AP BIOLOGY

Detailed explanation-1: -The oxygen released during photosynthesis is from the water. The plants will absorb water as well as carbon dioxide during photosynthesis. Later these water molecules are converted into oxygen and sugar. The oxygen is then released into the atmosphere whereas the sugar molecules are stored for energy.

Detailed explanation-2: -Within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose. The plant then releases the oxygen back into the air, and stores energy within the glucose molecules.

Detailed explanation-3: -Scientists confirmed van Niel’s hypothesis that oxygen released from photosynthesis comes from water with the use of 18O, a heavy isotope, as a tracer to follow the fate of oxygen atoms during photosynthesis. The experiments showed that the O2 from plants was labeled with 18O only if water was the source of the tracer.

Detailed explanation-4: -Oxygen liberated during photosynthesis comes from the splitting or hydrolysis of water in the green plants. Cornelius van Niel experimentally proved for the first time that the oxygen liberated during photosynthesis comes from water and not from carbon dioxide.

Detailed explanation-5: -The scientist who showed O2 is released from the water molecule is Antoine Lavoisier. He replicated the experiment of Henry Cavendish and confirmed the constituents of water.