Question

what are the sources of oxygen and carbon dioxide in air

Answer 1

The oxygen cycle is the biogeochemical cycleof oxygen within its four main reservoirs: the atmosphere (air), the total content of biological matter within the biosphere (the global sum of all ecosystems), the hydrosphere (the combined mass of water found on, under, and over the surface of planet Earth), and the lithosphere/Earth's crust. The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth's atmosphere and life on Earth (see the Great Oxygenation Event).

Answer 2

The carbon dioxide breathed out is a by-product of the process of cell respiration, as is water. In this process, energy is produced in the mitochondria of cells. This energy is our physical "life force". Both oxygen and glucose are required for this. Glucose contains carbon. That's where the carbon in carbon dioxide comes from. Glucose plus oxygen produces carbon dioxide, water and energy. When this process stops, the cell dies.