The aim of this study is to explore how nature of science is addressed in biology textbooks according to grade level and the chapters. The textbooks examined within the scope of the study are Biology 9 and Biology 10 textbooks. The analysis of the textbooks was based on the Reconceptualized Family Resemblance Approach. The study was conducted through content analysis based on an analytical framework in which aspects of NOS were included. According to the findings, it was determined that there were a total of 246 representations in the Biology 9 textbook about the nature of science. While 165 of these representations are related to the cognitive-epistemic structure of science, 81 are related to the social-institutional aspect. The findings also showed that there were a total of 178 representations related to the NOS in the Biology 10 textbook. While 82 of these representations are related to the cognitive-epistemic structure of science, 96 are related to the social-institutional aspect. No representations about political power structures were found in either textbook. The most frequent representations regarding the cognitive-epistemic structure of science were identified in the dimension of scientific practices in both textbooks. In the social-institutional dimension of science, the most representations were found in the financial aspect science in Biology 9 textbook, and in the scientific ethos sub-dimension in Biology 10 textbook. Chapter 3 in Biology 9 textbook and chapter 3 in Biology 10 textbook are the chapters that contain the most representations to NOS. The results showed that the social-institutional aspect of science is neglected in biology education in accordance with results about other science disciplines in the literature.