I am to conduct a lab investigating how different wavelengths of light affects photosynthesis in Egeria pondweeds.

The idea is to put color filters on light bulbs and shine them on the pondweed in a sodium hydrogen carbonate solution. Then to measure the oxygen, I have an oxygen sensor which measures dissolved oxygen (mg/L).

Now, what I have a trouble with is if measuring the dissolved oxygen is the right way to measure the rate of photosynthesis depending on color of light? Will it work?

  • 1
    $\begingroup$ One experiment I saw online, was that during 5 minutes you measure the oxygen dispersed, and it will show you the mg/L depending on time. $\endgroup$
    – Timothy
    Dec 16, 2021 at 23:07
  • $\begingroup$ That solution might just kill the plants. $\endgroup$ Dec 17, 2021 at 5:50
  • $\begingroup$ Why not do it in a standardised pondwater, unless you don't mind the results being for only that sodium bicarb solution? $\endgroup$ Dec 18, 2021 at 13:19
  • $\begingroup$ A couple thoughts. The plant is undergoing cellular respiration too, so I am not sure that there will be a net oxygen out. I assume that the sodium hudrogen carbonate is going to provide a source of carbon dioxide to a closed system, but even then the plant will release carbon dioxide from respiration from sugar that it has made and burned. $\endgroup$ Dec 19, 2021 at 1:07
  • $\begingroup$ Is the atmosphere sealed and airtight? You could possibly have Sodium Hydrogen Carbonate in a water reservoir in the container, but not in the water that the pondweeds are growing in. $\endgroup$ Dec 19, 2021 at 1:12

1 Answer 1


Bubble formation might be easier to measure than oxygen concentration. Bubbles can be measured optically Or acoustically.

A sealed container with a little carbon dioxide gas might work.

See below article.

“Acoustic effects during photosynthesis of aquatic plants enable new research opportunities”

Helmut G. Kratochvil and Michael Pollirer http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5349586/

  • $\begingroup$ You can also work out via displacement - pondweed underneath an inverted container, traps bubbles that escape (gentle agitation might help) and measure volume . $\endgroup$
    – bob1
    Jan 18 at 1:30

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