Theme: Systems Systems are defined by placing boundaries around inter-related entities to make them easier to study. There are systems in nature as well as man-made systems. Any change to a part of the system could affect the rest of the system to different extents. That is, a part of the system may not work (well) if another is missing or not working (well). Conversely, when the parts are put together, they can perform functions that cannot be carried out by the parts alone. Essential Takeaways: - A system is a whole consisting of parts that work together to perform a function. - Parts of a system can influence one another and hence the whole system. - Inputs to a system can determine the outputs of the system.