MOGADISHU, Somalia (AP) — The two Somali sisters were studying to be doctors. They were in a minibus on their way to university on Saturday morning when their world exploded. Now, 22-year-old Amina Mohamud is in critical condition. Her sister, 25-year-old Fadumo Mohamud, is dead. Their mother calls Saturday the darkest day of her life.Families wailed in Mogadishu on Sunday after a truck bomb at a busy security checkpoint detonated during rush hour. University students, the future of a country rebuilding from decades of conflict, made up most of the 79 people killed.It was the worst attack in Mogadishu, often the target of the al-Shabab extremist group, in more than two years. International condemnation has poured in. Pope Francis on Sunday appealed to the world for prayers.And the mother of Amina and Fadumo, Sharifo Roble, was distraught as her younger daughter was placed on a stretcher and wheeled toward a plane that would take more than a dozen other severely wounded people to Turkey for desperately needed care.“I sent my two daughters to university yesterday. One died in the blast and the other one is in severe condition,” Roble said. “I had to struggle with their upbringing because I was acting as both mother and father.” The sisters’ father died years ago. Roble can only pray that her younger daughter one day will come home and continue her studies. Somalia needs it, she said.Health authorities in Mogadishu have pleaded for blood donations to help treat the 125 people wounded in the bombing, which occurred after a weekend as the Muslim nation returned to school and work. Nearly every student on the Mohamud sisters’ minibus was killed. The truck bomb exploded next to it after police at the checkpoint blocked the truck from entering the city, Somalia’s police chief said.Families across Mogadishu held funerals the same day. Others, like Roble, joined Somali President Mohamed Abdullahi Mohamed in seeing off their badly hurt loved ones on the Turkish plane. The plane also held the bodies of two Turkish brothers who died in the blast.Another plane was expected to arrive from Qatar to airlift others to treatment, Somali officials said.“We pray for those martyred in this attack to rest in heaven,” said Somalia’s security minister, Abukar Islow Duale, “and those who were injured to have quick recovery.”The al-Qaida-linked al-Shabab, which controls parts of Somalia and whose reach extends to attacking luxury malls and schools in neighboring Kenya, has remained silent. It has not claimed responsibility as usual. Al-Shabab also was blamed for the devastating truck bombing in Mogadishu in October 2017 that killed more than 500 people. The group never claimed responsibility for the blast that led to widespread public outrage. Some analysts said al-Shabab didn’t dare claim credit for the 2017 attack as its strategy of trying to sway public opinion by exposing government weakness had badly backfired.