Which of the following is NOT a role of microorganisms in the ecosystem?

The role of microorganisms in ecosystems is vast and includes various essential functions. Among the options provided, photosynthesis is primarily the function of certain types of plants, algae, and some bacteria known as phototrophic microorganisms, rather than the broader category of microorganisms as a whole. While some microorganisms, like cyanobacteria, do perform photosynthesis and contribute to oxygen production, the statement that photosynthesis is a role of microorganisms generally oversimplifies their contributions.

On the other hand, offering symbiotic relationships, producing oxygen, and decomposing organic matter are well-established roles of microorganisms. Symbiotic relationships, such as those between mycorrhizal fungi and plant roots, enhance nutrient absorption. The production of oxygen occurs through processes such as photosynthesis carried out by specific groups of microorganisms, particularly in aquatic environments. Decomposition is a critical process facilitated by microorganisms, which break down complex organic materials, recycling nutrients back into the ecosystem. Thus, while some microorganisms engage in photosynthesis, it does not represent the broad role of all microorganisms compared to the other options listed.