The document summarizes a study analyzing the level of conceptual demand of practical work in the biology and geology curriculum for Portuguese high schools. The study used Bernstein's theory of pedagogic discourse to examine emphasis on practical work and its conceptual demand based on complexity of knowledge, interrelation of knowledges, and cognitive skills. The results showed practical work is underrepresented and conceptual demand varies between biology and geology subjects and between general vs. specific guidelines. Recontextualization processes may decrease conceptual demand transmitted to teachers. The meaning and findings are discussed, and the study explores assumptions and instruments for analyzing conceptual demand of practical work in science curricula.