The term 'Alga and Fungus' can be summarized by the crossword solution 'LICHEN, ' which is a composite organism consisting of a symbiotic relationship between an alga and a fungus. Lichens are found in many different habitats, from deserts to rainforests, and are known for their ability to survive in extreme environments. They are also used as indicators of air quality, as they are sensitive to pollutants.