Plasma membranes allow certain materials to pass through them. Investigate how this property contributes to homeostasis.

this

The Plasma membrane maintains the homeostasis throughout a cell because it filters what substances go in and out of the cell. If there is too much of a substance in a cell the plasma membrane quickly disposes it and when there is not enough of a substance in a cell the plasma membrane lets the substance in.

or this

A major role of the plasma membrane is transporting substances into and out of the cell. The plasma membrane is selectively permeable, allowing only certain substances to pass through. ... Cell transport helps cells maintain homeostasis by keeping conditions within normal ranges inside all of an organism's cells.

one of them should have been the answer ;)