Thread: Heavy oxygen in water question

Okay, I'm stumped guys. I looked everywhere online, can't figure it out. It's for my open university course so I don't have lots of sources to go to other than my book and online...doesn't help me.

The question is, in a suspension of Chlorella they're added heavy isotope of oxygen 18O2 and regular isotope of oxygen 16O2

[They show a chart of the heavy oxygen being in steady decline, while the regular oxygen increases during light and decreases during dark]

1) Why is there a decrease of heavy oxygen isotope concentration in both light and dark?
2) Why is there an increase in the regular oxygen isotope concentration in the light, and what is the source of of the isotope?

Please help, I'm totally flummoxed. :?

-nerdgirl

I suggest reading about aquariums and what causes the oxygen levels to increase or decrease there.

not sure if this is really helpful, but a google search for "chlorella oxygen isotopes" brings up the following paper : Origin of the chlorophyll b formyl oxygen in Chlorella vulgaris., which seems to indicate that O-18 gets incorporated in the cell structure of Chlorella, which would explain why it happens both in light and dark conditions
the increase of O-16 in the light is probably the normal chlorophyl reaction at work ?

Thank you guys, that helps a bunch

-nerdgirl

Originally Posted by nerd_girl

Thank you guys, that helps a bunch

-nerdgirl

Okay, nerdgirl, how are you going to answer the question? Because I wanted to give my answer but not until you had finished your homework. It's a little different than what Marnix wrote.

remember that i have no expert knowledge of this subject whatsoever - i just try to deduce from what little knowledge i have + what i can find from searching the internet

i would not in the least be surprised if harold proves my conclusion gloriously wrong

Originally Posted by marnixR

remember that i have no expert knowledge of this subject whatsoever - i just try to deduce from what little knowledge i have + what i can find from searching the internet

i would not in the least be surprised if harold proves my conclusion gloriously wrong

One of the real biologists will probably be coming around shortly to slap us both around.

The thing is we never studied about this topic in class, nor can I find anything in the textbook. I think the second question is easy and I think I got it right, but there's nothing about heavy oxygen with chlorella anywhere online (I tried to google that information too)... I think it's a bit of a ridiculous question frankly and it's very hard to get a hold of a teacher in the open university..and I gotta submit an answer by tomorrow anyway so I figure no point fussing about it just ask you guys. I did write something down..not sure if it's correct at all but better than nothing :?


-nerdgirl

I don't think you need to know anything specific about Chlorella to answer this one. When you googled aquariums and oxygen, what processed did you find that caused oxygen to decrease in the aquarium? Which of those would apply to your suspension of algae in water?

I guess nerd girl has turned in her homework by now.

My answer is that the dissolved oxygen, whether it is heavy or regular oxygen, is continually depleted by plant respiration and decay of dead cells. This happens in both light and dark.

The increase of oxygen-16 during daylight is due to photosynthesis. The new oxygen is coming from dissolved carbon dioxide, not the dissolved oxygen, and so it is the regular oxygen-16 isotope.

Originally Posted by Harold14370

I guess nerd girl has turned in her homework by now.

My answer is that the dissolved oxygen, whether it is heavy or regular oxygen, is continually depleted by plant respiration and decay of dead cells. This happens in both light and dark.

The increase of oxygen-16 during daylight is due to photosynthesis. The new oxygen is coming from dissolved carbon dioxide, not the dissolved oxygen, and so it is the regular oxygen-16 isotope.

Sounds like a perfect answer to me.

Just a quickie:

The oxygen that is released from photosynthesis is derived from water (the so-called "water-splitting" reaction.

Haha I should have caught that, egg on my face

Thanks for the correction, guys. I knew CO2 was being used up, but it turns out that goes into making carbohydrates.