Simbolon, J. F. “Pengaruh Model Pembelajaran Self Directed Learning Terhadap Peningkatan Kualitas Perkuliahan Fisiologi Tumbuhan Di Program Studi Pendidikan Biologi STKIP Riama Medan”. Jurnal Ilmiah Aquinas, vol. 3, no. 2, July 2020, pp. 216-30, https://ejournal.ust.ac.id/index.php/Aquinas/article/view/732.