Question

Why leaf has smooth upper surface and rough lower surface?

Answer 1

because in lower part there is guard cells for stamato but on upper part have chlorophyll , stomata which helps in photosynthesis.

Answer 2

There is a lower and upper surface of a leaf, and the upper surface of the leaf is in the sunlight. With more sunlight, the upper surface makes more food and has more chlorophyll on it. Since chlorophyll is green and there is more green on the upper surface, the upper surface is darker.