Evolution is the process by which this occurs and it is spread out over many generations. Thus, the short minimal definition of biological evolution is, Evolution is a process that results in heritable changes in a population spread over many generations. This is a good working scientific definition of evolution; one that can be used to distinguish between evolution and similar changes that are not evolution.
Bone, cartilage, or dentine is used in the Ostracoderm fish and turtles. Chitin forms the exoskeleton in arthropods including insects, arachnids such as spiders, crustaceans such as crabs and lobsters (see arthropod exoskeleton), and in some fungi and bacteria. Calcium carbonates constitute the shells of molluscs (see Mollusc shell), brachiopods, and some tube-building polychaete worms.
(2) A polysaccharide which makes up the cell walls of fungi and exoskeleton of insects. Supplement. Examples of organisms with chitin are the arthropods in their exoskeletons, some arachnids in their hard outer covering, molluscs in their radula, cephalopods in their beaks, and some fungi species in their cell walls.Chitin resembles keratin (protein component in human hair and nails) in structural function.2) A polysaccharide which makes up the cell walls of fungi and exoskeleton of insects. Supplement. Examples of organisms with chitin are the arthropods in their exoskeletons, some arachnids in their hard outer covering, molluscs in their radula, cephalopods in their beaks, and some fungi species in their cell walls.