Question

in some plants like desert plants about meres has a thick waxy coating of youth in all its outer surface can we think of a reason for this

Answer 1

yes this wax coating helps the desert plants to conserve their water inside them otherwise if the waxy coating will not their the water go through transpiration and in desert it's hard to get water.

Answer 2

if you have noticed the leaves and stem of many plant have broad surface wait......yes so they have this thick waxy coating in it outer in order to seal and protect moisture they already have the smaller or fewer leaves plants has less water which gets lost during transportation since it has less surface area .