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Classification of Living Things

Chapter 7

7 – 1 Classification

1.5 million different living things known

Thousands each year discovered

Various sizes

Taxonomy – branch of biology

Naming living things

Supermarket organization

Early Classification Schemes

Two major groups

Plant kingdom and animal kingdom

Subdivisions

Plants – grasses, herbs, trees

Animals – fish, creeping creatures, fowl, beasts, cattle

Fourth century B.C.

Aristotle – animals:

air-dwellers, land-dwellers, water-dwellers

Theophrastus – plants

Stem structure

mid-1600’s – John Ray

18,000 different types of plants and animals

Genus

Carolus Linnaeus – founder of modern taxonomy

Background

Linnaeus published his system of taxonomy in a book entitled Systema Naturae ( Classification of Nature ). Originally published in 1737, it went through 10 editions by 1758. His classification system allowed for the addition of new species. Also, because his classification system was easily adapted to the modern system of classification based on evolutionary relationships.

Classification Categories

Kingdom

Phylum

Class

Order

Family

Genus

Species

Background

The modern classification system is analagous to the system for addressing mail. First, the country to which a letter is being sent must be identified; then, the correct state; then, the right city; then, the proper street; the, the family name; and finally, the first name of the individual to whom the letter is addressed.

Naming Organisms

Nomenclature

Binomial nomenclature

Scientific name

Two word Latin name

The number of shared characteristics of each group becomes greater as one moves from phylum to species.

Classification categories are sometimes subdivided. For example a phylum may be divided into several subphyla. A single species may be divided into subspecies.

Background

When naming a new species, taxonomists designate a single specimen of a species as the official standard for the species. This is called the type method.

The new definition of a species is applicable to organisms that reproduce sexually. For organisms that reproduce asexually, such as the ameba and paramecium, structural characteristics are used to distinguish between species.

Modern Taxonomy

Species – natural group or population

Theory of evolution – new species arise, or evolve, over long periods of time from preexisting species.

Phylogeny – is the evolutionary history of a species or a group of organisms.

Information used to classify

Structural

Biochemical

Cytological

Embryological

Behavioral

Fossil

Taxonomy in Perspective

Taxonomy is a dynamic and important field of biology.

Background: The rules governing the naming of organisms are provided in three publications:

The International Code of Botanical Nomenclature

The International Rules of Zoological Nomenclature

The International Bacteriological Code of Nomenclature

7.2 Major Taxonomic Groups

Early classification: two groups – plants and animals

Six –kingdom system ( figure 7-9, p.133 )

Archaebacteria ( Prokaryotic )

Eubacteria ( Prokaryotic )

Protista ( Eukaryotic )

Fungi are molds, yeast, mushrooms, rust, smuts

Plantae are mosses, liverworts, ferns, seed plants

Animalia are multicellular, organ or organ system level of organization

Biologists use a procedure

Taxonomic key is a tool used to identify organisms already classified by taxonomists.

Most keys are dichotomous.

Series of paired statements.

Each set of choices are arranged in such a way that each step produces a smaller grouping.

Evolution: A Unifying Theme

As a unifying theme in biology, evolution explains why there is such diversity of life on earth today as well as how various groups of organisms are related. It is also explains how the organisms of today are related to organisms of the past.

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