Which organism is a species of fungus that produces an external growth on organic matter?

• A. Yeast
• B. Mold
• C. Mildew
• D. Fungus

Answer: (B)

Understanding how fungi grow helps here. Mold is a filamentous fungus that forms visible hyphae extending across surfaces, producing external growth on organic matter. This filamentous growth is what you typically notice on bread, fruit, or damp walls. Yeast, by contrast, are unicellular fungi that reproduce by budding and don’t form that kind of outward filamentous growth. Mildew describes a powdery appearance seen on some mold forms, but it isn’t a single species and doesn’t define the general growth pattern. Fungus is too broad a term to identify a specific growth form, whereas mold specifically captures the external, filamentous growth on substrates.