An Introduction to Classification

Biology 11

Taxonomy

• the science of classifying organisms.

Binomial Nomenclature

• a method of naming organisms by using two names – the genus name and the species name. Scientific names are italicized and the first part is always capitalized.

Species

• a group of organisms that look alike and can interbreed under conditions to produce fertile offspring.

Taxa

• categories that are used to classify organisms.

Protista

• a kingdom originally proposed for all unicellular organisms such as the amoeba. More recently, multicellular algae have been added to the kingdom.

Monera

• a kingdom used in a five-kingdom system; it includes organisms that lack a true nucleus (prokaryotes).

Archeabacteria

• used in the six kingdom system, a group of prokaryotic microorganisms distinct from eubacteria that possess a cell wall not containing peptidoglycan and that lice in harsh environments such as salt lakes and thermal vents.

Eubacteria• in a six-kingdom system a group of prokaryotic

microorganisms that possess a peptidoglycan cell wall and reproduce by binary fission.

Phylogeny

• the history of the evolution of a species or a group of organisms

Phylogenic Tree

• a diagram that can be used to show the evolutionary relationships of different species. The tree begins with the most ancestral form and branches out to include all descendants.

Dichotomous Key

• a two-part key used to identify living things. Di means two.

Viruses

• microscopic particles capable of reproducing only within living cells.

Capsid

• the protective protein coat that surrounds the outside of viruses

Bacteriophage

• a category of viruses that infect and destroy bacterial cells

Host Range

• the limited number of host species, tissues, or cells that a virus or other parasite can infect.

Lysis

• the destruction or bursting open of a cell. For example when an invading virus replicates in a bacterium and many viruses are released.

Virulent Phage

• a bacteriophage that causes the lysis of the host cell.

Temperate Phage

• a bacteriophage that does not cause the lysis of the host cell.

Lysogeny

• the dormant state of a virus

Oncogenic Viruses

• viruses that cause cancer by adding specific genes to an infected cell turning it into a cancer cell.

Vaccines

• solutions that are prepared from viral components or inactivated viruses

1. What are the two main purposes of taxonomy?

• The two main purposes of taxonomy are to identify organisms and to represent relationships among those organisms.

2. Who was the first person who attempted to classify organisms and how did he arrange organisms?

• The first individual who attempted to classify organisms was the Greek philosopher Aristotle. Aristotle believed in a hierarchy of complexity where humans dominated over all other living things. His “ladder of nature” placed the simplest organisms on the bottom rung while humans were placed on the top rung.

3. What characteristics did Linnaeus use as the basis for his classification system?

• Carolus Linnaeus, a Swedish botanist designed a classification system based on an organism’s physical and structural features. The more common structures organisms shared the more closely related they were.

4. What language is used to name organisms and what is that name usually based on?

• Organisms are all given a scientific name using Latin words. This provides a common language for all scientists regardless of their national origin. The names are commonly based on a particular characteristic of the organism such as color or habitat.

• An example of this would be Castor canadensis . This is the scientific name for a beaver; Castor means beaver and canadensis means from Canada.

5. What are the advantages of using the two name system?

• A two part naming system uses the genus and species name to form the scientific name of the organism. The advantage is that the two part name can indicate similarities in anatomy, embryology and evolutionary history.

• For example, if two organisms share the same genus name than this indicates a close relationship; Ursus horribilis (grizzly bear) and Ursus americanus (balck bear).

6. What are the seven levels of taxa used in our current classification system?

• The seven levels of taxa used in our current classification system are: Kingdom, Phylum, Class, Order, Family, Genus and Species.

7. Using point form, outline the steps of progression from the original two kingdom classification system to the

present day six kingdom system.

• The following steps outline the progression from a two kingdom system to our present day six kingdom system.

• The first classification system consisted of only two kingdoms, plants and animals.

• The discovery of single celled organisms that did not fit into either a plant or animal kingdom prompted scientists to create a third kingdom called Protista.

• Soon after scientists discovered that some of these small organisms lacked a true nucleus and this resulted in the creation of a fourth kingdom called Monera. Monera contained all prokaryotes while the other three kingdoms contained eukaryotes.

7. Using point form, outline the steps of progression from the original two kingdom classification system to the

present day six kingdom system.

• Later on scientists recognized that mushrooms and moulds were significantly different from the plants they were currently classified with. Due to these differences a fifth kingdom was created called Fungi.

• The five kingdom system that had been proposed in 1969 by Robert Whitaker has been widely accepted since that time until recently. The work of scientist Carl Woese revealed that ancient bacteria are significantly different from other bacteria and therefore should be placed in a separate kingdom.

7. Using point form, outline the steps of progression from the original two kingdom classification system to the

present day six kingdom system.

• Due to these differences a sixth kingdom has been added and Monera has been replaced by Archeabacteria and Eubacteria.

• The current six kingdom system consists of the following kingdoms: Archeabacteria, Eubacteria, Protista, Fungi, Plantae and Animalia.

8. How are evolutionary relationships between organisms represented?

• Evolutionary relationships of organisms can be represented in a phylogenic tree. The tree begins with the most ancestral form and all the descendents are placed on branches of the tree.

9. What did the DNA sequencing studies of Carol Bult and Carl Woese reveal?

• The study of the DNA sequences of archaebactria revealed that the genes are actually more closely related to those of humans than to those of eubacteria. Woese now believes that bacteria should not even be in the name and the kingdom should simply be archae.

10. How has the work of Bult and Woes influenced and changed our classification system?

• The work of Bult and Woese has scientists considering replacing the traditional kingdom system with a domain system they feel better reflects the evolutionary history of life.