What role do decomposers play in an ecosystem?

Decomposers play a vital role in ecosystems by breaking down dead organic matter, such as fallen leaves, dead plants, and animal remains. This decomposition process is essential for recycling nutrients back into the soil, which in turn supports plant growth. As decomposers break down these materials, they release nutrients like nitrogen and phosphorus, making them available for uptake by plants, the primary producers in the ecosystem. This nutrient recycling is fundamental for maintaining the health and balance of the ecosystem, as it ensures that resources are continuously reused and supports the overall productivity of the environment.

The other options describe functions that are not associated with decomposers. For instance, decomposers do not compete with primary producers for sunlight, as they obtain their energy from organic matter rather than directly from photosynthesis. Additionally, they do not produce energy through photosynthesis since that process is specific to plants and some microorganisms. Lastly, filtering pollutants is typically a function of certain organisms or systems within the ecosystem but not directly performed by decomposers. Thus, option A accurately captures the essential role of decomposers in nutrient cycling within an ecosystem.