What Defines Something as Living?

Take a look at your surroundings. Do you see anything that possesses life? You, of course, are alive, as are any individuals you can observe, such as friends or family members. Can you spot an animal? How about a plant? These entities are also alive. But what about the soil that a plant grows in? The food in your lunch box? Are these things considered alive?

Initially, it may appear simple to distinguish between what is alive and what is not. However, upon closer examination, it can become more challenging. Consider the smallest elements in our world. Are electrons alive? What about viruses and bacteria?

Even scientists hold different opinions on what constitutes life. According to NASA, life is defined as “a self-sustaining chemical system capable of Darwinian evolution.” Some experts provide more specific definitions, outlining seven characteristics of life.

What are these characteristics? The first is organization. This means that living things are composed of cells. To be classified as alive, something must have specialized components that perform specific functions. Second, living things must have metabolism. This encompasses all the biochemical reactions that occur within a living organism.

The third characteristic is homeostasis. This refers to the ability of living things to regulate the conditions within their bodies. Living things also undergo growth and reproduction, although this can manifest in various ways. Living things must also respond to changes in their environment. Lastly, the final characteristic of life is evolution. Living things must possess the capacity to change over time.

However, not all experts agree with these characteristics of life. After all, it is relatively easy to find examples that do not align with these criteria. Take, for instance, the mule. Like most animal hybrids, it is unable to reproduce. Nevertheless, most individuals would still consider the mule to be alive. Nonetheless, the characteristics of life serve as a starting point for comprehending what defines something as living.

There are still many unanswered questions. For example, what about viruses? Experts hold conflicting opinions on whether they are living organisms. Some argue that they are not, as viruses cannot reproduce without assistance from a host cell. Moreover, they are not composed of cells. On the other hand, others disagree, as viruses possess many other characteristics of life.

What about life on other planets? Will it resemble life on Earth? Most likely not. Consequently, those in search of extraterrestrial life must maintain open minds regarding what constitutes life. Our understanding of this concept will likely continue to develop as humans venture deeper into the universe.

What are your thoughts? Do you classify viruses as living organisms? Do the characteristics of life seem accurate to you? How do you envision alien life? Humans are still seeking definitive answers to these questions and many more.

Give It a Try

Are you eager to learn? Seek the assistance of an adult who can guide you through one or more of these enjoyable educational activities!

  • Imagine how life on another planet might appear. Create a drawing of an alien life form and give it a name. Reflect on its characteristics, such as its diet, social behavior, movement, and preferred habitat. Write a brief paragraph describing your imaginary alien life form on the back of your drawing.
  • Life is diverse and challenging to define. Explore some rare creatures that exist on Earth. Read about a few of them and then summarize what you’ve learned for a friend or family member.
  • Expand your knowledge about viruses and take a stance on whether they are considered living organisms or not. Create a poster to educate others about viruses, including your opinion on their status as living entities and at least one supporting reason for your viewpoint.


  • https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-biology-and-the-scientific-method/a/what-is-life (accessed 06 Oct. 2020)
  • https://www.forbes.com/sites/jvchamary/2019/03/27/what-is-life/#65457da51c77 (accessed 06 Oct. 2020)
  • http://bioprinciples.biosci.gatech.edu/module-1-evolution/what-is-life-2/ (accessed 06 Oct. 2020)
  • https://www.britannica.com/science/life (accessed 06 Oct. 2020)
  • https://www.sciencefocus.com/space/what-would-alien-life-actually-look-like/ (accessed 06 Oct. 2020)

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