Small Molecules

Small molecules don't really relate that much to growing, but they are extremly important to our life. A small molecule is something like H2O (water)

Medium Molecules

Medium molecules are like amino acids which are what basically makes us grow because theu are thwe base of protein. 

Large Molecules

A large molecule could be like a lipid (fat). Lipids may make you grow in a way you dont want, so stay away from fatty foods. But there are some huge molecules such as proteins which is what pretty much makes your muscles grow.