Teachers are highly reliant on textbooks for teaching. In the Republic of Korea, science textbooks help students to understand scientific terms through inquiry activities. However, there is a lack of analysis on whether the inquiry activities suggested in these textbooks appropriately cover the terms included in the main text. Therefore, this study assesses the life science units included in widely used lower secondary school science textbooks in the Republic of Korea by analysing the connection between the terms presented in the inquiry activities and the main text using the NetMiner 4.0 programme. The results reveal that the life science units included in the lower secondary school science textbooks are well structured for learning life science terms through the inquiry activities, as the terms presented in the inquiry activities and the main text are well connected. However, the number of terms included in each unit greatly differs and needs to be supplemented with the optimization of the number of terms per unit. The results provide basic data for the future development of lower secondary school science textbooks. Future research should analyse how the terms used in inquiry activities and the main text are connected in real science classes.