Me straight away where would waxes be most common on desert plants? on the inside of the plant roots on the outside of the plant leaves on the inside of cell walls of the stem on the outside of the flower’s pollen grains

Desert plants commonly have small wax coated leaves to prevent moisture and water from evaporating. It is an important feature in desert plants to adapt to the arid climate. The wax on the leaves also protect the leaves from the chilling temperature of the desert at night. 

They are all decomposition reactions.