Breathing is the first step of respiration which involve exchange of gases between the air in the alveoli and the blood capillaries around the alveoli in this exchange the blood takes up oxygen from alveoli and release CO2 to the alveolier air as such and exchange occur because the concentration of oxygen is more in alveolie so oxygen from high concentration to lower concentration due to the process of diffusion that has more concentration of carbon dioxide as compared to the alveoli air due to simple diffusion the exchange of gases is called external respiration.
