Combustion - the burning of fuels and harmful gases in the atmosphere through factories.
decomposition - when skulls and bones are decomposed to give out carbon dioxide.
diffusion - when the the molecules move from a region of higher concentration to a region of lower concentration.
respiration - when person breathes in oxygen and out carbon dioxide.
photosynthesis - is the process where trees make glucose and oxygen with the help of sunlight and mineral and water from soils.
