The following passage outlines the process of gravitropism in plant roots:

Auxin is actively transported to, and accumulates at, the ........................ side of a horizontally-oriented root. In root cells, a high concentration of auxin ........................ cell elongation, which is the opposite effect to that seen in shoots. This asymmetric distribution causes the cells on the opposite side to grow faster, resulting in the root bending .........................

Which option is the correct sequence of missing words?