Characteristics of living organisms

Every living organism carries out seven characteristic life processes: movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition.

Movement

• An action by an organism, or part of an organism, that causes a change of position or place.
• Occurs in both animals and plants, although plants usually move only parts of themselves and do so more slowly.

Respiration

• The chemical reactions in cells that break down nutrient molecules to release energy for metabolism.
• It is a process distinct from breathing (gas exchange).

Sensitivity

• The ability to detect and respond to changes (stimuli) in the internal or external environment, making appropriate responses.

Growth

• A permanent increase in size and dry mass, brought about by an increase in cell number, cell size, or both.

Reproduction

• The processes that make more of the same kind of organism, ensuring the continuation of a species.

Excretion

• The removal of toxic waste products of metabolism, such as carbon dioxide and urea, and of substances in excess of requirements.
• It must not be confused with egestion, which removes undigested food that was never part of metabolism.

Nutrition

• The taking in of materials needed for energy, growth, and development.
• It takes different forms in autotrophs, which make their own food (e.g. plants), and heterotrophs, which consume other organisms (e.g. animals).

Together, these seven processes define what it means to be alive, and each carries a precise definition that examiners expect students to reproduce accurately.