Through the use of oxygen $-18$ (heavy oxygen),scientists have found that the oxygen released during photosynthesis comes from molecules of

What was the contribution of Cornelius van Niel to the study of photosynthesis?

$A$ milestone contribution to the understanding of photosynthesis was made by Cornelius van Niel,which was based on the studies of

Who provided evidence for the production of glucose when plants grow?

The fact that oxygen released during photosynthesis comes from water was proved by $O^{18}$ isotope experiments conducted by:

Variegated leaves of a plant were supplied with radioactive carbon dioxide $(^{14}CO_2)$ during an experiment. Leaf $X$ was kept in the dark and leaf $Y$ was kept in the light. At the end of the experiment,the radioactivity in the leaves was measured and found to be as shown in the diagram. What is the most likely explanation for the level of radioactivity found in the yellow zone of leaf $Y$?