If you supply a light continuously to a piece of a plant submerged in water do you produce oxygen? Would this mean if you remove the light source your plant would release Carbon dioxide? My container has bubbles all over it and I am not sure what I have accomplished.
This is quite a complicated question because several different things may be happening.
1) Yes, if you illuminate a plant (I presume you are using an aquatic/water plant) it will produce oxygen. You can put the plant under a funnel and collect the bubbles in an upturned test tube. If the gas is collected fresh, it will relight a glowing splint. However, if the gas takes more than 24 hours to collect, or if you leave it for several hours before testing it, you may not relight a glowing splint. I think this is because the oxygen dissolves in the water and the nitrogen which is in solution in the water (there is usually air dissolved in water) comes out of solution so that the gas you have collected becomes almost the same as air (which does NOT relight a glowing splint). It is often useful to put some NaHCO3 (sodium hydrogen carbonate) in the water so the plant has a good supply of CO2 and to put it in sunlight or under a bank of suitable bright lights (not just a reading lamp).
2) Yes, if you switch the lights off, the plant will become a net producer of CO2. However, CO2 is more soluble in water, so it coes not bubble off. You can detect this CO2 by using appropriate indicators and showing that the water becomes more acid.
3) But, sometimes water just produces bubbles even without any plant in it! If the water is under pressure in the water pipes before you open the tap, then the water has lots of air dissolved in it and this will come out of solution when you leave it to stand. If you boil water, it will get rid of the air.
I hope this enables you to guess at what is happening in your equipment. It may raise more questions in your mind and you may find that you can design an experiment to test whether your guess is correct.
Let us know what you think was happening and whether you were able to test whether your hunch was correct.
John Hewitson
