[ronthepon]

Now, for a science project I have to illuminate leaves with lights of different wavelengths and plot a rate-wavelength graph.

Now how on earth do I measure the rate of photosynthesis?

I have considered placing the leaves in bags posessing light polarising abilities (called cellofane or something of that sort). Then, I shall measure the oxygen released by studying the time for which an Incense stick will remain burning inside.
Is this a good idea?

Or is there a better alternative?

(I love this site)

[Tim_Lou]

well, maybe the increase of mass of the plant/leaves? mass can be easily measured.

[ronthepon]

Well, mass is not a good idea, because a plant also has a good deal of other matter coming and going, further the true rate of photosynthesis focusses on conversion of low energy mass to high energy mass...

Thanks anyway.

[sebbysteiny]

Yeah, the mass is a great idea.

From E = mc^2, the energy absorbed by the plant will increase the mass of the plant. Now all you need is science to invent a super sensitive mass metre and your experiment will work a treat.

There is one way to actually measure the concentration. Put a sample of the air into a measuring cylinder. Put the measuring cylinder upsidedown into water. Use a substance that absorbes oxygen into the cylinder and measure the volume of water that has entered the test tube. Use this to find the %age. If you can find a suitable oxygen absorber, it should work without much problems.

[ronthepon]

Okay, here is why mass wont be good even if we get supersensitive mass measurers.

1- There is active movement of matter through phloem in leaves.

2- Transpiration: water movements are enormous.

3- Carbon-di-oxide in and Oxygen out movements need not be exact enough compared to each other.

So the fluctuations will be so enormous compared to energy related mass, that its not an excellent idea...

As for the oxygen absorber, I could try burning a little peice of charcoal until all oxygen is used up. Then I dissolve the carbon-di-oxide into the water below by pressurising.

[UncleAl]

Google
photosynthesis "action spectrum" 34,000 hits

http://www.phschool.com/science/biol...th/action.html

Does Uncle Al get an A in the course for being minimally competent?

[sebbysteiny]

At the risk of pursuing the most silly tangent to a thread ever, with a super sensitive mass meter, you could make the measurements. Just make sure your measuring the WHOLE system, air, water, soil, etc, and the mass of the whole system will increase as the solar energy is absorbed. Just ensure you make your measurements at exactly the same temperature, so you might need a supersensitive thermomitor as well and a super fine thermostat. No probs.

[Tim_Lou]

nevermind

[Tim_Lou]

after some more thinking, the best way to do this seems to be putting leaves underwater, and collect air bubbles. for a give amount of time, measure the air produced.

[sebbysteiny]

correct me if I'm wrong, but doesn't photosynthesis require carbon dioxide gas?