Many studies worldwide have shown that students and pre-service teachers have misconceptions about cell biology concepts. In most cases, teachers are the source of their students' misconceptions. In this regard, we conducted this study to investigate if Moroccan pre-service teachers of life and earth sciences have a good understanding of cell biology concepts, and to find which concepts they misconceive. We developed and validated a three-tier diagnostic test with 20 items concerning cell biology concepts. The test was based on knowledge related to cell biology included in the Moroccan secondary school life and earth sciences' curriculum, which the pre-service teachers will teach. The use of a three-tier test allowed us to differentiate incorrect answers due to misconceptions from those related to a lack of knowledge and correct answers related to strong knowledge, from lucky guess. This study shows that pre-service teachers share several cell biology misconceptions, and that they misconceive the following concepts: cell, gene, hormone, nerve impulse and immune response. Misconceptions detected may impede pre-service teachers' learning and may be transmitted to their students, which requires development of a training strategy to overcome these obstacles.