Purba, S. T., S. Rajagukguk, and M. D. Yana. “ANALISIS KESULITAN BELAJAR SISWA DALAM MEMAHAMI MATERI SISTEM REGULASI MANUSIA DI KELAS XI SMA SWASTA KARTIKA 1-4 PEMATANGSIANTAR TAHUN AJARAN 2020/2021: ANALYSIS OF STUDENTS’ LEARNING DIFFICULTIES IN UNDERSTANDING THE MATERIALS HUMAN REGULATION SYSTEM IN CLASS XI SMA PRIVATE KARTIKA 1-4 ADMINISTRATION FOR THE 2020/2021 ACADEMIC YEAR”. MetaBio : Jurnal Pendidikan (Edisi Elektronik), vol. 3, no. 2, Oct. 2021, pp. 24-33, https://jurnal.usi.ac.id/index.php/metabio/article/view/40.