The term you're referring to which scientists implement to describe "different forms of life on Earth" is perhaps "Organism".
DNA Fingerprinting is a way to find a specific individual. It is more specific than simply identifying a specie or a particular trait. It is a sort of personal identifier. DNA uses micro satellite to make to make identification much easier. DNA fingerprinting is prevalent in the world of criminal forensic.
The three liquids will form three layers, the bottom layer is more dense and the top layer is less dense
