1. Why do organisms need a scientific name?
CLASSIFICATION
Why do organisms need a scientific name?
There is a student study guide sheet that goes with this Powerpoint lesson for TEKS Biology.

2. TAXONOMY:
Discipline of classifying organisms and assigning each organism a universally accepted name.
In the United Kingdom, the word buzzard refers to a hawk, whereas in many parts of the United States, buzzard refers to a vulture.
TURKEY VULTURE
(Cathartes aura)

3. WHY CLASSIFY?
1. Why do biologists use a classification system to study the diversity of life?
to name organisms and group them in a logical manner.
Ask students: What characteristics do these organisms have that might lead scientists to group them together?
What differences do they have that distinguish one from the other?

4. HOW TO CLASSIFY?
2. How do taxonomists group organisms when they classify them?
Into groups that have biological significance.
What is this first organism?
How does this second organism relate to the first?
And the third?
And the fourth?
All of these organisms are known as birds. When we hear the word bird, we immediately form a mental picture in our minds of what birds look like.

5. WHY CLASSIFY? 3. How does classification make life easier?
grouping things makes them easier to find and work with
3a. What are some things we classify?
Think of all the different types of music there is. What if you wanted to buy a new CD at the store? How do you go about finding the CD?
When you grocery shop? How do you know where to look for Lucky Charms cereal?
At school, what are some ways that we classify students?
Think of how much more difficult our lives would be without the alphabet, without numbers, without the Dewey decimal system, without a phonebook.

6. LINNAEUS’S SYSTEM OF CLASSIFICATION
Charles Linnaeus, a Swedish botanist, developed a hierarchical system of classification including seven levels called taxa.
They are, from largest to smallest:
Domain
Kingdom
Phylum
Class Order
Family
Genus Species
You may want to have students draw a pyramid and draw 6 horizontal lines across to divide the pyramid up into 7 sections. Then have the students list the 7 taxonomic categories from bottom to top, starting with Kingdom at the bottom in the widest section and ending with species at the top in the smallest section.

7. LINNAEUS’S SYSTEM OF CLASSIFICATION
The Kingdom is the largest and most inclusive of the taxonomic categories.
Only 6 kindgoms for all living organisms: Bacteria, Archae, Protista, Fungi, Plantae, Animalia
Species is the smallest and least inclusive of the taxonomic categories.

8. Species Camelus bactrianus
Genus Camelus
Family Camelidae
Order Artiodactyla
Tell students that you’ve already discussed the two smallest categories, species and genus. Now work your way up to the rank of kingdom by having students examine how camels are classified.
Explain that the scientific name of a camel with two humps is Camelus bactrianus. (Bactria was an ancient country in Asia.) As you can see, the genus Camelus also includes another species, Camelus dromedarius, the dromedary, which has only one hump. In deciding how to place organisms into these larger taxa, Linnaeus grouped species according to anatomical similarities and differences.
Family: The South American llama bears some resemblance to Bactrian camels and dromedaries. But the llama is more similar to other South American species than it is to European and Asian camels. Therefore, llamas are placed in a different genus, Lama; their species name is Lama glama. Several genera that share many similarities, like Camelus and Lama, are grouped into a larger category, the family—in this case, Camelidae.
Order: Closely related families are grouped into the next larger rank—an order. Camels and llamas (family Camelidae) are grouped with several other animal families, including deer (family Cervidae) and cattle (family Bovidae), into the order Artiodactyla, hoofed animals with an even number of toes.
Class: Similar orders, in turn, are grouped into the next larger rank, a class. The order Artiodactyla is placed in the class Mammalia, which includes all animals that are homeotherms, have body hair, and produce milk for their young.
Phylum: Classes are grouped into a phylum. A phylum includes organisms that are different but share important characteristics. The class Mammalia is grouped with birds (class Aves), reptiles (class Reptilia), amphibians (class Amphibia), and all classes of fish into the phylum Chordata. These organisms share important body-plan features, among them a nerve cord along the back.
Kingdom: The largest and most inclusive of Linnaeus’s taxonomic categories is the kingdom. All multicellular animals are placed in the kingdom Animalia.
Make sure students understand that the pyramid shows the taxonomic categories for one species, Camelus bactrianus, and that the more inclusive taxa include many more organisms than shown.
Ask: What basic body feature do all members of the phylum Chordata share?
Answer: a nerve cord along the back
Ask: What are four kinds of animals in the order Artiodactyla?
Sample Answer: Bactrian camel, dromedary camel, llama, and giraffe
Class Mammalia
Phylum Chordata
Kingdom Animalia
Bactrian Dromedary Llama Giraffe Albert’s Coral Sea star
camel camel squirrel snake

9. LINNAEUS’S SYSTEM OF CLASSIFICATION
The more taxonomic levels that two organisms share, the more closely related they are considered to be.

