Most leaves have the upper surface more green and shiny than the lower ones. Why?

In most of leaves the upper surface will be more green and shiny than the lower surface. Why?

Why the arteries are more elastic than the vein?

Cyclobutane is more reactive than cyclopentane. Why ?

Why do leaves have stomata?

A steel plate of face area 2 cm^(2) and the thickness 1.0cm is fixed at the lower face. A tangential force of 10N is applied on the upper surface. Find the lateral displacement of the upper surface with respect to the lower surface. Rigidity modulus of steel =8.4xx10^(10)Nm^(-2)

Why is there more pressure in artries than veins?