Plasma Membrane Permeability

Impermeable

nothing is able to cross the membrane

Freely Permeable

any material can cross the membrane without difficulty

Selectively permeable

the membrane allows some material to pass through while inhibiting other material from crossing

What are the passive processes of permeability?

Diffusion, osmosis, and facilitated diffusion

Diffusion

passive molecular movement from an area of relatively high concentration to an area of relatively low concentration

Osmosis

the diffusion of water molecules (rather than solutes) across a selectively permeable membrane

Facilitated Diffusion

passive transportation of solutes across a barrier with the assistance of a carrier protein

What are the types of active processes?

Active transport, endocytosis, and exocytosis

Active Transport

the ATP-dependent

Endocytosis

the packaging of extracellular materials into a vesicle for importation into the cell

What are the types of endocytosis?

Pinocytosis, phagocytosis, and receptor-mediated endocytosis

Pinocytosis

when vesicles form at the plasma membrane and bring extracellular fluid and small molecules into the cell

Phagocytosis

when vesicles form at the plasma membrane and bring solid particles into the cell

Receptor-mediated endocytosis

when target molecules bind to specific receptor proteins on the membrane surface, triggering vesicle formation

Exocytosis

the release fluids and/or solids from cells when intracellular vesicles fuse with the plasma membrane