Oxygen (O2)is
A)a gas which principally originates from volcanic sources.
B)a by-product of photosynthesis.
C)one of the gases from Earth's earliest atmospheres.
D)now measured at 78.084% by volume in the homosphere.
E)not essential to life on the planet.

Question

Quizplus · Accepted Answer

Oxygen is a by-product of photosynthesis, which is the process by which green plants and some other organisms use sunlight to synthesize foods with the release of oxygen as a side product.