Unit B

Module 3 ~ Lesson 4

Taxonomy

Much like the periodic table of elements is universal to all scientists to identify the natural elements, biologists have developed rules of taxonomy that allow scientists to easily identify and communicate about species in an ecosystem.

There is estimated to be somewhere between 10 and 100 million different species of organisms in the world. The field of taxonomy is the practice of classifying organisms. All organisms are classified into three domains. The three domains are Bacteria, Archaea, and Eukarya.

These rules of taxonomy are why a robin and a human are named differently. Different names are given to different organisms so that people are able to communicate better.

By Annina Breen [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons

The domain system is an evolutionary model of classification based on cell structure. This system proposes that a common ancestor cell gave rise to three different cell types, each representing a domain.

The three domains are the Archaea (archaebacteria), the Bacteria (eubacteria), and the Eukarya (eukaryotes). The Eukarya are then divided into four kingdoms: Protists, Fungi, Animalia, and Plantae. Organisms are placed into kingdoms depending on cell type, their ability to make food, and the number of cells in their body. For example, a daisy is classified as part of the Plantae kingdom because it is multi-cellular, it contains a nucleus, it contains a chloroplast that carries out photosynthesis, and the cells have a cell wall.

Domains are subdivided into kingdoms. There are four kingdoms in the Eukarya domain: Protista, Fungi, Plantae, and Animalia. Each of these kingdoms is further subdivided into phyla, then class, order, family, genus, and species. Within each subdivision, the groups become more and more similar in physical characteristics and genetic makeup

Read

Read "The Classification of Organisms", "Classification in Transition", "The Three Domains of Life", and "The Levels of Classification" on pages 85 to 88 of your textbook.

Self-Check

Why are fungi no longer classified in the same Kingdom as plants?

While fungi do not move, they lack chloroplasts and are not photosynthetic; they use digestive enzymes to break down food sources into absorbable molecules.

What is the benefit for scientists to use binomial nomenclature rather than common names?

Scientific names are universal, whereas a common name may be confusing and not the same in different regions. For example, panther, puma, and mountain lion all refer to the same species, Puma concolor.