Bio- is a prefix (a word part that comes at the beginning of other words) that means “life” or “living things.” It comes from the ancient Greek word bios, which means life.

When you see bio- at the start of a word, you know that word has something to do with living organisms. Biology is the study of life and living things. A biography tells the story of someone's life. Something biodegradable can be broken down naturally by living organisms like bacteria and fungi, returning safely to the earth.

You'll find bio- in dozens of words you encounter in science class and everyday life: biosphere (the parts of Earth where life exists), biome (a large area with similar climate and living things, like a desert or rainforest), biochemistry (the chemistry of living things), and biopsy (when doctors take a small sample of living tissue to examine).

The prefix appears in newer words too. Biofuel comes from living or recently living materials like corn or algae. Your biorhythms are the natural cycles in your body, like when you feel sleepy or alert. Even biotechnology uses that ancient Greek root, connecting cutting-edge science back to the simple idea of life itself.