Biology » The Study of Life » Themes and Concepts of Biology

What is Life?

By the end of this lesson and the next few, you should be able to 

  • Identify and describe the properties of life
  • Describe the levels of organization among living things
  • Recognize and interpret a phylogenetic tree
  • List examples of different sub-disciplines in biology

Biologists Study the Diversity of Life

The study of one living thing always involves studying other living things. Knowing how human life depends on nature and other living things is the only way that humans can expect to understand how to keep Earth healthy.


Biology students studying life in the environment. Image Attribution: The College at Brockport

With this knowledge, researchers can find ways to prevent diseases. Scientists can also find ways to help save living things that are in danger of becoming extinct. They can also solve other various problems.

What is Life?

Biology is the science that studies life, but what exactly is life? This may sound like a silly question with an obvious response, but it is not always easy to define life. For example, a branch of biology called virology studies viruses. Viruses exhibit some of the characteristics of living entities but lack others.


Image Attribution: Image modified by Khan Academy from “Enveloped icosahedral virus,” by Anderson Brito (CC BY-SA 3.0)

It turns out that although viruses can attack living organisms, cause diseases, and even reproduce, they do not meet the criteria that biologists use to define life. Consequently, virologists are not biologists, strictly speaking. Similarly, some biologists study the early molecular evolution that gave rise to life; since the events that preceded life are not biological events, these scientists are also excluded from biology in the strict sense of the term.

From its earliest beginnings, biology has wrestled with three questions: What are the shared properties that make something “alive”? And once we know something is alive, how do we find meaningful levels of organization in its structure? And, finally, when faced with the remarkable diversity of life, how do we organize the different kinds of organisms so that we can better understand them?

As new organisms are discovered every day, biologists continue to seek answers to these and other questions. In the next lesson, we will look at the important properties that biologists use to differentiate living things from nonliving things.

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