Define a taxon. Give some examples of taxa at different hierarchical levels.

Define a taxon. Give some examples of taxa at different hierarchical levels.

Source: NCERT Class 11 Biology Chapter 1 – The Living World Question 6

A taxon (plural: taxa) is a group of organisms that are classified together based on similarities and differences in their characteristics. The taxa are arranged in a hierarchical system, with each level of the hierarchy representing a different degree of similarity between the organisms. The major hierarchical levels in taxonomy are:

Kingdom: This is the highest level of classification, and it groups organisms into broad categories based on fundamental characteristics, such as whether they are prokaryotic (bacteria) or eukaryotic (animals, plants, fungi).

Phylum: This level of classification groups organisms that are more closely related than those in different kingdoms, based on more specific characteristics such as body plans, internal structure and physiology.

Class: This level of classification groups organisms that share even more similarities and characteristics,

Order: This level of classification groups organisms that are even more closely related,

Family: This level of classification groups organisms that share many characteristics,

Genus: This level of classification groups organisms that are very closely related,

Species: This is the most specific level of classification, and it groups organisms that can interbreed and produce viable offspring.

Some examples of taxa at different hierarchical levels:

Kingdom: Plantae (plants)

Phylum: Chlorophyta (green algae)

Class: Magnoliopsida (dicotyledons)

Order: Asterales (asters and daisies)

Family: Asteraceae (daisy family)

Genus: Helianthus (sunflowers)

Species: Helianthus annuus (common sunflower)

It is important to notice that the classification systems are always subject to revision as new data becomes available and our understanding of the relationships between different organisms evolves.

Additionally to the traditional Linnaean system of classification, there are other systems that have been proposed to arrange the organisms such as the Phylogenetic system which is based on evolutionary relationships instead of morphological features, this approach is known as Phylogenetics.

In phylogenetics, taxa are known as clades, these are groups of organisms that share a common ancestor and includes the ancestor itself and all its descendants. The clades are arranged in a tree-like structure, which is called a phylogenetic tree, that reflects the evolutionary relationships between different groups of organisms.

For example, in the animal kingdom, one of the main clades is the bilateria, which includes all animals that have bilateral symmetry, such as worms, insects, fish, birds, and mammals.

Another system is the cladistics which is a method of inferring evolutionary relationships among species based on the presence or absence of certain characteristics. Cladistics aims to identify the most recent common ancestor for each group of species and to arrange these groups in a nested hierarchy of clades, each of which represents a monophyletic group, which is defined as consisting of an ancestral species and all of its descendants.

Taxa, whether they are clades or Linnaean taxa, are important tools for understanding the diversity of life on Earth and the relationships between different groups of organisms. They provide a way to organize and communicate information about different species and make predictions about their behavior and ecology.