Final answer:
Oxygen's primary biological role is in aerobic cellular respiration, providing energy to cells and removing metabolic wastes. It reaches the cells via the bloodstream, which also transports nutrients, hormones, and immune cells.
Step-by-step explanation:
Oxygen is critical for life because it is the essential element used by cells for aerobic cellular respiration. The process of respiration within the human body involves the inhalation of air into the lungs, where oxygen is absorbed into the bloodstream and bound to hemoglobin to form oxyhemoglobin.
This oxygen-rich blood is then circulated throughout the body to supply the tissues. Every cell requires oxygen to perform metabolic processes that generate energy. Without oxygen, cells would not be able to produce the energy needed for survival.
Oxygen also plays a critical role in the removal of metabolic wastes such as carbon dioxide, which is transported back to the lungs to be expelled. Furthermore, oxygen is a byproduct of photosynthesis, a process that also contributes to maintaining Earth's atmosphere. In addition to its role in respiration, blood also carries nutrients and hormones, and assists in fighting infections by transporting white blood cells and other immune cells to areas of need.