A shell is a biotic element because it is part of the body of an animal. It is also considered to be a biotic element because it can be used as a means of protection.
The shells of some animals, such as snails and mollusks, are made of calcium carbonate. These shells are part of the animal’s skeleton and they protect the soft body tissues inside the shell from predators (such as crabs) who would like to eat them.
Other animals, like turtles or oysters have shells that are made mostly of keratin (the same protein found in hair and nails). These shells protect their bodies but do not form part of their skeletons.
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Last modified: October 30, 2022