Chlorophyll b can take over the role of chlorophyll a in cyanobacteria's photosystem II. By introducing a gene responsible for chlorophyll b production into a specific strain of cyanobacteria, researchers found that chlorophyll b levels increased significantly when combined with a light-harvesting protein from peas. This substitution did not affect the overall function of photosystem II, indicating that chlorophyll b can effectively replace chlorophyll a in this complex. The presence of the light-harvesting protein was crucial for this process to occur efficiently. This study suggests that the availability of chlorophylls, rather than their specific binding properties, determines which type is used in photosystem II.