Compared with the LBL mode, the application of the PBL mode significantly improved the final exam scores of Chemical Biology undergraduates in Immunochemistry. This was specifically reflected in the excellent rate, pass rate, and failure rate. The excellent rates and pass rates of students in Grades 2019 and 2020 were significantly higher than those of Grade 2018, while the failure rates were significantly lower than the control group (Fig. 1–2, Table 2). Besides this, the teaching evaluation of the PBL application in Grades 2019 and 2020 was good and was highly praised by the teachers and students in this subject (Table 3). According to different score ranges, the excellent and pass rates of undergraduates in Grade 2019 and 2020 were similar, but the percentage of undergraduates in Grade 2019 was significantly higher than that of the students in Grade 2020 in the range of 70–79 points, and conversely much lower in the range of 60–69 points (Table 2). The difference in these two ranges might be induced by the increased numbers and difficulty levels of exam questions in 2021. Because the number of questions in the exam bank of the Immunochemistry Course online was expanded from 200 to 470, which was used for random questions extraction. For the Immunochemistry Course, the combination of theory and practice, and problems discovery and solution are closely reflected, and the demand for teaching mode is similar to PBL teaching[14], so PBL teaching will be in good agreement with Immunochemistry Course. However, PBL teaching aims to train the students' comprehensive ability, rather than improve the test scores, so there are still some limitations in the selection of assessment indicators in this course.
Immunochemistry is an interdisciplinary subject that uses the theories and methods of Chemistry to study the problems of Life Science. It can provide the theoretical basis for the research and development of new drugs and the prevention and treatment of diseases by interfering with the pathogenesis of human diseases[13, 15]. Therefore, for the Immunochemistry Course with abstract contents, quickly digesting and updating the theoretical knowledge is particularly important for students to keep up with the times. In addition, reading English articles and translating them into Chinese is also difficult for students to learn in this course. With the progress of science and technology, LBL mode is difficult to meet the students' learning demand in academic frontiers knowledge. But the advantages of PBL teaching mode with the classic cases analysis and classroom report are reflected in connecting complex and scattered theories in the books together, and organically integrating the related knowledge involved in different disciplines, which will help the students to master the scientific knowledge behind the problems independently and gradually form the systematic knowledge framework[16–18]. The case analysis and discussion in each chapter will gradually improve the student’s ability in English reading and lay a good foundation for enriching the subject knowledge and expanding the thought in scientific research. The results of the questionnaire survey also confirmed that the combination of PBL and LBL modes can promote the students to digest theoretical knowledge, activate their enthusiasm and curiosity, and improve their abilities of self-directed learning and solving problems independently. Besides these, case analysis and group reports can also greatly cultivate the self-expression and cooperative awareness of students. Hence, for the related fields of Basic Medicine and Clinical Medicine in medical colleges and universities, the application of PBL mode can improve the students' classroom efficiency, knowledge reserve, and comprehensive abilities, which will be very positive and meaningful.
At present, the PBL teaching method has been promoted in various medical colleges and universities[19–20], but there are still some problems in practical teaching, which are mainly reflected in the following three aspects. Firstly, the practical and effective application is still scarce. The main reasons are that there are great differences in training objectives, teaching syllabus, and curriculum setting of different disciplines, and the teachers' acceptance and appreciation of the new teaching mode are far from enough. At present, Immunochemistry Course at our university is only offered to undergraduates majoring in Chemical Biology and doesn’t involve related majors. Therefore, this study lacks the evaluation of the teaching effect of Immunochemistry Courses in different specialties of medical universities. In view of the gradual revision of the training programs in related majors, Immunochemistry Course will be gradually opened in related majors of the School of Biology and Engineering in our university, such as Biotechnology and Biomedical Engineering. In the future, the teaching effect of PBL in other majors will be comprehensively analyzed and compared. Secondly, colleges and universities have set the fixed teacher-student ratio on the basis of LBL teaching mode, which makes PBL mode difficult to effectively carry out in classes with many students, and the students may not independently acquire the knowledge and solve the problems through the cases analysis and group discussion[21–22]. Therefore, it is very important to promote the teaching of small classes and the PBL teaching mode. Thirdly, less class time and a lack of teaching resources in the curriculum sets are not conducive for students to devote themselves to learning[23]. Therefore, the practical teaching and reasonable allocation of teaching resources in the Immunochemistry Course must be emphasized, and the PBL teaching method needs to be actively adopted to guide the students to learn efficiently. In short, the effect of the PBL teaching method is not immediate, which may take at least 1–2 years to show. Therefore, long-term follow-up research and in-depth exploration are particularly necessary.