The Most Amazing Thing about Trees
A great reminder of how difficult it must be for a tree to move water up xylem vessels to such a great height. Plant biology is always way more complex and confusing than you would think.
PMG Biology
Biology posts related to EdExcel IGCSE specifications
PMG Biology 
What makes these different types of trees grow very tall or otherwise?
Growth in trees is regulated by a genetic program. Tall trees have a selective advantage over trees that grow less well as they get more light. So genes that promote growth are selected for.
Roots have no chlorophyll and grow in darkness. So how do roots obtain their food?
They gain sugars, amino acids and other food molecules from the leaves via the phloem.