, the most diverse group. e.g. Rose, Lily

5. Key features - Have prominent chloroplasts for photosynthesis; membrane-bound organelles; the most diverse group among all kingdoms.

• Meaning - Heterotrophic, multicellular eukaryotes; cells lack a cell wall; cannot produce their own food.
• Nutrition - Mode of nutrition is holozoic (food obtained by ingestion); food is digested in an internal cavity; food is stored as glycogen or fat.
• Reproduction - By sexual reproduction - copulation of male and female followed by embryological development.
• Other features - Follow a definite growth pattern; higher forms have elaborate sensory and neuromotor mechanisms (nervous system and sensory organs); most are capable of locomotion.
• Cell structure - Has a nucleus and membrane-bound organelles; no chloroplasts (hence cannot photosynthesise); no cell wall (unlike plants and fungi).

Viruses

• Viruses are non-living outside a host, but become active inside living cells.
• They are nucleoproteins with a protein coat (capsid) and genetic material (DNA or RNA).
• They can have different structures, like helical or polyhedral.
• Cause diseases like influenza, AIDS, mumps, smallpox in humans and mosaic disease in plants.
• They can form crystalline structures outside the host and do not fit in the Whittaker classification.

Viroids

• Viroids are the smallest infectious agents, discovered by T.O. Diener (1971).
• They consist of only RNA, without a protein coat.
• Cause plant diseases like potato spindle tuber disease.
• Have low molecular weight and a simple structure.
• Can replicate independently inside host plants.

Prions

• Prions are infectious proteins without DNA or RNA.
• They cause neurodegenerative diseases in humans and animals.
• Examples include CJD, mad cow disease (BSE), and scrapie.
• Disease occurs due to the misfolding of normal proteins.
• Lead to brain damage and death.

Lichens

• Lichens are a symbiotic association between algae and fungi.
• Algae prepare food, while fungi provide shelter and nutrients.
• Lichens act as pollution indicators and are absent in polluted areas.
• Based on structure, lichens are of three types: crustose (crust-like and tightly attached), foliose (leaf-like and loosely attached), and fruticose (branched or bushy).
• Examples include Lecanora (crustose), Peltigera (foliose), and Ramalina (fruticose).