The gas that living beings need to breathe is oxygen. Oxygen is essential for cellular respiration, a process by which cells convert nutrients into energy. Most animals and humans inhale oxygen from the atmosphere, which is absorbed into the bloodstream via the lungs. This vital gas is produced by plants during photosynthesis, which converts carbon dioxide and sunlight into oxygen and glucose. Without sufficient oxygen, organisms can experience severe health impacts, highlighting its crucial role in sustaining life.