According to the National Science Foundation, all fungi are heterotrophic, which means that they absorb nutrients, or energy, from other organisms. Some fungi are saprophytes and feed on dead or decaying matter. Other fungi, on the other hand, are symbionts, which means they absorb nutrients from living organisms without harming or killing them.
Fungi absorb nutrients by growing through the substrate, the organic material on which they are living. They do this by extending hyphae, the tubular structures that enclose the cytoplasm, into the organic material. Numerous hyphae slowly work through the organic material and secrete digestive enzymes. This process helps to break down the substrate, which makes it easier for the fungi to absorb the substrate’s nutrients. The hyphae extend themselves over a large area of the substrate to maximize contact with the substrate. Creating intimate contact with the substrate makes the nutrient absorption process more efficient. The nutrients diffuse, or transfer, into the hyphae much more easily. This process of extending itself into substrates makes fungi more susceptible to dryness and ion imbalances. However, because fungi usually grow on moist substrates, this is usually not a problem.
Fungi are commonly known for breaking down, or feeding on, dead and decaying matter such as fallen leaves and rotten wood. A common symbiotic relationship is mycorrhizae, which is a beneficial relationship between the roots of a plant and the fungi.