Decomposers break down the remains of dead plants, animals, and other organisms. Microbes and fungi are examples of decomposers. The oxygen-carbon dioxide cycle refers to how organisms metabolize oxygen and release carbon dioxide, while other organisms metabolize carbon dioxide and release oxygen. In terms of this cycle, the decomposers metabolize oxygen and release carbon dioxide.
Carbon dioxide, along with other matter broken down by decomposers (such as nitrogen), is stored in the ground on both land and sea. This provides nutrients to the primary producers. Examples of primary producers are plants and microbes capable of photosynthesis (such as cyanobacteria). The primary producers then use these nutrients to fuel photosynthesis, which provides oxygen for the consumers. When both the producers and consumers die, the decomposers break down their remains and the cycle begins anew.