Practices in line with individual development have a critical role in Project Based Learning (PBL). The projects in a competition carried out by The Turkish Ministry of National Education (TMNE) are important at this viewpoint. The PBL practices need to be suitable for the related curriculum. Therefore the Turkish Science and Technology Curriculum does not need to include extra-curricular knowledge. In this study, the 388 science projects ranked 100th or above in the competition carried out by TMNE for six years were examined by using a qualitative research method known as content analysis to identify the extra-curricular biological knowledge. Evaluating the data, it is concluded that the extra-curricular biological knowledge was widely used in student projects. Extra-curricular biological content related to the daily life may be useful in learning practices as it has a parallelism with PBL process which has a wide and a processed structure.