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Classification of Life

Introduction

When you see an organism that you have never seen before, you probably put it into a group without even thinking. If it is green and leafy, you probably call it a plant. If it is long and slithers, you probably call it as a snake. How do you make these decisions? You look at the physical features of the organism and think about what it has in common with other organisms.

Classification is the arrangement of organisms into orderly groups based on shared characteristics.

Because there are millions of different organisms on the planet, scientists have devised a system for sorting organisms into groups. Once sorted, the organisms are given a scientific name based on the groups they are a part of. Scientists classify, or put into categories, living things by their physical features, but also by how closely related they are. Lions and tigers look like each other more than they look like bears, but are lions and tigers related? Evolutionarily speaking, yes. Lions and tigers both evolved from a common ancestor. So it turns out that the two cats are actually more closely related to each other than to bears. How an organism looks and how it is related to other organisms determines how it is classified.

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Why Classify? Classification makes it easier for scientists to answer the following questions:

1. How many known species are there? 2. What are the characteristics of each species? 3. What are the relationships between species?

Levels of Classification

There are eight levels of classification: domain, kingdom, phylum, class, order, family, genus, and species. The level with the largest number of organisms in it is the domain, whereas the species level consists of a single type of organism. The diagram to the right illustrates the classification categories for organisms, with the broadest category (domain) at the top, and the most specific category (species) at the bottom.

History of Classification People have been concerned with classifying organisms for

thousands of years. Over 2,000 years ago, a Greek philosopher, Aristotle, developed a classification system that divided living things into several groups that we still use today, including mammals, insects, and reptiles. Carolus Linnaeus (CARE-ole-us lin-AY-us) was a Swedish physician and botanist who lived from 1707 to 1778. Linnaeus built on Aristotle's work to create his own classification system. He invented the way we name organisms today, with each organism having a two-word name. Linnaeus is considered the inventor of modern taxonomy, the science of identifying, classifying, and naming organisms.

Defining a Species

Even though naming species is straightforward, deciding if two organisms are the same species can sometimes be difficult. Linnaeus defined each species by the distinctive physical characteristics shared by the organisms. But two members of the same species may look quite different. For example, people from different parts of the world sometimes look very different, but we are all the same species. So how is a species defined? A species is defined as a group of similar individuals that can interbreed with one another and produce fertile offspring. A species does not produce fertile offspring with other species.

Binomial Nomenclature (also known as Scientific Naming) Linnaeus developed binomial nomenclature, a way to give a scientific name to every organism. In this

system, each organism receives a two-part name in which the first word is the genus (a group of species), and the second word refers to one species in that genus. For example, the coyote's scientific name is Canis latrans. Latrans is the species and Canis is the genus, a larger group that includes dogs, wolves, and other dog-

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like animals. The names may seem strange, but the names are written in Latin or Greek and are italicized (if typed) or underlined (if hand-written). The first word is always capitalized and the second is lowercase. Scientific names are always the same for a specific organism, no matter how many common names it might have. Scientific names are important because scientists all around the world know organisms by their scientific names; it is a common language for them.

Dichotomous Keys

Dichotomous keys are guides that aid

in the classification of organisms. They consist of several pairs of descriptive statements. When one of the two choices is selected, the reader is led to another set of descriptive statements. Once all statements have been selected, the scientific name of the organism is provided. To the right is an example using sharks.

Review of “Classification Basics” Reading

1. Why is classification useful?

2. As you move down the levels of classification, what happens to the number of organisms in each group?

3. Describe the formatting rules for a scientific name.

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Classification Notes: Guided Reading Introduction

__________________________________ is the arrangement of organisms into orderly groups based

on shared characteristics.

Why Classify?

Classifying organisms answers the following questions:

o How many ___________ _____________ are there?

o What are the _______________________ of each species?

o What are the _______________________ between species?

Levels of Classification

There are _____ levels of classification:

The _________________ category is at the top and the most _____________ category is at the

bottom.

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History of Classification

The first classification system was created by ____________ over 2,000 years ago.

