Learning the cell, one of the basic subjects of science education, by preservice teachers in a comprehensive way is important for making sense of its vital activities and teaching the subject in a meaningful way in the future. The study aimed to determine preservice science teachers' cognitive structures related to the cell and its organelles before and after the Biology course. The study group consists of 32 preservice science teachers. The single-group interrupted time series design was adopted in the study. Data were collected through the word association test. As a result of the data analysis, it was determined that some organelles could not be associated with other organelles, there was no knowledge about the peroxisome organelle before the intervention. It was observed that more comprehensive and interrelated cognitive structures were formed after the intervention and the peroxisome organelle was also added to this structure.