Classification Notes

1. Taxonomy is the branch of biology concerned with the grouping and naming of organisms. It is the science of naming and classifying organisms. Biologists who study taxonomy are called taxonomists.

2. Classification is the grouping of objects or information based on similarities. It is one tool early scientists have used to gain understanding of nature.

1. Aristotle’s system (more than 2,000 years ago)
   • Plants were classified as herbs, shrubs, and trees.
   • Animals were grouped according to where they lived- on land, in the air, or in the water.
   • Later observations convinced scientists that Aristotle’s system did not work. They observed that some animals, such as frogs, live both on land and in water. Scientists also realized that Aristotle’s classification system did not show natural relationships among organisms.
2. Carolus Linnaeus ( 18^th century Swedish botanist)—founded taxonomy
   • Binomial nomenclature is a system by which each species is given a 2 word Latin name.
   • Linnaeus selected physical characteristics that led to classification based on close relationships of organisms.

Example for plants: He based his classification of flowering plants on the numbers and similarities of their reproductive structures.

Example for animals: He selected characteristics of organisms that also led eventually to classifications based on evolutionary relationships.

·        Linnaeus’ system uses 2 scientific names:

The first part of the name is the genus- - Genus refers to the relatively small group of organisms to which a particular type of organism belongs.

The second part of the name is the species- -This is usually a description of some important characteristic.

            Example: Red maple- - common name

                          Acer rubrum- -scientific name

Common names are the everyday names given to organisms.  An organism can have several common names for the same organism; however, the scientific name is always the same for a specific organism.

A scientific name is composed of the genus and species.

There are 3 Rules to Follow When Writing Scientific Names:

1.      Always capitalize the genus name.

2.      Always leave the species in lower case.

3.      Always underline both names (unless typing use italics).

Example: Homo sapiens - -humans or if typing, Homo sapiens

                        Felis domesticus- cat       Canis familiaris- dog          Rana pipiens- frog

Classification system of organisms from largest to smallest:

Kingdom - Phylum or Division – Class – Order – Family – Genus – Species

Ex: The leopard frog is known by the scientific name Rana pipiens. The wood frog is known as Rana sylvatica.

What is the smallest classification division these frogs have in common? ___________

Taxonomists have developed special guides known as dichotomous keys to aid in identifying organisms. A dichotomous keys consists of several pairs of descriptive statements that have only two alternative responses. 

Branching Diagrams--shows the evolutionary relationships between organisms that are in the same kingdom

A branching diagram like the one shown can be made by using a dichotomous key.

Each unique characteristic, such as lungs, that is used to assign an organism to a group is how scientists assign names.

A branching diagram shows what makes each species unique from the other, that they came from a common ancestor and the evolutionary relationships between them.     

6 kingdoms—Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia

*Note: The first kingdom used to be referred to as the kingdom Monera (bacteria), which now is divided into Archaebacteria (archae means ancient) and Eubacteria.

The phylogenic tree below shows how organisms are divided into 6 kingdoms.

 A. Fungi; B. Eubacteria; C. Protista; D. Archaebacteria

1. prokaryote: no nucleus

2. eukaryote: have a nucleus

3. peptidoglycan: carbohydrates that fill the outside layer of the plasma  membrane

4. autotrophic: when an organism captures energy from sunlight or chemicals and uses it to produce its own food from inorganic compounds (producer)

5. heterotrophic: when an organism obtains energy from foods it consumes (consumer)