|MadSci Network: Cell Biology|
You are both right. As mold grows it sends out hyphae similar to roots of a plant. As with a tree, we see the structure above the ground but below the ground are roots extending outward. With mold it is much the same. On a piece of bread, there might be a visible portion, but below the surface the hyphae could extend well beyond the fuzzy colony on top. The mold organism needs oxygen to grow so the hyphae usually do not extend too deeply into the food.
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