Taxonomy

Taxonomy

Middle School

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Learning Objectives

• Define taxonomy and explain its importance for understanding the diversity of life.

• Describe the Linnaean system of classification and its eight levels.

• Explain how binomial nomenclature gives every species a unique scientific name.

• Differentiate between classification by physical traits and by evolutionary history.

Key Vocabulary

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Taxonomy

The scientific method of organizing living things into groups based on their shared characteristics.

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Binomial Nomenclature

The formal system of naming species using two Latin words: the genus and species name.

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Phylogenetic Tree

A diagram showing the evolutionary history and relationships among a group of different organisms.

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Cladogram

A diagram showing evolutionary history and the order by which certain traits appeared in organisms.

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Species

A group of similar organisms that can mate with each other and produce fertile offspring.

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What is Taxonomy?

• Taxonomy is how biologists scientifically classify and organize all living things on Earth.

• There are about 8.6 million species, so this classification system is very important.

• Its purpose is to understand similarities and differences between various living organisms.

• Organisms are sorted into groups called taxa, from kingdom to species.

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Multiple Choice

What is the primary reason why biologists classify organisms?

• To create a complete list of all living things.

• To organize and understand the vast diversity of life on Earth.

• To determine which species are the most advanced.

• To assign every organism a unique name.

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Early Classification Systems

• Aristotle, a Greek philosopher, developed one of the first classification systems.

• His “Great Chain of Being” ranked organisms into eleven different levels.

• He introduced the key ideas of genus (a general group) and species.

• These early systems grouped animals based on obvious physical traits like movement.

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Multiple Choice

How did Aristotle arrange organisms in his 'Great Chain of Being'?

• Based on how complex or 'advanced' he believed them to be.

• Based on their method of obtaining energy.

• Based on their cell structure.

• Based on their evolutionary relationships.

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The Linnaean Hierarchy

• Carolus Linnaeus introduced this system for classifying organisms into 8 hierarchical levels.

• The 8 levels are: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

• As you go down the levels, organisms become more closely related and similar.

• A house cat and wolf are in Class Mammalia, but have different families.

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Multiple Choice

According to the Linnaean hierarchy, which of the following is true?

• Organisms in the same Genus are more closely related than organisms in the same Family.

• The Kingdom is the smallest and most specific level.

• The Domain is the least inclusive group.

• Organisms in the same Class are more closely related than organisms in the same Order.

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Criteria for Classification

• Cell Structure: Is it a prokaryote (no nucleus) or a eukaryote (has a nucleus)?

• Number of Cells: Is it unicellular (one cell) or multicellular (many cells)?

• Reproduction: Does it reproduce asexually (one parent) or sexually (two parents)?

• Energy: Is it an autotroph (makes food) or a heterotroph (eats other organisms)?

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Multiple Choice

An organism that is made of many cells and makes its own food would be described as...

• Multicellular and Autotrophic.

• Unicellular and Autotrophic.

• Multicellular and Heterotrophic.

• Unicellular and Heterotrophic.

Binomial Nomenclature

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Human

• ​The scientific name for a human is Homo sapiens.

• ​​The genus name, Homo, is always capitalized.

• ​The species name, sapiens, is written in lowercase.

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House Cat

• ​A house cat’s scientific name is Felis catus.

• ​​Felis is the genus name for this species.

• ​The species name, catus, is never capitalized.

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Apple

• ​The scientific name for an apple is Malus domestica.

• ​​The genus name for this type of apple is Malus.

• ​Its species name, domestica, has a lowercase letter.

Multiple Choice

Which two levels of classification are used to create an organism's scientific name in binomial nomenclature?

• Kingdom and Phylum

• Family and Genus

• Genus and species

• Order and Family

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Modern Phylogenetic Classification

Phylogenetic Tree

• A phylogenetic tree is a diagram that shows the evolutionary history among different organisms.

• This modern classification method focuses on the evolutionary relationships between living things.

• These relationships are often confirmed by looking at genetic similarities in their DNA.

Cladogram

• A cladogram is a diagram that shows the order in which certain traits appeared.

• It shows which organisms share a common ancestor and all of its descendants.

• This group is called a clade, showing how birds evolved from reptiles.

Multiple Choice

What is the main difference between the original Linnaean system and modern phylogenetic classification?

• Phylogenetic classification focuses on evolutionary history, not just physical traits.

• The Linnaean system is a diagram, while phylogeny is a written list.

• Phylogenetic classification is only for animals, not plants.

• The Linnaean system uses eight levels, while phylogeny uses only five.

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Common Misconceptions About Classification

Misconception	Correction
Classification is based on simple traits like movement or habitat.	Classification uses evolutionary history, genetics, and cell structure.
Humans are at the "top" of evolution.	Evolution is a branching tree, not a ladder with humans at the top.
The Linnaean classification system is outdated and no longer used.	It is the foundation of modern taxonomy, updated with genetic data.
Scientific names are not that important.	They are essential for clear global communication about species.

Multiple Choice

If two different organisms belong to the same Order, what does this tell us about their other shared classification levels?

• They do not have to share any other levels.

• They must also belong to the same Family.

• They must also belong to the same Class.

• They must also belong to the same Genus.

Multiple Choice

Which set of characteristics best describes an organism in the Animalia Kingdom?

• Unicellular, Prokaryote, Autotroph, reproduces asexually.

• Multicellular, Eukaryote, Autotroph, reproduces sexually.

• Multicellular, Eukaryote, Heterotroph, reproduces sexually.

• Unicellular, Eukaryote, Heterotroph, reproduces asexually.

Multiple Choice

A cladogram shows that birds are part of the reptile clade because they evolved from ancient reptiles. How does the traditional Linnaean system potentially obscure this relationship?

• By grouping birds and reptiles into the same Kingdom.

• By placing birds and reptiles in separate Classes based on physical differences.

• By focusing only on the cellular structure of birds and reptiles.

• By not using Genus and species names for birds and reptiles.

Multiple Choice

Scientists discover a new unicellular organism that has no nucleus and lives in an extremely hot volcanic vent. Based on this information, what is the most likely Domain for this organism and why?

• Domain Eukarya, because it is a single-celled organism.

• Domain Bacteria, because all bacteria are unicellular.

• Domain Archaea, because it is a prokaryote that lives in extreme environments.

• Domain Plantae, because it does not have a cell wall.

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Summary

• Taxonomy is the science of classifying all living things on Earth.

• The Linnaean system uses an eight-level hierarchy to classify organisms.

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

• More shared classification levels mean organisms are more closely related.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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