Nitrogenase dioxygen sensitivity

There is another knock-on problem with oxygenic photosynthesis. Nitrogenase is very sensitive to dioxygen. One solution is a physical partition, to create a small space where an older pre-oxygen condition can be preserved, despite being in an aerobic habitat. A key part of the apparatus in many cyanobacteria is the heterocyst, a walled-off microhabitat where very oxygen-sensitive nitrogenase can be protected. 

---