Classification of Living Things (Taxonomy)

Learning Objectives

Explain why scientists classify living things.

List the major levels of classification in order from broadest to most specific.

Describe the system of binomial nomenclature for naming species.

Identify the six kingdoms of life.

Organizing the Web of Life

There are millions of different species on Earth. To study them, biologists need a way to organize them into groups based on their shared characteristics. Taxonomy is the science of classifying and naming living things.

The Linnaean System

The system we use today was developed by Carl Linnaeus. It's a hierarchical system with several levels, like a set of nesting boxes. The levels go from the broadest, most inclusive category to the most specific.

The eight major levels are:

1.Domain (Broadest)

2.Kingdom

3.Phylum

4.Class

5.Order

6.Family

7.Genus

8.Species (Most Specific)

A good mnemonic to remember this order is "Dear King Philip Came Over For Good Soup."

Binomial Nomenclature: A Two-Part Name

Linnaeus also created a system for naming organisms called binomial nomenclature. Every species is given a unique, two-part scientific name.

The first part is the Genus, and it is always capitalized.

The second part is the species, and it is always lowercase.

The entire name is written in italics.

For example, the scientific name for a wolf is Canis lupus. The name for humans is Homo sapiens. This universal system allows scientists all over the world to communicate clearly, regardless of their language.

The Six Kingdoms

All living things are broadly sorted into six major kingdoms:

Archaebacteria: Ancient, single-celled organisms that often live in extreme environments (like hot springs).

Eubacteria: Common, single-celled bacteria found all around us.

Protista: A diverse group of mostly single-celled eukaryotes (cells with a nucleus), like amoebas and algae.

Fungi: Multicellular decomposers that absorb their food, like mushrooms and molds.

Plantae: Multicellular organisms that make their own food through photosynthesis.

Animalia: Multicellular organisms that eat other organisms for energy and are able to move.

Key Terms

Taxonomy: The scientific study of how living things are classified.
Binomial Nomenclature: The two-part scientific naming system for organisms, consisting of the genus and species.
Genus: A classification grouping that consists of a number of similar, closely related species.
Species: A group of similar organisms that can mate with each other and produce fertile offspring.
Kingdom: The second broadest level of taxonomic classification.