Source: Video Images: Prokaryote cell image, Public Domain: http://bit.ly/VX5oUg; Eukaryote cell image, Public Domain:http://bit.ly/RSS1jz; Skeleton image, Aaron Mullally; Worm image, Creative Commons: http://bit.ly/TVIquw
An invertebrate is an organism that does not have a backbone.
A vertebrate is an organism that has a backbone.
A cell is the basic unit of life.
Homeostasis is an organisms ability to maintain a constant internal environment.