Final answer:
Mucor is a saprophytic fungus because it feeds on decomposing organic matter, which plays an essential role in nutrient cycling. Ustilago is a parasitic fungus as it feeds on living host tissues, which can lead to disease and harm the host.
Step-by-step explanation:
Mucor is referred to as a saprophytic fungus because it obtains its nutrients from decomposing organic matter. This type of fungus releases exoenzymes that break down complex organic substances, such as cellulose and lignin from dead wood, into absorbable nutrients like glucose. This process not only sustains the fungus but also plays an essential ecological role in nutrient cycling by releasing carbon, nitrogen, and other elements into the environment.
On the other hand, Ustilago, often called a parasitic fungus, feeds on living organisms by establishing a biotrophic relationship with its host. These fungi invade the living cells of plants and extract nutrients directly from their cytosol using specialized structures called haustoria. This type of relationship benefits the fungi while harming the host, as it leads to the depletion of the host's resources and potentially causes disease.
Examples of parasitic fungi include those responsible for plant diseases like powdery mildews and rusts, and animal diseases such as mucormycosis caused by Mucorales. In agriculture and human health, it's crucial to understand these distinctions because saprophytic fungi like Mucor contribute to ecosystem balance, whereas parasitic fungi like Ustilago can cause significant crop damage and health issues.