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Photosynthesis and Oxygen Levels

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  • 20-05-2013 3:26pm
    #1
    bridgetown1
    Registered Users Posts: 150 ✭✭


    (the following was done using vernier sensors and software)

    I have some Ranunculus aquatilis in about 250cm3 of pondwater in a small (about 300cm3) gas chamber. I have an Oxygen gas sensor about 2cm above water surface and the chamber is airtight. In darkness the Oxygen concentration dropped gently, as I expected, from 20.31% to 20.28% over a 10 minute period. Yet when I exposed it to light it began to drop even faster, from 20.28% down to 19.98% over the following 20 minutes. Why the increase rate of oxygen uptake when I expected oxygen production due to photosynthesis?

    Only after 37 minutes did oxygen levels begin to rise again, and after 8 further minutes did it pass the original ambient level of 21.31%. Other seemingly anomalous results which I obtained can be explained by presuming some sort of time lag between oxygen production by Ranunculus and it's diffusion into the atmosphere above.

    But why was there an increased rate of oxygen uptake for the first period of time after I exposed the Ranunculus to light?


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    #2
    steddyeddy
    Registered Users Posts: 27,564 ✭✭✭✭steddyeddy


    bridgetown1 wrote: »
    (the following was done using vernier sensors and software)

    I have some Ranunculus aquatilis in about 250cm3 of pondwater in a small (about 300cm3) gas chamber. I have an Oxygen gas sensor about 2cm above water surface and the chamber is airtight. In darkness the Oxygen concentration dropped gently, as I expected, from 20.31% to 20.28% over a 10 minute period. Yet when I exposed it to light it began to drop even faster, from 20.28% down to 19.98% over the following 20 minutes. Why the increase rate of oxygen uptake when I expected oxygen production due to photosynthesis?

    Only after 37 minutes did oxygen levels begin to rise again, and after 8 further minutes did it pass the original ambient level of 21.31%. Other seemingly anomalous results which I obtained can be explained by presuming some sort of time lag between oxygen production by Ranunculus and it's diffusion into the atmosphere above.

    But why was there an increased rate of oxygen uptake for the first period of time after I exposed the Ranunculus to light?

    So during photosynthesis O2 consumption increased would I be right in saying this? Can I ask what type of light you are currently using by the way? I would maybe put it down to mitochondrial consumption of O2 but the more aqautic plants are thought to engage in O2 recylcing.


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