This study aims to comparatively examine pre-service teachers' cognitive structures regarding plastics and bioplastics. For this purpose, a qualitative research method, specifically a case study, was employed. The study group was determined through convenient sampling and consisted of 60 pre-service teachers continuing their education at a state university. Research data were collected using a word association test developed by the researchers. The obtained data were analyzed through content analysis to reveal the cognitive structures of pre-service teachers regarding plastics and bioplastics. As a result of the analyses, it was concluded that the cognitive structures of pre-service teachers related to plastics and bioplastics are gathered under four main themes: "areas of use," "physical- chemical structures," "effects on the environment," and "effects on health." It was determined that pre-service teachers generally focus on the negative aspects of plastics and the positive aspects of bioplastics. They tend to perceive plastics as harmful to health and environmentally polluting, while they perceive bioplastics as ecologically friendly and harmless to health. Additionally, deficiencies in knowledge about the subject and the presence of certain alternative concepts among teacher candidates have been identified. The study concludes by providing recommendations based on the obtained results.

Keywords: Plastic, cognitive structure, bioplastic, word association test, pre-service teachers