On...the identification and classification of living things

First of all, let's define what a living thing is, it is an organism that has these characteristics:
1.    They have cell(s).
2.    They reproduce
3.    Grow and develop.
4.    Use energy and matter.
5.    Maintain homeostasis.
6.    Respond to stimuli.
7.    They are organized (tissues, membranes).
Even though, there exists a special kind of microorganism that doesn't has all of the characteristics but pose a threat to this definition of a living thing: VIRUSES.

There are various ways of classifying all of the living things, in order:

1. Kingdom
2. Phylia
3. Class
4. Order
5. Family
6. Genus
7. Species: A group of organisms with similar physical traits that can reproduce and produce fertile offspring.

While on the field scientists and amateurs use various tools in order to identify an organism but one of the most common of them is the dichotomous key that has branches each with two divisions per step that asks whether an organisms posseses a trait or not until leaving only one possible species an answer.

Bibliography:

• "Classifying Living Organisms." York Science. N.p., 2010. Web. 12 Aug 2010. <http://yorksci.wikispaces.com/Classifying+Living+Organisms>. 
• Rice, George. "Are Viruses Alive? ." Microbial Life. N.p., 2010. Web. 12 Aug 2010. <http://serc.carleton.edu/microbelife/yellowstone/viruslive.html>.