Final answer:
Oxygen deficient atmospheres are those with less than 19.5 percent oxygen. Atmospheres normally contain approximately 20.9 percent oxygen, which is crucial for bodily functions like ATP production.
Step-by-step explanation:
Oxygen deficient atmospheres are those having less than 19.5 percent oxygen in the air. In an environment with a normal atmospheric composition, oxygen accounts for approximately 20.9 percent of the air, which is essential for life and especially for the production of ATP in the body. In situations where the oxygen level falls below the safe threshold of 19.5 percent, individuals can experience hypoxia, leading to symptoms such as fatigue, headaches, and confusion. These symptoms can occur if there – such as at high altitudes – the partial pressure of oxygen in the atmosphere drops, making it more difficult for the body to achieve the same level of oxygen saturation as at sea level. Therefore, D. 19.5 is the correct answer to the question: Oxygen deficient atmospheres are those having less than _____ percent oxygen in the air.