The internet is more and more present in worldwide education. There are innumerable projects thatstimulate its usage for aiding the teaching-learning process. This new trend modies the reality of thewhole school. However, many copies of identical information are found in several sites: graphs, gures,texts, links and even errors. The aim of this work is to analyse the biochemical issues photosynthesisand cellular respiration available in web pages, taking into account contents quality, trustworthinessand eectiveness. Firstly, 6th secondary level students were inquired by a questionnaire on their use ofinternet resources. More than 80 percent of them were regular users. The result conrms the alreadyknown potential of internet in education. Fourteen sites were analysed regarding to contents, presenceof bibliographical references, authorship, titles of responsibles and adequacy to the target public. Inrelation to contents, presence of conceptual errors, illustrations and other stimulant elements wereanalysed. None of the sites presented biblioghraphic references; less than half divulged responsiblenames and their graduation. The great majority do not mention intended public target. In general,the sites did not contained grave conceptual errors, except for two that mention estoma insteadestroma, cilica/acilica phosphorylation (for cyclic and acyclic), grama (for grana) and place oxygenas essential for anaerobic respiration. However, one of these sites was the only one that mentionedenzymes and regulation steps of cellular respiration. Half of the sites presented identical texts andgures. None used livened up resources. The majority showed contents as virtual versions of printedbooks. Illustrations did not present necessary legends. None of the analysed sites, thus, was consideredexcellent. Trustworthiness is also questionable as much of the contents arte clearly copies of otherpages, recurrent even on the errors. Our data strengthen the need for rigorous evaluation concerningof scholarly research of biochemical themes on the web.