This lesson will introduce the characteristics of living things such as the basic characteristics of life and how living things are structured and classified.

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What's Covered

Welcome to this lesson today on organisms, their characteristics, classifications, and their structural organization. Today you will learn all about:

  1. Characteristics that all organisms have in common
  2. The structural organization of organisms
  3. How scientists classify organisms

1. Characteristics That All Organisms Have in Common

Organisms are living things; it's just the scientific word for living things. It could be anything from a small unicellular organism to an elephant to a human to a plant. Anything that's alive and living is an organism. The following are five characteristics that all living things have in common

  1. All living things use energy.
  2. All living things will respond to their environment.
  3. All living things are composed of cells. Cells are the basic units of all life. To be alive, something has to be made up of cells.
  4. All living things will be able to maintain homeostasis, which means they can maintain their internal environment.
  5. All living things are able to grow and reproduce.

Terms to Know


A cell is the basic unit of life.


Homeostasis is an organisms ability to maintain a constant internal environment.

2. The Structural Organization of Organisms

The way living things are structured is from very, very small to large. All living things are made up of atoms and these atoms compose molecules.


You know the human body is made up of a lot of water and water is made up of hydrogen and oxygen. So you're made up of atoms, which compose molecules, and those molecules then compose cells. Now, some living things are only made up of one cell. So for those type of living things, its structure would be atoms make up molecules, which make up that cell.

But for complex organisms like humans, you continue farther down the line here. So our cells will make up tissues and those tissues will then make up organs. Then those organs can make up organ systems and finally, our organ systems will make up the entire organism.

Example All of your organ systems together, such as your digestive system, your nervous system, your lymphatic system, et cetera all work together to make up a full organism of yourself.

To summarize, atoms make up molecules, which make up cells, which make up tissues, which make up organs, which make up organ systems, which make up an entire organism.

The image below can be used to visually understand the process.

3. How Scientists Classify Organisms

Scientists like to classify organisms into different groups based on characteristics they have in common. Every living thing is classified by scientists into kingdom, phylum, class, order, family, genus, and species.

To better understand, take a look at the classification of a panda bear.

You'll notice the inverted triangle. As you move down these groups, they're getting smaller and smaller and smaller. Now, if you think of every living thing in the entire world, it fits into one of five groups, so these groups are actually very, very large. But as you move down our groupings, as you get all the way down to species, it becomes very, very specific where only one organism fits into each type of species. So you’re getting more specific as you move down our classification.

  • KINGDOM: Kingdom is the first classification. All living things can be classified into one of five kingdoms:
    1. Monera
    2. Protista
    3. Fungi
    4. Plantae
    5. Animalia.
  • PHYLUM: Our next level of classification is the phylum. Within the kingdom Animalia, there are actually about 30 different phyla. The phylum for panda bear is a Chordata; this means is that it's a vertebrate, or it has a backbone. Humans have a backbone and thus fit into the same kingdom and phylum as a panda bear. A clam does not have a backbone, so it would be considered in invertebrate and would belong to a different phylum, but would still be in the same kingdom as a panda bear because it's still an animal.

Terms to Know


A vertebrate is an organism that has a backbone.


An invertebrate is an organism that does not have a backbone.

  • CLASS: Then you move down to its class. The panda’s class is Mammalia, which tells us it's a mammal. All mammals share certain characteristics in common. Humans are also considered mammals, so humans are in the same kingdom, phylum, and class as a panda bear.
  • ORDER: The order for a panda bear is Carnivora because it is a carnivore. It eats meat.
  • FAMILY: A panda’s family is Ursidae; that family is a family of bears. Humans do not share this characteristics in common with the panda bear.
  • GENUS & SPECIES: This is when you hear the scientific name of an animal. The scientific name is its genus and species together. The species is specific only to the panda bear; no other animal in the world is the same species as a panda bear.


This lesson has been an overview on the characteristics that all organisms have in common, such as energy, the structural organization of organisms and how scientists classify organisms.

Keep up the learning and have a great day!


Terms to Know
  • Cell

    A cell is the basic unit of life.

  • Homeostasis

    Homeostasis is an organisms ability to maintain a constant internal environment.

  • Invertebrate

    An invertebrate is an organism that does not have a backbone.

  • Vertebrate

    A vertebrate is an organism that has a backbone.