AP BIOLOGY

Detailed explanation-1: -Oxygen played a key role in the evolution of complex organisms, according to new research published in BMC Evolutionary Biology. The study shows that the complexity of life forms increased earlier than was thought, and in parallel with the availability of oxygen as an energy source.

Detailed explanation-2: -But over time, new forms of life evolved that use or expel oxygen in respiration, and atmospheric oxygen levels continued to increase. “The production and burial of plant matter over long periods causes oxygen levels to rise, ” explains Poulsen.

Detailed explanation-3: -According to Bekker, increases in atmospheric oxygen levels resulted in low concentrations of greenhouse gases, such as methane and carbon dioxide. This ushered in global glaciations by maintaining surface conditions below the water-freezing temperature.

Detailed explanation-4: -The increased presence of oxygen produces a more efficient energy source in the form of aerobic metabolism, producing 16–18 times more adenosine triphosphate (ATP) per hexose sugar than anaerobic metabolism.