BELGRADE — Staunch religious and political conservatives have teamed up to challenge Serbia’s recently revamped school curriculum over descriptions of gender and sexual identity, sparking a formal review that could result in a textbook ban. From biology to history and sociology, the Serbian Orthodox Church and a fringe right-wing party have demanded the replacement of textbooks they say “promote LGBT ideology.” As a result, Serbia’s education minister is awaiting a recommendation from the National Education Council on the scientific soundness of the materials but also on whether it serves the “national interest” to present such ideas to schoolchildren.