Photosynthesis and respiration

[sophie_1003]

Am brushing up on the above topics and think I'm finally getting the hang of photosynthesis. With regards to cellular respiration though am getting more and more confused! Understand that the equation is
glucose+oxygen----->carbon dioxide+water(+energy)
also understand that the glucose is stored in the plant from photosynthesis but am confused about the oxygen. Some sources say plants take this in from the air whereas others say the plant uses the oxygen that is created as a by-product of photosynthesis; which is correct please?

[NazNomad]

I always thought that plants got Oxygen by breaking down the CO² (as you say, a by-product of photosynthesis).

[wildwood]

AFAIK the carbon dioxide in the air plus light produces sugars and the unneeded oxygen is respired out to make room for more CO². Without the oxygen produced by primitive photosynthetic plants like algae, air breathing animals could not have evolved.

[gen2]

The oxygen in the air and the oxygen that is the by-product of photosynthesis are identical. The plant cannot tell where each individual molecule came from, it will use whatever is available.

During periods of active photosynthesis (daytime), the oxygen most readily available probably came from photosynthesis. At night, it has to diffuse in from the air.

All your sources are correct.

[beso]

An interesting aside.

The chlorophyll and haemoglobin molecules are quite similar. Respiration and photosynthesis are essentially the same reaction running in opposite directions.

[sophie_1003]

Thanks all! The more I look into it the more complicated it gets but we only require a simple explanation so think it will be enough to say it gets it from the air!