Thread: plants breathing at night.

Hi,

It is true that plants do not do photosynthesis at night. My belief was plants always take in carbondioxide and give out oxygen, no matter day or night.

But I have seen some people say that plants give out carbondioxide at night. Which is correct ? Is that really true that plants give out carbondioxide at night ???

Yes.

It actually depends on the plant. Crassulacean acid metabolism plants store CO2 at night. This is because they are adapted to dry climates and so they keep their stomata closed during the day and can't take any CO2 in. There are 3 main types of photosynthesis done by plants: CAM, C4 (Kratz Anatomy plants), and C3. C4 and C3 plants tend not to fix carbon dioxide during the night.

First of all, photosynthesis has two parts. The light dependent reactions, and the light independent ones. The light dependent part is the use of light to "steal" electrons from water. This is the process that produces oxygen, the plants take an electron off of water and they use that to reduce NADP+, which is subsequently used to make ATP. The light independent part is carbon fixation, this is done by an enzyme called RuBisCo, that fixes carbon dioxide to ribulose bisphosphate and produces two 3GP, which is a component in glycolysis that can be used for glucogenesis.

Plants produce CO2 during respiration, just like us, when they break down glucose. They do this day and night, but when they are doing photosynthesis they tend to take more CO2 out of the air than they put in.

In a confined area with limited oxygen replenishment - such as a shallow pond - a thick growth of submerged plants undergoing respiration at night can reduce the oxygen levels to near zero.

I once measured that, as a student of limnology, in a gravel pit catchbasin with coontail growing in patches - very few fish could have lived in that pond. Most species would have suffocated at night.

Almost all chemical reactions will run backwards at some rate - including photosynthetic splitting of CO2 in the leaves of plants.

Plants don't split CO2, they split H2O.

It has nothing to do with reactions running backwards. They release CO2 through the process of respiration and glycolysis, just like animals.

They reduce CO2 during the carbon fixation steps of the light-independent reactions of photosynthesis.

Both processes go on at all times, except carbon fixation tends to be more active during the day. They only release Oxygen during the day since they require light to do it.