( Diffusion ( ( is ( ( the ( net movement ) ) ( of ( molecules ( from ( areas ( of ( ( higher concentration ) ( to ( areas ( where ( they ( are ( in ( lower concentration ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Diffusion)) (VP (VBZ is) (NP (NP (DT the) (JJ net) (NN movement)) (PP (IN of) (NP (NP (NNS molecules)) (PP (IN from) (NP (NP (NNS areas)) (PP (IN of) (NP (NP (JJR higher) (NN concentration)) (PP (TO to) (NP (NP (NNS areas)) (SBAR (WHADVP (WRB where)) (S (NP (PRP they)) (VP (VBP are) (PP (IN in) (NP (JJR lower) (NN concentration)))))))))))))))) (. .)))
Diffusion is the net movement of molecules from areas of higher concentration to areas  where they are in lower concentration.
(ROOT (S (NP (NNP Diffusion)) (VP (VBZ is) (NP (NP (DT the) (NN term)) (PP (IN for) (NP (NP (DT the) (NN movement)) (PP (IN of) (NP (NP (NNS molecules)) (PP (IN from) (NP (NP (DT an) (NN area)) (PP (IN of) (NP (NP (JJ high) (NN concentration)) (PP (TO to) (NP (NP (DT an) (NN area)) (PP (IN of) (NP (JJ low) (NN concentration))))))))))))))) (. .)))