Mold is a microscopic, multicellular organism belonging to the fungal kingdom. It’s much like a microscopic plant, but it is not a plant because it does not contain chlorophyll, the green pigment plants use for photosynthesis. Without chlorophyll, mold cannot make its own food from sunlight. Instead, mold absorbs nutrients directly from its surroundings by growing on and into organic materials, breaking them down in the process. This makes mold beneficial in nature as a decomposer but potentially problematic indoors.