What effect did the increase in atmospheric oxygen by photosynthetic organisms have on earth in terms of the biosphere?

Increase in atmospheric oxygen by the photosynthetic organism to the biosphere evolved more complex forms of life. Many different plants, animals consuming plants, bacteria decomposing dead plants and animals evolved.These forms a food web in the biosphere. The remains of dead plants and animals release nutrients to the soil and ocean which are reabsorbed by the other growing plants.This food exchange  and energy exchange make the biosphere a self supporting and self regulating system .

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.