How Does Light Affect the Reproduction of Mold on Bread?
Common bread mold is a class of fungus. Hundreds of other fungi exist, many of which are able to contaminate food and render it inedible. Mold spores are present almost everywhere in the air. Light by itself does not directly affect the growth and reproduction of mold, but a wavelength of light known as "ultraviolet" can inhibit mold growth.
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Biology of Molds
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Molds are multicellular organisms that are fungi. Molds absorb nutritients from the surrounding environment on which they grow. They do not require light for photosynthesis (unlike plant cells). Fungi can process the nutrients around them only by extruding narrow root structures called "rhizoids" into whatever organic material they are growing in, which can be decaying plant or animal matter. Rhizoids release enzymes to break down the animal or plant material into simpler compounds for absorption. Fungi reproduce by spreading airborne spores.
Fungi
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Fungi are divided into four classes, of which the zygomycota strain is common bread mold. Certain fungi are beneficial to plant life, such as the mycorrhizae strain, which live in certain plant roots and help supply it with nutrients. Other molds such as penicillium produce penicillin, an antibiotic. Some fungi can be parasitic and cause diseases such as ringworm. Fungi such as certain mushrooms are edible, and yeasts are beneficial fungi used in making bread.
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Growth Conditions
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The optimal growth conditions for fungi are warmth and moisture. Bread mold will sprout if preservatives have not been added to the dough. Once spores infest bread, mold will grow unless it loses all the moisture in its surroundings. Foods such as bread can be protected from mold by refrigeration, as colder temperatures inhibit its growth. Mold can tolerate high levels of acidity in its surroundings, and will also grow in jars of jam and yogurt.
Effects of Light
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Ambient light has minimal effect on mold growth. Sunlight may retard bread mold growth by drying the bread. Moisture is needed for fungi roots (rhizoids) as a medium for its enzymes to break down the bread into compounds it can absorb for nourishment. Ultraviolet light has been shown to inhibit mold growth because the nature of ultraviolet light breaks down DNA in mold cells, effectively killing them. Ultraviolet light is part of the electromagnetic spectrum, which also includes visible light.
Health Risks
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Molds can reproduce in a variety of food environments, from bread to jams in glass jars to cheeses and meats. This occurs when foods are exposed to air, and the ambient conditions have the right temperature and moisture content to be conducive to spore germination. Typically foods contaminated by mold should be discarded. This is due to fungal roots being able to penetrate very deeply, and bacteria often breed side by side with fungi in the food. Certain molds also produce "mycotoxins," which are poisonous. Some consumables such as hard cheese can be kept, as long as the moldy part of the cheese is cut away at least an inch below the growth.
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References
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