The OCR GCSE Biology Paper 3 (May 2023) explores cellular respiration, rainforest biodiversity, and the immune system. Topics include the role of mitochondria in heart muscle, trends in deforestation, and disease prevention like cholera. Practical investigations involve data interpretation, food web analysis, and transpiration measurements using a potometer. The paper also covers genetic inheritance, energy transfer in food chains, and homeostasis. Ethical considerations and real-world applications, such as conserving biodiversity and preventing communicable diseases, are emphasized. Experimental design and critical thinking are central to understanding biological processes and their environmental impacts.