Modern-day Research

A long time passed before this proposal was proven correct. Following World War 11, radioactive isotopes of many elements became available for research. A radioactive isotope of oxygen known as 0¹⁸ made possible the utilization of carbon dioxide and water in photosynthesis wherein the oxygen of the carbon dioxide was different from the oxygen of the water. A carefully arranged experiment was devised wherein the oxygen of carbon dioxide was O¹⁶ and the oxygen of the water was 0¹⁸. This difference enabled researchers to trace the source where the oxygen in each compound formed. The chemical properties of the two types of oxygen were exactly alike; only the weights differed. In this way, it was clearly established that all the oxygen liberated in photosynthesis comes from the breakdown of water. An equation could now be written as shown in figure 9-6. Unlike the water on the left side of the equation, the water on the right side is manufactured water.

Figure 9-6 An upgraded equation for photosynthesis, showing that water is manufactured.