Biology

IntroductionYour pupils—the black circles in the center of your eyes—do much more than let light in. They continuously a...

IntroductionYour heart keeps beating without you thinking about it because it is controlled by built-in electrical circu...

IntroductionEye color is one of the most noticeable human traits, yet many people are surprised to learn that it is not ...

IntroductionTaste and smell work together to create the rich experience we call flavor. Taste detects a few basic sensat...

IntroductionHearing turns vibrations in the air into meaning. Inside your ear a finely tuned sequence of mechanical, flu...

IntroductionWe notice every day that some sounds seem louder than others even when they come from the same source or tak...

IntroductionYour eyes constantly adjust to changes in light so you can see across a range of environments—from bright su...

IntroductionFingernails and hair are parts of our bodies that keep growing throughout much of life. At first glance this...

IntroductionMuscles grow stronger through a combination of mechanical stress, biological repair, and adaptation. When yo...

IntroductionMost people have experienced a smell that suddenly floods the mind with a clear memory: the scent of a parti...

IntroductionAll multicellular organisms begin as a single cell. From that starting point, trillions of cells diversify i...

IntroductionYour eyes are constantly exposed to dust, microbes, oil, and tiny debris. Yet most of the time they stay cle...

IntroductionPeople have different blood types because of small differences on the surface of their red blood cells. Thos...