Answer 1

GMO's have been useful for enhanced crop output in different ways:  

1. genetically modified crops are more tolerant of abiotic stresses (cold, drought, salt, heat)
2. These genetic modifications have helped to reduce post-harvest losses implying less damage to crop yield.
3. Genetic modification has reduced reliance on chemical pesticides by creating pest-resistant crops. eg. Tobacco, leading to greater crop yield.
4. The creation of insect-resistant crops such as Bt cotton and Bt corn has enhanced crop yield.
5. Increased efficiency of mineral usage by GM plants prevents early exhaustion of fertility of soil resulting in increased yield.