Appearance of black spots when the bread is exposed to air

Why is there the appearance of black spots when the bread is exposed to air for a long period of time?

Answer:

MOLD FORMATION ON BREAD WHICH LEADS TO ITS SPOILAGE

•  If the bread is kept open for a few days, we can see the appearance of black spots . These are nothing but the grown molds which form due to deposition of Rhizopus fungus 
• spores on the surface of bread.
• The common bread mold plant or Rhizopus fungus consists of fine, thread-like projections called hyphae and thin stems having a knob-like structure called sporangia.
• Each sporangia contains hundreds of tiny spores. When the spore case bursts, these tiny spores are dispersed in air and produce more plants under favorable conditions .