The part of a circuit that closes or opens the circuit is called a switch.

Here's why:

* Closed circuit: When a switch is closed, it provides a continuous path for electricity to flow through the circuit. This allows the circuit to function.

* Open circuit: When a switch is open, it breaks the path for electricity. This stops the flow of electricity and prevents the circuit from working.

Think of a switch like a gate in a path. When the gate is open (switch closed), you can walk through (electricity can flow). When the gate is closed (switch open), you can't walk through (electricity can't flow).