Classification and Taxonomy

Classification and Taxonomy

Middle School

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Learning Objectives

• Describe the purpose of taxonomy and two systems of classification.

• List the eight levels of the Linnaean classification system in the correct order.

• Explain how to write a scientific name using binomial nomenclature.

• Interpret a simple cladogram to understand how different species are related.

Key Vocabulary

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Taxon

A specific group of organisms in a classification system, like a kingdom, phylum, or class.

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Binomial Nomenclature

The formal two-part naming system for species, using genus and species names like Homo sapiens.

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Domain

The highest and most general taxonomic rank, which is ranked right above the kingdom level.

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Phylogenetic Tree

A branching diagram that shows the evolutionary history and relationships among a group of different organisms.

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Cladogram

A diagram that shows the evolutionary history and common ancestry among a group of related organisms.

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How Scientists Classify

Physical Characteristics

• Scientists compare physical features of organisms to understand how they might be related.

• This includes looking at skeletal structures and specific body adaptations for their environment.

• They also study how different living things develop, such as from an egg.

Chemical Characteristics

• Scientists analyze chemical data, like DNA and RNA, to find genetic similarities.

• Similarities in the genetic code often mean that two species are closely related.

• Tracking genetic mutations helps explain how species can change over many generations.

Multiple Choice

According to the slide, what are the two primary types of characteristics scientists use to determine relationships between organisms?

• Skeletal structures and DNA analysis

• Living in the same habitat and eating the same food

• Taxonomy and Classification

• Physical characteristics and Chemical characteristics

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The Linnaean System of Classification

• This system organizes organisms into eight ranked levels based on shared characteristics.

• The levels are Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species.

• Organisms become more closely related as you move from domain to species.

• The more classification levels that two organisms share, the more related they are.

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Multiple Choice

Based on the hierarchy provided, if two organisms belong to the same Order, which of these other levels must they also share?

• Species

• Family

• Genus

• Class

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Binomial Nomenclature

• Binomial nomenclature is a two-part scientific naming system for living things.

• The scientific name consists of two Latin words written in italics.

• The first word is the genus (capitalized); the second is the species (lowercase).

• For example, a domestic cat’s scientific name is Felis catus.

Multiple Choice

Which of the following scientific names is written correctly according to the rules of binomial nomenclature?

• Canis Lupus

• Felis catus

• malus Domestica

• Homo Sapiens

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What Is Phylogenetic Classification?

• It groups organisms based on their shared evolutionary history and common ancestors.

• A phylogenetic tree shows this history and groups organisms into clades.

• For example, these trees show that birds evolved directly from reptiles.

• This is different from the Linnaean system which separates birds and reptiles.

Multiple Choice

What does a cladogram or phylogenetic tree primarily represent?

• The evolutionary history and common ancestry of organisms.

• The eight levels of the Linnaean classification system.

• The physical similarities between different organisms.

• The geographic location where different species live.

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Common Misconceptions About Classification

Misconception	Correction
Classification is only based on how an organism looks.	Modern classification also uses genetic information like DNA to see how organisms are related.
A scientific name is just the species name.	A scientific name has two parts: the genus and the species.
The Linnaean system and phylogenetic trees are separate.	The Linnaean system is organized to show evolutionary relationships from phylogenetic trees.

Multiple Choice

A scientist discovers two different species of frog. Based on the Linnaean hierarchy, which of the following shared classifications would indicate the closest relationship between them?

• Shared Kingdom

• Shared Phylum

• Shared Family

• Shared Genus

Multiple Choice

Why is using binomial nomenclature, like Malus domestica for an apple, more useful for scientists than using a common name?

• Because Latin names sound more scientific.

• Because common names are too difficult to remember.

• Because it describes the physical appearance of the organism.

• Because it provides a unique, standardized name understood globally to avoid confusion.

Multiple Choice

A cladogram shows that sharks are at the base, followed by ray-finned fish, and then amphibians. What does this arrangement imply about the evolutionary history of these groups?

• Sharks, ray-finned fish, and amphibians all evolved at the same time.

• Sharks are the most complex and recently evolved group of the three.

• Amphibians evolved before sharks.

• Ray-finned fish share a more recent common ancestor with amphibians than they do with sharks.

Multiple Choice

If genetic analysis revealed that an organism placed in the genus Felis is actually not a descendant of the same ancestor as other Felis species, what is the most likely outcome for its classification?

• The entire phylogenetic classification system would be abandoned.

• It would remain in the genus Felis because of its physical similarities.

• Its species name would be changed, but its genus would stay the same.

• It would be moved to a different genus or a new genus would be created to reflect its true evolutionary history.

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Summary

• Taxonomy classifies organisms using the 8-level Linnaean system.

• Binomial nomenclature gives every species a unique two-part scientific name.

• Phylogenetic classification shows evolutionary history using physical and genetic evidence.

• The more levels organisms share, the more closely they are related.

Poll

On a scale of 1-4, how confident are you about classifying organisms using the concepts from today's review?

• 1

• 2

• 3

• 4