<![CDATA[This study aimed to describe students' understanding profile of the material on the evolution of antibiotic resistance, including students' level of understanding, subconcepts that are difficult to comprehend, reasoning patterns, misconceptions, and factors that influence students' understanding. This study employed a mixed methods approach with a sequential explanatory design. The research sample consisted of 143 twelfth-grade students from SMA Negeri 1 Tanjung Morawa, selected using a purposive cluster sampling technique. Data were collected through multiple-choice tests, essay tests, two-tier diagnostic tests, questionnaires, and interviews, then analyzed using descriptive quantitative and qualitative methods. The results showed that students' level of understanding varied and tended to be in the moderate to low category. The subconcepts of mutation and/or gene transfer as the source of resistant traits, as well as the impact of improper antibiotic use, were the most difficult materials for students to understand. In addition, students still experienced misconceptions in explaining the relationship between mutation, natural selection, and the development of antibiotic resistance. Factors that supported students' understanding included the relevance of the material to daily life, the use of case examples, visual media, discussion, and the way teachers explained the material. Based on these findings, learning about the evolution of antibiotic resistance needs to be developed through more contextual and visual learning strategies oriented toward strengthening conceptual understanding. Keywords: Antibiotic Resistance, Evolution, Misconception, Student Understanding, Two-Tier ]]>
