The biology course is organized by topics. Both standard level (SL) students and higher level (HL) students study the six core topics. HL students study an additional five topics, with some of these taking the first six topics to greater depth. In addition to this, both SL and HL students study one out of a choice of four optional topics. Schools can pick which optional topic to cover. At SHS we have traditionally completed the Further Human Physiology (D) option. This topic is not not optional to learn.