What is the function of the waxy, transport top layer of leaves ?

The layer should be the waxy cuticle, and its function is mainly to reduce water loss by evaporation from the leaves.

That's why the stem of a cactus is waxy, this is because the layer can prevent the cactus from losing too much water, especially when the cactus is usually found in desert area where water is not always available.

The waxy cuticle is mostly found only on the top of the leaves, this is because sunlight shines directly to the top of the leaf instead of the bottom of leaf, plus, there are stomata at the bottom of leaves, which is like pores for water loss of the plant and carbon dioxide absorption, which is necessary for photosynthesis.

not the best question format lol but what i think might as scale color is controlled by a single gene with two alleles, the green allele and the yellow allele. when moths that are homozygous for green scales are mated with moths that are homozygous for yellow scales, 100% of the offspring have green scales.