b.endocytosis. simple diffusion is a passive transport that doesn't require energy just like putting a dye on the litter of water and it moves to higher gradient into lower gardient .facilitated diffusion is a type of active transport w/ a barrier in it it requires energy to some biochemical through to pass it is kinda like osmosis but in osmosis it doesnt need energy to pass through it only acts as barrier it just like diffusion in diffusion it has no membrane.it acts the same principle from higher gradient to lower.
