Sift together flour, baking powder, sugar, and salt in a medium bowl. Cut in shortening with a pastry blender until mixture resembles coarse meal. Dissolve soda in buttermilk; pour evenly over flour mixture, stirring until dry ingredients are moistened.
Turn dough out onto a floured surface; knead 10 to 12 times.
Roll dough to 1/2-inch thickness; cut with a 2-inch biscuit cutter. Place biscuits on a greased baking sheet. Bake at 450° for 10 minutes or until lightly browned.