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Classification Objectives

• Explain why scientists classify living things. • Understand that taxonomists study biological relationships to classify

organisms. • Describe the evidence scientists use to classify organisms. • List the seven levels of classification. • Describe and list the six kingdoms of living organisms

The BIG Idea

• Scientists have developed a system for classifying the great diversity of living things.

Key Concepts

• Scientists develop systems for classifying living things. • Biologists use seven levels of classification.

Scientists classify mill ions of species

• 400 years ago, scientists classified organisms based on their appearance and behavior. “If they looked the same, then they must be related,” is what a scientist would say to you.

• These, however, can suggest false connections. For example, caterpillars look like worms. However, caterpillars are actually an earlier stage of a butterfly’s life.

• As the discovery of new species increased, scientists needed an easy and universal way to classify organisms.

Scientists use classification and taxonomy to organize life.

• Classification is the process of arranging organisms into groups based on similarit ies. Taxonomy is the science of naming and classifying organisms.

• A good system of classification allows you to organize a large amount of information so that it is easy to find and to understand. The system

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should provide a tool for comparing very large groups of organisms as well as smaller groups.

• A good system of taxonomy allows people to communicate about organisms. Before the 1700s, scientists had not agreed on a system of naming and grouping organisms.

• All organisms are given a name in Latin. Even though these names may sound confusing, the common name can be more confusing. In England, the bird called a robin is only distantly related to the bird called a robin in the United States. A daddy longlegs in the States is a spider, whereas in England it is a relative of the mosquito.

• Clearly, biologists need both a system for organizing and a system for naming. Each name should refer to one specific type of organism. That way, scientists can use the species name and be sure that everybody knows exactly which organism they are talking about.

Scientists use classification to organize life into groups.

• To classify organisms, scientists use similarit ies and differences among species.

• Sometimes these differences are easy to see, such as whether an animal has fur, feathers, or scales.

• Other times, seeing the differences requires special lab equipment, such as equipment to study DNA.

What is the difference between classification and taxonomy?

Classification is the process of organizing living things into

groups based on similarities. Taxonomy is the science of

naming and classifying organisms.

Which process allows scientific grouping? Classification

Which process allows scientific naming? Taxonomy

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• A classification system can help you identify unfamiliar organisms. For example, if you had never heard of a caracal but were told that it was a kind of cat, you already would know many things about it. It has fur, fangs, and sharp claws. It’s a meat eater, not a plant eater. You would know these things because the caracal share those characteristics with all of the members of the cat family.

• The more characteristics two organisms share, the more similar their name would be in the classification system.

These are two different types of cats. What characteristics do

they have in common?

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How does a scientist classify organisms relative to other

species? They look for similarities and differences.

What is used to classify organisms in the laboratory? DNA

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Taxonomists study biological relationships • Scientists need a simple, standard way to arrange all of the different

species, including those that are extinct. • Taxonomists are scientists who classify and name the organisms based

on their similarities and differences into taxons. • A taxon is a group of organisms that share certain traits. Taxons can be

broad, like animals and plants, or more specific, like cats and roses. • As we learned in geology, a species found in the fossil record might be

the ancestor of many species found on Earth today. Taxonomists study the relationship between species, trying to discover how one species evolved as compared with another species.

• Species that share ancestors are grouped together. Why is this important?

• Remember, scientists compare a variety of characteristics or traits when classifying organisms. A trait is a characteristic or behavior that can be used to tell two species apart, such as size or bone structure. If two organisms share a trait, taxonomists try to determine if they share the trait because they share an ancestor.

• Therefore, organisms that share common traits may share a common ancestor. Likewise, if organisms share a common ancestor, they are likely to share common traits. These two statements support how scientists classify organisms. This is why scientists group organisms together that share a common ancestor.

How do taxonomists use biological relationships to classify

organisms? (In other words, if two species share a common

ancestor, how might they be grouped?) Taxonomists group

species that share common ancestors closer together than

species that do not.

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• Taxonomists look at the evidence an organism provides to help classify it. There are two types of evidence: physical and genetic.

• Physical Evidence o Physical evidence, in general, refers to two things of an organism:

its internal structure and its outward appearance. o Some example of physical evidence include color, size, weight,

and even how an organism obtains energy. o All of this physical evidence helps scientists see that all living

organisms are related by evolution. How do they find this out? o Recall that skeletons, shells, and other hard parts of an organism

can become fossil ized. Scientists can observe and measure fossilized bones or pieces of bones and compare them to each other. They can also compare bones of species that are extinct with bones of modern species. If they share similarities, they can infer that they may be related.

o Some species are more closely related than others. In this case, it means they share a more recent ancestor.

o From these studies, scientists can obtain clues about how an organisms may have lived, how it moved, and even what type of food it ate.

