leaf-cuter ants cultivate fungus. The ants keep conditions optimal for fungus growth and carry leaf fragments for the fungus to grow on. Then the ants feed on pieces of the fungus. which kind of relationship exists between the fungus and the ants?

The relationship between the fungus and the ants is mutualistic. Both organisms benefit from each other's presence and actions. The ants provide the fungus with optimal growing conditions and a nutrient source (leaf fragments), while the fungus provides the ants with a food source.