The things us Americans call biscuits get their leavening not organically from yeast, but chemically from the baking powder. Our dough rises because agents in it release carbon dioxide. Organic leavening creates carbon dioxide through fermentation. Chemical leavening creates it through a chemical process called neutralization. When an acid and an alkaline react - neutralize each other - the by-product is carbon dioxide.
Baking powder contains two pairs of of acid and alkaline ingredients in a stable base. One pair reacts when it gets wet, the other when it gets hot. The first pair does its job during the mixing process when the liquid is added to the remaining ingredients. The second pair is heat-sensitive but not water sensitive and activates when it reaches about 150F.
Which points out another interesting difference between these 'quick breads' and yeast breads: The yeast gets killed off at about 145F, which means that our yeast breads stop rising after about the first five minutes in the oven, while quick breads are just getting statred at that point.