Final answer:
Oxygen binds to hemoglobin forming oxyhemoglobin during external respiration, which takes place in the lungs as oxygen diffuses across the respiratory membrane into the bloodstream.
Step-by-step explanation:
During external respiration, oxygen binds to hemoglobin to form oxyhemoglobin. External respiration refers to the process where oxygen diffuses across the respiratory membrane from the alveoli to the capillaries in the lungs. Here, oxygen binds to the iron ions in hemoglobin within red blood cells, creating oxyhemoglobin. This is essential for transporting oxygen to the body's tissues.
It is important to note that while internal respiration involves the exchange of gases at the tissue level and cellular respiration is the process by which cells use oxygen to produce energy, it is during external respiration that hemoglobin binds to oxygen in the lungs.