The OCR GCSE Biology Paper 3 (June 2019) covers reflex arcs, cellular respiration, and genetic inheritance. Topics include deforestation, water cycles, and human impacts on biodiversity. Key concepts such as selective breeding, food webs, and bioaccumulation in killer whales are explored alongside practical investigations on reflexes and aseptic techniques. The paper emphasizes experimental design, data analysis, and ethical considerations, with real-world applications in disease prevention, climate change, and conservation. Hormonal control in reproduction and genetic disorders in horses are also central themes.