The Characteristics of Life
What Does It Mean to Be Alive?
What does it really mean to be alive?
What makes you different from the phone or laptop you're using to read this article?
And what makes you similar to a plant—or even a bacterium?
Biology is the study of life. You, a plant, and a bacterium are all considered living organisms. So that brings us to a big question: What defines life?
Are viruses actually alive? It's one of biology's most debated questions — and your answer needs to be backed by evidence.
This isn't a fill-in-the-blank worksheet. This activity asks you to read real scientific information about viruses, analyze whether they meet the characteristics of life, form your own position, and defend it in writing using evidence and reasoning. That's the kind of thinking that biology exams — and science in general — actually reward.
What's inside:
A 4-page informational reading passage about viruses and the characteristics of life, written to be accessible without being oversimplified
An annotation guide that teaches you how to read scientifically, marking key evidence, identifying claims, and staying engaged with the text rather than just reading passively
A graphic organizer to help you sort and organize your evidence before you start writing, so your argument is structured before you put a single sentence on the page
A writing prompt and drafting pages that walk you through building a complete Claim-Evidence-Reasoning response — the format used in biology courses and science assessments across the country
A peer review checklist to evaluate your work (or a classmate's) before submitting a final response
A grading rubric is included so you know exactly what a strong response looks like before you write it
Perfect for:
Students in Grades 9–12 studying biology, life science, or the characteristics of life
Preparing for assessments that include scientific writing or extended response questions
Anyone who wants to practice forming and defending a scientific argument — a skill that comes up repeatedly through high school and beyond
Parents looking for a structured, intellectually challenging activity that goes beyond standard practice problems
This activity can be completed completely independently at home. Read, annotate, organize your evidence, and write your response. Everything you need to complete it is included, including the rubric so you can assess your own work honestly before you're done.
The 7 Characteristics of Life
Biologists generally use a set of characteristics to define what it means to be alive. These include:
Organization/Order
Response to Stimuli
Reproduction
Growth and Development
Homeostasis
Metabolism
Evolution
We’ll take a closer look at what each of these means, but it’s important to remember:
⚠️ This list isn’t set in stone.
These seven traits are commonly used, but not the only way biologists define life. It’s not about checking off a perfect list—it’s about observing patterns that living things tend to share.
Organization / Order
Living things are highly organized at every level.
Unicellular organisms, or one-celled organisms, have an internal structure that includes atoms, molecules, and organelles, all working together within a single cell.
Multicellular organisms, or many celled organisms, show even more complexity: cells → tissues → organs → organ systems → organism.
Response to Stimuli
Living things respond to changes in their environment.
A plant grows toward sunlight.
Bacteria move away from harmful chemicals.
You pull your hand back from a hot stove.
Reproduction
All living things reproduce.
Unicellular organisms divide to make new cells.
Multicellular organisms reproduce sexually or asexually.
In either case, genetic material is passed to offspring.
Growth and Development
Living organisms grow and go through life stages.
A unicellular organism increases in size.
Humans grow from infants to adults, going through physical and developmental changes.
Homeostasis
Homeostasis is the ability to maintain a stable internal environment.
For example, humans regulate body temperature, blood sugar levels, and water balance, even when the external environment changes.
Metabolism
Metabolism refers to all the chemical processes that occur in an organism to maintain life.
Living things must create and use energy—whether from sunlight (like plants) or food (like animals).
Evolution
Populations of living organisms change over time.
Individuals with traits that are better suited to their environment tend to survive and reproduce.
Over generations, these advantageous traits become more common, a process called evolution.
The Exceptions
As we mentioned earlier, these characteristics are useful—but not universal. Some living things don’t meet every criterion. And some nonliving things seem to meet a few!
Here are some examples that challenge the list:
A Honeycomb
Honeycombs are organized structures that grow as bees build them—but they aren’t alive.
They don’t metabolize, respond to stimuli, or reproduce.
👉 It’s a product of life, not life itself.
A Mule
Mules (a hybrid of a horse and a donkey) cannot reproduce.
But they grow, respond, metabolize, and are made of cells.
👉 Despite one missing trait, mules are considered alive.
A Virus
Viruses can evolve and reproduce, but only inside a host.
They don’t have cells or their own metabolism.
👉 Most biologists do not consider viruses alive—but it’s still debated!
In Conclusion
Scientists are still exploring what it truly means to be alive. The characteristics of life help us make sense of the living world, but they’re not absolute. As we study life on Earth—and potentially beyond—it’s important to stay open to new discoveries and exceptions.
So now we ask you:
What do you think it means to be alive?
