The economic crisis and the COVID-19 pandemic since 2019 forced both public and private schools in Lebanon to close for an extended period of time. Many topics were suspended from the curriculum due to decreasing the number of learning days. The predominant causes of learning loss are lengthy gaps or cutouts in students' education. This study aims to investigate the impact of school closure on students' learning, specifically the learning loss in biology at the secondary level during the period between 2019-2022. This is a mixed research: qualitative data was collected through document analysis to compare the topics covered in biology and the official exams for grade 12-Life Science section during the last two academic years with those covered and implemented before the dual crisis; and quantitative data through teachers' questionnaire implemented to address the biology learning loss. The results revealed a huge learning loss in biology, more than 50 % of the biology program was not covered in grades 10, 11-S and 12-LS, and a decline in the quality of the official exams. Similar results were obtained in a parallel study addressing Lebanese secondary students' learning loss in mathematics. [This research was presented at ICSES conference held in Antalya between 10 and 13 November, 2022.]