Characteristics of Living Things

Living things are complex.

The study of Biology examines all aspects of living things, from the very atoms that make up our molecules, to the interaction that we have with the environment.

Fortunately for us, living things can be organized into several levels that nest within each other. This organization is based on the increasing complexity of the structure and/or function of each level. Collectively, we call this a Hierarchy of Organizations. It is a pattern that all living things are a part of. Once you learn about the pattern (how life is organized) you'll see it everywhere!

Spend a few minutes studying this picture. What traits do these 6 groups have in common?

They are all living organisms that share certain characteristics!

Organization of Life

Look at the diagram showing you the Hierarchy of Organization below. Start with the atom and trace each level of organization in your own body from smallest to biggest. Note that you (a human, a living thing) take part in every level of the hierarchy!

Study the table below to learn more about each level. You will be expected to know the definitions and examples for each, as well as the order of the levels.

Organization of Life
Level	Definition	Example
Biosphere	The portion of the Earth and atmosphere where life exists	The air, water, and terrestrial areas where life can exist; biomes plus the atmosphere
Ecosystem	The living things in an area, along with their environment	The seashore includes all the animals, plants, and algae as well as the wind, minerals/rocks, water, and weather
Community	All of the populations that live in a defined area	All the animals, plants, fungi, and bacteria that live together in a forest
Population	A group of individuals in the same species within a defined area	Squirrels in your neighborhood, algae growing in a test tube
Organism	A living thing (maybe unicellular- see cell)	Blue Whale, Mushroom, Pine Tree
Organ System	A group of organs that work together to perform a function	Circulatory System, Nervous System
Organ	A group of different tissues that work together to perform a function	Heart, Brain, Kidney, Skin
Tissue	A group of cells that perform a similar function	Muscle tissue, Blood
Cells	The basic unit of structure and function in living things	Muscle cell, E.colibacterium
Organelle	One of many cell structures that have a specialized function	Nucleus, ribosome, mitochondria, chloroplasts
Macromolecule	A large, complex molecule; essential molecule for life's processes/structures	Carbohydrates, Proteins
Molecule	Different atoms that are chemically bonded together	Water, Carbon Dioxide
Atom	The basic unit of matter; building blocks of molecules	Carbon, Hydrogen, or Oxygen atoms are common in living things

Why are the Characteristics of Living Things Important?

You might be wondering why Biologists have a list of the characteristics of life. We can all pretty much tell if something is alive or not, right?

A rock: not living.
A spider: alive.

It seems simple enough, but sometimes it is not so obvious.

Understanding the characteristics that make something alive helps us to define what is essential for survival. It also helps us better identify new forms of life, whether that be new species on our own planet, or perhaps on others. Scientists still debate which characteristics are essential or most important to define life.

Humans, a venus fly trap, mushrooms, and even bacteria share all of these characteristics for life:

Made of one or more cells
Obtain and use energy
Respond to the stimuli
Reproduce
Grow and Develop
Maintain Homeostasis
Display adaptation over time

Let's Recap

Watch this presentation for a review of the characteristics of living things.

Characteristics of Living Things Challenge and Before You Go

Practice Time! Use the knowledge you learned from the lesson to complete the practice activities below.

Before You Go - You Need To Know

The following key points are from the explore section of the lesson. You must know the following information before moving to the next lesson. This is just a summary of the key points.

What is the organization of life?

Atoms, molecules, macromolecules, organelle, cell, tissue, organ, organ system, organism, population, community, ecosystem, biosphere

What are the characteristics that all living things have in common?

Cells, reproduce, homeostasis, heredity, response, growth and development, adaptation, energy

Are viruses living or nonliving?

Nonliving – not made of cells and cannot reproduce without a host

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