Answer:
The Answer is Diffusion
Step-by-step explanation:
Diffusion is the spontaneous movement of gases, without the use of any energy or effort by the body, between the alveoli and the capillaries in the lungs. Oxygen moves by diffusion from an area of higher concentration inside the lungs to an area of lower concentration in the blood. It is then carried away by red blood cells. The blood leaving the lungs now has a high concentration of oxygen. It travels round the circulatory system to the cells in tissues and organs.