This is a possessive - "The skin of the apple" so it goes "The apple's skin was rather tough" If there's more than one apple you'd say "The apples' skins were rather tough"
Large animals typically have thick, tough skin, since they are heavy and there is a lot of stress placed on that skin by the weight of the flesh that it contains. In addition, tough skin protects against various potential dangers such as scratchy thorns, bites, etc.
You could say The apple's skin was rather tough. The apple skin was rather tough is even better.
Yes! Tough but smooth
The stratum corneum is the tough outer layer of the skin.
A tough waterproof skin.
Land animals which have tough and dry skin are called reptiles:)
yes it has tough skin
They allowed them to move away from water.
possibly because there aren't as many nerves on your elbow's skin as any other skin.
A porpoise has tough leather like skin body covering, that protects them from some predators.
yes