6.12: lassification of Organisms Name: ate: 1 2 3 What s In Name? Lexile 870L Shakespeare famously wrote in Romeo and Juliet, What s in a name? That which we call a rose by any other name would smell as sweet. These words are meant to say that it doesn t matter what we call something. It may not matter to fiction writers what things are called, but it is very important to scientists. Scientists need a way to organize and classify groups of life forms. How scientists do that has changed over time, as we have learned more and more about the world around us. s science learns discovers more about the characteristics of organisms, we have gotten better at classifying them. The most basic level of classification is prokaryote and eukaryote. Prokaryotes are those organisms that don t have a nucleus or a cell membrane. They are species of bacteria and archae. Eukaryotes are those organisms that we can often readily identify by sight. Each of their cells have a nucleus and a membrane. They are animals, flowers, mushrooms and protists. domain is the largest rank of organism. There are three domains: Eukarya, acteria, and rchaea. Eukarya is the domain composed of eukaryotes: organisms that have a cell nucleus and a membrane that encloses a complex structure. Most of the organisms we commonly think of as animals fall within this domain. It includes all plants, fungi, and protists. acteria is the domain composed of bacteria. These prokaryotes include the oldest fossils on Earth. Though some bacteria cause disease, others can cure illness. rchaea is the domain composed of archae. These prokaryotes often reside in extreme places like the boiling water of a hot spring or the oxygen deprived ocean floor. 1
6.12: lassification of Organisms 4 5 6 7 8 Every living being on the planet falls into one of these three domains. ll eukaryotes are a part of the Eukarya domain. ll bacteria are a part of the acteria domain and all of archaea fall into the rchaea domain. The next smallest classification group is Kingdom. The eukaryotic Kingdoms are: nimalia, Fungi, Plantae, and Protista. The prokaryotic Kingdoms are Eubacteria and rchaea. Organisms are classified at this level based on the complexity of their cell make up, and how they obtain nutrients, reproduce, and move. There are two ways an organism can get nutrients. utotrophs make their own, while heterotrophs consume other organisms to get what they need to survive. Most bacteria and archae are autotrophs. Many plants are photoautotrophic. They use light from the sun to manufacture the food they need to survive. People are heterotrophs. We can walk around all day with our arms outstretched to the sun and still need to consume other organisms to get the nutrients we need to survive. Some organisms have only one cell and called unicellular. These organisms include bacteria, protists, archae, and some fungi. ecause they only have one cell, these organisms are usually tiny. However, some are large enough to be seen with the naked eye. These organisms must carry out all life processes within that one cell. In contrast, multicellular organisms have more than one cell. In multicellular organisms cells serve specialized purposes and depend on each other to make sure the life processes of the organism succeed. There are two types of reproduction. In asexual reproduction, the offspring come from a single parent and only carry the genes of that parent. There are many different ways for an organism to reproduce asexually. They can even simply divide into two daughter organisms in a process called binary fission. Many unicellular organisms reproduce asexually. In sexual reproduction, a new organism is created by the joining of two different sets of genetic material. This happens with most multicellular organisms. 2
6.12: lassification of Organisms 9 10 The final criterion for determining an animal s Kingdom is looking at how they can move. nimals which can move by themselves are called motile, while animals that cannot move by themselves are called sessile. Naming and classifying organisms is a tricky process that must incorporate new discoveries and information. Knowing the basics can help you think like a scientist when you read about scientific discoveries. 3
6.12: lassification of Organisms 1 Humans are likely to be eukaryotic and motile prokaryotic and motile 3 ased on the information in this passage, the reader can reasonably conclude that scientists will never change the classification system again eukaryotic and sessile prokaryotic and sessile scientists know everything there is to know about all organisms scientists have never changed the classification system 2 unicellular protist probably has a complex cell structure new scientific discoveries could change the current classification system has specialized cells has one cell has no cells 4 In the word photoautotroph, photo probably means: Picture Light Nutrients Synthesis 4
6.12: lassification of Organisms 5 Which of the following is the best summary of the story? 6 Humans are called heterotrophs, because they Eukaryotes and prokaryotes are different. One has a nucleus with a cell membrane and the other does not. Humans are eukaryotes. eat other organisms to get the nutrients they need to survive have a complex cell structure There are many ways to classify organisms. They can be either bacteria or archaea. are motile have a nucleus and a cell membrane There are three omains of life. ll living creatures are a part of the Eukaryotic, acteria or rchaea omain. There are six Kingdoms and organisms are grouped into Kingdoms based on the complexity of their cell structure, how the reproduce, how they obtain nutrients and how they move. Organisms are everywhere. Some have a complex cell structure and some are unicellular. Some organisms thrive in extreme places. They are called archaea and can even live hot springs and on ocean floors. 5