The fermentation process is caused by the living organisms called yeast feeding on the sugar in the dough. As the yeast feed on the sugar they release CO² which causes the bread to rise but once the bread in the oven reaches 140° all the yeast are killed off and the fermentation process stops.
In humans, the yolk sac is the
site of origin for blood cells and primordial germ cells. The human yolk sac is
a membrane located outside the embryo and it is connected by a tube through the
umbilical opening to the embryo's midgut. The yolk sac serves as an early site
for the formation of blood and in time, is incorporated into the primitive gut
of the embryo.
Assuming this is multiple choice, the answer would be "niche". An organism's niche is where that certain organism fits into an ecosystem, or what their part to play is.
