Mealworms sense changes in their environment and move toward conditions they prefer. Place them in a shoe box with one end open to light and the other covered, then watch where they go. Next, set out one wet paper towel and one dry paper towel. Place the mealworms between them. After 30 seconds, check which towel they chose. By the end, you learn whether they prefer light or dark, wet or dry — and how they react to vinegar-soaked towels.

Sensing a change and reacting to it happens even inside a single living cell. You place a culture of living organisms on a microscope slide and watch their normal movement. Then you introduce different substances one at a time — salt, vinegar, caffeinated coffee, decaffeinated coffee, sugar, and cotton fibers. After each addition, the cells respond in distinct ways. Some may speed up. Others may stop moving entirely. New structures may become visible on the organism. That range of reactions reveals how cells respond to both mechanical and chemical changes in their environment.

Sometimes a living thing stops reacting to a repeated change — a process called habituation. Male bettas flare their fins and gills to warn rival males away. You place a mirror against the tank and the betta reacts. Then you remove the mirror and show it again after one minute. Each time you present the mirror counts as one trial. You repeat trials until the betta stops reacting. The next day you test again to see if the fish remembers. Two distinct patterns emerge: extinction, where the warning fails to work, and habituation, where the fish simply gets used to it.