<prompt> Yolk sac is derived fromHypoblastsEpiblastsSyncytiotrophoblastNone  <response>: Ans. is a i.e., HypoblastsThe yolk sac develops from hypoblast cells. By the end of 2nd week the lower half of primary yalk sac pinches off to form definitive yolk sac, while a second wave of hypoblast cells form inner lining of definitive yolk sac. 