10. THINKING CRITICALLY Kingdom Phylum Class Order Family Genus Species
Organism
Cat
Wolf
Fly
Kingdom
Animalia
Phylum
Chordata
Arthropoda
Class
Mammalia
Insecta
Order
Carnivora
Diptera
Family
Felidae
Canidae
Muscidae
Genus
Felis
Canis
Musca
Species
F. domesticus
C. lupus
M. domestica
Have students study this chart. The next slide lists three questions to answer using this chart. You may have to advance to the next slide, let students read the question and then come back to the chart so they can find the answer.

11. THINKING CRITICALLY 1. What type of animal is Musca domestica?
2. From the table, which 2 animals are most closely related?
3. At what classification level does the evolutionary relationship between cats and wolves diverge (become different)?
Animal; insect
Cat and Wolf
Family Level

12. LINNAEUS’S SYSTEM OF CLASSIFICATION
What do the scientific names of the polar, grizzly and panda bears tell you about their similarity to each other?
The shared genus name Ursus indicates that the grizzly bear and polar bear are more closely related. The panda bear is a little more distantly related because it does not belong to the same genus as the other two. Pandas were believed to be a type of raccoon and only in the 20th century did genetic testing reveal that they are in fact bears. They are in a subfamily Ailurinae of the family Ursidae; all other bears are in the subfamily Ursinae. Aliuropoda melanoleuca means “black and white cat-foot”.
Ursus maritimus
Ursus arctos horribilis
Ailuropoda melanoleuca
Pictures reproduced with permission from WWF. © 2004 WWF- World Wide Fund For Nature (Formerly World Wildlife Fund). All Rights Reserved

13. ASSIGNING SCIENTIFIC NAMES
Many organisms may have several different common names.
The cougar is also known as the mountain lion, panther, or puma …thus the need for a scientific name.
Felis concolor
Photo courtesy Texas Parks and Wildlife Department © 2004

14. ASSIGNING SCIENTIFIC NAMES
Linnaeus also developed Binomial Nomenclature, a two-word naming system for naming all species on earth.
Botanists study plants.

15. ASSIGNING SCIENTIFIC NAMES
Step 1:
a. The first part of the scientific name is the Genus.
capitalized
underlined (or italics)
Homo sapien
Ursus arctos horribilis

16. ASSIGNING SCIENTIFIC NAMES
Step 2:
a. The second part of the scientific name is the species name.
not capitalized
Underlined (or italics)
Homo sapien
Ask students to notice how both words appear: in italics or they may both be underlined.
Ursus arctos horribilis

17. Binomial Nomenclature
Tell students that in the 1730s, Swedish botanist Carl Linnaeus, developed a two-word naming system called binomial nomenclature. In binomial nomenclature, each species is assigned a two-part scientific name. Scientific names are written in italics. The first word begins with a capital letter, and the second word is lowercased.
Explain that the polar bear is called Ursus maritimus. The first part of the name—Ursus—is the genus to which the organism belongs. A genus (plural: genera) is a group of similar species. The genus Ursus contains five other species of bears, including Ursus arctos, the brown bear or “grizzly.” The second part of a scientific name—in these examples, maritimus or arctos—is unique to each species. A species, remember, is a group of individuals able to interbreed and produce fertile offspring. The species name is often a description of an important trait or the organism’s habitat. The Latin word maritimus, refers to the sea, because polar bears often live on pack ice that floats in the sea.
Click to reveal the scientific name of the red maple: Acer rubrum.
Ask students to identify the genus and species of this organism. A volunteer can go to the board to circle the genus and underline the species.
Click to reveal the correct answer.
Explain that the genus Acer consists of all maple trees. The species rubrum describes the red maple’s color.
Ursus maritimus
Acer rubrum
Genus species
Genus species

18. EVOLUTIONARY CLASSIFICATION
Biologists group organisms into categories that represent lines of evolutionary descent, not just physical similarities.

