The seven characteristics of living things are movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. Biology students often remember these characteristics using the acronym MRS GREN.
Nutrition and respiration are closely related concepts. Respiration is a chemical reaction by which living things convert food into energy. On the other hand, nutrition is the ability to take food into the body. Animals demonstrate nutrition by eating plants or other animals, but plants demonstrate nutrition by making their own food from sunlight.
Sensitivity is the ability to notice and react to changes in the environment. When a mouse runs into its hole after seeing a hawk, it is showing sensitivity. Plants also show sensitivity when they grow toward the light. Sensitivity is sometimes called irritability.
Movement occurs in both plants and animals. In the case of animals, it often refers to a change in location, as when a deer runs or a bird flies. However, movement can also refer to the motion of a single part of an organism. Plants show movement when a leaf bud opens or when a flower closes at night.
Reproduction means that living things can produce offspring, while growth means that living things can become larger or increase the number of cells in their bodies. Excretion is the ability to clear waste from the body. For example, humans excrete nitrogen when they urinate and carbon dioxide when they breathe out. Plants excrete oxygen through their leaves.
Some biologists list homeostasis as an eighth characteristic of life. Homeostasis means living things can keep the environment inside their bodies constant. The ability of humans to keep a constant body temperature by sweating in the heat and shivering in the cold is an example of homeostasis.