Question

animal consumes a large amount of oxygen but still the percent of oxygen remains constant explain why it is so​

Answer 1

Answer:

because plants are continously producing oxygen

Answer 2

Photosynthesis is the ultimate source of virtually all biomass on Earth, and it occurs according to the equation

12 H2O + 6 CO2 → C6H12O6 + 6H2O + 6 O2. (Eq. 1)

That is, six O2 produced per one glucose molecule formed, or alternatively one O2 per one C. Biomass, of course, does not consist of glucose alone, but the sugars produced by photosynthesis are the starting material of the carbon backbones of all other biomolecules, and the production of further biomolecules (by plants, and by all life forms) requires energy that is obtained by burning the sugars, or by burning something whose biosynthesis can ultimately traced to the sugars. All life forms including humans are ultimately formed from the products of photosynthesis.

The burn process is called (cellular) respiration and it burns glucose according to the equation

C6H12O6 + 6O2 → 6CO2 + 6H2O. (Eq. 2)

You see that the stoichiometric relationship between C and O is the same as in photosynthesis, one O2 per one C.

Eq. 1 requires energy, obtained from light, while Eq. 2 releases energy.

All biomass finally burns to CO2. A plant decays, insects and bacteria consume its biomass. An animal dies and decays. The Winner Worm (see Edgar Allan Poe) takes every human, and with the help of bacteria, turns us to CO2. Biomass contains other elements than C and O, but those are mostly either just recycled or metabolized in such a way that the oxygen content of the input form taken from the earth, water or atmosphere to form biomass is the same as the form that is released when the biomass fully decays.

This is the reason why the oxygen concentration of the atmosphere remains stable unless other factors come to the play. There are other factors. In fact, we surely know that other factors must have affected because the oxygen concentration is now 21 %. It is not around zero because large amounts of organic matter have become buried in the ground and disappeared. The burial (which in rare cases can lead to formation of fossil fuels) orphanizes the oxygen that was formed during the production of this biomass according to Eq. 1, and the orphan oxygen stays in the atmosphere because Eq. 2 does not affect the buried matter. Burial of organic matter is not the only known process that affects the oxygen concentration, but the main one. For the last ~100 million years, the oxygen concentration has been relatively stable, but not always. But even when changes have occurred, they have been slow, with time constants of millions of years.