( ( ( This fat ) ( -LRB- ( ( brown fat ) -RRB- ) ) ) ( produces ( ( heat . ) ( It ( ( does this ) ( by ( not ( ( ( storing ( ( released energy ) ( in ( ( the form ) ( of ATP ) ) ) ) ) ( but instead ) ) ( ( releasing ( the energy ) ) ( as heat ) ) ) ) ) ) ) ) ) )
(ROOT (S (NP (NP (DT This) (NN fat)) (PRN (-LRB- -LRB-) (NP (JJ brown) (NN fat)) (-RRB- -RRB-))) (VP (VBZ produces) (NP (NP (NNP heat) (. .)) (SBAR (S (NP (PRP It)) (VP (VBZ does) (NP (DT this)) (PP (IN by) (S (RB not) (VP (VP (VBG storing) (VP (VBN released) (NP (NN energy)) (PP (IN in) (NP (NP (DT the) (NN form)) (PP (IN of) (NP (NNP ATP))))))) (CONJP (CC but) (RB instead)) (VP (VBG releasing) (NP (DT the) (NN energy)) (PP (IN as) (NP (NN heat))))))))))))))
This fat  (brown fat) produces heat.  It does this by not storing released energy in the form of ATP but instead releasing the energy as heat
(ROOT (S (NP (NNP Heat)) (VP (VBZ is) (VP (VBN produced) (SBAR (WHADVP (WRB when)) (S (NP (NN paper)) (VP (VBZ is) (VP (VBN burned))))))) (. .)))
Heat is produced when paper is burned.