Binomial Nomenclature: Definition, Classification & System

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  • 0:02 Binomial Nomenclature…
  • 1:47 Binomial Nomenclature Rules
  • 2:26 Higher Classification
  • 3:33 Practice Example
  • 4:16 Lesson Summary
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Lesson Transcript
Angela Lynn Swafford

Lynn has a BS and MS in biology and has taught many college biology courses.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

Life on Earth is incredibly diverse, with over one million species. But have you ever wondered how all these organisms are named? In this lesson, you'll learn about the scientific naming system called binomial nomenclature.

Binomial Nomenclature Definition

The most well-known living things have common names. For example, you are probably familiar with the small, red insects dotted with little black spots. You might call them 'ladybugs' or 'ladybird beetles.' But did you know there are actually many different species of these insects? Just using common names may make it difficult for scientists to differentiate between them, so every species is given a unique scientific name.

Binomial nomenclature is the formal naming system for living things that all scientists use. It gives every species a two-part scientific name. For example, a ladybug found in the United States goes by the fancy name of Harmonia axyridis.

The first part of a scientific name, like Harmonia, is called the genus. A genus is typically the name for a small group of closely related organisms. The second part of a scientific name, axyridis in this example, is the specific epithet. It is used to identify a particular species as separate from others belonging to the same genus. Together, the genus plus the specific epithet is the full scientific name for an organism.

I bet that you actually already know the scientific name for at least one animal, although you may not have realized it. Ever heard of the dinosaur T. rex? T. rex is actually a scientific name - the 'T' is just an abbreviation of the genus Tyrannosaurus. So the scientific name is actually Tyrannosaurus rex.

Binomial Nomenclature Rules

Because scientific names are unique species identifiers, they ensure that there is never any confusion as to which organism a scientist may be referring. Additionally, there are some important rules that must be followed to keep all binomial names standardized:

  1. The entire two-part name must be written in italics (or underlined when handwritten).
  2. The genus name is always written first.
  3. The genus name must be capitalized.
  4. The specific epithet is never capitalized.

Higher Classification

In addition to giving a species a binomial scientific name, it must also belong to higher levels of classification. Each level of classification is called a taxon (plural is taxa). The broadest taxon is the domain. All living things fit into only three domains: archaea, bacteria, and eukarya. Nested within each of these domains, there are kingdoms. Each kingdom contains phyla (singular is phylum). The taxonomic levels below phylum are class, order, family, genus, and species.

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Additional Activities

What's In a Name

In this activity, students will apply what they've learned during the lesson to name organisms they are familiar with in their life. For example, students may have a pet cat or dog. Thus, they would look up the scientific name for a house cat, Felis catus. Students can then do further research to learn about the other categories of taxonomy that a house cat falls into, such as the family, order, class, phylum, kingdom, and domain. Students may see that animals that are more similar, such as cats and dogs, have more taxonomic categories in common. This is addressed in the reflection questions.


Now that you're familiar with binomial nomenclature, we're going to practice naming some organisms that you are familiar with from your everyday life. For this activity, you will find the taxonomic classification for five organisms that you regularly see. You'll not only look up the binomial nomenclature, but also the other taxonomic categories. Then, answer the reflection questions.

OrganismBinomial NomenclatureFamilyOrderClassPhylumKingdomDomain

Reflection Questions:

  1. What domain and kingdom did most of your organisms fall into? Why do you think that is?
  2. What did you notice about the taxonomic organization of organisms that had more similar features?
  3. Why do you think it is important for scientists to have a specific organization system for living things?

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