Microbiology is one of the Biology Topics that involves the study of microorganisms, including bacteria, viruses, and fungi.
Explain the term Species and Hierarchical Classification
The main aim of a taxonomic study is to assign an organism an appropriate place within the systematic framework of classification. This framework is called a taxonomic hierarchy by which the taxonomic groups are arranged in a definite order, from higher to lower categories. A category is called a taxon (plural taxa). The taxa or categories used in the classification of plants or animals are kingdoms, phylum, classes, orders, families, genera, and species. However, in the case of plants, the term division is used as a category in place of phylum, while the remaining categories have the same terminology. All the members of a taxon show similar characteristics, which are different from those of other taxa.
Linnaeus’s scheme of arranging organisms into an ascending series of groups of ever-increasing inclusiveness forms the hierarchical system of classification.
Both in animal and plant kingdoms, the lowest category is a species and the highest is a kingdom; the rest of the categories lie within this framework. The categories in the hierarchy are placed in ascending order. As we go upwards from the species towards the kingdom, the number of similar characters decreases.
1. Species:
It is a basic unit for understanding taxonomy as well as evolution. Species is a group of individuals with similar morphological characters, which are able to breed among themselves and produce fertile offspring of their own kind. Individuals of the same species resemble each other closely both structurally and functionally.
Linnaeus recognized only five hierarchic levels within the animal kingdom. These were Class, Order, Genus, Species, and Variety. Later on, ‘variety’ was discarded and two new taxonomic categories, namely, Phylum and Family were added to the Linnaean hierarchy. Thus, six taxonomic categories, namely, Phylum, Class, Order, Family, Genus, and Species form the basic taxonomic hierarchy of animals. Any given animal must belong to one of these six categories.
Example: Horse and ass belong to the same genera (Equus) but both have different species, i.e., Horse – E. cabalus and Ass – E. asinus.
Mule does not form a Distinct Species
It is important to note that the species is the basic level for all modern classifications. The species is an isolated reproductive unit that does not mate with members of other reproductive isolates. Thus, species are the most unambiguous of all taxa in the hierarchy. A species is a group of similar organisms that are able to breed together and produce fertile offspring. For example, human beings, dogs, cats, etc., form distinct species. But when a horse (Equus cabalus) and an ass (Equus asinus) belonging to different species interbreed, the product is a mule that is sterile, i.e., incapable of reproducing.
2. Genus:
It is a group of species that are related and have fewer characteristics in common as compared to species. Members of a genus have identical reproductive organs.
Example: Banyan and fig trees differ from each other in vegetative characteristics such as shape, size, and surface of the leaf, but resemble their reproductive organs such as inflorescence, flower, fruit, and seed. Thus, they belong to the same genus Ficus.
3. Family:
It is represented by a group of related genera that are more similar to each other than to the genera of other families.
Example: A cat (Felts domestica) and a lion (Panthera leo) belong to the “cat” family Felidae. They both possess similar structures and have retractive claws.
4. Order:
It is an assemblage of families resembling one another in a few characters.
Example: A tiger (Panthera tigris) and a wolf (Canis lupus) share common characteristics such as jaws with powerful incisors and large, sharp canines, adapted for flesh-eating. Hence, both are placed in the same order Carnivora.
5. Class:
It represents organisms of related orders.
Example: Chordates such as rats, dogs, bats, dolphins, camel, rhinoceros, kangaroos, and monkeys belong to the Mammalia class as they have a characteristic hairy exoskeleton, mammary (milk) glands, external ear, etc.
6. Phylum:
It includes all organisms belonging to different classes having a few common characteristics.
Example: All animals which have a notochord present in the embryo belong to the phylum Chordata.
7. Kingdom:
It includes all organisms that share a set of distinguishing common characteristics.
Examples: Plant kingdom, Animal kingdom, etc.
Classification of Some Organisms
| Taxa | Potato | Wheat | Paramecium | Human being |
| Scientific name | Solanum tuberosum | Triticum aestivum | Paramecium caudatum | Homo sapiens |
| Kingdom | Plantae | Plantae | Protista | Animalia |
| Phylum/Division | Angiospermae | Angiospermae | Protozoa | Chordata |
| Subphylum/Subdivision | – | – | Ciliophora | Vertebrata |
| Class | Dicotyledonae | Monocotyledonae | Ciliata | Mammalia |
| Order | Polemoniales | Germinates | Holotricha | Primates |
| Family | Solanaceae | Gramineae | – | Hominidae |
| Genus | Solanum | Triticum | Paramecium | Homo |
| Species | Tuberosum | Aestivum | Caudatum | Sapiens |