Organisms respond to changes in their internal and external environments (A-level only)

This topic explores how organisms detect and respond to changes in their internal and external environments to ensure survival. It details the structural and functional differences between nervous and hormonal coordination systems, including the electrochemical generation of action potentials, synaptic transmission, and the second messenger model of hormone action. A central focus is the principle of homeostasis, examining how negative feedback mechanisms maintain physiological stability in contexts such as blood glucose regulation, osmoregulation, and thermoregulation.