Balance of Oxygen in Earth: Plants Role

[Allen_Wolf]

In equation of photosynthesis were see 6 O2 is produced
In equation of respiration we see that 6 O2 is used.
But if plants produce and take back the same amount of O2 then how is the balance of oxygen in Earth maintained?

 

[Ygggdrasil]

Not all the sugars that the plants produce from photosynthesis are used for respiration. These sugars are the building blocks for producing most of the tissues of the plant.

 

[BillTre]

Plants do more photosynthesis than respiration when light is present and less when light is absent. They are not in a linked a one-to-one relationship.

You can have an aquarium with green water (lots of suspended algae) and some fish.
During the day, the water has a lot of oxygen due to the photosynthesis of the many algae cells in the water and everyone is happy.
However, at night, no photosynthesis is occurring, but the algae cells still have to use oxygen for respiration. This can deplete the dissolved oxygen in the water which can, in extreme case cause the death of the fish.

 

[Allen_Wolf]

And one more thing. Plants take 6H2O and give back 6H2O. Are the plants just giving out the water they took in during photosynthesis or making and giving back water. (During respiration )?

 

[Ygggdrasil]

And one more thing. Plants take 6H2O and give back 6H2O. Are the plants just giving out the water they took in during photosynthesis or making and giving back water. (During respiration )?

A seed will eventually grow into a plant. Consider conservation of matter. What are the main materials that compose the plant? Where do those materials come from?