The most obvious similarity between fungi and animals is their trophic level, that is, their place in the food chain. Neither fungi nor animals are producers as plants are. Both must use external food sources for energy. Fungi and animals share a molecule called chitin that is not found in plants. Fungi and many invertebrate animals use this complex carbohydrate for structural purposes.
In fungi, chitin is the structural component of the cell walls. In animals, it appears in hard structures such as the exoskeletons of insects and the beaks of octopuses and other mollusks. On a molecular level, chitin is similar to the plant molecule cellulose, used in plant cell walls and other structures, but the chitin molecule has a modification that makes it stronger than cellulose.
By studying a large number of features found among various members of Domain Eukaryota, taxonomists have developed a phylogeny tree called a cladogram that places fungi together on a branch with animals, separate from the branch for green plants. Today, we know that fungi are not plants, but the botanical history of fungi provides an interesting perspective on our scientific biases, on how we classify organisms and how these impact our collective knowledge.
Taxonomic classifications are in constant flux, as we refine our understanding of the incredible diversity that surrounds us. Even in the age of genomics, we have only just scratched the surface of this diversity. Today, we have the luxury of molecular tools for classification, but taxonomic classifications can be traced back before the discovery of DNA, the concept of evolution and the invention of the microscope.
Early classifications were limited by the tools and views available to them. We must keep this caveat in mind when examining some of the early attempts at classifying life.
Mushrooms were the earliest representatives of fungi to be classified. Based on observations of mushrooms, early taxonomists determined that fungi are immobile fungi are not immobile and they have rigid cell walls that support them.
Molecular phylogenetic studies revealed that fungi are more closely related to animals than plants. Both fungi and animals are without chlorophyll. Both are having heterotrophic mode of nutrition not self synthesizers like plants. In both, the cells are eukaryotic with organelles like mitochondrion, ER, Golgi etc. Both store carbohydrate as glycogen reserve food. Both are having chitin; cell wall of fungus is primarily made up of chitin whereas in some animals, chitin is present in the exoskeletal structures of insects, spiders and crustaceans.
Generally both are multicellular Exception: Yeast is unicellular fungus.
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