Living creatures primarily breathe in oxygen to survive. Oxygen is crucial for cellular respiration, a process through which cells generate energy by converting glucose and other nutrients into adenosine triphosphate (ATP). This energy powers various biological functions, including movement, growth, and repair. While some organisms, such as anaerobic bacteria, can survive without oxygen, the majority of multicellular life forms on Earth, including humans and animals, require it. Oxygen is obtained from the atmosphere or water, and plants play a vital role in producing it through photosynthesis, releasing oxygen as a byproduct and maintaining atmospheric balance.