“A species is a group of organisms which can interbreed freely among them and produce fertile offspring, but are reproductively isolated from all other such groups in nature.” In the definition of species we must emphasize “in nature” because two organisms related to two different but closely related species can cross-breed under artificial conditions. Carolus Linnaeus divided nature into three kingdom s: mineral, vegetable and animal . Linnaeus used five ranks in classification: class, order, genus, species, and variety . Linnaeus is best known for his introduction of the method still used to formulate the scientific name of every species i.e. binominal nomenclature . Oldest system classifies all organisms into two kingdoms i.e. Plantae ( organisms that can prepare food from simple inorganic materials and thus can store energy, are autotroph) and Animalia( organisms that cannot synthesize their food and depend on autotrophs or others are heterotrophs ...
