glucose and oxygen are required for cellular respiration. as the law of conversation states, in a biochemical reaction, mass is conserved. the mass of hydrogen in the glucose is therefore conserved in the water molecules products.
when water vapor in the atmosphere loses heat and cools down, condensation happens. as the water vapor cools down and condenses, it attaches to small particles of dust floating in the atmosphere, forming tiny liquid water droplets.
the energy is radiant to thermal.