Photosynthesis+oxygen+production

How do we "show" photosynthesis? Four possibilities.

Release of oxygen. The text suggests growing Elodea underwater and counting the rate of bubble release. This is done with light sources covered with cellophane. Besides being a fire hazard so close to a bulb, the cellophane really isn't a very good filter as it transmits blue light no matter what color it is.

So, let's grow Elodea, or perhaps the green alga Chlorella, and capture the oxygen in a balloon. The challenge here is demonstrating that it is oxygen. Could time flames, but is this explosive? Could rust a nail, but this seems too slow. Could 'rust' ferric green to ferrous red. Could oxidize some indicator, but likely expensive. Could use an Clark-type oxygen electrode, ha ha!

Uptake of carbon dioxide. Could use a carbon dioxide meter, again, ha ha! Could trap carbon dioxide in KOH soluiton or lime water. Then titrate this using a biuret or a serological pipette fitted with a tube and clamp.

Increase in carbohydrate stores. Could measure carbo content in a culture of algae (and perhaps a plant) going from some time in the dark to the light. Should become depleted and then restock. Might be able to see this with IKI or better yet anthrone reagent and a color wheel (or spec). This doesn't really show photosynthesis very clearly. The pros do this with radioactive carbon dioxide incorporation into carbohydrate fraction.

Increase in biomass. Again, not very direct. Just showing grow of algal culture without any added carbon compounds. There is an increase in biomass build of fixed carbon. Where could it come from? The air?