•Inputs and outputs of a system
•Structure of the system (multiple levels), e.g., organisms, populations, communities, ecosystems
•Processes that occur within it, e.g., photosynthesis, cellular respiration
•Relationships between components, e.g., food webs, energy transfer
•Structures and processes in the system can affect the system in focus
•Change over various timescales, e.g., short-term or evolution over generations
•Recurring patterns, cycles and feedback loops
•Other factors such as biological, political, historical etc.