Biological Classification System
* The first classifications were made to identify organisms that were useful to man for food, shelter and clothing.
* Aristotle devised the first scientific method of classification.
* Later, Carl Linnaeus came up with the two kingdom system of classification.
* All plants were put in the Kingdom Plantae while all animals were put in the Kingdom Animalia.
* In 1996, RR.H.Whittaker proposed a Five Kingdom Classification system.
* Three more kingdoms: Moners, Protista and Fungi were added to the existing kingdoms of Plantae and Animalia.
* The main criteria that Whittaker used for this classification system were cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships.
Kingdom Monera
* Bacteria are the sole members of Kingdom Monera.
* Different bacteria synthesise their food in different ways.
* Based on their shape, bacteria can be classified into four types: spherical coccus, rod- shaped bacillus, comma- shaped vibrium and spiral sprillium.
* Bacteria reproduce by fission. They can also reproduce sexually by a primitive DNA transfer from one bacterium to another.
* Eubacteria like cyanobacteria are the true bacteria.
* There are also special bacteria called archaebacteria hat live in extreme conditions.
* Mycoplasmas are the bacteria that do not have a cell wall.
Kingdom Protista
* All unicellular eukaryotes come under Kingdom Protista.
* Members of this kingdom are primarily aquatic.
* Some protists also have a flagella or a cilium.
* They reproduce both asexually through cell fusion and sexually via zygote formation.
* Chrysophytes, dianoflagellates, euglenoids, slime moulds and protozoans are some examples of protists.
* Chrysophytes include diatoms and golden algae.
* Dianoflagellates are colourful protists found both in marine and fresh water.
* Euglenoids have two flagella, one short and the other long one.
* Slime moulds are saprophytic protists.
* There are four types of protozoans: amoeboid protozoans, flagellated protozoans, ciliated protozoans and sporozoans.
Kingdom Fungi
* Common mushrooms, toadstools and the mould on leftover bread are all examples of fungi.
* With the exception of yeasts, which are unicellular, fungi are usually filamentous.
* Fungi consist of long, slender thread- like structures called hyphae.
* Fungi can be saprophytic, parasitic as well as symbiotic typified by lichens.
* Fungi can reproduce vegetatively, asexually and sexually.
* They reproduce both sexually and asexually via spores. These spores are produced in structures called fruiting bodies.
* There are three steps in the sexual cycles: Plasmogamy, Karyogamy and Meiosis.
* There are four main classes of fungi: Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes.
Kingdom Plantae and Animalia
* Kingdom Plantae comprises all eukaryotic, chlorophyll-containing organisms called plants.
* Plant cells are characterised by the presence of a cell wall, which is made up of cellulose.
* Most plants are autotrophs, but they can be insectivorous and parasites as well.
* Plants have two alternate phases in their life cycle: the diploid sporophytic and the haploid gametophytic phases.
* The phenomenon of alternation of sexual and asexual forms in the lifecycle is referred to as “alternation of generation”.
* Kingdom Animalia comprises only heterotrophic, multi-cellular eukaryotic organisms.
* Animal cells have no cell wall.
* Animals reproduce sexually after a male and female copulate, which is followed by embryological development.
* Most animals are motile.
Viruses, Viroids and Lichens
* Viruses and viroids are acellular organisms.
* In addition to proteins, viruses have a genetic make-up compromising either RNA or DNA.
* Viruses are known to cause diseases such as the common cold, mumps and small pox.
* Like viruses, viroids are also infectious, only they are smaller.
* Lichens, though they may look like single organisms, actually have two organisms inside them: algae and fungi.