Classification of Living Things
Grade 6 · Science · Study Guide
Learn how scientists organize and name the incredible diversity of life on Earth.
With millions of species on Earth, scientists need an organized system to group and name living things. This system is called taxonomy. In the 1700s, Carl Linnaeus invented the system we still use today: a hierarchical classification that groups organisms from broadest to most specific.
The major levels of classification, from broadest to most specific, are: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species. A helpful mnemonic is: 'Dear King Philip Came Over For Great Soup.' The domain is the broadest level — all life is divided into three domains: Bacteria, Archaea, and Eukarya. Eukarya includes all organisms with a true nucleus, divided into four kingdoms: Animalia, Plantae, Fungi, and Protista.
Every species has a two-part scientific name written in Latin called binomial nomenclature. The first part is the genus (capitalized) and the second is the species (lowercase). Both are italicized. Humans are Homo sapiens — Homo is our genus and sapiens means 'wise.' This system means scientists worldwide use the same name for each organism, regardless of language.
Organisms are grouped together based on shared characteristics, including body structure, cell type, how they get food, and DNA similarities. Modern classification increasingly relies on genetic data, which reveals evolutionary relationships that physical traits sometimes hide. All organisms in the same species can interbreed and produce fertile offspring.
| Level | Category | Name |
|---|---|---|
| Domain | Broadest | Eukarya |
| Kingdom | Animalia | |
| Phylum | Chordata | |
| Class | Mammalia | |
| Order | Carnivora | |
| Family | Felidae | |
| Genus | Felis | |
| Species | Most specific | Felis catus |
Key terms
- Taxonomy
- The science of classifying and naming living organisms.
- Classification
- The grouping of organisms based on shared characteristics.
- Domain
- The broadest level of classification; all life is in Bacteria, Archaea, or Eukarya.
- Kingdom
- The second-broadest level; Eukarya includes Animalia, Plantae, Fungi, and Protista.
- Species
- The most specific level; organisms that can interbreed and produce fertile offspring.
- Binomial nomenclature
- The two-part naming system using genus and species (e.g., Homo sapiens).
- Genus
- The classification level just above species; the first part of a scientific name.
- Carl Linnaeus
- 18th-century Swedish scientist who created the modern classification system.
Flashcards
- Taxonomy
- The science of classifying and naming living things.
- Binomial nomenclature
- Two-part scientific naming system: Genus species (e.g., Homo sapiens).
- Domain
- Broadest classification level: Bacteria, Archaea, or Eukarya.
- Kingdom
- Second-broadest level; major kingdoms include Animalia, Plantae, Fungi, Protista.
- Species
- The most specific level; members can interbreed and produce fertile offspring.
- Carl Linnaeus
- Creator of the modern biological classification system in the 1700s.
Practice questions
What is the two-part naming system for organisms called?
- Taxonomy
- Binomial nomenclature
- Domain system
- Phylogeny
Show answer
Answer: Binomial nomenclature
Binomial nomenclature uses a two-part Latin name (genus + species) to give every organism a unique, universally recognized scientific name.
The species level is the most specific level of classification.
Show answer
Answer: True
Species is the most specific classification level. Only individuals that can interbreed and produce fertile offspring belong to the same species.
The broadest level of classification is the ___.
Show answer
Answer: domain
The domain is the broadest level. The three domains are Bacteria, Archaea, and Eukarya — they encompass all known life.
In the scientific name Homo sapiens, which part is the genus?
- sapiens
- Homo
- Both parts together
- Neither part
Show answer
Answer: Homo
In binomial nomenclature, the first word (capitalized) is the genus and the second (lowercase) is the species. Homo = genus, sapiens = species.
Plants and animals belong to the same Kingdom.
Show answer
Answer: False
Plants belong to Kingdom Plantae and animals to Kingdom Animalia — they are different kingdoms within the Domain Eukarya.
Fun facts
- Scientists have named about 1.9 million species, but estimate there may be 8 to 10 million species on Earth — most undiscovered.
- The scientific name for the giant panda is Ailuropoda melanoleuca, which means 'black and white cat-foot' in Greek.
- Tardigrades (water bears) are the only animals known to survive in outer space without any protection — they represent an entire phylum of microscopic animals.
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