Photosynthesis produces oxygen when carbon dioxide and water are chemically converted into glucose with the help of sunlight. Respiration is a process whose reciprocal is photosynthesis. In respiration, oxygen is combined with glucose to chemically release energy for metabolism. The products of this reaction are water and carbon dioxide. The next most abundant gas on the table is water vapor .
Water vapor varies in concentration in the atmosphere both spatially and temporally.
The highest concentrations of water vapor are found near the equator over the oceans and tropical rain forests. Cold polar areas and subtropical continental deserts are locations where the volume of water vapor can approach zero percent. The condensation of water vapor creates precipitaion that falls to the Earth's surface providing needed fresh water for plants and animals. It helps warm the Earth's atmosphere through the greenhouse effect . The fifth most abundant gas in the atmosphere is carbon dioxide .