By the cell membrane located on the outside of an animal or plant cell.
Materials pass through the cell membrane, which acts as a barrier between the cell's interior and the external environment. The cell membrane is selectively permeable, allowing certain substances to pass through while blocking others.
The Cell Membrane
permeability
A+ through nuclear pores
What you are considering when you are referring to how easily materials can pass through a membrane is how permeable the cell wall or membrane is.
cell membrane
permeability
permeability
the cell membrane
Mary Jane Mary Jane
endocytosisfacilitated diffusionexocytosissimple diffusionactive transportpassive transport
They pass through the cell walls and or membranes depending on wether or not its a plant or animal cell. Animal cells have only membranes. Plant cells have both.