Like all living things, humans are "open systems." We're part of - not separate from - our environment, and we continually exchange materials, energy and information with it. What happens when we eat a piece of fruit, for instance? First, we use our senses (taste, smell, sight, touch, hearing) to gather information (Is it ripe?). Then, the fruit's material compounds enter our bodies. As we digest the fruit and break down and absorb its nutrients, energy accumulated from photosynthesis is released. We use this energy to burn carbohydrates through a process called cellular respiration. Being open systems, we return byproducts of respiration - carbon dioxide (CO2) and water vapor (H2O) - back to the atmosphere; and we return some of the fruit¿s water and indigestible solid materials to the earth the form of liquid and solid waste.