The air sacs are called Alveoli
deoxygenated blood
leaves have pores on there underside that allow carbon dioxide in and let oxygen out
Oxygen (O2) enters your body through breathing air, which contains oxygen in it. This oxygen goes into your lungs where it is put into the bloodstream, supplied to cells in your body, returned to the lungs as carbon dioxide (CO2), and exhaled through the lungs.
Carbon dioxide is the product; oxygen and carbon are the reactants.
When carbon reacts with oxygen to form carbon dioxide, carbon dioxide is the product of the reaction.
The preponderance of oxygen is carried through the rectum
These are called the "alveoli".
Oxygen and carbon dioxide are moved to and from body tissues via the circulatory system. These materials diffuse through the cell membrane, and then diffuse through the capillary wall into or out of the bloodstream.
I wouldn't exactly characterize it as separating carbon dioxide and oxygen, however, I think the answer you are looking for is the lungs which takes up oxygen into the bloodstream and expels carbon dioxide out of the bloodstream into the lungs so we can breathe it out again.
To deliver oxygen to the bloodstream and to remove carbon dioxide from the bloodstream.
The process in which oxygen enters the bloodstream through the alveolus and carbon dioxide exits the bloodstream also through the same alveolus to be exhaled.
Carbon Dioxide
The red blood cells in your body contain oxygen and carbon dioxide. So, as the red blood cells travel through your bloodstream, the oxygen travels through to your heart, then your lungs, along with the oxygen.
Oxygen becomes carbon dioxide when it acts as a means of transporting carbon out of the cell. Oxygen (O2) is brought to any cell in the body by the bloodstream, where it picks up some of the cells carbon (C) waste. Hence, it becomes CO2, or carbon dioxide.
Alveoli and bloodstream
Alveoli
Oxygen and carbon dioxide travel into and out of the bloodstream via diffusion across alveolar and capillary membranes.