1.1: CHARACTERISTICS OF LIVING ORGANISMS
SUMMARY
Every living organism carries out seven characteristic life processes: movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition. Movement involves a change of position or place and occurs in both animals and plants. Respiration is the chemical breakdown of nutrients inside cells to release energy — a process distinct from breathing. Sensitivity allows organisms to detect and respond to changes in their environment, while growth is measured as a permanent increase in dry mass. Reproduction ensures the continuation of a species by producing new individuals of the same kind.
Excretion removes toxic waste products of metabolism, such as carbon dioxide and urea, and must not be confused with egestion, which removes undigested food that was never part of metabolism. Nutrition is the intake of materials needed for energy, growth, and development, and takes different forms in autotrophs and heterotrophs. Together, these seven processes define what it means to be alive, and each carries a precise definition that examiners expect students to reproduce accurately.