I think Plants do:
6CO2 + 6H2O -> C6H12O + 6O2
I'm thinking that plants take 12 + 6 moles of oxygen and give back 12 mols of breathable oxygen and 1 mol of Cellulose.
I've read that a person needs about 550 liters pure oxygen (not air) per day, which I believe is about 785 g of oxygen (1L /22.4 L/g * 32 g/mol * 550 L).
I've read that grass is the most common plant, and is about 85% water.
Cellulose is about 162 g/mol, O2 is 16 g/mol, so for every cycle of photosynthesis, a plant's increase in sugar weight yields about ((6*16)/162) = 59% weight in oxygen. Since this sugar weight is only 15%, a plants total weight in growth will produce .59 * .15 = 8% weight in oxygen.
Does that mean that if a person needs 785 g of oxygen per day, there needs to be 9812.5 g (about 21.6 bl) of new plant growth that same day?