Ch 2 covers Whittaker's five-kingdom classification system based on cell structure, body organisation, mode of nutrition, reproduction, and phylogenetic relationships.
Monera: prokaryotic — bacteria (cocci, bacilli, spirilla; Gram +/−), cyanobacteria, mycoplasma (no cell wall). Protista: unicellular eukaryotes — Chrysophytes (diatoms), Dinoflagellates, Euglenoids, Slime moulds, Protozoans (Amoeba, Paramecium, Plasmodium). Fungi: eukaryotic heterotrophs, cell wall of chitin, absorptive nutrition — Phycomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes.
Viruses: non-cellular, contain DNA or RNA + protein coat (capsid). Obligate intracellular parasites. TMV, bacteriophage, HIV. Viroids: small RNA without protein coat (cause plant diseases). Prions: misfolded proteins (mad cow disease). Lichens: symbiotic association of algae (photobiont) + fungus (mycobiont) — pioneer colonisers.
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Viruses show no metabolism, cannot reproduce on their own, lack cellular structure, and don't show life outside a host. They can be crystallised like chemicals. They are considered at the boundary of living and non-living — they "come alive" only inside a host cell by hijacking its machinery to replicate.
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