Characteristics of Living Things

About this topic

Living things share seven characteristics, remembered as MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition. Movement means changing position or parts, respiration releases energy from food, sensitivity is detecting and responding to the environment, and growth is an increase in size or number of cells.

Reproduction produces offspring, excretion removes waste, and nutrition takes in materials for energy and growth. A thing must show all seven to be considered alive. Viruses and fire are common test cases that fail some of them.

Consider a mushroom growing on a log. It takes in nutrients from decaying wood, grows larger, releases spores to reproduce, and responds to moisture, so it ticks the boxes even though it never moves visibly. A rock, by contrast, may change shape through erosion but does none of the other things. Biologists use this checklist when classifying strange new organisms or deciding whether a sample from another planet could be life.

A common misconception is that anything that moves is alive, or that anything that does not move is not. Clouds drift and cars move, yet neither is alive, while plants move only slowly. Another trap is mixing up respiration with breathing: respiration is the chemical release of energy in cells, whereas breathing is just gas exchange. When revising, make up your own memorable example for each letter of MRS GREN.