Answer:
2.Diffusion
Step-by-step explanation:
As we metabolize certain nutrients for the correct functioning of our cells, carbon dioxide is produced as a result. We need oxygen in order to metabolize them, so we need to have a system to incorporate it, and to eliminate the carbon dioxide produced.
This system is provided by the interaction between the respiratory system, which allows the enter of oxygen into the body and gets rid of the carbon dioxide, and the circulatory system, which acts transporting carbon dioxide and oxygen to and from the lungs, respectively.
The surface available for the gaseous exchange is enlarged by the pulmonary alveoli. The alveoli are the terminal aerial spaces of the respiratory system and the structures where the exchange between the air and blood is produced. Each alveolus is surrounded by a net of capillaries, where oxygen is freed from the hemoglobin and moves into the cells by diffusion. Carbon dioxide, diffuses out of the cells into the capillaries, where most of it dissolves in the plasma of the blood.