CBSE Class 8 Answered

The human body consists of living cells except for a few structures in the body which consist of dead cells. These include the hair, finger nails and toe nails. These structures have a growth region at the base where the cells are born and bind tightly together. Newer cells continuously force the old cells outward. These specialised skin cells build up a massive cytoskeleton made of special filaments known as keratin. The cells do not live very long and when they die, keratin is left behind tightly bound together into the fingernail or hair, and this elongates by adding more at the base. As in human beings, in animals, structures such as scales, claws, horns, feathers, beaks, turtle shells, etc. are also non-living or dead.