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Classification of Organisms. Classifying Organisms. One important branch of biology investigates biodiversity , the variety of organisms considered at all levels from populations to ecosystems.

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Classifying organisms
Classifying Organisms

  • One important branch of biology investigates biodiversity, the variety of organisms considered at all levels from populations to ecosystems.

  • Since the early 1980’s Terry Erwin & others have been working to catalog insect species in plots of tropical rain forest

    • They fog the treetops with insecticide & catch the falling insects in a net

Classification is

A way of grouping objects together based on similarities

In the beginning---plants were grouped based on people who ate them—



The history of the Tomato-1820 Colonel Robert Gibbon Johnson announced that at noon on September 26, he would eat a basket of tomatoes in front of the Salem NY courthouse—aka “love apple”

Classification is…

Aristotle greek philosopher

Developed 1st method of classification

Classified into 2 major groups

Plants: herbs, shrubs or trees

Animals: According to where they lived: land, water or air

Aristotle: Greek Philosopher

Carolus linnaeus

Swedish naturalist

Methods still used today

Selected physical characteristics based on close relationships of organisms

Each category represents a level of grouping from larger, more general to smaller, more specific categories

Plants: based on reproductive structures

Animals: based on evolutionary traits

Carolus Linnaeus

Carolus linnaeus1

Invented the 2-word naming system to identify species


Bi (2) Nomial (name)

Scientific Name:

Genus: 1st word: consist of closely related species

Species: 2nd word: consist of description of the species.

Carolus Linnaeus

Rules of binomal monemclature

Genus is ALWAYS capitalized & is 1st

Species is ALWAYS lowercase & is 2nd


Homo sapiens

Felix tigerus

F. leo

F. domestica



  • Species names come from Latin roots and are needed to be the same for all countries and in every language

  • The name of a species is often descriptive


  • Biologists refer to variations of a species that live in different geographic areas as subspecies

  • A subspecies name follows the species identifier

Subspecies alabama beach mouse
Subspecies: Alabama Beach Mouse

This mouse is one of several subspecies of old field mice which live only in coastal sand dune areas. Living isolated from other beach mice for thousands of years has allowed each subspecies to develop its own slightly unique characteristics suited to its particular beach environment.

Peromyscus polionotus ammobates

Other Subspecies: Perdido Key beach mouse, Choctawhatchee beach mouse, Santa Rosa beach mouse, and St. Andrews beach mouse. They differ from the ABM and each other in coloration and body size

Classification of organisms

Scientific & Common Names

Many organisms have common names that can be misleading.

Example: a sea horse is a fish, not a horse.

Also, it is confusing when a species has more than one common name.

Common names

Do not tell you how organisms are related or classified

Can be misleading

Confusion can occur when organisms have more than one name

All newly discovered species are given Latin names because it is no longer used

Common Names

Taxonomy is
Taxonomy is…

  • Taxonomy (tak SAH nuh mee) is the branch of biology that groups and names organisms based on studies of their different characteristics

  • Biologists who study taxonomy are called taxonomists


  • Is a useful tool – if a child has eaten a mushroom & You do not know whether it is poisonous…

  • Important to the economy- often discover new sources of lumber, medicines & energy…

Dichotomous key

Organisms can be identified easily by using a dichotomous key

Animals around the world use the same identification system

A key is made up of sets of numbered statements. Each set deals with a single characteristic of an organism, such as leaf shape or arrangement

Dichotomous Key

Systematic key

  • More than 200 years ago, Linnaeus grouped organisms according to similarities that he could readily see.

  • Modern biologists consider not only visible similarities, but also similarities in embryos, chromosomes, proteins, and DNA

  • Systematics is the classifying of organisms in terms of their natural relationships

Cladistics key

  • In 1966, Willi Hennig developed cladistics, a system of phylogenetic analysis that uses shared or derived characteristics as the only criteria for grouping taxa

How are evolutionary relationships determined
How are evolutionary relationships determined? key

  • Evolutionary relationships are determined on the basis of similarities in structure, breeding behavior, geographical distribution, chromosomes, and biochemistry.

  • The presence of many shared physical structures implies that species are closely related and may have evolved from a common ancestor.

1 structural similarities
1. Structural similarities key

  • For example, plant taxonomists use structural evidence to classify dandelions and sunflowers in the same family, Asteraceae, because they have similar flower and fruit structures.

  • Taxonomists observe and compare features among members of different taxa and use this information to infer their evolutionary history.

2 breeding behavior
2. Breeding Behavior key

  • Sometimes, breeding behavior provides important clues to relationships among species.

  • For example, two species of frogs, Hyla versicolor and Hyla chrysoscelis, live in the same area and look similar. During the breeding season, however, there is an obvious difference in their mating behavior.

  • Scientists concluded that the frogs were two separate species.

Gray Treefrog

Gray Treefrog

3 geographical distribution
3. Geographical Distribution key

















Ancestral Species

Classification of organisms

Geographical distribution key

  • These finches probably spread into different niches on the volcanic islands and evolved over time into many distinct species. The fact that they share a common ancestry is supported by their geographical distribution in addition to their genetic similarities.

