Summary - Unit 3 - AQA Organisms exchange substances with their environment

These notes provide a concise and exam-focused summary of Unit 3: Exchange and Transport Systems, aligned with the AQA A-level Biology specification. They cover the structure and function of gas exchange systems in both single-celled and multicellular organisms, including adaptations in insects, fish, and mammals. Key concepts such as surface area to volume ratio, diffusion gradients, and exchange surfaces are clearly explained. The content also explores the structure of the human lung and ventilation, digestion and absorption in the human digestive system, and the transport of water and minerals in the xylem, as well as translocation in the phloem of plants. Please note: the topic of haemoglobin terminology in humans is not included in these notes. Designed for clarity and depth, the material highlights essential processes and structures involved in effective exchange and transport in living organisms.