*** This hypothesis was later confirmed by Samuel Ruben and Martin Kamen, who utilized radioisotopes to trace the flow of oxygen in plants. Specifically, they allowed two groups of plants to undergo photosynthesis. The first group of plants was given radioactively-labeled water and unlabeled carbon dioxide. By comparison, the second group of plants was given radioactively-labeled carbon dioxide and unlabeled water.Results showed that the oxygen released from the first group of plants was radioactive, confirming that water is the source of the oxygen produced by photosynthesis. While seemingly simple, later studies went on to demonstrate that photosynthesis is acombination of two separate processes, each involving multiple steps.

- Experiment designed by Samuel Ruben and Martin Kamen (1941)

- To determine which of these original compounds contribute to the O2 end product, an isotopic tracer experiment can be performed using 18O:

H218O + CO2 yields 18O2 H2O+C1802 yields O2

- Experiment 1: Showed that the oxygen from plants was labeled with the radioactive tracer oxygen-18 only if water was the source of the tracer Experiment 2: When oxygen-18 was introduced into the plant in the form of carbon dioxide, the tracer did not show in the released oxygen Therefore, these experiments confirmed that water is the source of oxygen in photosynthesis, and not carbon dioxide.

- http://www-plb.ucdavis.edu/courses/bis/2A/bis2a-F10/PhotosyntheticO2.pdf

- Animation link: http://bcs.whfreeman.com/thelifewire/content/chp08/0802001.html

An experiment designed by Samuel Ruben and Martin Kamen (1941)

Aim: to