How would a decaying tree be classified

The answer is non-living and biotic. Non-living because the processes that characterize a living organism (such as respiration, growth, response to stimuli, nutrition, and etcetera ) cease in the tree. Biotic because the tree is still composed of molecules associated with life such as proteins, carbohydrates, cellulose, lignin, and etcetera, even though the tree is dead.

is in the form atp or adenosine triphosphate

several tissues working together form an organ, and several organs together make up an organisms.

the group of cell that carries out special jobs are tissue.