The hollow bones of birds, which keep birds lightweight foe flying, is an example of what

An "adaptation." It's the natural way that birds of flight adapt to their needs or environment which makes them more efficient.

the unequal cytoplasmic division that  results  in  one egg  and three polar bodies ensures that a fertilized  egg has  ample nutrients  forits journey  to  the uterus.

not sure if this is what you'r looking for eubacteria and archaebacteria