Module 11 Classification of Organisms Brainpop - Classification

I. Isn’t everything living thing either a plant or an animal? A. Aristotle is credited with the first true classification system. He grouped all living things into two basic groups: plant and animal. OR

B. Linnaeus further classified plants and animals by dividing them into related groups. He used the Latin language, because Latin was not longer spoken conversationally and thus was less likely to change. 1. He first grouped related organisms. He called this a genus. For example, all of the dog-like creatures were grouped as the genus Canis.

2. He next gave every different type of organism in the group a specific name, which he called specie. For example, the dog became Canis familiaris and the wolf Canis lupus. Notice the genus is capitalized but the specie begins with a lower case letter! Both are italicized or underlined.

What name do you use for this organism? Loxosceles reclusa (Brown Recluse) 3. Every organism was given a two-word name, the genus and specie. This practice of binomial nomenclature continues today, giving each organism a “scientific name”. 4. The benefit of binomial nomenclature includes eliminating confusion due to common names (ex. cottonmouth and water moccasin are actually the same animal) and allows scientists around the world to more easily communicate. What name do you use for this organism?

C. Even after the microbial world was discovered, the two “kingdom” system continued. (Yes, science can be very slow to change.) D. As knowledge of the diversity of organisms increased, Whittaker (in 1969) expanded classification to include five kingdoms.

E. The science of classification, taxonomy, now allowed scientists to assign seven levels of taxa to living organisms: King Phillip Came Over For Green Soup

1. The kingdom is the most general of these seven taxa, thus the kingdom would contain the greatest number of organisms. 2. Specie is the most specific of these seven taxa, thus the specie would contain only one type of organism. A specie is defined as a group of organisms which can interbreed and produce fertile offspring.

F. Today, we use three domains, which are divided into six kingdoms F. Today, we use three domains, which are divided into six kingdoms. These domains are based on new information about possible evolutionary relationships.

Which level is the most general? The most specific? At what taxonomic level do the dog and human become different? What is the family name of the dog? Which organism is most closely related to the dog? What is the scientific name of the dog? A genus is composed of a number of related? A group of related phyla are? Which taxon contains the largest # of organisms?

II. What happens when you find an organism and you are stymied? A. Dichotomous keys are tools that use a series of paired statements and the visible characteristics of the organism. Of course, a dichotomous key is only useful if the organism has already been classified and given a scientific name.

1. Always start at statement 1 (or the beginning point) 2. Decide which path best describes the organism (Statement A or Statement B) 3. Follow that path to find the next choice (Go to …) 4. When you can go no further, you will find the name!

B. If the organism has NOT been classified, taxonomists must begin the process of classification. In order to correctly classify an organism, scientists use many modern tools: 1. Morphology describes the physical characteristics of an organism. Typically, this is enough information to place the organism within a domain and kingdom. Example: Presence of a nucleus places the organism in Domain Eukarya

2. DNA and biochemical analysis allow scientists to test less visible, but distinguishing, characteristics. Example: Gram staining a bacteria cell allows scientists to distinguish between archaea and prokarya. Gram-positive anthrax bacteria (purple rods) in cerebrospinal fluid sample. If present, a gram-negative bacterial species would appear pink. (The other cells are white blood cells) Gram-negative E. Coli bacteria.

3. Comparing embryology allows scientists to group organisms that share common fetal development. Example: The diagram below would suggest the last two organisms are most closely related.

4. Evolutionary phylogeny describes the evolutionary relationships between organisms. These relationships are deduced based on shared traits that may have been passed from ancestor to new species. Traits may include physical traits (ex. presence of jaws), or may be genetic traits (shared genes). These relationships can be illustrated in a phylogenetic tree or cladogram: How to Build a Cladogram