Characteristics of living organisms

Living organisms take in materials, release energy, respond to their surroundings and carry out other activities that maintain life. These shared life processes are called the characteristics of living organisms. Each characteristic describes something living things do, rather than simply a feature of their appearance.

Movement in living organisms

Movement is an action by an organism, or part of an organism, that causes a change in position or place.

Movement does not have to involve the whole organism travelling from one location to another. An animal walking changes its location, but a plant shoot bending also shows movement because part of the organism changes position.

Respiration in living cells

Cells need a usable supply of energy to carry out their activities. Respiration is the set of chemical reactions in cells that break down nutrient molecules and release energy for metabolism, the chemical reactions that occur within an organism.

The energy released supports activities such as movement, growth and building new cell materials. Respiration is not the same as breathing: breathing moves air, whereas respiration releases energy through chemical reactions inside cells.

Sensitivity to changing conditions

Sensitivity is the ability to detect and respond to changes in the internal or external environment. These changes may involve light, temperature, chemicals, touch or conditions inside the body.

Sensitivity includes both detecting a change and responding to it. For example, pulling a hand away from a hot object is a response to an external change. Such responses help organisms function as conditions change.

Growth of living organisms

Growth is a permanent increase in size and dry mass. Dry mass is the mass of an organism’s material excluding its water.

Growth therefore involves a lasting increase in body material. An increase in size caused only by taking in water does not, by itself, show growth.

Reproduction of living organisms

Reproduction means producing more organisms of the same kind. The new organisms are called offspring.

Reproduction allows a species to continue as older organisms die. It is a characteristic of living organisms even though not every individual produces offspring.

Excretion of unwanted substances

Excretion is the removal of waste products of metabolism and substances in excess of requirements.

Chemical reactions in cells produce waste materials. If these wastes accumulate, they may harm the organism. Excretion removes them, along with substances present in greater amounts than the organism needs.

Nutrition in living organisms

Nutrition is the taking in of materials for energy, growth and development. Organisms need both substances that supply energy and raw materials for building and maintaining their bodies.

Nutrition and respiration are linked but distinct: nutrition supplies materials, while respiration breaks down nutrient molecules to release energy. These materials and the released energy allow organisms to build new tissues and carry out their other life processes.