( Diffusion ( ( is ( where ( elements ( ( move ( from ( ( an area ) ( of ( high concentration ) ) ) ) ) ( to ( ( an area ) ( of ( low concentration ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Diffusion)) (VP (VBZ is) (SBAR (WHADVP (WRB where)) (S (NP (NNS elements)) (VP (VBP move) (PP (IN from) (NP (NP (DT an) (NN area)) (PP (IN of) (NP (JJ high) (NN concentration))))) (PP (TO to) (NP (NP (DT an) (NN area)) (PP (IN of) (NP (JJ low) (NN concentration))))))))) (. .)))
Diffusion is      where elements move from an area of high concentration to an      area of low concentration.
(ROOT (S (NP (NNP Diffusion)) (VP (VBZ is) (NP (NP (DT the) (NN process)) (SBAR (WHPP (IN in) (WHNP (WDT which))) (S (NP (DT a) (NN substance)) (ADVP (RB naturally)) (VP (VBZ moves) (PP (IN from) (NP (NP (DT an) (NN area)) (PP (IN of) (NP (NP (JJR higher)) (PP (TO to) (NP (JJR lower) (NN concentration)))))))))))) (. .)))
Diffusion is the process in which a substance naturally moves from an area of higher to lower concentration.