4 chromosomal comparison
4. Chromosomal Comparison key

  • Both the number and structure of chromosomes, as seen during mitosis and meiosis, provide evidence about relationships among species.

    • For example, cauliflower, cabbage, kale, and broccoli look different but have chromosomes that are almost identical in structure.

  • Therefore, biologists propose that these plants are related.

Classification of organisms

Phylogenetic Classification: Models key

  • The evolutionary history of a species is called its phylogeny (fy LAH juh nee).

  • A classification system that shows the evolutionary history of species is a phylogenetic classification and reveals the evolutionary relationships of species.

Cladistics key

  • One biological system of classification that is based on phylogeny is cladistics (kla DIHS tiks).

  • Scientists who use cladistics assume that as groups of organisms diverge and evolve from a common ancestral group, they retain some unique inherited characteristics that taxonomists call derived traits.

Shared characteristics
Shared characteristics key

  • Is a feature that all members of a group have in common

  • Example: hair in mammals or feathers in birds

Derived characteristics
Derived characteristics key

  • Is a feature that evolved only within the group under consideration

  • Example: feathers are though to be a derived characteristic for birds b/c scientists hypothesize that feathers evolved only within the bird lineage and were not inherited from the ancestors that birds share with reptiles

Classification of organisms

Cladistics key







Feathers with

shaft, veins,

and barbs

Flight feathers;

arms as long

as legs

3-toed foot;




Light bones

Order of taxa

A group of organisms is called a taxon (plural, taxa key

The smallest taxon is species. Organisms that look alike and successfully interbreed belong to the same species.

The next largest taxon is a genus—a group of similar species that have similar features and are closely related

Order of Taxa



Order of taxa1
Order of Taxa key

  • Kingdom, Phylum, Class, Order, Family, Genus, & Species

    Can you remember it this way?

  • King Phillip Came Over For Graduation Saturday.

  • Kings Play Chess On Fine Glass Surfaces.

Important facts
Important Facts key

  • Linnaeus version of hierarchy of organization was made of only 2 kingdoms-animals & plants

  • Modern biologists adopted his system, but added several other kingdoms, as well as domains (categories above kingdoms)

  • **there are 3 domains of life

Classification of organisms

Eukarya key





















3 domains of life

The three domain names are Bacteria, Archaea, and Eukarya key

All living things seem to be related by ancestry to one of these

3 Domains of Life

Domain bacteria
Domain Bacteria key

  • Is made of small, single-celled prokaryotic organisms

  • Usually have a cell wall & reproduce by cellular reproduction

  • Each bacteria has a cell wall, plasma membrane, cytoplasm (that lacks organelles)

  • Do not have a true nucleus

  • Oldest known fossils appear as bacteria

Domain archaea
Domain Archaea key

  • Consist of prokaryotes named Archaea

  • Have distinctive cell membranes, & genetic properties

  • Some are autotrophs

  • Some produce methane (as waste)

  • Many inhabit harsh environments (sulfur springs, deep-sea thermal vents, salty lakes…)

  • Thought to be the earliest organisms on Earth

Domain eukarya
Domain Eukarya key

  • Most familiar group

  • Consist of eukaryotic organisms

  • Have true nucleus, complex cellular organelles

  • Include Plants, Animals, Fungi, and a variety of single-celled organisms

Woese and the 6 kingdoms
Woese and the 6 Kingdoms key

  • Biologists Carl Woese proposed in 1977 a 6-kingdom system that divided the then 5 kingdom into two new kingdoms; Archaebactera and Eubacteria

  • In 1990, Woese introduced

    the 3 domain system that is

    still used today

Kingdom eubacteria
Kingdom Eubacteria key

  • Aligns with the domain Bacteria

  • Eubacteria means “true bacteria” because it distinguishes this group from archaea which are no longer considered to be bacteria

Blue-Green Bacteria

Kingdom archaebacteria
Kingdom Archaebacteria key

  • Aligns with the domain Archaea

  • Archaebacteria means “ancient Bacteria”

  • Are found in extreme habitats where there is usually no oxygen available



Thermal Vents

Kingdom protista

Eukaryote that are not plants, animals or fungi. key

Unicellular organisms

Examples are amoebas, paramecium, euglenas, Seaweed, Diatoms…

Kingdom Protista

Kingdom fungi

Unicellular or multi-cellular eukaryote that absorbs nutrients from organic materials in the environment

There are around 70,000 species of fungi

Include puffballs, mushrooms, rusts, smuts, mildew, and molds.

Kingdom Fungi

Kingdom plantae

Consist of eukaryotic, autotroph, multicellular plants that contain chloroplasts, use photosynthesis and have cell walls

There are more than 250,000 known species of plants

Kingdom Plantae

Kingdom animalia

Animals are eukaryotic, multicellular heterotrophs that develop from embryos

Most have symmetrical body organization & move around their environment to find food

Nearly all are able to move from place to place.

Animal cells do not have cell walls

Kingdom Animalia

Future taxonomic systems
Future taxonomic systems develop from embryos

  • Because taxonomy systems are changing, modern biologists are suggesting changes for the now six-kingdom, three-domain system

  • Suggestions like subkingdoms…