To genetically transform an entire organism, you must insert the new gene into every cell in the organism. Which organism is better suited for complete and total genetic transformation - one composed of many cells, or one composed of a single cell? Why?

The answer is an unicellular organism.

Explanation:

There are many reasons why unicellular organisms, like bacteria, are better for understanding mutations. First of all, as there's only one cell, the amount of DNA is less, and therefore, easier to completely change. Also, unicellular organisms reproduce faster and without recombination, in most cases. Meaning that the mutation or change will be inherited doubtlessly.