To understand how the environment functions, we often look at it as a 'system'. A system is essentially a group of interacting, interrelated, or interdependent elements forming a complex whole. In Environmental Systems and Societies, we categorize these systems as open, closed, or isolated, based on how they exchange matter and energy with their surroundings.

An open system exchanges BOTH matter and energy with its surroundings.

Real-World Example: A Lake Ecosystem
Consider a lake: it's like a bustling city of organisms! Fish, algae, insects and even the microorganisms - everyone's busy exchanging materials and energy. Water and nutrients flow into the lake from streams or groundwater, and organisms use sunlight (energy) to photosynthesize. Fish may swim out, birds may fly in, water evaporates - this place is always interacting with the world around it. It's like a constant party where guests (matter and energy) are always arriving and leaving!

Now, think about a party where people can't enter or leave, but they can still talk and text with friends outside. This is a closed system! It can exchange energy but not matter with its surroundings.
 

Real-world example Our home planet, Earth! 🌎 It's pretty much a giant party floating in space. Energy, like sunlight, can enter, and energy, like heat, can leave. But generally, matter stays where it is (except for a few lightweight gases like helium escaping or a few spacecrafts we occasionally send out).

This is like a party happening in a vault! No one can get in or out, and no communication is allowed with the outside world. In an isolated system, neither matter nor energy is exchanged with the surroundings.

Real-world example -The Universe 🌌 is a pretty classic example of an isolated system (as far as we know). It doesn't interact with anything else because, well, there's nothing else out there!