___________________________ _______________________________ invented the way we name

organisms today, with each organism having a two-word name.

__________________ is the science of identifying, classifying, and naming organisms.

Defining a Species

A _____________ is a group of similar individuals that can interbreed with one another and produce

fertile offspring.

Binomial Nomenclature (aka Scientific Naming)

Linnaeus developed _______________________ _____________________, which is a way to give a

scientific name to every organism.

o In this system, the first word is the _____________ and the second is the ____________.

o The names are written in ______________ or ______________.

o The names are also italicized if ______________ or underlined if _________________________.

o The first word is always _______________________ and the second is _______________________.

______________________ names are always the same for a specific organism, no matter how many

_________________ names it might have.

Scientific names allow scientists all around the word to communicate in a common

_______________________.

Dichotomous Keys

_____________________ __________ are guides that aid in the classification of organisms.

They consist of several _______ of descriptive statements that lead to the scientific name of the

organism.

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Dichotomous Pamishans Help! Scientists have discovered quite a few new creatures on planet Pamishan. They need your help to identify and classify them. Use the dichotomous key to identify these creatures.

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Pamishan Dichotomous Key

1. a. The creature has a large wide head...................................................................................... go to 2

b. The creature has a small narrow head................................................................................ go to 11

2. a. It has 3 eyes .......................................................................................................................... go to 3

b. It has 2 eyes .......................................................................................................................... go to 7

3. a. There is a star in the middle of its chest................................................................................ go to 4

b. There is no star in the middle of its chest ............................................................................ go to 6

4. a. The creature has hair spikes ........................................................................... Broadus hairytritops

b. The creature has no hair spikes............................................................................................. go to 5

5. a. The bottom of the creature is arch-shaped .................................................... Broadus staryarchus

b. The bottom of the creature is M-shaped ...................................................... Broadus staryemmus

6. a. The creature has an arch-shaped bottom .............................................................. Broadus archus

b. The creature has an M-shaped bottom.................................................................. Broadus tritops

7. a. The creature has hairy spikes ............................................................................................... go to 8

b. The creature has no spikes.................................................................................................. go to 10

8. a. There is a star in the middle of its body .......................................................... Broadus hairystarus

b. There is no star in the middle of its body ............................................................................. go to 9

9. a. The creature has an arch shaped bottom ............................................................... Broadus hairus

b. The creature has an M shaped bottom ......................................................... Broadus hairyemmus

10. a. The body is symmetrical ........................................................................................ Broadus emmus

b. The body is not symmetrical........................................................................... Broadus mismatchus

11. a. The creature has no antennae ............................................................................................ go to 12

b. The creature has antennae ................................................................................................ go to 14

12. a. There are spikes on the face ................................................................................. Narrowus wolfus

b. There are no spikes on the face ......................................................................................... go to 13

13. a. The creature has no spike anywhere .................................................................. Narrowus blankus

b. There are spikes on the right leg ................................................................. Narrowus starboardus

14. a. The creature has 2 eyes....................................................................................................... go to 15

b. The creature has 1 eye......................................................................................... Narrowus cyclops

15. a. The creature has a mouth................................................................................................... go to 16

b. The creature has no mouth................................................................................................. go to 17

16. a. There are spikes on the left leg ............................................................................. Narrowus portus

b. There are no spikes at all ................................................................................. Narrowus georginia

17. a. The creature has spikes ...................................................................................................... go to 18

b. The creature has no spikes .................................................................................. Narrowus plainus

18. a. There are spikes on the head ............................................................................................. go to 19

b. There are spikes on the right leg.................................................................... Narrowus montanian

19. a. There are spikes covering the face ....................................................................... Narrowus fuzzus

b. There are spikes only on the outside edge of head .......................................... Narrowus beardus

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Domains & Kingdoms Domains

Domains are the largest level of classification, meaning they have the largest number of

organisms within them. There are three domains, each with its own set of characteristics.

Archaea: To be in the domain Archaea, an organism must be a prokaryote that lives in extreme environments. This domain only has one kingdom in it.

