Watching How Plants Make Oxygen (image) Uppsala University Share Print E-Mail Caption This is the structure of the oxygen evolving complex in photosystem II in a light-activated state. Water molecules are shown as blue spheres, the four manganese ions in purple, the calcium ion in green and the bridging oxygen ions in red. The blue mesh is the experimental electron density, and the blue sticks are the protein side chains holding the catalytic complex. Credit Johannes Messinger Usage Restrictions May only be published in connection to reports about the research by Messinger et al. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.