It's Alive!

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!


Life Science

learning style
Kinesthetic, Visual
personality style
Grade Level
Middle School (6-8), High School (9-12)
Lesson Type
Skill Sharpener

Lesson Plan - Get It!

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  • “Hurt no living thing:
  • Ladybird, nor butterfly,
  • Nor moth with dusty wing,
  • Nor cricket chirping cheerily,
  • Nor grasshopper so light of leap,
  • Nor dancing gnat, nor beetle fat,
  • Nor harmless worms that creep.”

- Christina Georgina Rossetti

  • What thoughts or images crossed your mind when reading this poem?

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.

  • What is a living thing?
  • How is it determined whether something is living or nonliving?

By the end of this lesson, you should be able to better differentiate between what lives and what does not!

  • Do you separate your candies by color before eating them?
  • When your family does laundry, is it sorted by color first?

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:

  • an organism’s cell type.
  • its habitat.
  • the way an organism obtains food and energy.
  • structure and function of its features.
  • the common ancestry of organisms.

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.

biological classification

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:

  • Bacteria
  • Archaea
  • Eukarya

and then into one of six kingdoms:

  • Chromista (Eubacteria)
  • Archaebacteria
  • Protista
  • Fungi
  • Plantae
  • Animalia

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!

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