19. EVOLUTIONARY CLASSIFICATION
Classification using Cladograms
a. Cladograms are diagrams that show the evolutionary relationships among a group of organisms.
A phylogenetic tree is a specific type of cladogram where the branch lengths are proportional to the predicted or hypothetical evolutionary time between organisms or sequences. Cladograms are branched diagrams, similar in appearance to family trees, that illustrate patterns of relatedness where the branch lengths are not necessarily proportional to the evolutionary time between related organisms or sequences.

20. Cladograms 1 2
Tell students that modern evolutionary classification uses a method called cladistic analysis. Cladistic analysis compares carefully selected traits to determine the order in which groups of organisms branched off from their common ancestors. This information is then used to link clades together into a branching classification diagram called a cladogram. A cladogram links groups of organisms by showing how evolutionary lines, or lineages, branched off from common ancestors.
To help students understand how cladograms are constructed, have them think back to the process of speciation. A speciation event, in which one ancestral species splits into two new ones, is the basis of each branch point, or node, in a cladogram. That node represents the last point at which the two new lineages shared a common ancestor. As shown in Step 1, a node splits a lineage into two separate lines of evolutionary ancestry. Each node represents the last point at which species in lineages above the node shared a common ancestor. The bottom, or “root,” of a cladogram represents the common ancestor shared by all of the organisms in the cladogram. A cladogram’s branching patterns indicate degrees of relatedness among organisms.
Ask: In Step 1, the ancestral lineage splits into two new lineages. On a cladogram, what is this place, where a split like this occurs, called?
Answer: a node
Click to reveal Step 2.
Because lineages 3 and 4 share a common ancestor more recently with each other than they do with lineage 2, you know that lineages 3 and 4 are more closely related to each other than either is to lineage 2. The same is true for lineages 2, 3, and 4. In terms of ancestry, they are more closely related to each other than any of them is to lineage 1.
Ask: In Step 2, what does the node on the right side represent for lineages 3 and 4?
Answer: the last point at which lineages 3 and 4 shared a common ancestor
Click to reveal Step 3.
Explain that the cladogram in Step 3 represents how lineages branched over time from the first branch in Step 1. This cladogram shows the evolutionary relationships among vertebrates—animals with backbones. Does it surprise you that amphibians are more closely related to mammals than they are to ray-finned fish? In terms of ancestry, it’s true. 3

21. Interpreting a Cladogram
Clade Tetrapoda
Clade Amniota
Clade Mammalia
Clade Carnivora
Clade Felidae
Amphibians
Reptiles
Marsupials
Dogs/Relatives
Cats
Retractable claws
Specialized shearing teeth
Tell students that four limbs is a derived character for clade Tetrapoda.
Ask: But what about snakes?
Answer: Accept all reasonable answers.
Explain that snakes are definitely reptiles, which are tetrapods. But snakes certainly don’t have four limbs. The ancestors of snakes, however, did have four limbs. Somewhere in the lineage leading to modern snakes, that trait was lost.
Tell students that, because distantly related groups of organisms can sometimes lose the same character, systematists are cautious about using the absence of a trait as a character in their analyses. After all, whales don’t have four limbs either, but snakes are certainly more closely related to other reptiles than they are to whales.
Make sure students understand that derived characters are used in cladograms to explain the branching of lineages. Explain to students that when considering whether a given character is derived, scientists use an “outgroup” for comparison. An outgroup is an organism, or group of organisms, that evolved before the clade being analyzed. For example, reptiles are an outgroup for clade Mammalia. Likewise, amphibians are an outgroup for clade Reptilia. Help students understand why kangaroos are considered an outgroup for the clade Carnivora by asking the following questions.
Ask: Does a kangaroo have hair?
Answer: yes
Ask: If a kangaroo has hair, can hair be a derived trait for the clade Carnivora?
Answer: No. If hair were a derived trait for Carnivora, then only carnivores would have hair, which is not true.
Ask: Specialized shearing teeth are used by carnivores to eat meat. Kangaroos are herbivores. Are they likely to have specialized shearing teeth, then?
Answer: no
Explain that because the outgroup for the clade does not have specialized shearing teeth, that trait is likely to be derived for clade Carnivora. Using dogs and their relatives as the outgroup for clade Felidae, you can follow a similar process to illustrate that retractable claws is a derived trait for that clade.
Explain that a node is a point at which two groups branched off from each other. It also represents the last point at which those two groups shared a common ancestor.
Ask: What is the lowest node?
Answer: The lowest node represents the last common ancestor of all four-limbed animals—members of the clade Tetrapoda.
Ask: What do the forks in this cladogram show?
Answer: The forks in this cladogram show the order in which various groups branched off from the tetrapod lineage over the course of evolution.
Explain that the positions of various characters in the cladogram reflect the order in which those characteristics arose in this lineage. In the lineage leading to cats, for example, specialized shearing teeth evolved before retractable claws. Furthermore, each derived character listed along the main trunk of the cladogram defines a clade.
Ask: What is the derived character for the clade Mammalia?
Answer: hair
Ask: What is a derived character shared only by the clade Felidae?
Answer: retractable claws
Remind students that derived characters that occur “lower” on the cladogram than the branch point for a clade are not derived for that particular clade. Hair, for example, is not a derived character for the clade Carnivora.
Hair
Amniotic egg
Four limbs

