The present study aims to determine the biological topics that students have difficulties learning, the reasons why secondary school students have difficulties in learning biology, and ways to improve the effectiveness of students' biology learning. For these purposes, a self-administered questionnaire including three open-ended questions was employed to collect the data. It was administered to 207 11th grade students in the district of Rize, Turkey. The data were analyzed both qualitatively and quantitatively. There were five topics that the students had the most difficulties learning: Matter cycles, endocrine system and hormones, aerobic respiration, cell division, and genes and chromosomes. The main reasons for learning difficulties were the nature of the topic, teachers' style of teaching, students' learning and studying habits, students' negative feelings and attitudes towards the topic and a lack of resources. To overcome these difficulties and make their biology learning more effective, the participants suggested such strategies as teaching biology through the use of visual materials, teaching through practical work, reducing the content of the biology curriculum, using various study techniques, teaching biology through connecting the topics with daily life, making biology learning interesting, and increasing the number of biology questions in the university entrance examination. The findings were discussed in relation to the relevant literature. (Contains 5 tables.)