What is the by-product of bacterial photosynthesis?

If a photosynthesising plant releases oxygen containing more than the normal amount of $^{18}O$,it is concluded that the plant has been supplied with:

What does the experiment of two leaves explain in the context of photosynthesis?

The first important biological investigation which led to the conclusion that plants make their substance from water and not from soil was carried out by

Name the scientist who demonstrated the effect of different wavelengths of light on photosynthesis using green algae and aerobic bacteria.

Which scientist conducted the experiment shown below?