( ( Biological membranes ) ( ( ( ( surround cells ) and ) ( serve ( to ( keep ( ( the insides ) ( separated ( from ( the outsides ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Biological) (NNS membranes)) (VP (VP (VBP surround) (NP (NNS cells))) (CC and) (VP (VBP serve) (S (VP (TO to) (VP (VB keep) (NP (NP (DT the) (NNS insides)) (VP (VBN separated) (PP (IN from) (NP (DT the) (NNS outsides)))))))))) (. .)))
Biological membranes surround cells and serve to keep the insides separated from the outsides.
(ROOT (S (NP (JJ Biological) (NNS membranes)) (VP (VP (VBP surround) (NP (NNS cells))) (CC and) (VP (VBP serve) (S (VP (TO to) (VP (VB keep) (NP (NP (DT the) (NNS insides)) (VP (VBN separated) (PP (IN from) (NP (DT the) (NNS outsides)))))))))) (. .)))