Subject: how/why do shade leaves grow bigger than sun leaves in a tree

doing a assignment,we did some research and collected data of 100 leavses,50 
in shade and 50 in sun of a oak tree.i have understood that shade leaves are 
bigger so they are able to catch the filtered sun light from the sun leaves 
that are directly exposed.and that sun leaves are smaller in area.what i want 
to know is how they come to grow like that  and any other information on the 
diffences between the 2 types of leaves.iv researched using the internet and i 
am unable 2 find more information,so i woukld appreciate your help.thanks.

Re: how/why do shade leaves grow bigger than sun leaves in a tree