There are plenty of plants producing oxygen by photosynthesis.
Also, human's only use 5% of the oxygen in the air in respiration, there is 21% in the air.
Mostly because they are made up of living cells, but in the bigger picture they are not alive.
You can use old pieces of paper as scratch paper, make papier mache, use it as padding for packages, or make origami.
10 because meiosis divides the number of chromosomes by two.
