cell membrane
All particles trying to get into the cell must get through the cell membrane. The cell membrane is selectively permeable, which means that it can select what goes in and what goes out. The structure of a cell membrane is called a lipid bilayer, which is two layers of phospholipids.
The mitochondria uses the most oxygen in a cell because it is where cellular respiration takes place, producing the majority of the cell's ATP energy supply through the consumption of oxygen and glucose.
The lungs take in oxygen directly from the air.
Oxygen is diffused into the cells when the cells need oxygen to carry out their functions. Oxygen is carried inside a red blood cell where the oxygen is bound to the hemoglobin. Red blood cells travel in the blood as part of the circulatory system and diffuse or give oxygen to the cells which need them. Oxygen is important for many cellular functions.
the cell
The lungs are responsible for directly accepting oxygen from the atmosphere during the process of breathing. Oxygen is taken in through the lungs' alveoli, which are tiny air sacs where gas exchange occurs, allowing oxygen to enter the bloodstream and carbon dioxide to be released.
Iron found as part of hemoglobin which comprises most of each red blood cell (RBC).
Eye
Iron Ion
The lungs are the part of the human body that absorbs oxygen directly from the air. When you breathe, the lungs take in oxygen from the air and transfer it to the bloodstream to be transported to cells throughout the body.
I don't know of any common cell that uses oxygen gas. The cells that I know of use dissolved oxygen delivered by the bloodstream.
hemoglobin