Desmosome is a modification of

The membrane that covers the cytoplasm on the outermost side is:

$A$: Pumps are proteins that use energy to transport substances.
$R$: Pumps are highly specific like enzymes.

The cell envelope is a chemically complex structure consisting of a tightly bound three-layered structure. Which layer is semi-permeable in nature?

Who proposed the concept of the unit membrane for the tripartite structure?

Who proposed the most widely accepted model of the plasma membrane?