Bacteria: To be in the domain Bacteria, an organism must be a prokaryote that lives in many different environments. This domain only has one kingdom in it.

Eukarya: To be in the domain Eukarya, an organism must be a eukaryote. This domain has four different kingdoms in it.

Kingdoms

There are six kingdoms that make up the second level of classification. To be part of each

kingdom, an organism must have a particular set of characteristics.

Archaebacteria: Archaebacteria is the only kingdom within the Archaea domain. Archaebacteria are prokaryotes, meaning that they are unicellular organisms without a nucleus but with a cell wall. They have been on Earth for at least 3 billion years ("archae" means ancient) and live in extreme environments, like deep sea vents or hot springs. Archaebacteria can be producers (also called autotrophs) or decomposers (a type of heterotroph, which are organisms that do not make their own food) and reproduce asexually.

Eubacteria: Eubacteria is the only kingdom within the Bacteria domain. Eubacteria are another type of prokaryote but they live in many different environments (even in human stomachs). Apart from where they live, Eubacteria have exactly the same traits as Archaebacteria.

Protista: Protista is one of four kingdoms within the Eukarya domain. Protists are a type of eukaryote, which means their cells have a nucleus, and are mostly unicellular. Some of them have a cell wall and they can be producers, consumers, or decomposers – meaning they can be both autotrophs and heterotrophs. Some reproduce asexually, while others reproduce sexually and they are mostly aquatic (water-dwelling).

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Fungi: Fungi are another of the four kingdoms within the Eukarya domain. They are another type of eukaryote and they are mostly multicellular. Like plants, they have cell walls but, unlike plants, they are decomposers. Fungi reproduce both sexually and asexually and can live in water or on land.

Plantae: Plantae is the third of the four kingdoms within the Eukarya domain. They are multicellular autotrophs, meaning they make their own food. Some reproduce sexually and others reproduce asexually and they can live in water or on land.

Animalia: Animalia is the last of the four kingdoms within the Eukarya domain. They are also multicellular organisms but they are consumers, meaning they have to eat other organisms for energy, and they do not have cell walls. They reproduce sexually and can live in water or on land.

Eukaryotes

Prokaryotes

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Review of “Domains & Kingdoms” Reading

1. What is the main difference between Archaea and Bacteria?

2. What is the main difference between the domain Eukarya and the other two domains?

3. List three characteristics of each kingdom that you would use to separate it from the others. A. Animalia

B. Plantae

C. Fungi

D. Protista

E. Eubacteria

F. Archaebacteria

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Formative Assessment: Levels & Kingdoms

DIRECTIONS: List the levels of classification in order from BROADEST to MOST SPECIFIC.

DIRECTIONS: Match the kingdom name to its description.

WORD BANK: Animalia (A), Archaebacteria (AB), Eubacteria (E), Fungi (F), Plantae (PL), Protista (P)

_______ 1. I am so tiny that you need a microscope to see me. I only have one cell, which does not have a nucleus. I reproduce asexually, basically cloning myself. I am living on your desk right now.

_______ 2. I can be big or small, but I always have many cells. All of my cells have a nucleus and I am a

heterotroph, so I can't make my own food. My relatives and I almost always reproduce sexually. My cells lack cell walls.

_______ 3. I am a tiny organism and I live in a pond. My little body only has one cell, but I do have a nucleus. I

am a decomposer, but some of my relatives are producers and consumers. _______ 4. Some people might think I'm a plant because I am eukaryotic and I have a cell wall, but I'm not.

Please don't think I'm gross just because I'm a decomposer. I am multicellular, but some of my relatives are unicellular.

_______ 5. My relatives existed when Earth was young. We may be really teeny-tiny, but we are strong. I may

not have a nucleus, but I can survive in boiling water or deep under the ocean near a volcanic vent. _______ 6. I am eukaryotic. I have millions of cells in my body, which all have cell walls. I am an autotroph (I

use sunlight to make my own food). Some of my relatives reproduce asexually, but I reproduce sexually.