What is the classification of organisms that feed on living or dead matter?

The classification of organisms that feed on living or dead matter primarily falls under the category of fungi. Fungi are known for their role as decomposers in various ecosystems, breaking down organic matter, which includes both living organisms and their remains. This process is vital for nutrient cycling in the environment because it allows for the recycling of nutrients that are locked up in dead organic material.

In addition to decomposing organic matter, some fungi can also form symbiotic relationships with living organisms, such as mycorrhizal fungi that associate with plant roots, helping them access nutrients in exchange for carbohydrates. This dual capability—breaking down dead matter and interacting with living creatures—highlights the key role fungi play in both living ecosystems and in decomposing organic materials.

Other options involve different functions or classifications: bacteria can also break down dead organic material, but they are not typically classified as "feeders" in the same context as fungi, and viruses cannot be classified in this way since they require a host to reproduce and do not metabolize organic matter. Algae primarily perform photosynthesis and are not directly categorized as feeders on organic matter. Thus, fungi correctly represent the organisms that engage in feeding on both living and dead matter.