Systematics of Living Organisms
1) Systematics:“Systematics is the study of kinds and diversity of organisms and their comparative and evolutionary relations (G. Simpson,1961).
2) Taxonomy: Taxonomy means the classification following certain rules or principles. Word Taxonomy comes from two Greek words, taxis-meaning arrangement, and nomous meaning law or rule. The term taxonomy was first introduced by A.P.de Candolle (Swiss Botanist)[1778-1841].
3) Classification: Arrangement of organisms or groups of organisms on the basis of similarities and dissimilarities among them.
4) Artificial classification: It is the classification that is based on a few easily observable and non-evolutionary feature such as habit, color, form, etc: often irrespective of their affinity(relationship) with other organisms. e.g Linnaeus systems of classification.
5) Natural Classification: Classification based on objectively significant Character which includes external and internal character. E.g Bentham and Hooker’s system of classification.
6) Phylogenetic classification: It is the classification based on common evolutionary descent. E.g. Engler and Prantles classification.
7) Taxa or Taxon: It is referred to as a concrete unit of classification which represents the group of one or more population of a living organism (H.J. Lam 1948).
8) Category: It is a level or a rank given to the particular taxa or taxon in classification.
9) Three domains of life: Carl Woese in 1990 proposed three domains of life to classify life forms. They are Archaea, Bacteria, and Eukarya. A domain is a unit larger than the Kingdom in the system of classification.
10) Chemotaxonomy: Classification based on chemical constituents of organisms.
11) Numerical Taxonomy: The system is based on the quantification of character and develops an algorithm for classification.
12) Cladogram: It is a typical branching pattern which represent a hypothetical relationship denoting a comparison of organisms and their common ancestors.
13) Phylogeny: It is the study of relationships among different groups of organisms during evolution.
14) DNA Barcoding: DNA barcoding, is a new method for the identification of any species based on its DNA sequence from a tiny tissue sample.
15) Taxonomic Categories: Classification involves a hierarchy of steps in which each step represents a rank or category.
16) Compulsory categories / obligate categories:
There are 7 compulsory categories. These are
kingdom, Division/Phylum, class, Order, Family, Genus, Species.
17) Facultative categories: Categories present between compulsory categories are called facultative or intermediate categories. E.g. Sub-order, Sub-family etc.
18) Species: It is a group of organisms that can interbreed among themselves under the natural conditions to produce fertile offspring. It is the principal natural taxonomic unit.
19) Genus: Genus is a group of species bearing a close resemblance to one another in their morphological characters but they do not interbreed. E.g. Tiger, Leopard, Lion all three belong to the same genus "Panthera".
20) Family: A family represents a group of closely related genera. e.g. genera like Hibiscus, Gossypium, Sida, Bombax are included in the same family Malvaceae.
21) Cohort/Order: An order is a group of closely related families showing definite affinities.
22) Class: Class is the assemblage of closely related orders. Orders Carnivora and order Primates belong to class Mammalia. Thus monkeys, gorillas, gibbons(Primates) and dogs, cats, tiger(Carnivora) belong to the same class.
23) Division/Phylum: The division is a category composed of related classes e.g. division. Angiospermae includes two classes Dicotyledonae and Monocotyledonae (In animal classification division is a sub-unit of category/Phylum).
24) Sub-Kingdom: Different divisions having some similarities form sub-kingdom. E.g.The divisions Angiospermae and Gymnospermae belong to the sub-kingdom Phanerogams or Spermatophyta.
25) Kingdom: It is the highest taxonomic category composed of different sub-kingdoms e.g sub-kingdom Phanerogams and Cryptogams form the Plant kingdom or Kingdom Plantae which include all the plants while all animals are included in Kingdom-Animalia.
26) Vernacular / Local names / Common names:
The name which is given to the organism by the local people in their local language is called the vernacular name. these names are short and easy to remember.
27) Scientific name: To overcome the difficulties raised by common names, scientists have given scientific names to all the known organisms.
28) Binomial nomenclature: The act of naming any organism by giving two names is called binomial nomenclature. in binomial nomenclature, the first name indicates the name of the genus while the second name indicates the name of the species.
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29) ICBN: International Code of Botanical Nomenclature(ICBN) has been set up to confirm the scientific names.
30) Two kingdom classification system:
Carl Linnaeus classified living organisms in two kingdoms based on the mode of nutrition, whether they are migratory, sedentary.
31) Five kingdom classification system:
R.H Whittaker (1969) proposed Five Kingdom system of classification. This system shows the Phylogenetic relationship between the organism. The five kingdoms are
1) Kingdom Monera :
2) Kingdom Protista
3) Kingdom Plantae
4) Kingdom Fungi
5) kingdom Animalia
32) Kingdom monera: It contains unicellular organisms with prokaryotic cellular organization.
33) Omnipresent: The organism which is found everywhere is called omnipresent.
34) Photoautotrophs: The autotrophic organisms using sunlight as a source of energy to prepare their food are called photoautotrophs.
35) Chemoautotrophs: The autotrophic organisms using some chemicals as a source of energy to prepare their food are called chemoautotrophs.
