Final answer:
Decomposers break down dead matter and waste, recycling essential nutrients like carbon and nitrogen back into the ecosystem, which supports plant growth and sustains the food web.
Step-by-step explanation:
One function of the decomposer in a food web is to break down dead organisms and waste materials. Decomposers, such as bacteria, fungi, and earthworms, perform a critical role by returning essential nutrients like carbon and nitrogen back into the ecosystem. These nutrients are vital for the growth of primary producers like plants, which form the foundation for other trophic levels in the food web. By breaking down complex organic materials into simpler forms, decomposers release these elements into the soil, making them accessible to plants and thereby sustaining the cycle of life.