School science textbooks are an amalgamation of concepts collected from different fields of Science like Physics, Chemistry and Biology. The actual number of concepts in the different domains of science are enormous. Educationists have to make a decision of choosing some concept that they think are necessary for students to know at a certain age. Moreover, these concepts have to be arranged in a certain order of arrangement from first chapter to the last in a textbook. The aim of this paper is to question the ontological basis of filtering concepts from the larger world of science to placing them in a school science textbook. Through two informal studies presented in this paper, the author has tried to demonstrate that different groups of people can form concept maps of a topic that are very different in structure compared to what is given in NCERT textbook. If there are multiple ways of arranging the same set of concepts, then how do educationist validate one set of arrangement of topics against the other? The result of study puts light on the fact that currently there are no criteria available for judging the ontological validity of concepts that are present in existing textbooks in school science curriculum. The selection of topics is dependent upon limited individual knowledge base of the expert who is writing the chapter. The article briefly provides a framework by which ontology of a subject can be developed collaboratively by a community of teachers and subject matter experts. This ontology can be used as a valid guide for choosing and arranging topics in a school level science textbook.