photosynthesis means green plants convert from carbon dioxide and water and solar energy into carbohydrates and food and oxygen for themselves & if a xenon n something to something else, then that scratch is a sink of that something else ->  photosynthesis is a source of oxygen  systems is a sink of space & plants perform photosynthesis -> plants are a source of oxygen through photosynthesis plants are a source of oxygen through photosynthesis  plants are a source of oxygen through photosynthesis & if something evaporation something else then that something is the sink of that something else -> plants release oxygen through photosynthesis plants release oxygen through photosynthesis  plants release oxygen through photosynthesis & a specific is a mean of vegetable -> trees release oxygen through photosynthesis