Classification of Living Things

Classification of Living Things

Middle School

​

Learning Objectives

• Define taxonomy and explain why we classify living things.

• Describe the Linnaean system's eight levels and binomial nomenclature.

• Explain the key differences between the three domains and six kingdoms.

• Compare the Linnaean and phylogenetic systems for classifying organisms.

• Identify the key features of the six kingdoms of life.

Key Vocabulary

​

Taxonomy

The scientific study of naming, defining, and classifying organisms based on their shared characteristics.

​

Binomial Nomenclature

A two-part naming system using the genus and species to give a unique name to organisms.

​

Autotroph

An organism that can produce its own food, typically using light, carbon dioxide, and water.

​

Heterotroph

An organism that cannot make its own food and gets nutrition from other organic substances.

​

Eukaryotic

A cell that contains a nucleus and other membrane-bound organelles, characteristic of complex organisms.

​

Prokaryotic

A single-celled organism that lacks a membrane-bound nucleus or any other membrane-bound organelles.

​

​

What is Taxonomy?

• Taxonomy is the science of naming, grouping, and classifying all living things.

• ​It organizes life forms to help scientists find, identify, and study them.

• Early systems, like Aristotle’s, were based on simple physical features.

• Carolus Linnaeus is known as the inventor of modern taxonomy.

​

Multiple Choice

According to the slide, who is credited as the inventor of modern taxonomy?

• A taxonomist

• Charles Darwin

• Aristotle

• Carolus Linnaeus

​

​

The Linnaean System & Binomial Nomenclature

• The Linnaean system classifies organisms into groups called taxa based on shared traits.

• It uses a hierarchy with eight main levels, from Domain to Species.

• Binomial nomenclature gives each organism a unique, two-part scientific name in italics.

• The name has the capitalized Genus and lowercase species, like Homo sapiens.

​

Multiple Choice

Which of the following correctly represents the format for binomial nomenclature?

• species Genus

• Domain Kingdom

• Genus species

• Genus Species

​

​

The Three Domains and Six Kingdoms

• All life is classified into one of three domains: Archaea, Bacteria, and Eukarya.

• The Eukarya domain includes all organisms whose cells contain a nucleus.

• Within the domains are six kingdoms: Bacteria, Archaea, Protista, Fungi, Plantae, and Animalia.

• Organisms are placed in kingdoms based on cell count, nucleus, and how they get energy.

​

Multiple Choice

An organism that is multicellular and has a nucleus in its cells would be classified into which domain?

• Eukarya

• Monera

• Bacteria

• Archaea

Kingdoms: Archaea, Eubacteria, and Protista

​

Kingdom Archaea

• ​These organisms are unicellular and do not have a nucleus.

• ​​They are known for living in very extreme environmental conditions.

• ​This includes hot, cold, salty, or no-oxygen environments.

​

Kingdom Eubacteria

• ​These are also unicellular organisms that lack a nucleus.

• ​​They are commonly found in everyday places all around us.

• ​They play important roles in many ecosystems on Earth.

​

Kingdom Protista

• ​These are mostly unicellular organisms that have a nucleus.

• ​​This diverse group includes both autotrophs and heterotrophs.

• ​Examples include organisms like algae, amoeba, and paramecium.

Multiple Choice

A scientist discovers a new unicellular organism that lives in a boiling hot spring and does not have a nucleus. In which kingdom would it most likely be classified?

• Protista

• Archaea

• Fungi

• Eubacteria

Comparing Three Kingdoms

​

Kingdom Fungi

• Fungi are mostly multicellular and are unable to move.

• They are heterotrophs, absorbing nutrients from other organisms.

• Their cells are surrounded by a protective cell wall.

​

Kingdom Plantae

• Plants are multicellular organisms that are unable to move.

• They are autotrophs, making their own food using sunlight.

• Like fungi, their cells also have a protective cell wall.

​

Kingdom Animalia

• Animals are multicellular, and most are able to move.

• They are heterotrophs that eat other organisms to get energy.

• Unlike fungi and plants, their cells do not have a wall.

Multiple Choice

What is a key difference between organisms in Kingdom Animalia and Kingdom Plantae?

• Animals are heterotrophs and motile, while plants are autotrophs and sessile.

• Animals are autotrophs, while plants are heterotrophs.

• Animals are unicellular, while plants are multicellular.

• Animals have cell walls, while plants do not.

​

​

Comparing Classification Systems

Linnaean Classification

• ​Groups organisms based on visible physical traits and characteristics.

• ​​It was the primary method used for centuries to organize life.

• ​This method does not show the evolutionary history between species.

Phylogenetic Classification

• ​Groups organisms based on their shared evolutionary history and ancestry.

• ​​It shows how closely related different species are to one another.

• ​Uses diagrams like phylogenetic trees to illustrate these relationships.

Multiple Choice

What is the primary basis for phylogenetic classification?

• Where an organism lives

• Evolutionary history and relationships

• Shared physical traits

• What an organism eats

​

Common Misconceptions About Classification

Misconception	Correction
Fungi are a type of plant.	Fungi absorb nutrients; plants make their own food.
All single-celled organisms are bacteria.	Archaea and protists can also be single-celled.
Classification is only based on looks.	It relies on evolutionary relationships and genetic similarity.
Sponges and jellyfish are plants or fungi.	They are classified in the Kingdom Animalia.

Multiple Choice

An organism is named Acer rubrum. What can you determine about its classification from this name?

• Its family is Acer and its genus is rubrum.

• Its class is Acer and its order is rubrum.

• Its kingdom is Acer and its phylum is rubrum.

• Its genus is Acer and its species is rubrum.

Multiple Choice

How can you distinguish between an organism in Kingdom Fungi and one in Kingdom Protista?

• Fungi lack a cell wall, while Protists have one.

• Fungi are prokaryotic, while Protists are eukaryotic.

• Fungi are mostly multicellular and sessile, while Protists are mostly unicellular and motile.

• Fungi are autotrophs, while Protists are heterotrophs.

Multiple Choice

Scientists discover a new organism that is multicellular, has a cell wall, and makes its own food. A cladogram shows it shares a recent common ancestor with ferns. How would this organism likely be classified?

• In Kingdom Plantae, because it is an autotroph with a cell wall.

• In Kingdom Protista, because it has a common ancestor with other eukaryotes.

• In Kingdom Fungi, because it has a cell wall.

• In Kingdom Animalia, because it is multicellular.

Multiple Choice

If two organisms are in the same Order, what can you conclude about their relationship compared to two organisms in the same Phylum?

• Organisms in the same Phylum are always more closely related.

• They are equally related.

• Organisms in the same Order are more closely related.

• They are not related at all.

​

Summary

• Taxonomy is the science of classifying life using the Linnaean system's hierarchy.

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

• Life is divided into three domains and six kingdoms based on cell characteristics.

• Phylogenetic classification focuses on evolutionary history and relationships between organisms.

Poll

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

• 1

• 2

• 3

• 4