To get energy and to stay healthy

Selective absorption of molecules across it

Lipid bilayer with proteins in between this layer,carbohydrates,phospholipids

It indicates cell death within the affected tissue

It can block the blood vessels in the body preventing normal blood flow hence leading to death.

To know how different mechanisms work in the body especially at the biochemical level

These are shared human motives due to evolution examples are,fear,food, music,sex