Question

if the earth has gravitational pull and all the things go downwards to the earth then why the plants grow upward to the earth

Answer 1

no many plants don't like u say potato
they can't get all nourishment from soil so they come up to the surface as an adaptation or response to light and water

Answer 2

This anti gravity effect shown by plants is called gravitoprism. There is a hormone called Auxins in plant body which induces rapid cell division. 

Now, as we know if the plant shoot is straight up, gravity causes more Auxins concentration in the bottom, thus the tree grows straight up. But if it is tilted sideways, the Auxins' concentration increases more on the lower side, thus causing increased cell growth there and consecutive bending upward of the shoot! 
Simple but highly efficient mechanism! :