The two layers of phospholipids that make up the cell membrane form a structure know as the

answer; i believe that the correct answer is(d) nondisjunction during meiosis;

fumikage isn't really a bird, and tsuyu does have teeth. tsuyu has a transformation quirk which still allows her to be partially human. otherwise we'd have a large frog running around. fumikage has teeth because again, he isn't a bird. his head was a quirk mixture if i'm correct.

i'd have to say the answer is probable the second option "the geosphere interacting with the atmosphere"