Question

Most of the Earth's oxygen occurs in the form of minerals in the crust and mantle. The oxygen that is available in the atmosphere is used primarily by plants, animals, and bacteria to perform cellular respiration. Why is running out of oxygen still not a real concern?

Answer 1

oxygen is recycled through the interrelated processes of photosynthesis and cellular respiration

Step-by-step explanation:

More than 99% of the Earth's oxygen is bound in minerals, which are found in the crust and mantle. However, atmospheric oxygen is not being depleted. The levels are kept relatively constant through the interrelated processes of photosynthesis and cellular respiration. Cyanobacteria, algae, and land-based plants perform photosynthesis. As starting material, they use the carbon dioxide that is breathed out by plants, animals, and aerobic bacteria. Photosynthesis produces glucose that plants—and the animals that eat them—can use to generate cellular energy. Photosynthesis also produces oxygen as a waste product. The waste oxygen enters the atmosphere, where plants, animals, and aerobic bacteria use it as starting material for performing cellular respiration.

Answer 2

There are plenty of plants producing oxygen by photosynthesis.
Also, human's only use 5% of the oxygen in the air in respiration, there is 21% in the air.