Answer:
respiratory system
Explanation:
The bronchi become smaller the closer they get to the lung tissue and are then considered bronchioles. These passageways then evolve into tiny air sacs called alveoli, which is the site of oxygen and carbon dioxide exchange in the respiratory system.
Fossils are the remains or impression of the dead animals and plants that lived in the past.
III. enzyme pathways in the mitochondria produce ATP in a process that requires oxygen.
It form the contraction and relaxation of muscle