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- In the modern system of classification, living organisms are grouped under five kingdoms, as proposed by Whittaker (1966).
- The Kingdom Monera includes bacteria and blue green algae, both of which possess prokaryotic cells.
- Bacteria are unicellular prokaryotes that have a wide distribution, in all kinds of habitats.
- Bacteria can be distinguished into different forms such as cocci, spirilli and vibriae.
- Bacterial cells may or may not have flagella. When present, the distribution of flagella varies.
- Bacterial cell wall is composed of murein - a peptidoglycan.
- Bacteria can be distinguished into autotrophs and heterotrophs based on their mode of nutrition.
- Bacteria generally reproduce by fission. Other processes like budding and endospore formation also occur.
- Sexual reproduction in bacteria involves processes like transformation and transduction.
- Blue green algae (cyanobacteria) represent another major group of prokaryotes.
- Cyanobacteria are characterised by the presence of phycocyanin (blue) and chlorophyll (green) pigments.
- The Kingdom Protista includes primitive unicellular eukaryotic organisms.
- Protista are mainly represented by unicellular algae (such as diatoms) and protozoans - rhizopods, flagellates, ciliates and sporozoans.
- Diatoms belong to a group called 'golden brown algae'. They have a plant body represented by a single cell called frustule. It is enclosed in two overlapping valves.
- Diatoms reproduce by simple cell division. Sexual reproduction also occurs and involves the formation of auxospory.
- Protozoans are represented by single-celled animals. They can be classified into four groups-sarcodines or rhizopods with pseudopodia, flagellates with flagella, ciliates with 'cilia' as the locomotor structures and sporozoans without locomotor structures (endoparasites).
- Kingdom Mycota exclusively includes the fungi.
- Fungi are a group of heterotrophic (saprotrophic or parasitic) primitive eukaryotes.
- Fungal plant body is called mycelium. It may be unicellular and multicellular. The multicellular mycelium forms filamentous structures called hyphae.
- Fungi reproduce by fission, budding and sexual methods.
- Sexual reproduction occurs by various modes such as plasmogamy and gametangial contact.
- Kingdom metaphyta includes the advanced group of plants such as higher algae, bryophytes and tracheophytes.
- Three groups of algae - green algae, red algae and brown algae are included in metaphyta.
- Bryophytes include a group of semi terrestrial plants. They are commonly described as 'amphibians of the plant kingdom' since they require water to complete their life cycle.
- The life cycle of bryophytes includes an alternation of two generations - a gametophytic generation which produces gametes and a sporophytic generation which produces spores.
- The adult plant body is a gametophyte. It contains reproductive structures called antheridia which produces male gametes and archegonia which produces the egg cell.
- The fertilised egg develops into a sporophyte which remains attached to the gametophyte, leading a parasitic life.
- The sporophyte produces spores which germinate to form the gametophyte.
- Tracheophytes include plants which are truly terrestrial and hence contain vascular tissues - xylem and phloem.
- Tracheophytes include three groups of advanced plants -pteridophytes, gymnosperms and angiosperms.
- Pteridophytes are commonly called ferns. They show a well developed plant body which is a sporophyte.
- The plant body contains well developed leaves called fronds. Some of the leaves are called sporophylls since they contain structures called sori.
- Sori enclose spore producing structures called sporangia.
- Sporangia release spores which germinate to produce the gametophyte.
- The gametophyte, which is called prothallus contains anteridia and archegonia which produce sperms and egg respectively.
- The zygote formed from fertilization develops into a sporophyte.
- Gymnosperms are a group of advanced plants which produce seeds that are not enclosed in fruits. Hence, commonly called as 'naked-seeded plants'.
- The adult plant body is a sporophyte which shows well developed roots, stem and leaves.
- The plant body produces microsporophylly containing microsporangia and megasporophylls containing megasporangia.
- Microsporangia produce microspores which represent the reduced gametophytic generation. Megasporangia produce megaspores (ovules) representing the reduced gametophytic generation.
- Angiosperms occur in diverse habitats and can be herbs, shrubs or trees. They can be annuals, biennials or perennials.
- Angiosperms can be broadly distinguished into dicots and monocots, which exhibit certain characteristic differences between them.
- The most significant aspect of angiosperm reproduction is the phenomenon of double fertilization and triple fusion.
- Kingdom Metazoa includes all the multicellular animals. They can be distinguished broadly into invertebrates and chordates.
- Invertebrates account for nearly 95% of animal Species. Chordates include the vertebrate.