• Genetic Evidence (Molecular Evidence) o In the early 20th century scientists discovered that organisms

inherit their traits through structures called genes. In the mid 1950s, the observed that genes are made of DNA.

o Today, scientists can use laboratory machines to catalog each component of an organism’s DNA. They can use this information to compare one organism’s DNA to that of another.

o Scientists compare the genes of one organism to the genes of another organisms to see if they are similar. If they are, then they are more closely related.

o Genetic evidence can (sometimes) help prove physical evidence. Physical evidence only allows us so much information

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about an organism. Genetic information gives us a more concrete relationship between two organisms and how closely they are related.

Linnaeus was the first to develop an advanced classification system.

• A scientist named Carolus Linnaeus developed systems for both naming species and organizing them into groups.

• All 4,000 species that Linnaeus named were plants or animals. • Today, scientists have named over a million species. Linnaeus used

appearance to group species. However, with more modern techniques, scientists have been able to refine the classification system.

Biologists use binomial nomenclature to name organisms.

• You cannot use one word to name a species. For example, if you were told to go to Chicago and find someone named “John” you’d probably find 5,000 people named John. To help avoid this, you would be given a last name, too. The same thing happens in science by using two words to identify an organism.

• A genus is the group of species that have similar characteristics. You combine this with the name of the species and you get its scientific name.

• This system was invented by Linnaeus and is the basis of modern taxonomy. We call this binomial nomenclature. This is a fancy name for “two names in a list of names.” This system provides that you name something using two names, or two words.

• Most scientific names are in Latin terms.

What are some types of physical evidence a scientist could use

to classify an organism? Color, size, weight, etc.

How is DNA used to classify animals? Scientists can compare

the genes of organisms to see if they are similar.

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• In addition to the genus and species, the classification system includes several larger groups.

• Linnaeus’s system of binomial nomenclature made communication about certain species much easier. When naming an organism the use of a genus name as well as a species name is necessary.

• If the genus name is not included in the scientific name, the identity of a species can be a mystery. For example the species name gracilis which means “graceful” or “slender” and be used to identify several organisms:

o Aubrieta gracilis is a type of flower. o Chameleo gracilis is a type of lizard. o Mammillaria gracilis is a type of cactus.

• It is not until you introduce the genus name that you know which are you talking about.

• People also follow certain rules when they write scientific names. What did you notice about the scientific writing of the names above? The easiest thing to see is that the name is italicized. You may have noticed that the genus name comes first and its first letter capitalized. Notice how the species name is not capitalized but is italicized.

What two things are combined to make a scientific name?

The genus and species named.

Using the rules above, write the following in proper scientific

name format: Species: Sapien, Genus: Homo

Homo sapien (name must be italicized, genus first and

capitalized)

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Organisms can be classified into seven levels • You’ve learned about genus and species. They are the last two levels of

classification. The largest level is the first level, which contains the most species. Here is the complete list:

1. Kingdom 2. Phylum 3. Class 4. Order 5. Family 6. Genus 7. Species

• Look in your book on page 33 to see how the farther you go into the levels of classification, the fewer organisms there are. This is because the farther you go into the levels, the less an organism will have in common with other organisms.

• The classification tree provides a great tool to scientists studying organisms. Say you wanted to study about all animals; you would do this looking at one kingdom because it contains all animals. If you wanted to study all types of turtles, you would look at a certain order because it contains all types of turtles. If you wanted to only learn about turtles that live in or near water, you would research those in a certain family.

• The kingdom in the broadest organization of organisms and the species is the most specific.

Taxonomy changes as scientist make discoveries

• The list of species continues to grow today. Early scientists classified everything into one of two groups: plants or animals. Microscopes

Which level of classification in the seven-level system includes

the most species? __________________________________

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and other advances in technology have allowed scientists to observe that there are three different types of cells. This lead to the development of a higher level of classification beyond the kingdom. Scientists called this the domain.

• All kingdoms are placed into one of the three domains. Kingdoms that contain organisms with eukaryotic cells are placed into the domain Eukarya. Kingdoms that contain organisms with prokaryotic cells are placed into one of two domains: Bacteria or Archaea.

• All living things on Earth can be classified into one of six kingdoms. 1. Kingdom plantae includes plants such as trees, grass, and moss. 2. Kingdom animalia includes animals, from lions and tigers and

bears (oh my) to bugs and multicellular microbes. 3. Kingdom protista includes organisms that don’t fit easily into

animals, plants, or fungi. They are either unicellular organisms or have a simple multicellular structure.

4. Kingdom fungi includes mushrooms, molds, and yeasts. 5. Kingdom archaea contains organisms that are similar to

bacteria, but have a cell structure that is so different that scientists separate it into its own kingdom.

6. Kingdom bacteria are unicellular organisms with no nucleus. • We’ll take a closer look at each of the kingdoms as the year progresses.

Some of the information we will learn is already familiar to you.

Which kingdoms include multicellular organisms?

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