You will learn the concept of classification, why its important, and how to build a simple classification system.
After completing this tutorial, you will be able to complete the following:
The almost 2 million species on Earth are ordered into a grand scheme of taxonomic classification, in which organisms are grouped into larger and larger taxa representing their descent from common ancestors. However, scientists cannot immediately classify every specimen they encounter. A taxonomic key is used to identify different species.
A dichotomous key is a specific type of taxonomic key that allows similar organisms to be identified using a series of descriptions or statements, called leads, which are arranged in pairs. For each pair, the user chooses the lead that applies to the specimen. Depending on the lead that is chosen, the key either identifies the organism or directs the user to another pair. The process is repeated until the specimen is identified.
A key may identify a specimen at the level of species, but many keys limit identification to larger taxonomic categories such as genus, family, or order. A good key uses specific and quantitative criteria whenever possible and may be limited to a certain life cycle (e.g., mature earthworms or adult insects). For species whose color changes seasonally (e.g., some birds), a key may rely less on color as a criterion.
A dichotomous key does not often represent a phylogenic category or classification scheme but is instead an ecologically relevant guide to species that inhabit an area together. The nodes and branches in a dichotomous key do not necessarily correspond with the branches and nodes of the organisms' phylogeny. Dichotomous keys are used by ecologists, microbiologists, entomologists, and marine biologists, among others.
|Approximate Time||25 Minutes|
|Pre-requisite Concepts||Students should be familiar with the terms kingdom and species.|
|Type of Tutorial||Concept Development|
|Key Vocabulary||biology, classification, classify, dichotomous key method, taxonomic key, taxonomy|