What is Mold?

Molds are fungi (singular- fungus). Molds grow virtually everywhere throughout the natural and man built environment. Tiny particles of mold are present in indoor and outdoor air. For molds to grow and reproduce, they need only a food source, such as leaves, wood, paper, dust or any organic material, and moisture. In nature, molds help break down dead materials and can be found growing on soil, foods, plant matter, and other items. Because molds grow by digesting the organic material, they gradually destroy whatever they grow on. Mold growth on surfaces can often be seen in the form of discoloration, frequently green, gray, brown, or black but also white and other colors.

Most fungi reproduce by creating microscopic cells called "spores" that are generated by these organisms in great numbers. Spores act like seeds, forming new mold growths (colonies) when they find the right conditions. Spores are usually composed of one to a few cells. The spores may be sexual or asexual and are variable in shape, size and color. Some spores grow in clumps that are stuck together. Others grow in long, fragile chains that are easily dispersed into the air if the fungus is disturbed. If adequate moisture is present when a spore lands on a suitable food source, it uses nutrients stored within it to start growing. The mycelium will germinate from the spore, growing radially, to form a circular growth or colony sending out small extensions called hyphae, similar to the root from a germinating seed. This is the beginning of a mold colony. Unlike people or animals, which digest food after being taken into the body, fungi secrete enzymes from the growing tips of the hyphae to digest its food before entering the organism. The resulting nutrients diffuse into the organism through the cell wall at the tip. As the hypha elongates, it splits and lengthens, eventually creating a complex network of hyphae called a mycelium. Often the mycelium is white and furry, but as many fungal colonies mature they may acquire the color of their spores, black, yellow, brown, or green. Within days a single spore can easily produce a mature colony containing millions of spores.

Yeast
A less familiar fungus is the yeast. The yeast fungus is unicellular, composed of single cells that continually divide by budding or fission. Although yeasts are quite different in their appearance than mycelial fungi, their means of obtaining food is identical. Whether the fungus body is composed of mycelium or yeast, both will function for feeding and reproduction.

Not all Molds are bad.
One genus of mold, Penicillium, comprises hundreds of known species: some produce the antibiotic penicillin, and others turn milk curd into cheese. Some species of Penicillium create the blue-green growth found on long forgotten oranges at the back of a refrigerator drawer.

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