the wall and membrane of Giardia cysts may be compared to that of gram-positive cells. a giardia cyst has an outer wall encloses a membrane. the outer wall is composed of a tightly packed layer of chitinous elements and is of the order of 300-500 nanometres thick [Kulda and Nohynkova 1978, Sheffield and Bjorvatn 1977]. this is much thicker than bacteria cells thus giving the cyst greater protection agianst the external environment.