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Q & A: plant respiration

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Most recent answer: 10/22/2007
Q:
In school we learnt that plants breathe in Carbon Dioxide, and out oxygene. Vise versa of Humans. So for a science project I put a plant in a bottle thinking that it would breathe in the carbon dioxide, then not have any left and die. Except my plant has been in there for a while, and it hasn’t change a bit, except maybe it’s a bit more yellow. Why isn’t this working? Does the plants color have anything to do with what it breaths?
- Jillian
Nova Scotia
A:
You're asking amateurs here, but here's what I remember.

Animals like us have no way of converting carbon dioxide to sugars etc. All we can do is burn sugars etc and make use of the energy released. Plants also burn sugar and make use of the energy released, but in addition they can photosynthesize- use the energy of light to convert carbon dioxide (and water) to higher-energy forms like sugar.

Plants are always converting sugars and oxygen into water and carbon dioxide. They need to do this in order to grow, reproduce, transport nutrients, and do other things. But in the presence of light and the proper nutrients they will photosynthesize and make the reaction go the other way too.

I'm just guessing, but since your plants don't have much carbon dioxide they can't photosynthesize very much. Their green color comes from chlorophyll, the key molecule in photosynthesis. If they can't use much of it, they're probably programmed not to waste energy making very much of it. That would leave them looking a bit yellow.

You might check this with a biologist to see if I got it somewhat wrong.

Mike W.

(published on 10/22/2007)

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