restricting query-replace to region in emacs lisp script

[conscious]

I am writing a lisp routine to implement a sequence of query-replace
operations on a region. Before I run the query-replace I define a
region, e.g. by mark-paragraph. However, other than in normal
interactive operation in transient-mark-mode, the query-replace does
not restrict the query-replace to the marked region. Does anybody know
how to restrict the region for query-replacing with a lisp-routine?