Developing bird embryos excrete most of their nitrogenous waste as uric acid because .

Explanation:

1. Developing bird embryos excrete most of their nitrogenous waste as uric acid,there are many reasons of  this, one the reason is that   it has a low solubility in water and it  is less toxic to the embryo as compared to other forms of waste.

2. Birds and many other organisms like reptile excrete nitrogenous waste in the form of uric acid, because it reduces water loss compared to other nitrogenous wastes, but it  requires more metabolic energy as compared to others to produce.

a physical change is being made.

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.