Skin vs Shell
Skin is the outer covering of the body. The shell or exoskeleton is the outer covering that protects and also supports the animal’s body.
Skin exists in almost all mammals, reptiles, amphibians and birds although the type may vary. In humans although the skin appears to be hairless but it is said that the human body has more hair follicles than a Chimpanzee. Skin forms the largest organ in the body providing a cover for the internal organs, muscles, ligaments and bones and guarding it from the enviornmental effects. Shell is also rigid but outside the body. This is generally used to form the skeleton which on the inside provides place for the organs and muscles to attach to and also protects the animal from predators.
Skin is mainly formed of cells and has pigmentation that gives it its color. In humans the skin pigmentation varies widely among the population, hence, the different skin colours. Skin also partly absorbs some of the harmful ultra violet light from the sun. It also contains an enzyme that reverses the damage caused by this. In case the gene for the enzyme is not present in the DNA it results in high rates of skin cancer. The shell is formed of rigid and resistant components that can fulfill a variety of roles for the animal including, movement, senses, feeding, excretion. Etc. Shells of some fish and turtles are formed of bone, cartilage and dentine.
Skin apart from protecting the internal organs would also provide insulation and heat regulation, by sweating, storage for water an lipids, absorption of some atmospheric nutrients and water resistant barrier. In some organisms the skin is also the main respiratory organ and the main transport medium to transport nutrients throughout the body. Shells however would not provide most of these functions to the animal. Most animals with shells would not have an internal skeleton as this would act as an exoskeleton. However, animals like turtles have both and exoskeleton as well as an internal skeleton. Here the shell mainly acts as protection only.
1.Skin forms the outer covering for the body providing protection to the internal organs, however, the shells would generally form the exoskeleton also.
2.The skin is made up of cells whereas the shells may be made up of bone, cartilage or denting.
3.Skin performs a variety of functions for the body while the shells are not able to provide these.