Assertion: membrane's protein | /r/HasProperty | exposed to cell's external environment
Facets:
Source sentences:
text: Some of these form channels or pores through which certain substances can pass (facilitated diffusion), whilst others bind to a substance on one side of the membrane and carry it to the other side of the membrane (active transport) Proteins exposed to the cell's external environment often have carbohydrates attached to them which act as antigens (e.g. blood groups