To be considered alive, an object must exhibit all of the characteristics of living things. Listed below are the six rules used by scientists:
Living things are made of cells.
Living things obtain and use energy.
Living things grow and develop.
Living things reproduce.
Living things respond to their environment.
Living things adapt to their environment.
If something follows one or just a few of the rules listed above, it does not necessarily mean that it is living. Sugar crystals growing on the bottom of a syrup container is a good example of a nonliving object that displays at least one criteria for living organisms.
Decisions about whether things are alive or non-living remain problematic as not all life processes stop at the same time.
We are surrounded by living and non-living things. All animals and plants are living things and biology is the study of these living things. A cat playing with a ball is obviously living. A pigeon flying from tree to tree is also a living thing.
Sometimes it is not so easy to decide. Plants are living things but they do not play with balls or fly. Check out how to distinguish living things from non-living things at www.education.vic.gov.au and www.saburchill.com.