1. What are the tough patches of skin called that form when skin is exposed to great wear and tear? What is their function? What are they made out of?
Callus are caused by over-occuring friction , this causes the skin to thinken and become a protective layer so that blisters and sores dont presist. They are made from multiple layers of stratum corneum, on places that there is bone present the stratum corneum will thicken to create a corn.
2. Why does your skin become darker when it is exposed to a lot of sunlight?
The more sunlight your exposed to , the more melanin is produced causing darker pigmentation to occur in the skin .