In terms of permeability,the cell wall and plasmalemma are:

$A$ boy is studying the transport of a certain type of molecule into a cell. He finds that the transport slows down when the cells are poisoned with a chemical that inhibits energy production. Under normal circumstances,the molecules studied by the boy are probably transported by

Membrane proteins are held in the bilayer mainly by

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

Who proposed the $Fluid$ $Mosaic$ $Model$ for the cell membrane?

That the cell membrane is selectively permeable can be best deduced by