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.

Living cells are not static — they move food and waste through a process called protoplasmic streaming, the flowing movement inside living cells. You can observe this directly by placing a culture of living organisms on a microscope slide and watching their normal movement. Then you introduce different substances one at a time: salt crystals, vinegar, caffeinated coffee, decaffeinated coffee, sugar, and cotton fibers. After each addition, check how the cells respond. Some may speed up. Others may stop moving entirely. New structures may even become visible on the organism. The experiment reveals how cells react to both mechanical and chemical changes in their environment — and how that internal flow shifts in response.