22. Constructing a Cladogram
Derived Characters in Organisms
Organism
Derived Character
Backbone
Legs
Hair
Earthworm
Absent
Trout
Present
Lizard
Human
Group students and have those groups use the information on the table to construct a cladogram. Once they have finished, have volunteers answer the following questions.
Ask: What trait separates the least closely related animal from the other animals?
Answer: a backbone
Ask: Do you have enough information to determine where a frog should be placed on the cladogram? Explain your answer.
Answer: No. A frog would be inserted somewhere between the trout and the human, because a frog has a backbone and legs but lacks hair. However, without another derived character, it’s impossible to know if the frog lineage branched off before or after the lizard lineage.
Ask: Does your cladogram indicate that lizards and humans share a more recent common ancestor than either does with an earthworm? Explain your answer.
Answer: Yes, lizards and humans share a more recent ancestor, because the branching point between them is further up on the cladogram than the branching point between humans, lizards, and earthworms. Also, lizards and humans share the derived characters of legs and a backbone.

23. Cladogram

24. Dichotomous Keys
Series of paired statements that describe possible characteristics of an organism.
Step
Leaf Characteristics 1a
Compound leaf (leaf divided into leaflets)
Go to Step 2 1b
Simple leaf (leaf not divided into leaflets)
Go to Step 4 2a
Leaflets all attached at a central point
Buckeye 2b
Leaflets attached at several points
Go to Step 3 3a
Leaflets tapered with pointed tips
Pecan 3b
Leaflets oval with rounded tips
Locust 4a
Veins branched out from one central point
Go to Step 5 4b
Veins branched off main vein in the middle of the leaf
Go to Step 6 5a
Heart-shaped leaf
Redbud 5b
Star-shaped leaf
Sweet gum 6a
Leaf with jagged edges
Birch 6b
Leaf with smooth edges
Magnolia
Tell students that a dichotomous key is used to identify organisms. It consists of a series of paired statements or questions that describe alternative possible characteristics of an organism. The paired statements usually describe the presence or absence of certain visible characteristics or structures.
Explain that each set of choices is arranged so that each step produces a smaller subset. Make sure students understand that dichotomous keys are tools for identification—not classification.
Walk students through the use of a dichotomous key. Point to each step of the table as students consider the options.
Ask: Is this leaf compound or simple?
Answer: Simple. Go to Step 4.
Ask: Do these veins branch out from one central point or off a main vein in the middle of the leaf?
Answer: They branch off a main vein in the middle. Go to Step 6
Ask: Are the edges of this leaf smooth or jagged?
Answer: Jagged. This is a birch leaf.
Click to reveal the next leaf.
Ask a volunteer to walk the class through the use of the dichotomous key and to point to the steps as they progress.
Answer: locust