Contributor: Briana Sherbenou. Lesson ID: 12990
What does it mean to be alive? Does it mean happy and active? Are trees and mushrooms and bugs happy? Maybe, but there is scientifically more to being alive. Learn about the building blocks of life!
- Christina Georgina Rossetti
Poetry can be interpreted a thousand different ways, but perhaps you envisioned the critters she spoke of. These organisms are just one small part of a larger category: living things.
By the end of this lesson, you should be able to better differentiate between what lives and what does not!
Identifying characteristics of items can enable you to place them into groups. Similarly, there have been many different ideas about how to organize, or classify, living things.
Classification of living things
A Greek philosopher by the name of Aristotle (above, 384 B.C. – 322 B.C.) is known to be one of the first people to classify organisms. Aristotle placed all organisms into two large groups: plants and animals.
In the 1700s, Carolus Linnaeus (above), a Swedish physician and botanist, classified organisms based on similar structures. He placed all organisms into two main groups, called kingdoms.
Approximately 200 years later, American biologist Robert H. Whittaker proposed a five-kingdom system for classifying organisms.
The classification system of living things is still changing. The current classification method is called systematics. Using all evidence that is known about organisms, systematics can classify these organisms.
This evidence includes:
All living organisms are classified based on very basic, shared characteristics. Organisms within each group are then further divided into smaller groups. These smaller groups are based on more detailed similarities within each larger group.
There are eight total classifications for living things. The "Hierarchy of Biological Classification" pyramid displays seven of them with kingdom being the broadest and species the most specific category. It was only in recent decades that an eighth category was added to classify living things. All living organisms are now classified into one of three domains:
and then into one of six kingdoms:
It took scientists hundreds of years to determine the best way to classify living things. Perhaps they still don’t have it down perfectly. But it still begs the question, "What makes something living?"
Find out in the Got It? section!
Resources Referenced in the Lesson