Background Biologists have identified more than 1.5 million different species on Earth. This is only a fraction of what scientists believe the total number could be anywhere from 5 million to 100 million. Because of this abundance and diversity, scientists organize species with similar characteristics into groups based on their structure, function, and relationships. This is known as taxonomy or taxonomic classification. The current system of classification is based on the hierarchical system of Swedish scientist Carolus Linnaeus. Linnaeus grouped organisms based on common physical characteristics. However, with the ability to sequence genes, scientists are now able to bring classification to a whole new level. Organisms can be classified into groups based on their cellular structure, whether they have defined nuclei or not (eukaryotes versus prokaryotes) or if their entire body is made up of one cell (unicellular) or many cells (multicellular). Scientists can also look at how organisms function to help classify them. For example, organisms that make their own food are known as autotrophs, while organisms that need to consume other organisms in order to get the nutrients they need to survive are known as heterotrophs. How an organism reproduces is another way scientist separate organisms into smaller groups; asexually, in which only one parent passes a copy of its genes on to its offspring, or sexually, in which two parents combine their genes and the combination is passed on to their offspring. Gene sequencing played a big part in organizing the three domains. In 1990, Carl Woese used ribosomes to prove that all organisms can be placed into one of three s: Bacteria, Archaea, and Eukarya. The Bacteria and Archaea s consist of prokaryotes. This means that on the cellular level they do not have defined nuclei that is, their nuclei have no cell membrane or wall. Many members of the Archaea live in extreme environments (high heat, salt, or acid), such has hot springs, while members of the Bacteria are found all over Earth and are what we think of when we hear the word bacteria. The Eukarya (sometimes also spelled Eucarya) consists of anything that could be classified as a eukaryote, meaning that their cells have defined nuclei with cell membranes. Please continue to the next page. 1
6.12CD: Classification of Organisms Background, continued The three s are currently divided into six smaller groups known as Kingdoms. Bacteria Archaea Eukarya Kingdom Bacteria Kingdom Archaea Kingdom Protista Kingdom Plantae Kingdom Fungi Kingdom Animalia The Bacteria has only one kingdom, the Kingdom Bacteria. Kingdom Archaea -Prokaryotes that often live in extreme environments. Kingdom Bacteria - Prokaryotes that cannot live in extreme environments. The Archaea has only one kingdom, the Kingdom Archaea. The Eukarya consists of four kingdoms: Protista, Plantae, Fungi, and Animalia. Kingdom Protista consists of eukaryotic organisms that are primarily unicellular and other, simple multicellular relatives, such as slime mold or algae. Kingdom Protista uniceullar and simple multicellular eukaryotic organisms Kingdom Plantae are eukaryotes that are multicellular and are autotrophs (make their own food). This includes mosses, trees, and flowering plants. Kingdom Fungi are eukaryotes that are heterotrophs (get food from other sources) and get their nutrients by decomposing organic matter, like mushrooms or molds. The Kingdom Animalia consists of multicellular, heterotrophic, eukaryotes. This group includes insects, reptiles, birds, and mammals. Continue to the next page. 2 Kingdom Fungi - Fungi are eukaryotic heterotrophic multicellular
Background, continued The first classification system had only had two kingdoms, Kingdom Plantae and Kingdom Animalia. Kingdoms were the beginning or most basic category. Kingdom Plantae - Plants are autotrophic eukaryotic multicellular organisms. Kingdom Animalia - Animals are eukaryotic heterotrophic multicelluar organisms. As more and more organisms were discovered and scientists were able to make more detailed examinations of the organisms, new Kingdoms were added to the classification system. In 1969, R. H. Whittaker used the characteristics of body structure, reproduction cycle, and cell structure to classify all known organisms into five Kingdoms: Monera, Protista, Plantae, Fungi, Animalia. Kingdom Monera included what is today classified as Kingdom Bacteria and Kingdom Archea. Advances in technology allowed scientists to explore in areas once considered too harsh to support life. C.R. Woese discovered that prokaryotic organisms that lived in very extreme conditions were different from other prokaryotic organisms. At first these organisms were considered to be bacteria and were classified as Kingdom Monera, however as the ability to examine the genetic make up of organisms emerged, Dr. Woese determined these organisms were not typical of bacteria and had some characteristics found in eukaryotes. He named the organisms as Archaea and proposed the new three classification system. The Kingdom of Monera was eliminated and two new kingdoms were formed: Kingdom Bacteria and Kingdom Archaea. This area of study shows how science is fluid and constantly changing. With the increasing discoveries of new organisms and the continued advancement of technology, scientists are able to gather more and more information about living things. As history indicates, the classification system of today may be made obsolete with the discoveries of tomorrow. Sources: http://www.biology.iupui.edu/biocourses/n100/2k23domain.html retrieved 11/16/2012 http://biology.about.com/od/evolution/a/aa041708a.htm retrieved 11/16/2012 Complete the Background questions in your Student Journal. 3
Part I: In What Do I Belong? Scientists sort life forms into categories based on their characteristics. First, scientists look at the types of cells an organism has to identify whether the organism is a prokaryote or a eukaryote. Cells in a prokaryote: Lack a nucleus Lack structures with membranes inside the cell Cells in a eukaryote: Have a nucleus Have membranes that enclose complex structures, including the nucleus Scientists also look at whether an organism likes living in an extreme environment. An extreme environment might mean an extremely hot place, a very acidic one, or a very alkaline one. Considering this additional characteristic, scientists sort organisms into the three largest categories, called s. The three s are: Archaea a prokaryote; many thrive in extreme environments Bacteria a prokaryote that cannot live in extreme environments Eukarya any eukaryote Cut out the In What Do I Belong cards. Paste the cards in Part I of your Student Journal. Complete Part I in your Student Journal. 4
Part II: In What Kingdom Do I Belong? Scientists sort organisms into smaller categories than s, called Kingdoms. The six Kingdoms are: Bacteria, Archaea, Protista, Fungi, Plantae, and Animalia. CELL COMPOSITION Unicellular composed of a single cell Multicellular composed of multiple cells EATING Autotrophic makes own food Heterotrophic eats other organisms REPRODUCTION Asexual offspring arise from a single parent Sexual offspring arise from the mating of two parents Cut out the In What Kingdom Do I Belong cards. Paste the cards in Part II of your Student Journal. Part III: & Kingdom Slide Show 1. Search around your home, school, neighborhood, and the Internet for examples of the three domains and six kingdoms. 2. Use a digital camera to take pictures or find images from the Internet for each domain and kingdom. Collect at least two examples for each domain and kingdom. 3. Write a description of each domain and kingdom. 4. Create a slide show. The slide show should include a title page and at least one page per domain and kingdom with appropriate descriptions of each. 5. Place your photographs and descriptions on the appropriate slides. 6. Share your slide show with your class. Complete Parts II and III and the Reflections and Conclusions questions in your Student Journal. j 5