The correct answer is option 4, Fungi. Fungi play a crucial role as scavengers in the ecosystem. They are responsible for decomposing dead organic matter, such as dead plants and animals, and recycling nutrients back into the environment. Fungi have the unique ability to break down complex organic compounds, such as cellulose and lignin, which are resistant to decay. They secrete enzymes that break down these compounds into simpler forms that can be absorbed by other organisms. This process of decomposition is essential for nutrient cycling and the maintenance of healthy ecosystems. Bacteria, viruses, and algae also have important roles in the environment, but they are not specifically classified as scavengers like fungi.