Name: Date: Period:
Classification Notes
Section 1: Finding Order in Diversity
Why Classify?
· Natural Selection and other processes have led to a staggering diversity of organisms.
· Biologists have identified and named about 1.5 million species so far.
· They estimate that 200-100 million additional species have yet to be discovered.
How do we classify organisms?
To study the diversity of life, biologists use a classification system to name organisms and group then in a logical manner.
Taxonomy
In the discipline of taxonomy, scientists classify organisms and assign each organism a universally accepted name. When taxonomists classify organisms, they organize them into groups that have biological significance.
Assigning Scientific Names
Common names of organisms vary, so scientists assign one name for each species. Because 18th century scientists understood Latin and Greek, they used those languages for scientific names. This practice is still followed in naming new species.
Early Efforts at Naming Organisms
The first attempts at standard scientific names described the physical characteristics of a species in great detail. These names were not standardized because different scientists described different characteristics.
Binomial Nomenclature
Carolus Linneaus developed a naming system called binomial nomenclature.
In binomial nomenclature, each species is assigned a two-part scientific name.
· The scientific name is italicized.
· The first part of the name is capitalized. This part of the name is the genus to which the organism belongs. A genus is a group of closely related species.
· The second part of the name is lowercased. This part is unique to the species and usually describes important trait or where the organism lives.
Write the scientific name for grizzly bear. Ursus arctos
Ursus matitimus is the scientific name for what animal? Polar bear
What does matitimus mean in Latin? Sea
Linnaeus’s System of Classification
Linnaeus not only named species, he also grouped them into categories.
List the 7 levels of classification starting with the smallest to largest.
1. Species
2. Genus
3. Family
4. Order
5. Class
6. Phylum
7. Kingdom
Each level is called a taxon, or taxonomic category. Species and genus are the two smallest categories.
Have we increased or decreased the amount of complexity over the years?
Name: Date: Period:
Classification Notes
Section 2: Modern Evolutionary Classification
Linnaeus grouped species into larger taxa mainly according to visible similarities and differences. How are evolutionary relationships important in classification?
Phylogeny is the study of evolutionary relationships among organisms.
Evolutionary Classification
Biologists currently group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities.
The strategy of grouping organisms is based on evolutionary history and is called evolutionary classification.
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Two Different Methods of Classification
· Superficial Similarities - once led barnacles and limpets to be grouped together.
· Tracing Ancestry – barnacles and crabs share an evolutionary ancestor that is more recent than the ancestor that barnacles and limpets share. Barnacles and crabs are classified as crustaceans, and limpets are mollusks.
Classification Using Cladograms
Many biologists now use a method called cladistic analysis. Cladistic analysis identifies and considers only new characteristics that arise as lineages evolve.
Charateristics that appear in recent parts of a lineage but in its older members are called derived characters.
Derived characters can be used to construct a cladogram, a diagram that shows the evolutionary relationships among a group of organisms. Cladograms help scientists understand how one lineage branched from another in the course of evolution.
A cladogram shows the evolutionary relationships between crabs, barnacles, and limpets.
Similarities in DNA and RNA
The genes of many organisms show important similarities at the molecular level. Similarities in DNA can be used to help determine classification and evolutionary relationships.
DNA evidence shows evolutionary relationships of species. The more similar the DNA of two species, the more recently they shared a common ancestor, and the more closely they are related in evolutionary terms.
The more two species have diverged from each other, the less similar their DNA will be.