Classification of Living Things

• The classification of organisms and their schemes have evolved through time.
• Systematics is the science that deals with the study of the units of biodiversity putting special emphasis on the discovery of species, reconstructing evolutionary patterns and building classifications.
• Taxonomy is the science that deals more specifically on the classification, identification and nomenclature of organisms.
• Morphology deals with studying the form and structure of microorganisms as well as their specific structural features.
• Organisms can be classified as unicellular or multicellular in nature.
• Unicellular organisms are made up of only one cell that carries out all of the functions needed by the organism, while multicellular organisms use many different cells to function.
• Plants can be classified based on their morphological characteristics such as being vascular or non-vascular, flowering or non-flowering, and their ability to produce seeds or not.
• Animals can be classified based on their embryology.
• The germ layers are a fundamental aspect of the structure of the embryo at the end of this period of development.
• The germ layers include ectoderm, which forms the outer surface of the embryo; endoderm, which forms the inner surface lining the gut cavity; and mesoderm, which forms a layer in between the other two in most groups.
• Animals may develop either two or three embryonic germ layers.
• Animals having two embryonic layers (endoderm and ectoderm) are called diploblasts while those with three (endoderm, ectoderm and mesoderm) are called triploblasts.
• The three germ layers would differentiate to give rise to a specific organ or organ system.
• Homologous structures are those that are similar in related organisms because they were inherited from a common ancestor.
• Analogous structures are those that are similar in unrelated organisms.
• Ever since the structure of the DNA has been elucidated, techniques in DNA sequencing have been developed and used in various studies including taxonomy.
• Taxonomy deals with the classification, identification and nomenclature of organisms.
• Systematics is the study that deals with the diversity of living forms and the evolutionary relationships among living things through time.
• Genetic analysis showed that archaebacteria were significantly different from other bacteria and eukaryotes in terms of this rRNA sequence.
• Through time, naturalists and taxonomists have devised a way to classify organisms.
• In the 70s, Carl Woese and his collaborator George Fox used the small subunit ribosomal RNA of different organisms to create a tree that is genetics based.
• Similarities in the embryos of different species are likely to be evidence of common ancestry.
• This germ layer gives rise to all muscle tissues (including the cardiac tissues and muscles of the intestines), connective tissues such as the skeleton and blood cells, and most other visceral organs such as the kidneys and the spleen.
• DNA analysis is one of the most powerful tools at present.
• Modern taxonomy relies on comparing the nucleic acids or proteins from different organisms.
• The more similar the nucleic acids and proteins are between two organisms, the more closely related they are.
• The ectoderm develops into the outer epithelial covering of the body surface, the central nervous system, and a few other structures.
• Organisms with fairly similar anatomical features are assumed to be relatively closely related evolutionarily and they are likely to share a common ancestor.
• All vertebrate embryos have a notochord, a dorsal hollow nerve cord, pharyngeal slits and a post-anal tail.
• Comparative anatomy is an essential tool that helps determine evolutionary relationships between organisms and whether or not they share common ancestors.
• The mesoderm is the third germ layer; it forms between the endoderm and ectoderm in triploblasts.
• The endoderm gives rise to the lining of the digestive tract (including the stomach, intestines, liver, and pancreas), as well as to the lining of the trachea, bronchi, and lungs of the respiratory tract, along with a few other structures.
• Carl Linnaeus, a Swedish botanist, published a system for classifying organisms in the 1700s which became the basis for the modern classification systems.
• The Linnaean classification system consists of a hierarchy of groupings called taxa (singular, taxon) which includes the kingdom, phylum, class, order, family, genus and species.
• The kingdom is the largest group and the most inclusive while the species is the smallest and most exclusive group in the Linnaean classification system.
• Carl Linnaeus, also known as the father of taxonomy, developed a method of naming organisms, binomial nomenclature, which ensures the unique identification of the species.
• The Linnaean classification system underwent major revisions over the years, including the two-kingdom system introduced in 1735 by Linnaeus, the three-kingdom system introduced by Ernst Haeckel in the 1860s, and the four-kingdom system suggested by Herbert Copeland in 1956.
• The two-kingdom system of classification by Linnaeus distinguished two kingdoms of living things: Animalia for animals and Plantae for plants, classifying organisms based on nutrition and locomotion.
• The three-kingdom system of classification by Haeckel distinguished the organisms into three kingdoms: Animalia, Plantae, and Protista, accommodating the organisms that exhibited characteristics common to both plants and animals or were absent in the kingdoms introduced by Linnaeus, and classifying organisms based on morphological complexities and tissue system, division of labour, and mode of nutrition.
• Herbert Copeland suggested a fourth kingdom, kingdom Monera, which was composed of the prokaryotes (bacteria and blue-green algae), in 1956, these being the organisms that lack membrane-bound organelles.