Final answer:
During external respiration, oxygen diffuses from the alveoli, which have a higher concentration of oxygen, to the blood in the surrounding capillaries. This exchange is driven by the partial pressure differences between the alveoli and blood. option 2.
Step-by-step explanation:
During external respiration, the movement of oxygen is specifically from the alveoli to the blood. This process takes place within the lungs at the alveoli, which are tiny sacs surrounded by capillaries. As oxygen is inhaled into the alveoli, it diffuses across the respiratory membrane due to the partial pressure differences between the alveoli and the blood. Oxygen has a higher concentration in the alveoli and a lower concentration in the capillary blood, prompting diffusion from the alveoli (area of high concentration) to the blood (area of low concentration). Conversely, carbon dioxide diffuses out of the blood and enters the alveoli to be expelled from the body during exhalation. Therefore, the correct statement describing the movement of oxygen during external respiration is:
1. Oxygen diffuses from the alveoli to the blood.
This statement accurately represents the exchange of gases that occurs across the respiratory membrane during the phase of external respiration.