I don't see options to complete the sentence, so I will try my best to explain.
Respiration is the process of gas exchange between the lungs and the environment. The lungs pick up O2 from the environment during inspiration, and expel CO2 during expiration.
External Respiration is the gas exchange between the lungs and the blood.
- In the alveoli of the lungs, blood flows past during pulmonary circulation and through the process of diffusion, CO2 from the blood enters the alveoli and O2 from the alveoli enters the deoxygenated blood.
Internal Respiration is the gas exchange between the blood and the cells of the body.
- After picking up the O2 from the alveoli in the lungs, the newly oxygenated blood flows around the body and, through diffusion, sends the O2 to the body cells, and picks up the CO2, thus becoming deoxygenated.
Why do we need Oxygen to survive???
- Oxygen serves as the final electron acceptor in the electron transport chain of cellular respiration!