Question

what is the role of protein and lipid in plasma membrane

Answer 1

protein and lipid in cell membrane is a permeable membrane and don't let any harmful substances to get in the cell. Plasma membrane is composed of lipids and proteins. Lipids give flexibility to membranes and proteins maintain the chemical climate of the cell and help in transfer of molecules across the membrane.
The lipid bi layer is semi permeable, that is, it allows selected molecules to diffuse across the membrane.

Answer 2

Scattered in the lipid bolster of cholesterol molecules, which help to keep the membrane fluid consistent membrane proteins are important for transporting substances across the cell membrane.