Characteristics of living things show up everywhere. Here's the thing: It's not enough to exhibit one or two characteristics. In order to be considered a living thing, the thing in question must exhibit all the characteristics of living things. There are six distinct characteristics that all living things possess. Not four, not ten, six. If a particular thing shows all six of the characteristics of living things, it can be said to be a living organism. These are the six characteristics needed to be considered a living thing.
- Cellular structure. All living things are comprised of cells. These cells are highly complex and specialized. Specialized cells form specific tissue structures. These tissue structures form organs and different systems of the body of a living organism. Even single-celled organisms have a level of complexity within their respective single cells that far surpass non-living things.
- Finding and using energy. In other words, all living things have to eat. All living things have to find sources of energy (food) and use that energy to maintain life. Once the energy levels drop, a living thing must feed again. The technical term is metabolism.
- Growth and development. This characteristic of living things is very important. All living things must develop and grow, using energy to do so. The growth of some organisms can seem sall or even non-existent to the human eye, but every living thing must grow to survive. It has to mature in order to properly handle its environment.
- Reproduction. A major characteristic of living things is the ability for them to reproduce. In order for a species to survive it has to be able to pass its genetic material. This is what reproduction is. In humans, it's sex. Certain asexual organisms can inpregnate themselves in order to produce the necessary offspring to carry on the genetic material.
- Response to surroundings. A living thing must have the ability to maneuver through its environment. Certain triggers—like heat, light, cold, darkness—give the organism clues (that they respond to internally via nerves, hormones and chemical regulators) as to how to react in certain scenarios. Without this particular ability, a living thing wouldn't last too long.
- Adaptation and evolution. In order to be considered a living thing, an organism has to have the ability to change over time based on the changes of the environment around it. For lack of a better term, living things have to know how to roll with the punches. Once they can't adapt, they die off. Just look at the dinosaurs.