Convex mirror is used as rear view mirror in vehicles. Because the image is smaller, more image can fit onto the mirror, so a convex mirror provides for a larger field of view than a plane mirror. This is why they are useful.
An enzyme is a variety of catalyst and is the relation between tham. A catalyst is a chemical that increases the rate of a chemical reaction without itself being changed by the reaction.
Zoroastrianism, the ancient pre-Islamic religion of Iran that survives there in isolated areas and, more prosperously, in India, where the descendants of Zoroastrian Iranian (Persian) immigrants are known as Parsis, or Parsees.