The purpose of the study is to identify the necessary knowledge to be developed by biology teachers using the TPACK model for each of the five topics that are difficult to teach in Mongolian high schools. Five groups—“respiration,” “regulation of the living body,” “biotechnology, genetic engineering,” “enzymes,” and “immunity”—were selected as difficult groups for teaching according to the TPACK model. The study questioned 113 school biology teachers for content knowledge (CK), pedagogical content knowledge (PCK), technology content knowledge (TCK), and technological pedagogical content knowledge (TPCK). For each topic, TCK is the heaviest and CK the lightest compared to other types of knowledge for biology teachers. In terms of the correlation coefficient, for the groups, TCK and TPCK had the highest correlations. This research proposes the development of TCK and TPCK content modules for specific groups of secondary school biology teachers is crucial.