Mushrooms are fungi, which are actually genetically closer to animals than they are to plants. Scientists use a genealogical path known as the Tree of Life to trace the evolution of living organisms, and they have determined that fungi share a common ancestor with animals and are completely branched off from plants. Fungi and animals have to turn to external sources for their food sources, but plants can produce their own nutrients. Chitin, a complex carbohydrate responsible for cell wall structure, is a molecule that is shared by fungi and animals but is not found in plants.
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