The contemporary description of the membrane structure of a cell is known as the endosymbiont hypothesis fluid-mosaic model plasmagel-plasmasol hypothesis lock and key hypothesis induced-fit hypothesis

is called echinoderms

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.