The part of the cell that is stimulated by outside chemicals, triggering it to carry out specific functions, is the cell membrane.

Here's why:

* The cell membrane is the outer boundary of the cell. It acts as a barrier, controlling what enters and exits the cell.

* It contains receptors. These are specialized proteins that bind to specific molecules outside the cell, like hormones, neurotransmitters, or other signaling molecules.

* Binding of these molecules to receptors triggers a cascade of events inside the cell. This can involve activating enzymes, changing gene expression, or altering the cell's shape or movement.

So, in essence, the cell membrane acts like a "gatekeeper" and a "signal receiver" for the cell, enabling it to respond to its environment.