( Fission ( ( takes ( place ( when ( ( an animal ) ( simply ( divides ( into ( two parts ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Fission)) (VP (VBZ takes) (NP (NP (NN place)) (SBAR (WHADVP (WRB when)) (S (NP (DT an) (NN animal)) (ADVP (RB simply)) (VP (VBZ divides) (PP (IN into) (NP (CD two) (NNS parts)))))))) (. .)))
Fission takes place  when an animal simply divides into two parts.
(ROOT (S (NP (NNP Fission)) (VP (VBZ takes) (NP (NP (NN place)) (SBAR (WHADVP (WRB when)) (S (NP (DT an) (NN animal)) (ADVP (RB simply)) (VP (VBZ divides) (PP (IN into) (NP (CD two) (NNS parts)))))))) (. .)))