Biological Classification

The scientific ordering of organisms in a hierarchical series of groups is done on the basis of their similarities and differences.The similarities and differences can be in their morphology, anatomy or evolution.

Biological classification or scientific classification is a method to group and categorise organisms. The biological classification of plants and animals was first proposed by Aristotle.

Later Linnaeus classified all living organisms into two kingdoms – Plantae and Animalia. Linnaeus is known as Father of Taxonomy. The two kingdom classification system was discarded as it could not place many organisms in proper groups.
The three domain system included: Bacteria, eukarya and archae.
Whittaker proposed an elaborate five kingdom classification – Monera, Protista, Fungi, Plantae and Animalia. In five kingdom classifications, all the organisms are classified on the basis of:Modes of nutrition, Reproduction, Cellular organization, Complexity of organism’s body and Evolutionary trend.

Kingdom Monera: includes bacteria
Based on shape bacteria are grouped into four categories: Coccus, Bacillus, Vibrium and Spirillum. Bacteria are divided into two divisions: Archaebacteria and Eubacteria

Kingdom Protista: includes all single-celled eukaryotes (Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds and Protozoans)

Kingdom Fungi: includes all fungi
The kingdom fungi is divided into four classes: Phycomycetes, Ascomycetes,
Basidiomycetes and Deuteromycetes.
The fungi are generally filamentous in structure, except yeast. The body of fungi consists of long, slender thread-like structures called hyphae. The network of hyphae is known as mycelium. In some fungi, the hyphae are continuous tubes filled with multinucleated cytoplasm. These hyphae are called coenocytic hyphae. The cell wall of fungi is composed of chitin and polysaccharides.
Most fungi are heterotrophic and absorb soluble organic matter from dead organic matter and are called saprophytes. Some fungi depend on living plants and animals are called parasites. They can also live as symbionts.

Kingdom Plantae: includes all eukaryotic chlorophyll-containing organisms.
The kingdom plantae include Algae, bryophytes, Pteridophytes, Gymnosperms and Angiosperms. The life cycle of plants show alternation in two generations – gametophytic and sporophytic generations

Kingdom Animalia: includes multicellular, heterotrophic eukaryotic organisms that lack cell wall. The mode of nutrition of these organisms is holozoic. They reproduce mostly by the sexual mode. Some acellular organisms like viruses and viroids, and lichens are not classified in the five kingdom classification by Whittaker

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