36) Nucleoid: In Prokaryotes, DNA exists as a simple double-stranded circular single chromosome called a nucleoid. It lacks a nuclear membrane, Nucleolus and histone protein.
37) Plasmid: Smaller circular molecules of DNA that exist as extrachromosomal genetic elements called plasmids.
38) Cell wall: It is the outermost rigid protective layer which is presents in plant cell and Monerans. In Monerans, the cell wall is made up of peptidoglycan or murein which is a polymer of sugars and amino acids while in plant cells it is made up of cellulose.
39) Coccus: Spherical shape bacteria.
40) Bacillus: Rod shaped Bacteria.
41) Vibrio: Comma shaped bacteria.
42) Spirillum: Spiral shaped bacteria.
43) Archebacteria: The bacteria mostly found in the extreme environment. These are also known as extremophiles e.g. Methanogen (Found in marshy areas and rumen of cattle), Halophiles(Found in salty water), Thermoacidophiles (Found at high temperature and acidic medium).
44) Eubacteria: These are true bacteria with cell wall made up of peptidoglycan e.g Chlorobium (Green sulphur bacteria) and Chromatium.
45) Mycoplasma: These are the smallest of living form which does not possess a cell wall. These are also called PPLO (Pleuro Pneumonia Like Organism).
46) Kingdom Protista: This group includes all the unicellular but eukaryotic organisms. These organisms showed a link with all eukaryotic Kingdoms like Plantae, Fungi, and Animalia.
47) Plant-like Protist: These are known as Chrysophytes or Phytoplanktons. They are microscopic and mostly photosynthetic. They are chief producers of ocean E.g Diatoms.
48) Animal-like protists: They are also termed protozoans. They lack a cell wall. They are heterotrophs. They are believed to be the primitive animal forms.
49) Dinoflagellates: These are aquatic, Photosynthetic protistan organisms with a cell wall made up of cellulosic stiff plates of photosynthetic pigments which can be yellow, green, brown, blue, and red.
50) Red tide: Red tide is red due to the presence of Gonyaulax which is a dinoflagellate.
51) Fungi-Like Protist: They are commonly from the group Myxomycetes. These are saprophytic organisms found on decaying leaves.
52) Plasmodium: Myxomycetes aggregates to form a large cell mass called Plasmodium (Note: It is not a malaria parasite).
53) Euglenoids: Protistan which lacks cell wall but process a tough proteinaceous covering called Pellicle. These are flagellated heterotroph but can synthesize food in the presence of light like higher organisms.
54) Kingdom Plantae: Members of this kingdom are multicellular, having eukaryotic cells containing chlorophyll.
55) Insectivorous plant: These are semi-autotrophic plants. e.g: Venus flytrap, Pitcher plant
56) Kingdom Fungi: These are eukaryotic heterotrophs showing extracellular digestion. They are found in warms and humid places. They have a simple body that may be unicellular or made up of a long thread-like structure called hyphae.
57) Mycelium: In filamentous fungi, hyphae are interwoven to form a network-like structure called mycelium.
58) Coenocytic hyphae: The non-septate, multinucleate hyphae are called coenocytic hyphae
59) Chitin: The cell wall of the fungal cell is composed of a polysaccharide called chitin. It is also called fungal cellulose.
60) Phycomycetes: These are commonly called algal fungi. Mycelium is made up of aseptate coenocytic hyphae. e.g. Mucor, Rhizopus (bread mold), Albugo (Parasitic fungus on mustard).
61) Ascomycetes: These are called as sac-fungi. These fungi are mostly multicellular. Rarely unicellular varieties like yeast. The hyphae are branched and septate. e.g. Aspergillus, Penicillium, Claviceps, Neurospora, Saccharomyces.
62) Coprophilous: The fungi which grow on animal dung is called coprophilous.
63) Deuteromycetes: These are called imperfect fungi, which are known to reproduce only asexually. e.g Alternaria, Colletotrichum.
64) Basidiomycetes: These are commonly called club fungi. They have branched, septate hyphae. Eg Agaricus (mushrooms), Ganoderma(bracket fungi), Ustilago (smuts), Puccinia (rusts) etc.
65) Kingdom Animalia: Members of this kingdom are heterotrophs; adapted to holozoic nutrition.
66) Virus: Viruses, are groups of acellular organisms which are inactive outside a host cell; but once they enter their specific host cell, they take charge of the cellular machinery of the host cells and duplicate themselves. Viruses thus can be called infectious nucleoprotein particles.
67) Capsid: Protein coat of virus is called a capsid which is made up of smaller units called capsomeres.
68) Bacteriophages: Viruses that infect bacterial cells are called bacteriophages.
69) Viroids: These are the smallest known infectious pathogen which is composed of a short strand of circular single-stranded RNA that has no protein. It was first reported by T.O. Diener in 1971 which causes Potato Spindle tuber disease.
70) Lichen: It is the Co-existence of algae and fungi for mutual benefit. Algal partners are called phycobionts and Fungal partners are called Mycobionts.
