# What is the mechanism of photosynthesis?

I just want to know what particle in plants can change $\ce{H2O}$ into $\ce{O2}$ and what $\ce{CO2}$ does in this conversion system. What if we just use $\ce{H2O}$ and light to convert it into $\ce{O2}$? If light is what we need to convert $\ce{CO2}$ into glucose and $\ce{H2O}$ into oxygen, why can't scientists make a machine to do that?

## 2 Answers

I'm definitely not going to outline light harvesting in the light harvesting complexes (LHC), the role of the quinones in electron transfer, etc.

But let me give a short answer on your last question:-

The molecular aggregates, such as the LHCs, involved in the different steps of photosynthesis are not optimized for duration. In contrast to man-made machines, they don't have to! Remember that all these fragile molecular assemblies are part of a living system. If parts break, they will resynthesized and replaced.

While it is partly possible to mimic photosynthesis in the lab, it is the self-repair mechanisms that we are unable to replicate in artificial systems.

• You haven't heard any talks by Nocera recently. That's his argument about his catalysts - that they work because of self-repair. – Geoff Hutchison May 29 '15 at 17:32
• @GeoffHutchison It's indeed quite a while ago that I followed Nocera's work. I'm not working on photocatalytic water splitting anymore. But thanks for the hint :) – Klaus-Dieter Warzecha May 29 '15 at 17:35

Plants can do so because of the organelles in their cells called "Chloroplasts." These chloroplasts have the pigment chlorophyll, which gives plants their green color. Chlorophyll is found in different varieties, but one of them (Chlorophyll A) has the chemical formula C55H72O5N4Mg. This chlorophyll acts like a biological solar panel, providing chemical energy to carry out the photosynthesis "6CO2 + 6H2O + Energy --> C6H12O6 + 6O2 . Hope this helps!