To decide whether something is alive, biologists generally use a set of key criteria or characteristics that living organisms exhibit. These criteria include:
- Cellular organization: Living things are made up of one or more cells, which are the basic units of life.
- Metabolism: They carry out chemical processes to convert energy from the environment to sustain life functions.
- Growth and development: Living organisms grow in size and often undergo developmental changes.
- Reproduction: They have the ability to reproduce, either sexually or asexually, to produce offspring.
- Response to stimuli: Living things respond to changes in their environment, such as light, temperature, or touch.
- Movement: Many living organisms can move, either visibly (like walking or swimming) or at a cellular/molecular level.
- Homeostasis: They maintain a stable internal environment despite external changes.
These criteria help differentiate living organisms from non-living things, although not all living beings exhibit every characteristic at all times (for example, some sterile animals cannot reproduce but are still considered alive)
. In summary, if an entity shows cellular structure, metabolism, growth, reproduction, response to stimuli, movement, and homeostasis, it is considered alive.
