Yolk sac is derived from
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.
Hypoblasts
Epiblasts
Syncytiotrophoblast
None