The system of assembling organisms into groups or sets on the basis of likenesses and variances is called classification. It simplifies the study of wide variety of organisms in a very systematic manner. R.H. Whittaker proposed the five kingdoms of classification in 1969. This classification was based upon certain characters like mode of nutrition, thallus organization, cell structure, phylogenetic relationships and reproduction. This form of classification includes five kingdoms Monera, Protista, Fungi, Plantae and Animalia.
The bacteria are categorized underneath the Kingdom Monera. Bacteria occur everywhere and they are microscopic in nature. They possess cell wall and are prokaryotic. The cell wall is formed of amino acids and polysaccharides. Bacteria can be heterotrophic and autotrophic. The heterotrophic bacteria can be parasitic or saprophytic.The autotrophic bacteria can be chemosynthetic or photosynthetic.
Bacteria can be classified into four types based on their shape:
Coccus (pl.: cocci)- These bacteria’s are spherical in shape.
Bacillus (pl.: bacilli) – These bacteria’s are Rod-shaped,
Vibrium (pl.: vibrio) – These bacteria’s are Comma-shaped bacteria
Spirillum (pl.: spirilla)- These bacteria’s are Spiral shaped bacteria
Monera has since been divided into Archaebacteria and Eubacteria.
They are unicellular and eukaryotes. Some of them have cilia or flagella for mobility. Sexual reproduction is by a process of cell fusion and zygote formation. Kingdom Protista is categorized into subsequent groups:
Chrysophytes: The golden algae (desmids) and diatoms are fall under this group. They are found in marine and freshwater habitats.
Dinoflagellates: They are usually photosynthetic and marine. The colour they appear is dependent on the key pigments in their cells; they appear red, blue, brown, green or yellow.
Euglenoids: Most of them live in freshwater habitation in motionless water. Cell wall is absent in them and instead there is a protein rich layer; called pellicle.
Slime Moulds: These are saprophytic. They body moves along putrefying leaves and twigs and nourishes itself on organic material. Under favorable surroundings, they form an accumulation called plasmodium.
Protozoans: They are heterotrophs and survive either as parasites or predators.
The fungi are filamentous; excluding yeast (single celled). Their figure comprises of slender, long thread-like constructions; called hyphae. The web of hyphae is called mycelium. Some of the hyphae are unbroken tubes which are jam-packed with multi nucleated cytoplasm. Such hyphae are labelled Coenocytic hyphae. The other type of hyphae has cross-walls or septae. The cell wall of fungi is composed of polysaccharides and chitin.
Most of the fungi are saprophytes and are heterotrophic. Some of the fungi also survive as symbionts. Some are parasites. Some of the symbiont fungi live in association with algae, like lichens. Some of the symbiont fungi live in association with roots of higher plants, as mycorrhiza.
The kingdom is filled with all eukaryotes which have chloroplast. Most of them are autotrophic in nature, but some are heterotrophic as well. The Cell wall mainly comprises of cellulose.
Plants have two distinctive phases in their lifecycle. These phases alternate with each other. The diploid saprophytic and the haploid gametophytic phase. The lengths of the diploid and haploid phases vary among dissimilar groups of plants. Alternation of Generation is what this phenomenon is called.
All multicellular eukaryotes which are heterotrophs and lack cell wall are set aside under this kingdom. The animals are directly or indirectly dependent for food on plants. Their mode of nutrition is holozoic. Holozoic nutrition encompasses ingestion of food and then the use of internal cavity for digestion of food. Many of the animals are adept for locomotion. Sexual reproduction is by copulation of male and female which is followed by embryological development.