The physiological subset of birds are - 1) spirits 2) fat accumulation 3) gonadal development 4) gonadal degeneration 5) napping 6) fat accumulation.
I believe that would be natural selection
cell :- cell is the basic structural and functional unit of life.
Atom :- everything in the universe is made up of atom.
ATP- in the mitochondria.
please vote my answer brainliest. thanks!