Sari, P. W. dan Harahap, F. (2016) “ANALYSIS OF STUDENTS DIFFICULTIES IN LEARNING HEREDITY OF XII GRADE STUDENTS IN SMA SWASTA HARAPAN 1 MEDAN ACADEMIC YEAR 2015/2016”, Jurnal Pelita Pendidikan, 4(3). doi: 10.24114/jpp.v4i3.6611.